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doc/Tx-cal-theory: update with properly calibrated CMU200 and cabling setup
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 13 Feb 2018 03:18:38 +0000
parents 16aab86384a7
children 32bf19fb8a2a
comparison
equal deleted inserted replaced
110:630617d5ece3 111:7bcbbba94c41
64 by 0.5, whereas the lowest 4 (EGSM) or 6 (DCS) levels are raised and compacted 64 by 0.5, whereas the lowest 4 (EGSM) or 6 (DCS) levels are raised and compacted
65 together. The table in the LoCosto document (page 44) has the highest power 65 together. The table in the LoCosto document (page 44) has the highest power
66 level for each band reduced by 0.8, making it 32.2 dBm for EGSM and GSM850 and 66 level for each band reduced by 0.8, making it 32.2 dBm for EGSM and GSM850 and
67 29.2 dBm for DCS and PCS, while all other levels are set to the spec numbers. 67 29.2 dBm for DCS and PCS, while all other levels are set to the spec numbers.
68 68
69 In my own experience with getting the Tx power levels calibrated on our current 69 The calibration that was performed by Openmoko's factory (FIC?) on their GTA02
70 FCDEV3B boards, our hardware is able to hit all of the lowest spec power levels 70 units is similar to what the old Sara document calls for: the highest power
71 with good margin (the APC DAC value never goes below the 60-70 range), hence 71 level is set to 31.8 dBm for EGSM or GSM850 and to 28.8 dBm for DCS and PCS,
72 the low targets did not need to be shifted, but the highest spec power level 72 the next one down is 30.5/27.5 dBm instead of 05.05-spec-given 31/28 dBm, and
73 could not be achieved in every band. Following TI's practice with LoCosto, I 73 for the lowest 4 (EGSM or GSM850) or 6 (DCS and PCS) power levels the decrement
74 set the highest power level target to 32.2 dBm for the EGSM band and to 29.2 dBm 74 between levels is 1.5 instead of 2, putting the lowest EGSM or GSM850 power
75 for PCS, but I was consistently able to get the full 30 dBm out in the DCS band, 75 level at 7 dBm instead of 5 dBm, and the lowest DCS and PCS power levels at
76 hence I set the DCS band highest power level target to the official number of 76 3 dBm instead of 0 dBm.
77 30 dBm. It needs to be emphasized, however, that these results are quite
78 specific to our current flock of FCDEV3B hardware, and your results will most
79 likely be different if you are working with a different hw design such as a
80 non-FreeCalypso derivative of Openmoko's GTA02 design.
81 77
82 Update: the above calibration observations for the FCDEV3B should be held 78 It appears that OM/FIC were using some TI-provided calibration software without
83 doubly in doubt because the calibration status of my CMU200 itself is in 79 taking the time and effort to tune its settings for their own hardware: when we
84 question, i.e., it is not currently known if the measurements it reports are 80 recalibrate these OM-made devices in our own lab, we are able to hit all of the
85 really trustworthy. After the above paragraph was written, I replaced the 81 highest and lowest power levels given in the GSM 05.05 spec. On our own FCDEV3B
86 Rx/Tx module inside my CMU (the original one was good for Rx, but the Tx side 82 hardware we are likewise able to get the full 30 dBm in the DCS and PCS bands,
87 was dead), and after this internal module replacement the power measurements 83 but we are not able to get the full 33 dBm in the low band. Following TI's
88 reported by the instrument are 0.5 dB less than what it reported before. Which 84 practice with LoCosto, I set the highest power level target to 32.2 dBm for the
89 raises the questions: are the new measurements low by 0.5 dB relative to the 85 EGSM and GSM850 bands; for DCS and PCS the highest power level target is 30 dBm
90 real truth, or were the old ones high by 0.5 dB relative to the real truth? Or 86 per the spec. On the low end the power level targets are the official ones
91 is the real truth something else altogether? Until we raise a LOT more money 87 from the GSM 05.05 spec.
92 to get this CMU200 properly calibrated, we are limited to guesswork and the
93 true transmitter behaviour of our FCDEV3B hardware remains unknown.
94 88
95 Profiles for Tx levels calibration 89 Profiles for Tx levels calibration
96 ================================== 90 ==================================
97 91
98 Our fc-rfcal-txband program that performs the actual per-unit calibration of Tx 92 Our fc-rfcal-txband program that performs the actual per-unit calibration of Tx
99 power levels for each band requires a preconfigured txlevels calibration profile 93 power levels for each band requires a preconfigured txlevels calibration profile
100 for each band as one of its inputs; if you are performing calibration on 94 for each band as one of its inputs; if you are performing calibration on
101 individual units of a board design for which the correct profiles have already 95 individual units of a board design for which the correct profiles have already
102 been crafted, you simply use those given profiles (fcom1 for our current flock 96 been crafted, you simply use those given profiles (see the txlevels directory
103 of FCDEV3B boards), but if you are doing Tx power level calibration on a new 97 in the source tree for our current offerings), but if you are doing Tx power
104 board design for the first time, you first need to characterize the Tx output 98 level calibration on a new board design for the first time, you first need to
105 level behaviour of your new board design and craft the appropriate set of 99 characterize the Tx output level behaviour of your new board design and craft
106 profiles. 100 the appropriate set of profiles.
107 101
108 The profiles for txlevels calibration reside in /opt/freecalypso/rfcal/txlevels; 102 The profiles for txlevels calibration reside in /opt/freecalypso/rfcal/txlevels;
109 each per-band profile is sought in a file named profile_name-band_number, where 103 each per-band profile is sought in a file named profile_name-band_number, where
110 profile_name is the profile name argument given to fc-rfcal-txband and 104 profile_name is the profile name argument given to fc-rfcal-txband and
111 band_number is one of 850, 900, 1800 or 1900. For example, the profile set for 105 band_number is one of 850, 900, 1800 or 1900. For example, if you are using
112 our current FCDEV3B hardware is named fcom1 ("FreeCalypso hardware, Openmoko- 106 the rf3166-ideal profile set (appropriate for recalibrating Openmoko GTA02
113 based, version 1"), this hw platform is 900/1800/1900 MHz triband, and the 107 devices), the individual profile config files are rf3166-ideal-900,
114 individual profile config files are fcom1-900, fcom1-1800 and fcom1-1900. 108 rf3166-ideal-1800 and rf3166-ideal-1900 for the tri900 band configuration.
115 109
116 Each profile provides two key pieces of data: the list of fixed APC DAC values 110 Each profile provides two key pieces of data: the list of fixed APC DAC values
117 to be used as the basis set for constructing the piecewise linear model, and 111 to be used as the basis set for constructing the piecewise linear model, and
118 the list of power levels in dBm that will be the targets for the calibration. 112 the list of power levels in dBm that will be the targets for the calibration.
119 113
139 it reports are trustworthy, and that the insertion loss in your cabling setup 133 it reports are trustworthy, and that the insertion loss in your cabling setup
140 (all the way from the actual DUT's antenna connector or RF test port to your 134 (all the way from the actual DUT's antenna connector or RF test port to your
141 CMU200) really matches the numbers you have put in your cable configuration file 135 CMU200) really matches the numbers you have put in your cable configuration file
142 (see Cable-config-howto). If you fail to ensure these prerequisites, your 136 (see Cable-config-howto). If you fail to ensure these prerequisites, your
143 fc-rfcal-txbasis observations will be meaningless, as the cable insertion losses 137 fc-rfcal-txbasis observations will be meaningless, as the cable insertion losses
144 are typically of the same order of magnitude as the transmitter differences you 138 and instrument errors are typically of the same order of magnitude as the
145 are trying to determine. 139 transmitter differences you are trying to determine.
146 140
147 You will need to run fc-rfcal-txbasis with a guesstimated set of APC DAC values, 141 You will need to run fc-rfcal-txbasis with a guesstimated set of APC DAC values,
148 to be revised iteratively, and get a feel for what your DUT is putting out. 142 to be revised iteratively, and get a feel for what your DUT is putting out.
149 Are you able to hit the lowest spec power level consistently while the APC DAC 143 Are you able to hit the lowest spec power level consistently while the APC DAC
150 value remains well above zero? Are you able to hit the highest spec power level 144 value remains well above zero? Are you able to hit the highest spec power level