AWR1243: Sep size and number of steps PLL

radarJunkie

Expert 2090 points

Part Number: AWR1243

Hi,

I am trying to understand how to calculate the step size and the number of steps in the fmcw sweep. I want to know this so that I can understand the linearity measurements that I am currently performing.

If the step size and number of steps in the chirp can be known then I can figure out how many frequency points do I need to not overly perform optimistic or pessimistic measurements for linearity.

If possible, I would appreciate an expression or formula which can tell me the step size.

Thank you,

over 7 years ago

0 Raghunandan Kamath over 7 years ago

TI__Mastermind 22155 points

RJ,
One of our experts in this subject will get back to you ASAP.
Thanks,
Raghu

0 Kuangda Wang over 7 years ago in reply to Raghunandan Kamath

Prodigy 35 points

Is there an answer to this question? And what is the maximum PD rate of the PLL? Thanks!

0 radarJunkie over 7 years ago in reply to Kuangda Wang

Expert 2090 points

Hi Raghu:

I wanted to follow-up with you to check if there is some input to my earlier question on the PLL step size, and number of steps, update rate etc.

Regards,

RJ

0 radarJunkie over 7 years ago in reply to Raghunandan Kamath

Expert 2090 points

Hi Raghu,

Is there an update for me on the question that I have asked earlier ? I would really appreciate your feedback and help on this.

Regards,

RJ

0 Shankar Ram over 7 years ago

TI__Prodigy 270 points

Hi RJ,
The chirp start frequency is configurable in steps of 53.644Hz. During ramp, our transmitter frequency varies continuously with time. There will be no discrete steps observed.

Are you measuring linearity at Tx output? Can you please give more details on your measurement setup?

Thanks,
Shankar

0 Shankar Ram over 7 years ago in reply to Shankar Ram

TI__Prodigy 270 points

Hi RJ,
Regarding the second question, we use a closed loop PLL with an update rate of 900MHz.

Thanks,
Shankar

0 radarJunkie over 7 years ago in reply to Shankar Ram

Expert 2090 points

Hi Shankar:

Thank you so much for your replies.

The update rate reply helps answer my query. I am measuring linearity at the Tx output with a harmonic mixer and a spectrum analyzer.
The reason I asked for the update rate was because that way I can calculate the frequency change per sample time. If the synthesizer is moving at 10kHz per update time step, then I need to make sure the frequency measurement error of the spectrum analyzer is set in a manner which is not clouding the performance of the synthesizer. If no video bandwidth filter is used, the frequency versus time measurement error of the spectrum analyzer is +-900 kHz (95 CI). This would cause a very spiky measurement which would not reflect the actual behavior of the PLL.

Regards,

RJ

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AWR1243: Sep size and number of steps PLL