RF Issue Due To PA Timing
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This document discusses several issues related to transmitter timing and power amplifier settings in cellular devices. It notes that rich spurs have been observed in the 500-700MHz range during conducted spurious emission measurements, even across different channels and power control levels. Improper timing of power amplifier enable signals can also affect the maximum transmit power and calibration of certain bands. The timing of power amplifier on and range signals must be set correctly to avoid lower than expected output power or failures in band calibration. References are provided from Qualcomm and Slideshare documents discussing transmitter spur and GSM open-loop power control issues.
![Tx spur issue
There are rich spurs in 500 ~ 700 MHz range while doing
GSM DCS/PCS band conducted spurious measurement.
Even though in different channels and PCL, the issue
still exists[1].
2](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-2-320.jpg)
![Tx spur issue
When PA is off, the PA gain mode should be LPM
instead of HPM. Besides, the PA_EN signal should
disable after that ASM_EN signal disables[1].
3](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-3-320.jpg)
![GSM ORFS issue
Moreover, The PA enable signal start/stop time
adjustment can affect GSM ORFS performance as
well[2].
4](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-4-320.jpg)
![Potential Issues of Improper Tx Timing
For MIPI PA device, PA ON signal is expected earlier
than the PA range signal, since PA ON script sets PA to
the lowest gain state and overrides the settings in the
PA range script[2].
5](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-5-320.jpg)
![Potential Issues of Improper Tx Timing
Nevertheless, if PA ON is later than PA range timing, the
power will be lower than expected; e.g. Max Tx power is
merely ~20 dBm[2].
Failed to calibrate GSM850/900 due to improper PA
timing applied[2].
6](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-6-320.jpg)
![Reference
[1] Phase2 TxM Sky7791x Tx spur issue, Qualcomm
[2] Analysis of GSM ORFS issue, Slideshare
7](https://image.slidesharecdn.com/rfissueduetopatiming-180612093604/85/RF-Issue-Due-To-PA-Timing-7-320.jpg)
RF Issue Due To PA Timing
- 1. 1
- 2. Tx spur issue There are rich spurs in 500 ~ 700 MHz range while doing GSM DCS/PCS band conducted spurious measurement. Even though in different channels and PCL, the issue still exists[1]. 2
- 3. Tx spur issue When PA is off, the PA gain mode should be LPM instead of HPM. Besides, the PA_EN signal should disable after that ASM_EN signal disables[1]. 3
- 4. GSM ORFS issue Moreover, The PA enable signal start/stop time adjustment can affect GSM ORFS performance as well[2]. 4
- 5. Potential Issues of Improper Tx Timing For MIPI PA device, PA ON signal is expected earlier than the PA range signal, since PA ON script sets PA to the lowest gain state and overrides the settings in the PA range script[2]. 5
- 6. Potential Issues of Improper Tx Timing Nevertheless, if PA ON is later than PA range timing, the power will be lower than expected; e.g. Max Tx power is merely ~20 dBm[2]. Failed to calibrate GSM850/900 due to improper PA timing applied[2]. 6
- 7. Reference [1] Phase2 TxM Sky7791x Tx spur issue, Qualcomm [2] Analysis of GSM ORFS issue, Slideshare 7