FreeCalypso > hg > freecalypso-docs
comparison FCDEV3B-repackaging @ 4:1dbc8c5d9698
FCDEV3B-repackaging: triband vs. quadband section added
| author | Mychaela Falconia <falcon@freecalypso.org> |
|---|---|
| date | Wed, 10 Oct 2018 17:22:57 +0000 |
| parents | 4f873ec004f6 |
| children | f920c9a68d45 |
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| 3:4f873ec004f6 | 4:1dbc8c5d9698 |
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| 179 the bits which would otherwise come from Iota's voice ADC. | 179 the bits which would otherwise come from Iota's voice ADC. |
| 180 | 180 |
| 181 The above approach would provide a usable digital voice interface that would be | 181 The above approach would provide a usable digital voice interface that would be |
| 182 completely transparent (invisible) to the Calypso DSP and even to the ARM-side | 182 completely transparent (invisible) to the Calypso DSP and even to the ARM-side |
| 183 firmware, hence it should work without any nasty surprises. | 183 firmware, hence it should work without any nasty surprises. |
| 184 | |
| 185 Triband vs. quadband | |
| 186 ==================== | |
| 187 | |
| 188 One shortcoming of our current FreeCalypso modem solution is that it is triband | |
| 189 and not quadband; more specifically our standard hw build omits the GSM850 band, | |
| 190 or we can build a different configuration that supports GSM850 but omits EGSM | |
| 191 (the 900 MHz band). To the best of our knowledge the GSM850 band is used very | |
| 192 little these days, but being only triband makes us look bad compared to the | |
| 193 competition: all of the mainstream proprietary GSM modem modules are fully | |
| 194 quadband these days. | |
| 195 | |
| 196 It *is* possible to make a Calypso-based quadband modem, as TI had one: their | |
| 197 Leonardo reference board for the Calypso+Iota+Rita chipset existed in several | |
| 198 versions some of which were quadband, and their E-Sample board (Calypso+) which | |
| 199 used the same Rita RF block was also quadband. However, changing our current | |
| 200 FC modem design from triband to quadband would involve a highly invasive PCB | |
| 201 layout change: basically our entire modem PCB layout and particularly the GHz RF | |
| 202 section would have to be ripped up and reshuffled into a different arrangement. | |
| 203 Furthermore, if we as the FreeCalypso community do decide that we wish to | |
| 204 produce a quadband modem, I (Mother Mychaela) would NOT be comfortable with | |
| 205 entrusting the needed re-layout work to an "ordinary" PCB layout contractor who | |
| 206 is not a cellphone RF design expert, instead we would need to get a consultation | |
| 207 from an RF PCB design expert who has experience very specifically with GSM | |
| 208 cellphone design and not any other applications. Finding such an expert would | |
| 209 be a major task in itself, and that expert most certainly won't come cheap. | |
| 210 Therefore, a quadband FreeCalypso modem probably won't happen unless we get | |
| 211 someone with a lot of money to throw around. | |
| 212 | |
| 213 There is one exception, though: if anyone would like to see our FreeCalypso | |
| 214 modem repackaged into the SMT module form factor copied from BenQ M32 and pays | |
| 215 for that venture, the result would be naturally quadband as the layout of BenQ's | |
| 216 module follows the same floorplan in the RF section as TI's quadband Leonardo | |
| 217 and E-Sample layout. However, that approach would involve a step to reverse- | |
| 218 engineer BenQ's layout by slicing their board and imaging its inner layers, | |
| 219 hence anyone seeking this approach would need to be prepared to pay for that | |
| 220 step. | |
| 221 | |
| 222 If anyone ever does pay for the creation of a quadband version of our | |
| 223 FreeCalypso modem solution, be it in BenQ's physical form factor or some other, | |
| 224 this quadband modem will need a different firmware build configuration: there | |
| 225 is no way to have the same fw image work on both triband and quadband modems | |
| 226 given that the RFFE control signals are different, and there would be no way for | |
| 227 the fw to autodetect which hw it is running on. But all of the other design | |
| 228 guidelines listed above should still be followed, so we can have only two fw | |
| 229 build configurations (triband and quadband) without an explosion of further | |
| 230 build variants for different GPIO wiring and whatnot. |