freecalypso-docs: RFFE-notes annotate

annotate RFFE-notes @ 102:49be28a15768

USB-ID-assignments: new official document location Our master document for assignment of USB IDs that have been allocated to us by FTDI previously resided in doc/USB-IDs in freecalypso-hwlab repository. However, that hw lab hacks repository is not the right place for a long-term official policy document - the present repository is a much better place.

author	Mychaela Falconia <falcon@freecalypso.org>
date	Mon, 11 Sep 2023 06:32:05 +0000
parents	dd94e04b9539
children

rev	line source
34 dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	1 Every GSM phone handset or modem that is based on our beloved Calypso+Iota+Rita
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	2 chipset also contains a functional section (can be a single component or a group
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	3 of components) which we call the RFFE: radio frequency front end. This RFFE is
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	4 the functional block that provides frequency-filtered radio Rx paths from the
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	5 antenna interface to Rita LNA inputs, as well radio Tx paths from the PA to the
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	6 antenna. The choice of particular RFFE implementation (specifically in the Rx
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	7 direction) determines the device's GSM frequency band capabilities, i.e.,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	8 whether your GSM phone or modem is dual-band, triband or quadband.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	9
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	10 The least band-capable Calypso-based devices we are aware of are dual-band,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	11 i.e., we are not aware of anyone having ever made a Calypso-based GSM device
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	12 that supports only one GSM frequency band. The lowest-end configuration is
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	13 single-region dual-band, supporting one low band and one high band, either EU
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	14 bands or US bands. The next step up is triband, supporting two EU bands and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	15 one US band or vice-versa, and the best RFFE designs are quadband, supporting
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	16 all 4 possible GSM frequency bands.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	17
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	18 There are two particular RFFE designs that enjoy the privileged status of being
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	19 most native to FreeCalypso: TI's original Leonardo+ quadband reference design
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	20 and Openmoko's derivative design that is very polished, but is only triband.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	21 In absolute historical terms TI's Leonardo existed first and OM's version was a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	22 later derivative work, but for FreeCalypso the two got somewhat reversed with
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	23 our peculiar timeline:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	24
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	25 * The Mother bought her first Openmoko Neo FreeRunner in 2011, and lots of other
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	26 people in the community have been playing with Openmoko devices - whereas TI's
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	27 Leonardo development board has always been legendary unobtainium.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	28
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	29 * Openmoko's PCB layout has been liberated (freely published) in 2015, whereas
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	30 TI's Leonardo PCB design remained as elusive as ever.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	31
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	32 * Between 2015 and 2017 we've successfully produced our FCDEV3B board based on
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	33 Openmoko's PCB layout, featuring OM's triband RFFE, and we gained a lot of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	34 experience working with this RFFE as we recreated the previously lost theory
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	35 and tools for RF calibration.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	36
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	37 * In December of 2019 I was searching the world high and low for a real TI
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	38 Leonardo board so I could do some CMU200 experiments with its RFFE, but
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	39 instead I found the historical commercial Calypso modem module which we call
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	40 Tango, which is nothing less than a mass-produced version of the core of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	41 Leonardo, the full quadband version.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	42
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	43 The discovery of Tango modules has finally brought TI's original quadband RFFE
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	44 design back to its rightful place at the top of the quality hierarchy among
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	45 Calypso GSM devices, and we are finally able to study it as much as we have
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	46 studied OM's triband version in the preceding years.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	47
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	48 Leonardo and Openmoko RF sections
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	49 =================================
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	50
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	51 The RF sections of both Leonardo/Tango and Openmoko/FCDEV3B consist of TI's
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	52 Rita RF transceiver, a standalone PA (RF3133 or RF3166) and the part we focus
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	53 on as the RFFE. The best way to illustrate the essential divisions and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	54 interconnections between components is with a block diagram:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	55
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	56 +-------+
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	57 \| RF PA \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	58 \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	59 +--------------- HB Tx path ------+-->>>--+------+
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	60 \| +-------- LB Tx path ------+-->>>--+---+ \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	61 \| \| \| \| \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	62 +---+------+---+ +-------+ \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	63 \| HB Tx LB Tx \| \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	64 \| \| +-+--+--+
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	65 \| Rita \| \| RFFE \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	66 \| \| \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	67 \| LB LNA-+----- LB Rx path ---------------+- -+-- ANTENNA
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	68 \| DCS LNA-+---- DCS Rx path ---------------+- \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	69 \| PCS LNA-+---- PCS Rx path ---------------+- \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	70 \| \| \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	71 +--------------+ +-------+
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	72
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	73 HB = high bands (DCS & PCS, 1800 & 1900 MHz)
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	74 LB = low bands (GSM850 & EGSM, 850 & 900 MHz)
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	75
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	76 The block marked as RFFE on the above block diagram is the one that differs
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	77 between Leonardo/Tango and Openmoko/FCDEV3B, and it is this block that makes
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	78 one quadband and the other only triband. In the original Leonardo+ quadband
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	79 reference design the RFFE block is a single component (Epcos M034F) that is
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	80 called a Front End Module (FEM), whereas Openmoko replaced this integrated FEM
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	81 with an Antenna Switch Module (ASM) plus 3 discrete SAW filters. Both RFFE
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	82 designs implement the following functions:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	83
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	84 * They switch the antenna interface between Rx and Tx - a GSM MS never needs to
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	85 receive and transmit at the same time, thus an antenna switch is used instead
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	86 of more expensive duplexer or diplexer arrangements.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	87
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	88 * They accept RF Tx signal from one of two separate inputs (one for LB, one for
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	89 HB), and they provide the necessary low pass filters to suppress unwanted
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	90 harmonics present in the PA output.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	91
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	92 * Rx signals are fed to the RF transceiver on one of 3 separate Rx signal paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	93 as appropriate for the band in which reception takes place (LB, DCS or PCS),
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	94 and for each supported band the incoming signal is passed through an
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	95 appropriate SAW - a very narrow frequency-specific bandpass filter.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	96
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	97 RF Tx paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	98 ===========
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	99
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	100 There are only two RF Tx paths: one for GSM850 and EGSM (850 & 900 MHz) bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	101 combined, and the other for DCS and PCS (1800 & 1900 MHz) bands combined. Thus
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	102 the RF Tx section of a Calypso+Iota+Rita GSM phone or modem is exactly the same
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	103 between dual-band, triband and quadband designs - only Rx paths differ.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	104
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	105 Both Leonardo/Tango and Openmoko/FCDEV3B use PAs from the same family by RFMD,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	106 just different evolutionary versions: Leonardo and Tango use the slightly older
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	107 RF3133 PA whereas OM and FCDEV3B use the slightly newer RF3166. The two PAs
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	108 have exactly the same controls, and they are wired in exactly the same way
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	109 between Leonardo and Openmoko.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	110
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	111 Besides PA controls, there are two very important Tx path control signals that
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	112 are driven by Calypso and go to the FEM or ASM: RFFE LB & HB Tx switch controls.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	113 Both the M034F FEM used in Leonardo and Openmoko's triband ASM have two
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	114 baseband-controlled internal switches selecting between Rx and Tx. When these
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	115 switches are inactive (no voltage applied), both LB and HB RF paths are set up
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	116 for Rx; one of these Tx switches enables LB Tx path and the other enables HB Tx
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	117 path. There is also a third switch present both in M034F and in OM's ASM, but
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	118 that one is for different Rx bands as explained later in this article.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	119
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	120 RF Rx paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	121 ===========
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	122
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	123 TI's Rita RF transceiver supports all 4 GSM frequency bands internally for both
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	124 Rx and Tx, but in the Rx direction it has only 3 LNA inputs. GSM850 and EGSM
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	125 share the same LNA input, whereas each of DCS and PCS gets its own. There is
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	126 also a requirement that whenever reception takes place in a given band, the Rx
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	127 signal has to pass through a SAW filter specific to that band: thus dual-band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	128 designs have two SAW filters in them somewhere, triband designs have 3 and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	129 quadband designs have 4 of them.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	130
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	131 Triband design with Rita and other similar transceivers like Silabs Aero I/I+
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	132 is straightforward: the antenna switch module (ASM) puts out 3 Rx paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	133 corresponding to LB, DCS or PCS, each of the 3 is passed through its own SAW
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	134 filter, and then they go to the 3 LNA inputs. SAW filters in the DCS and PCS
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	135 Rx paths are unambiguous, whereas the third SAW filter in the LB Rx path can be
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	136 populated in one of two ways: populating an EGSM downlink band filter produces
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	137 a tri900 GSM device, populating a GSM850 DL band filter produces a tri850 GSM
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	138 device. Openmoko's triband RFFE which we've reproduced on our FCDEV3B is built
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	139 in exactly this manner.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	140
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	141 Quadband design with the same Rita transceiver is more complicated: there need
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	142 to be a total of 4 SAW filters, but they need to go to just 3 Rita LNA inputs.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	143 One can make a discrete design: use an antenna switch module that puts out 4
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	144 switched Rx paths, pass them through 4 discrete SAW filters, and then somehow
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	145 combine the outputs of GSM850 and EGSM filters onto the single LB LNA input.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	146 Huawei's MG01GSMT design appears to do something similar (except that it
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	147 supports a non-standard band in the place of GSM850), but I don't really
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	148 understand how this magic works in terms of PCB layout.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	149
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	150 The M034F integrated FEM that was chosen by TI Back In The Day is much neater:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	151 it is a quadband FEM, containing 4 SAW filters inside, but it was specifically
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	152 designed to interface with transceivers like TI Rita or Silabs Aero that have 3
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	153 Rx input paths - thus the magic that combines the output of GSM850 and EGSM SAW
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	154 filters is contained inside this FEM component.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	155
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	156 We do have an M034F.pdf datasheet for this magic component (came along with
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	157 Calypso and Leonardo docs), and the block diagram on page 6 shows the magic
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	158 quite clearly: there is a baseband-controlled switch selecting between EGSM Rx
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	159 and GSM850 Rx (in addition to the two usual Tx switches), this switch directs
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	160 the low band Rx path toward one of two different SAW filters, and the outputs
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	161 of those two filters are then joined. The high band Rx path always goes to both
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	162 DCS and PCS band SAW filters, and each of those high band Rx SAW filters gets
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	163 its own output going to its own dedicated Rita LNA input. Note the lack of a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	164 baseband-controlled switch between DCS and PCS in the high band Rx path!
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	165
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	166 For a long time prior to the 2019-12 breakthrough I was concerned about this
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	167 lack of a baseband-controlled switch between DCS and PCS in the high band Rx
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	168 path: this switch is present in every triband RFFE design I am familiar with,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	169 including the one we got from Openmoko, and I was concerned that feeding the
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	170 high band Rx path to both DCS and PCS SAW filters without a switch would
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	171 introduce a 3 dB penalty into these high band Rx paths. But when I got my
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	172 hands on the newly discovered Tango modem modules, looked at the GMagic numbers
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	173 written into their FFS as part of the manufacturer's production calibration and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	174 then independently verified them with our CMU200, all fears were dispelled: the
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	175 Rx performance of this M034 FEM in all 4 bands is exactly the same as our
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	176 current Openmoko-based triband RFFE, with GMagic around 200 half-dB units.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	177
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	178 RFFE switches and control signals
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	179 =================================
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	180
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	181 Both our new quadband M034F and our more mature OM-based triband ASM have 3
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	182 baseband-controlled switches inside: two Tx switches (one for LB Tx, one for HB
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	183 Tx) and one Rx band steering switch. The Rx switch is entirely different
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	184 between the two RFFE designs:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	185
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	186 * Our OM-based triband ASM has an Rx path steering switch between DCS and PCS
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	187 just like every other triband RFFE design I have seen, and of course being
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	188 triband, it has no capability of switching between GSM850 and EGSM.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	189
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	190 * Epcos M034F has a baseband-controlled Rx path steering switch between GSM850
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	191 and EGSM (seems unavoidably necessary in this architecture), but it has NO
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	192 switch between DCS and PCS - instead both high band Rx paths are "always on".
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	193
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	194 All 3 RFFE switches are controlled by Calypso TSPACT signals passed through PNP
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	195 transistors that act as inverting buffers. The assignments of which Calypso
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	196 TSPACT controls which RFFE switch were made by people who came before us, and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	197 these assignments are different (incompatible) between Leonardo/Tango and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	198 Openmoko/FCDEV3B.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	199
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	200 Leonardo RFFE control signal assignments (used on Tango) are as follows:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	201
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	202 TSPACT1 = Tx high bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	203 TSPACT2 = Tx low bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	204 TSPACT4 = Rx GSM850 band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	205
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	206 Openmoko's version (used on FCDEV3B) is as follows:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	207
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	208 TSPACT1 = Rx PCS band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	209 TSPACT2 = Tx high bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	210 TSPACT4 = Tx low bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	211
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	212 In the now-seemingly-unlikely event that we end up building a new FreeCalypso
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	213 GSM device (not Tango) with M034F quadband FEM, we have two sensible choices
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	214 for TSPACT control signal wiring. One option would be to copy Leonardo and
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	215 Tango, and the other option would be to use the following novel assignment:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	216
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	217 TSPACT2 = Tx high bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	218 TSPACT4 = Tx low bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	219 TSPACT5 = Rx GSM850 band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	220
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	221 The latter option can be made firmware-compatible with our current OM-based
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	222 triband RFFE, by having our firmware drive the signals as follows:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	223
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	224 TSPACT1 = Rx PCS band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	225 TSPACT2 = Tx high bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	226 TSPACT4 = Tx low bands
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	227 TSPACT5 = Rx GSM850 band
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	228
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	229 Right now this consideration is purely academic because there presently exists
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	230 no business case for building new FreeCalypso hardware, given the existence of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	231 Tango modules.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	232
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	233 RF magic glue: Rx paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	234 =======================
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	235
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	236 RF signal paths coming out of the 3 Rx SAW filters in our current OM-based
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	237 design or out of M034F Rx pins are differential pairs; Rita LNA inputs to which
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	238 these signal paths go are also differential. But these RF signal paths are not
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	239 simple pairs of PCB traces going from one chip to the other, instead every
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	240 existing design features "RF magic glue" matching networks in these signal
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	241 paths, made up of inductors and/or capacitors. These "magic glue" LC networks
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	242 exist in a seemingly endless number of permutations: every historical design I
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	243 got a chance to examine exhibits a slightly different LC network topology among
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	244 the 3 Rx signal paths that are present. Sometimes the same LC network topology
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	245 is replicated for all 3 Rx signal paths, othertimes the same board will feature
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	246 different LC network topologies for different Rx band signal paths.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	247
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	248 Openmoko's Rx path "magic glue" networks look neat and tidy, with the same
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	249 topology in all 3 Rx band signal paths. This topology consists of a series
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	250 inductor in each trace (6 of them in total for 3 differential pairs) and shunt
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	251 capacitor footprints both before and after these series inductors - but all of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	252 these shunt capacitor footprints are left unpopulated. Inductor values are
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	253 naturally a little different for each frequency band.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	254
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	255 Prior to the discovery of Tango modules, when I was thinking about designing
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	256 and building new FreeCalypso hw with our long-desired M034F quadband FEM, I had
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	257 the big dilemma of deciding what topology should be implemented for the "RF
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	258 magic glue" matching networks. OM's version looks very neat and tidy and it is
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	259 known to work well with OM's triband RFFE, but would it still work well if that
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	260 triband RFFE were to be replaced with M034F? The answer is very uncertain,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	261 especially considering that the output impedance specifications given in our
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	262 only available M034F.pdf datasheet look very weird.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	263
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	264 The discovery of Tango has saved the day in this department. The "magic glue"
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	265 Rx path matching networks implemented on this module are exactly the same as
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	266 what is depicted on our available Leonardo schematics (the ones we've had since
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	267 2011), and the fact that these modules once were a successful mass-produced
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	268 commercial product gives a huge confidence boost to what was previously just a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	269 schematic drawing of completely unknown working quality. These Leonardo Rx path
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	270 matching networks score very low on the scale of understandability (and they
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	271 feature entirely different topology for each of the 3 Rx band signal paths),
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	272 but the fact that we have a working reference in the form of Tango is all that
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	273 matters at the end of the day...
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	274
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	275 RF magic glue: Tx paths
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	276 =======================
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	277
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	278 RF Tx signal paths running from the PA to the FEM or ASM also pass through
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	279 matching networks made up of inductors and/or capacitors. The two versions of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	280 most interest to FreeCalypso are once again Leonardo and Openmoko. The version
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	281 of Leonardo that has been mass-produced as Tango has the same T network topology
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	282 in both LB and HB Tx paths:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	283
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	284 PA_OUT-----C1--+--C2-----FEM_IN
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	285 \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	286 C3
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	287 \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	288 GND
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	289
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	290 LB: C1=C2=47pF, C3 is unpopulated
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	291 HB: C1=C2=12pF, C3 is unpopulated
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	292
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	293 It needs to be noted that with the cap-to-ground leg unpopulated, the T network
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	294 is degenerate and is equivalent to a single series capacitor. It needs to be
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	295 understood that TI were not in the business of selling finished GSM phones or
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	296 modems - instead their primary business was selling chips, and their secondary
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	297 business was providing support for these chips, support that included reference
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	298 and development boards. Because Leonardo was a reference board rather than a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	299 finished product, it appears that TI designed this board with a provision for a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	300 possible matching network - the comment on the schematic drawing says "PA
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	301 matching possible" - but apparently no matching was needed, hence a degenerate
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	302 T network was populated. It is certainly a little strange that the makers of
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	303 Tango kept this degenerate T network and did not replace it with a single
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	304 series capacitor, but what do we know...
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	305
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	306 Openmoko used pi networks instead:
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	307
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	308 LB: PA_OUT-----+--10nH--+-----ASM_IN
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	309 \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	310 1pF NC
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	311 \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	312 GND GND
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	313
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	314 HB: PA_OUT-----+--33pF--+-----ASM_IN
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	315 \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	316 NC NC
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	317 \| \|
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	318 GND GND
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	319
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	320 The HB pi network is degenerate, reduced to a single series capacitor, and the
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	321 LB pi network is almost degenerate given how small that 1 pF cap to ground is.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	322 But pi networks have this advantage: a degenerate pi network is reduced to just
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	323 one component, whereas a degenerate T network requires two components to be
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	324 populated.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	325
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	326 It is also worth noting that both "from" and "to" components connected by these
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	327 matching networks are different between Leonardo and OM: Leonardo and Tango use
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	328 RF3133 PA, OM's version has RF3166; Leonardo FEM is M034F, OM's version has a
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	329 Darfon ASM instead.
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	330
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	331 In the now-seemingly-unlikely event that we end up building a new FreeCalypso
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	332 GSM device (not Tango) with M034F quadband FEM, which PA are we going to use,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	333 and what "RF magic glue" matching network topology for PA-to-FEM RF Tx paths?
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	334 The Mother's current preference is to use RF3166 and OM-style pi networks,
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	335 preferably with a consultation with some better-than-me RF expert - but all
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	336 such plans are extremely nebulous, written with forks on water.

FreeCalypso > hg > freecalypso-docs

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