• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 53 subscribers
  • Views 521 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC1310: transmit power variation at low power levels

Lutz Konstroffer
Prodigy 20 points
Part Number: CC1310

I have a customer who designed a 915 MHz transmitter without frequency hopping. The antenna has some gain so the output power must be reduced. Now we noticed that there is a strong variation in the transmit power (conducted measurement at an u.fl connector) from board to board. While at maximum power (power register setting 0xA73F) the variation is negligible, they see a variation of as much as 11 dB from board to board at power register setting 0x08C0.

My question: Is this just the normal behaviour?

  • 0
    TI__Guru**** 317180 points
    This is the case with most PAs. The reason is that the PA is a open loop amplifier (no feedback). When the PA is in saturation the variation in output power will be small but for low levels the PA will be in the linear region and then the output power will be a function of the gain of the output transistor. This gain will have a larger variation from sample to sample.
  • 0 in reply to TER
    Prodigy 20 points

    Thanks, that's what we assumed. One approach is to measure the TX power in production and to adjust the txPower register setting accordingly. Unfortunately, the SRF Studio does not give intermediate values for the txPower register between 0x08C0 ( -10 dBm) and 0x0041 ( 0 dBm). Is there a way to find intermediate steps?

  • 0 in reply to Lutz Konstroffer
    TI__Guru**** 317180 points
    Due to how the PA is implemented it's no steps available between - 10 dBm and 0 dBm. (To check you can try txPower = 0x00C0, 0x00C1 ...)