FreeCalypso > hg > fc-rfcal-tools
comparison doc/Tx-cal-theory @ 122:aa2533be2ec1
doc/Tx-cal-theory: channel calibration documented
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Wed, 14 Feb 2018 04:54:58 +0000 |
| parents | 76faa4f52a4d |
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| 121:76faa4f52a4d | 122:aa2533be2ec1 |
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| 183 | 183 |
| 184 Once you have a good set of profiles for the type of Calypso GSM device you are | 184 Once you have a good set of profiles for the type of Calypso GSM device you are |
| 185 calibrating, just run fc-rfcal-txband with the band number and the name of your | 185 calibrating, just run fc-rfcal-txband with the band number and the name of your |
| 186 profile. | 186 profile. |
| 187 | 187 |
| 188 Channel correction calibration | |
| 189 ============================== | |
| 190 | |
| 191 The APC DAC values given in the levels tables apply directly only to the | |
| 192 channels in the centre of each band. The transfer function from APC DAC control | |
| 193 values to power output levels in dBm depends on the frequency, and the APC DAC | |
| 194 values need to be adjusted for different subbands within each band in order to | |
| 195 produce the correct output power levels for all channels. TI's RF driver code | |
| 196 and calibration data structures provide for a Tx channel calibration, and all | |
| 197 historical commercial manufacturers of Calypso GSM devices that are known to us | |
| 198 have performed this Tx channel calibration on a per-unit basis on their | |
| 199 production lines. | |
| 200 | |
| 201 Our fc-rfcal-txband calibration tool implements Tx channel correction | |
| 202 calibration as of 2018-02, and we do it a little better than the way it was done | |
| 203 by the big folks Back In The Day. TI's RF data structures allow for up to 4 | |
| 204 channel calibration tables, to be used for different power levels, but | |
| 205 Openmoko's factory only did one channel calibration set (calibrated at the | |
| 206 highest power level for each band), using only one table out of the possible 4, | |
| 207 and this one table (calibrated at the highest power level) is then used for all | |
| 208 power levels. As far as we can tell, other Calypso GSM device manufacturers | |
| 209 have done likewise. | |
| 210 | |
| 211 Our Tx calibration implementation makes use of all 4 available channel | |
| 212 correction table slots. We divide the 15 power levels of EGSM and GSM850 bands | |
| 213 or the 16 power levels of DCS and PCS into 4 groups (5-7, 8-11, 12-15, 16-19 | |
| 214 for EGSM and GSM850; 0-3, 4-7, 8-11, 12-15 for DCS and PCS), perform channel | |
| 215 calibration at the highest power level in each group, and set the resulting | |
| 216 channel calibration table to be used for all 3 or 4 power levels in that group. | |
| 217 Our procedure produces Tx behaviour that is identical to Openmoko's for the | |
| 218 highest 3 or 4 power levels, but the lower power levels run with channel | |
| 219 calibration that was made closer to them, as opposed to the very highest power | |
| 220 level. The price of our approach is more time spent in RF calibration for each | |
| 221 unit on the production line, but our approach is perfectly suited for low volume | |
| 222 production and aftermarket recalibration services. | |
| 223 | |
| 188 Checking existing calibration | 224 Checking existing calibration |
| 189 ============================= | 225 ============================= |
| 190 | 226 |
| 191 fc-rfcal-txcheck is a completely non-invasive program (does not make any writes | 227 fc-rfcal-txcheck is a completely non-invasive program (does not make any writes |
| 192 to any L1 RF tables or to FFS) that steps through all power levels for the | 228 to any L1 RF tables or to FFS) that steps through all power levels for the |
| 193 specified band (5-19 for EGSM or GSM850, or 0-15 for DCS or PCS), performs a | 229 specified band (5-19 for EGSM or GSM850, or 0-15 for DCS or PCS), performs a |
| 194 power measurement at each level, and displays the measured result. | 230 power measurement at each level, and displays the measured result. By default |
| 231 the test is performed at the centre frequency of the specified band, but the | |
| 232 ARFCN to be used can also be specified on the command line. |