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annotate Quadband-ideas @ 22:9f9d2996c1ba

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MCSI-apparent-bug outdated article removed: see Calypso-digital-voice for up-to-date replacement
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 23 Oct 2019 00:26:36 +0000
parents 3fa4006696d0
children 00216b7cfc4d
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20
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Mychaela Falconia <falcon@freecalypso.org>
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1 Our current Openmoko-based Calypso+RF modem core is very very good, but it has
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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2 one shortcoming compared to TI's Leonardo+ reference design: it is triband
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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3 rather than quadband. This triband restriction stems from OM's use of discrete
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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4 antenna switch and SAW filter components as opposed to an integrated FEM (front
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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5 end module) like on Leonardo+. In addition to the band restriction, our current
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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6 triband RF design suffers from one other very unpleasant problem: we have no
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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7 datasheet for the antenna switch component which we have to use. We know from
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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8 Openmoko's BOM data that the manufacturer is Darfon and that the part number for
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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9 this antenna switch component is ASM4532T0P06-1, we are able to buy this part
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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10 from our Chinese grey market suppliers, we build our boards with these parts and
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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11 our boards do work perfectly fine when we get a good batch, but we have to do
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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12 this entire process blindly, without any datasheet or other documentation for
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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13 this mystery part.
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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14
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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15 This article outlines some ideas for how we may be able to move from this RFFE
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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16 to a different one, replacing our current mystery antenna switch with something
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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17 less mysterious and better documented, and improving our radio capability from
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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18 triband to quadband at the same time.
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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19
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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20 Epcos M034F
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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21 ===========
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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22
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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23 TI's Leonardo+ and E-Sample boards used a magic component made by Epcos (the
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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24 canonical SAW filter manufacturer during that era) called M034 or M034F (the
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Mychaela Falconia <falcon@freecalypso.org>
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25 exact proper designation is unclear). It was an integrated quadband FEM,
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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26 integrating the antenna switch and SAW filters in one component package, with a
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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27 special twist. The special twist is that even though there are 4 separate Rx
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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28 band SAW filters inside that M034 "chip" module, corresponding to its advertised
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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29 quadband capability, only 3 Rx signal path differential pairs come out of it,
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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30 neatly corresponding to the 3 LNA inputs on TI's Rita transceiver. This twist
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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31 is important because even though the Rita transceiver itself is fully quadband
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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32 internally, it has only 3 LNA inputs, with GSM850 and EGSM bands sharing the
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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33 same LNA input while each of DCS and PCS get their own.
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Mychaela Falconia <falcon@freecalypso.org>
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34
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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35 We do have an M034F.pdf datasheet for this magic component (came along with
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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36 Calypso and Leonardo docs), and the block diagram on page 6 shows the magic
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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37 quite clearly: there is a baseband-controlled switch selecting between EGSM Rx
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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38 and GSM850 Rx (in addition to the two usual Tx switches), this switch directs
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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39 the low band Rx path toward one of two different SAW filters, and the outputs
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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40 of those two filters are then joined. The high band Rx path always goes to both
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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41 DCS and PCS band SAW filters (I assume it is a 50/50 split of the total incoming
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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42 energy, with each path suffering by 3 dB as a result), and each of those high
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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43 band Rx SAW filters gets its own output going to its own dedicated Rita LNA
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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44 input.
3fa4006696d0 Quadband-ideas article written
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45
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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46 I (Mother Mychaela) would absolutely love to play with an M034-based quadband
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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47 Calypso+Iota+Rita board in my lab with the trusty CMU200 instrument, and to see
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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48 how well it actually performs, especially in comparison with our current
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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49 OM-based triband version. However, in all of my years of searching I have never
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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50 found a physical Leonardo board (any version), nor have we ever found any
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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51 Leonardo PCB layout files which would allow us to build a modern recreation -
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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52 thus the magic of M034 remains elusive.
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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53
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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54 Unless a miracle happens and we are able to obtain either a physical Leonardo+
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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55 board or a PADS PCB file for one, there is no quick or low-effort way to "just
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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56 try" this M034 RFFE. Instead if we wish to build a FreeCalypso board with this
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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57 RFFE, it would have to be "the full 9 yards": a full-blown PCB design and layout
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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58 effort. There is no way to just "drop" the M034 into our existing PCB design
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Mychaela Falconia <falcon@freecalypso.org>
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59 in the place of our current triband RFFE, it would have to be either a very
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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60 disruptive RF section layout change or an entirely new PCB layout, making this
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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61 idea very open-ended - an open-ended venture with quite uncertain outcome, but
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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62 with a high dollar cost attached to it. Given the massive effort required and
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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63 PCB layout labor costs, I currently have no active plans to pursue this idea
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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64 beyond hypothetical.
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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65
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Mychaela Falconia <falcon@freecalypso.org>
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66 Commissioning a new custom RF FEM
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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67 =================================
3fa4006696d0 Quadband-ideas article written
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68
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Mychaela Falconia <falcon@freecalypso.org>
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69 Here is a wild thought: what if instead of twisting over backwards trying to
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Mychaela Falconia <falcon@freecalypso.org>
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70 hammer an existing RF FEM like M034F into our not-quite-fitting PCB design, we
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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71 were to get an entirely new FEM made specially for us, made exactly the way we
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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72 need it? If we were to venture that way, I would ask for a FEM very similar
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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73 conceptually to M034F, but with a few changes:
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Mychaela Falconia <falcon@freecalypso.org>
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74
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Mychaela Falconia <falcon@freecalypso.org>
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75 1) Instead of diplexing between DCS and PCS SAW filter inputs with a 50/50
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Mychaela Falconia <falcon@freecalypso.org>
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76 energy split, implement another switch (just like the GSM850 Rx switch) for
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Mychaela Falconia <falcon@freecalypso.org>
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77 PCS Rx, exactly the same way how it is done in classic triband designs like
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Mychaela Falconia <falcon@freecalypso.org>
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78 our current OM-based one. This change should eliminate the extra 3 dB
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Mychaela Falconia <falcon@freecalypso.org>
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79 penalty which I assume (for lack of experimental data) must happen with the
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Mychaela Falconia <falcon@freecalypso.org>
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80 existing M034 FEM. Or as an alternative to making this change, if someone
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Mychaela Falconia <falcon@freecalypso.org>
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81 who is more knowledgeable than me in this area can explain to me why it isn't
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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82 necessary, I would accept that option as well.
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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83
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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84 2) I would ask for a rearranged pinout: the existing M034F pinout does not fit
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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85 at all into our OM-based PCB layout, but it would fit much better with some
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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86 rearrangement.
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Mychaela Falconia <falcon@freecalypso.org>
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87
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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88 3) The hypothetical M034-like FEM would fit into our OM-based PCB layout a lot
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Mychaela Falconia <falcon@freecalypso.org>
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89 better if it were made a little smaller than the 8.2x5.5 mm size of M034F.
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Mychaela Falconia <falcon@freecalypso.org>
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90 Considering that the original M034F was created some 15-16 y ago, I assume
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Mychaela Falconia <falcon@freecalypso.org>
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91 that it should be possible to make a smaller version in 2020 or 2021 or
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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92 whenever.
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Mychaela Falconia <falcon@freecalypso.org>
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93
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Mychaela Falconia <falcon@freecalypso.org>
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94 Timeline sequentiality
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Mychaela Falconia <falcon@freecalypso.org>
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95 ======================
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Mychaela Falconia <falcon@freecalypso.org>
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96
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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97 All of the above ideas will be considered on a less hypothetical level after we
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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98 get our already-committed FCM40 product built. FCM40 will be a modem module in
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Mychaela Falconia <falcon@freecalypso.org>
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99 the same 56.5x36 mm form factor as Huawei GTM900 (with a mostly-compatible FPC
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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100 interface with only a few changes), featuring the same OM-based triband modem
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Mychaela Falconia <falcon@freecalypso.org>
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101 core as FCDEV3B V2. The reason for this sequencing is that our current FCDEV3B
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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102 suffers from a couple of issues which FCM40 is expected to solve:
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Mychaela Falconia <falcon@freecalypso.org>
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103
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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104 1) FCDEV3B has a very tight PCB layout: not only do we have the tightly laid out
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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105 core from GTA02, but also the whole board is quite small for the implemented
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Mychaela Falconia <falcon@freecalypso.org>
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106 peripheral complexity, imposing further constraints from all sides. This
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Mychaela Falconia <falcon@freecalypso.org>
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107 tight and complex layout makes a poor choice of starting point for bold
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Mychaela Falconia <falcon@freecalypso.org>
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108 experiments like RFFE changes.
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Mychaela Falconia <falcon@freecalypso.org>
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109
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110 2) FCDEV3B is locked into Altium. Layout data migration from Altium to FOSS
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Mychaela Falconia <falcon@freecalypso.org>
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111 appears to be much less feasible than migration from PADS to FOSS, thus
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Mychaela Falconia <falcon@freecalypso.org>
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112 freeing our PCB layout from the clutches of proprietary software will most
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Mychaela Falconia <falcon@freecalypso.org>
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113 likely require giving up (or rather setting aside) all of FCDEV3B new layout
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Mychaela Falconia <falcon@freecalypso.org>
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114 and going back to the GTA02 starting point, which is in PADS format rather
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Mychaela Falconia <falcon@freecalypso.org>
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115 than Altium. Redoing all of FCDEV3B anew does not sound appealing at all,
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Mychaela Falconia <falcon@freecalypso.org>
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116 but the much simpler FCM40 board offers a perfect opportunity for a fresh
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Mychaela Falconia <falcon@freecalypso.org>
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117 start.
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118
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119 FCM40 will have exactly the same OM-based triband RFFE as our current FCDEV3B,
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Mychaela Falconia <falcon@freecalypso.org>
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120 but it will be a much simpler board, and if we can get it done in FOSS instead
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Mychaela Falconia <falcon@freecalypso.org>
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121 of continuing the Altium track, then we would have a very solid reference and a
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Mychaela Falconia <falcon@freecalypso.org>
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122 good starting point for potential RFFE change experiments.
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Mychaela Falconia <falcon@freecalypso.org>
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123
3fa4006696d0 Quadband-ideas article written
Mychaela Falconia <falcon@freecalypso.org>
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124 Firmware compatibility
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Mychaela Falconia <falcon@freecalypso.org>
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125 ======================
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Mychaela Falconia <falcon@freecalypso.org>
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126
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127 Our current FreeCalypso firmwares drive TSPACT RFFE control signals as follows
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Mychaela Falconia <falcon@freecalypso.org>
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128 on FC hw family targets (CONFIG_TARGET_FCFAM):
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129
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130 TSPACT1 = Rx PCS band
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Mychaela Falconia <falcon@freecalypso.org>
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131 TSPACT2 = Tx high bands
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Mychaela Falconia <falcon@freecalypso.org>
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132 TSPACT4 = Tx low bands
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Mychaela Falconia <falcon@freecalypso.org>
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133 TSPACT5 = Rx GSM850 band
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134
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135 The driving of TSPACT1, TSPACT2 and TSPACT4 matches the way these signals have
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136 been assigned by Openmoko and thus the way they function on our current OM-based
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137 triband RFFE, whereas TSPACT5 is a new signal which is not wired anywhere on
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138 our current FCDEV3B. This signal driving arrangement is expected to be
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139 compatible with all 3 RFFE hw possibilities under consideration:
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140
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141 * On our current OM-based triband RFFE it works as is.
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142
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143 * If we use Epcos M034 or a semi-clone thereof that has the two Tx switches and
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144 a GSM850 Rx switch but no PCS Rx switch, then we will need to connect TSPACT2,
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145 TSPACT4 and TSPACT5 per the table above, and leave TSPACT1 unconnected.
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146
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147 * If we get a new M034-like FEM custom-made with a full set of all 4 switches,
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148 then all 4 TSPACT signals will need to be connected per the table above.