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AWR1642: Regarding the issue of TX start time and ADC start time

He He
Prodigy 10 points
Part Number: AWR1642

Tool/software:

Hi ! Maybe I misunderstood. Could you help me analyze in detail the impact of two parameters on the mixer?

In the figure, TX START TIME controls the transmission of the antenna, while ADC START TIME controls the sampling process. The reference signal in the mixer is the same as the transmission signal. Due to the configuration of ADC START TIME, the starting frequency domain of ADC sampling is different from the transmission signal. Will this not cause distance errors? Is it compensated by internal components?

For example, the settings for SensorConfig are as follows. The start frequency is  77(GHz)+30.03(MHZ/us)*6(us) = 77.18(GHz). Due to the Tx start time setting, the frequency of the transmitted signal is less than 77.18GHz.Could you tell me the starting frequency of the transmitted signal and the reference signal in the mixer at this time?

Thanks！

  • +1
    TI__Mastermind 20605 points

    Hi He,

    Correct me if I am wrong but I think you might be confusing mixing (which happens after the receiver stage) with the A2D sampling. The sampling is done on the IF signal after the mixing in the front end. Therefore, no frequency component is missed out in the mixing stage. 

    The criteria for choosing the ADC start time however is the time needed for synth to settle. If there is not sufficient time, you can see some other frequency components appear in your IF signal. Please consider this is your analysis.

    Regards,

    Kaushik

  • +1 in reply to Kaushik Gowda
    Prodigy 10 points

    Hi Kaushik,

    I see! Thank you for reply!

    Please take a look at my following statement. Is this my correct understanding?

    The starting frequency in the configuration is 77GHz. According to the above configuration, after post-processing in mmwave studio, the starting frequency information is 77.1802GHz, which is equal to 77000 (MHz)+30.03 (MHz/us) * 6 (us). Therefore, the ADC start time is used for the synthesizer. After setting the ADC start time, the synthesizer will wait. At this time, the frequency of the signal starts to rise from 77GHz, but it is not transmitted until the time is up. The antenna will transmit signals at a frequency of starting frequency+ADC time * slope. Am I correct?

    I also tried to change the Tx start time. Does Tx Start time control the antenna is turned on or not? If I set the Tx start time to a value greater than the ADC sampling time, the antenna will not transmit. Is that right?

    Best Regards!

  • +1 in reply to He He
    TI__Mastermind 20605 points

    Hi He,

    Please find my responses below:

    1. The Tx starts transmitting before the sampling begins (Typical Tx turn time is before the ADC start time). The start frequency is offset according to the start of the sampling as that is what will be available at the time of sampling, and this is needed for your calculations from thereon.
    2. Tx start time controls when the antenna is turned on and not if it is turned on or not. Yes, Tx start time is supposed t be lesser than the ADC start time.

    Regards,

    Kaushik

  • 0 in reply to Kaushik Gowda
    Prodigy 10 points

    I get it , thanks!

  • 0 in reply to Kaushik Gowda
    Prodigy 20 points

    Hi Kaushik, 

    Thanks for your reply.

    I have similar questions about the parameter Tx Start Time, which appears in He's figure (above the parameter ADC Start Time).

    My questions are: 

    1. When Tx Start Time is non-zero, will the starting frequency of the transmission have an offset? For example, in He's setting, if I change the Tx Start Time to be 1us,  the starting frequency of the transmission will be 77GHz+30.03(MHZ/us)*1(us)=77.03003GHz. Am I right?
    2. When Tx Start Time is non-zero, will the Tx chirp sent to the mixer at the receiver have the same frequency offset described above?

    I'm interested in the starting frequency of the transmission because I want to use the phase of the radar signal.

    Thank you very much!

    Best,
    Qi 

  • 0 in reply to Qi DAI
    TI__Mastermind 20605 points

    Hi Qi,

    Please find my responses as follows:

    1. Yes. Your understanding here is correct. Ramping starts at the end of the idle time even if the Tx is not turned on.
    2. The signal sent will match the signal when the Tx is turned on as this is what is needed to obtain the IF.

    Regards,

    Kaushik