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CCS/CC1310: Receiver ADC I/Q output Sample Rate Calculation

Jianlin Zhou
Expert 1230 points
Part Number: CC1310

Tool/software: Code Composer Studio

Hello,

I'm following your CC1310 I/Q sample example and working on CC1310 Launchpad. I set my symbol rate to be the following value:

According to the I/Q sample application note :

The IQ sample rate is fixed to 4 times oversampling and the IQ sample size is 12 bits. This means that each IQ pair will occupy 3 bytes in RAM. 

1. Could you please tell me how could I calculte my I data sample rate and Q data sample rate based on my RF symbol rate setting?

2. When we are processing the I/Q samples, do we need to downsample 4 times or the I/Q sample output has already been averaged after your oversampling?

Thank you so much!

Is the symbol rate corresponding to the receiver ADC sampling rate? As there is no modulation, symbol rate should be data rate. If so, how could I back calculate ADC sample rate by using symbol rate? I/Q samples are all 12bits. Should I calculate by doing  Symbol rate / 12 or Symbol rate / 24?

  • 0
    TI__Guru* 86151 points
    First of all, you should follow the recommended settings from the app note and set the deviation to half the data rate. The symbol rate and data rate will always be the same. The sampling rate is 4 times the programmed symbol rate.

    Siri
  • 0 in reply to Siri
    Expert 1230 points

    Hello Siri,

    Thank you for your recomendation. I have changed deviation to 3.5kHz. I was using another CC1310 to do continuous TX without modulation and use SMA cable to connect both receiver and transmitter. I'm a little confused, as I'm now doing I/Q sample collection and not doing demodulation, or even my TX signal is just carrier which means I suppose to get DC. Is that right? In my case, will deviation value be a problem if it is not half of symbol rate for I/Q sample collection?

    Both I sample and Q sample are 12bits which is also the resolution of your ADC. In my test, I set my symbol rate was set to 7.2kBaud, so according to what your mentioned, in thereceiver ADC, the data rate is 4 times my symbol rate setting which should be 28.8kbps. Thus, I sample rate should be 2.4k sample per second. Is it correct?

    Thank you so much! Look forward for your reply!

    Best,

    Jianlin

  • 0 in reply to Jianlin Zhou
    TI__Guru* 86151 points

    Thank you for your recommendation. I have changed deviation to 3.5kHz. I was using another CC1310 to do continuous TX without modulation and use SMA cable to connect both receiver and transmitter. I'm a little confused, as I'm now doing I/Q sample collection and not doing demodulation, or even my TX signal is just carrier which means I suppose to get DC. Is that right?

    Yes, but you will see the carrier offset frequency between those two LPs (something in the range of < 10 kHz).

    In my case, will deviation value be a problem if it is not half of symbol rate for I/Q sample collection?

    No, the IQ sample collection do not require a specific deviation value. The code example use modulation index = 1.0. Please, first try to reproduce the results from the code example before you start modify the setup.

    Both I sample and Q sample are 12bits which is also the resolution of your ADC. In my test, I set my symbol rate was set to 7.2kBaud, so according to what your mentioned, in thereceiver ADC, the data rate is 4 times my symbol rate setting which should be 28.8kbps. Thus, I sample rate should be 2.4k sample per second. Is it correct?

    No, this is not correct. Symbol Rate and Data Rate is the same. The IQ (ADC) sample rate in your example is 28.8 kHz. 

    If you are thinking of the bit rate of the IQ samples that will be

    28.8 kHz*12 (bit per I and Q sample) * 2 (one I and 1 Q value) = 691.2 kbps

    Siri