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annotate RFFE-notes @ 95:8a45cd92e3c3

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TCH-tap-modes: new article
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 19 Dec 2022 02:02:28 +0000
parents dd94e04b9539
children
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dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
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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>
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2 chipset also contains a functional section (can be a single component or a group
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Mychaela Falconia <falcon@freecalypso.org>
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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>
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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>
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5 antenna interface to Rita LNA inputs, as well radio Tx paths from the PA to the
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Mychaela Falconia <falcon@freecalypso.org>
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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>
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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>
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8 whether your GSM phone or modem is dual-band, triband or quadband.
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9
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Mychaela Falconia <falcon@freecalypso.org>
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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>
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11 i.e., we are not aware of anyone having ever made a Calypso-based GSM device
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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12 that supports only one GSM frequency band. The lowest-end configuration is
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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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>
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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:
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15 one US band or vice-versa, and the best RFFE designs are quadband, supporting
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Mychaela Falconia <falcon@freecalypso.org>
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16 all 4 possible GSM frequency bands.
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Mychaela Falconia <falcon@freecalypso.org>
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17
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Mychaela Falconia <falcon@freecalypso.org>
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18 There are two particular RFFE designs that enjoy the privileged status of being
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Mychaela Falconia <falcon@freecalypso.org>
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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>
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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:
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21 In absolute historical terms TI's Leonardo existed first and OM's version was a
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22 later derivative work, but for FreeCalypso the two got somewhat reversed with
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Mychaela Falconia <falcon@freecalypso.org>
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23 our peculiar timeline:
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24
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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:
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26 people in the community have been playing with Openmoko devices - whereas TI's
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Mychaela Falconia <falcon@freecalypso.org>
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27 Leonardo development board has always been legendary unobtainium.
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28
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29 * Openmoko's PCB layout has been liberated (freely published) in 2015, whereas
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Mychaela Falconia <falcon@freecalypso.org>
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30 TI's Leonardo PCB design remained as elusive as ever.
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31
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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:
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33 Openmoko's PCB layout, featuring OM's triband RFFE, and we gained a lot of
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Mychaela Falconia <falcon@freecalypso.org>
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34 experience working with this RFFE as we recreated the previously lost theory
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Mychaela Falconia <falcon@freecalypso.org>
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35 and tools for RF calibration.
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36
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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>
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38 Leonardo board so I could do some CMU200 experiments with its RFFE, but
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Mychaela Falconia <falcon@freecalypso.org>
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39 instead I found the historical commercial Calypso modem module which we call
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Mychaela Falconia <falcon@freecalypso.org>
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40 Tango, which is nothing less than a mass-produced version of the core of
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Mychaela Falconia <falcon@freecalypso.org>
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41 Leonardo, the full quadband version.
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Mychaela Falconia <falcon@freecalypso.org>
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42
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
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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>
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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:
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45 Calypso GSM devices, and we are finally able to study it as much as we have
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Mychaela Falconia <falcon@freecalypso.org>
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46 studied OM's triband version in the preceding years.
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47
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48 Leonardo and Openmoko RF sections
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Mychaela Falconia <falcon@freecalypso.org>
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49 =================================
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50
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Mychaela Falconia <falcon@freecalypso.org>
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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:
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52 Rita RF transceiver, a standalone PA (RF3133 or RF3166) and the part we focus
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Mychaela Falconia <falcon@freecalypso.org>
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53 on as the RFFE. The best way to illustrate the essential divisions and
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Mychaela Falconia <falcon@freecalypso.org>
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54 interconnections between components is with a block diagram:
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55
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56 +-------+
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57 | RF PA |
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58 | |
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59 +--------------- HB Tx path ------+-->>>--+------+
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60 | +-------- LB Tx path ------+-->>>--+---+ |
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61 | | | | | |
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62 +---+------+---+ +-------+ | |
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63 | HB Tx LB Tx | | |
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64 | | +-+--+--+
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65 | Rita | | RFFE |
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66 | | | |
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67 | LB LNA-+----- LB Rx path ---------------+- -+-- ANTENNA
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parents:
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68 | DCS LNA-+---- DCS Rx path ---------------+- |
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69 | PCS LNA-+---- PCS Rx path ---------------+- |
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70 | | | |
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71 +--------------+ +-------+
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72
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73 HB = high bands (DCS & PCS, 1800 & 1900 MHz)
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Mychaela Falconia <falcon@freecalypso.org>
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74 LB = low bands (GSM850 & EGSM, 850 & 900 MHz)
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75
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76 The block marked as RFFE on the above block diagram is the one that differs
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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77 between Leonardo/Tango and Openmoko/FCDEV3B, and it is this block that makes
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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78 one quadband and the other only triband. In the original Leonardo+ quadband
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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79 reference design the RFFE block is a single component (Epcos M034F) that is
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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80 called a Front End Module (FEM), whereas Openmoko replaced this integrated FEM
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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81 with an Antenna Switch Module (ASM) plus 3 discrete SAW filters. Both RFFE
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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82 designs implement the following functions:
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Mychaela Falconia <falcon@freecalypso.org>
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83
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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:
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85 receive and transmit at the same time, thus an antenna switch is used instead
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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86 of more expensive duplexer or diplexer arrangements.
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87
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88 * They accept RF Tx signal from one of two separate inputs (one for LB, one for
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Mychaela Falconia <falcon@freecalypso.org>
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89 HB), and they provide the necessary low pass filters to suppress unwanted
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Mychaela Falconia <falcon@freecalypso.org>
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90 harmonics present in the PA output.
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91
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92 * Rx signals are fed to the RF transceiver on one of 3 separate Rx signal paths
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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93 as appropriate for the band in which reception takes place (LB, DCS or PCS),
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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94 and for each supported band the incoming signal is passed through an
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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95 appropriate SAW - a very narrow frequency-specific bandpass filter.
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96
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97 RF Tx paths
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98 ===========
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99
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100 There are only two RF Tx paths: one for GSM850 and EGSM (850 & 900 MHz) bands
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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101 combined, and the other for DCS and PCS (1800 & 1900 MHz) bands combined. Thus
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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102 the RF Tx section of a Calypso+Iota+Rita GSM phone or modem is exactly the same
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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103 between dual-band, triband and quadband designs - only Rx paths differ.
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104
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105 Both Leonardo/Tango and Openmoko/FCDEV3B use PAs from the same family by RFMD,
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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106 just different evolutionary versions: Leonardo and Tango use the slightly older
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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107 RF3133 PA whereas OM and FCDEV3B use the slightly newer RF3166. The two PAs
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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108 have exactly the same controls, and they are wired in exactly the same way
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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109 between Leonardo and Openmoko.
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110
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111 Besides PA controls, there are two very important Tx path control signals that
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Mychaela Falconia <falcon@freecalypso.org>
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112 are driven by Calypso and go to the FEM or ASM: RFFE LB & HB Tx switch controls.
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113 Both the M034F FEM used in Leonardo and Openmoko's triband ASM have two
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114 baseband-controlled internal switches selecting between Rx and Tx. When these
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Mychaela Falconia <falcon@freecalypso.org>
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115 switches are inactive (no voltage applied), both LB and HB RF paths are set up
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116 for Rx; one of these Tx switches enables LB Tx path and the other enables HB Tx
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117 path. There is also a third switch present both in M034F and in OM's ASM, but
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118 that one is for different Rx bands as explained later in this article.
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119
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120 RF Rx paths
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121 ===========
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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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.
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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:
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149
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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 =================================
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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
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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:
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244 the 3 Rx signal paths that are present. Sometimes the same LC network topology
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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245 is replicated for all 3 Rx signal paths, othertimes the same board will feature
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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246 different LC network topologies for different Rx band signal paths.
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247
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248 Openmoko's Rx path "magic glue" networks look neat and tidy, with the same
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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249 topology in all 3 Rx band signal paths. This topology consists of a series
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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250 inductor in each trace (6 of them in total for 3 differential pairs) and shunt
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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251 capacitor footprints both before and after these series inductors - but all of
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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252 these shunt capacitor footprints are left unpopulated. Inductor values are
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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253 naturally a little different for each frequency band.
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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254
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255 Prior to the discovery of Tango modules, when I was thinking about designing
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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256 and building new FreeCalypso hw with our long-desired M034F quadband FEM, I had
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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257 the big dilemma of deciding what topology should be implemented for the "RF
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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258 magic glue" matching networks. OM's version looks very neat and tidy and it is
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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259 known to work well with OM's triband RFFE, but would it still work well if that
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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260 triband RFFE were to be replaced with M034F? The answer is very uncertain,
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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261 especially considering that the output impedance specifications given in our
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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262 only available M034F.pdf datasheet look very weird.
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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263
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parents:
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264 The discovery of Tango has saved the day in this department. The "magic glue"
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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265 Rx path matching networks implemented on this module are exactly the same as
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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266 what is depicted on our available Leonardo schematics (the ones we've had since
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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267 2011), and the fact that these modules once were a successful mass-produced
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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268 commercial product gives a huge confidence boost to what was previously just a
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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269 schematic drawing of completely unknown working quality. These Leonardo Rx path
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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270 matching networks score very low on the scale of understandability (and they
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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271 feature entirely different topology for each of the 3 Rx band signal paths),
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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272 but the fact that we have a working reference in the form of Tango is all that
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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273 matters at the end of the day...
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parents:
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274
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275 RF magic glue: Tx paths
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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276 =======================
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277
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278 RF Tx signal paths running from the PA to the FEM or ASM also pass through
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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279 matching networks made up of inductors and/or capacitors. The two versions of
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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280 most interest to FreeCalypso are once again Leonardo and Openmoko. The version
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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281 of Leonardo that has been mass-produced as Tango has the same T network topology
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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282 in both LB and HB Tx paths:
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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283
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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284 PA_OUT-----C1--+--C2-----FEM_IN
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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285 |
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
parents:
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286 C3
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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287 |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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288 GND
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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289
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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290 LB: C1=C2=47pF, C3 is unpopulated
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
291 HB: C1=C2=12pF, C3 is unpopulated
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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292
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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
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
294 is degenerate and is equivalent to a single series capacitor. It needs to be
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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
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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
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
309 | |
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
parents:
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310 1pF NC
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
311 | |
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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
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
315 | |
dd94e04b9539 new RFFE-notes article replaces old Quadband-ideas
Mychaela Falconia <falcon@freecalypso.org>
parents:
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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.