AWR6843: ADC sampling rate

juncheng Wu

Prodigy 30 points

Part Number: AWR6843

Hi TI engineers,

I use sample code which project name is CPD with classification in toolbox 1.30.01.03.

I had some question about ADC sampling rate and the parameter name is called as digOutSampleRate in code.

Then i used the ADC data to simulate the sample code algorithm, and i set the sampling rate to 2.2MHz.

note that : [ I attached the radar to the absorber to get the ADC data, which means no target.]

the figure as shown

when range bin from 63 to 64, it would occur discontinuities.

So, i increased the ADC sampling rate from 2.2MHz to 2.25MHz

and the issue seems fixed.

So, I want to know why it would be fix by increase the sampling rate.

and it is allow to set small change about ADC sampling rate (I mean 2.2Mhz -> 2.25Mhz , the samll change is 0.05Mhz, Does it work ?)

i want to ask this because the sampling rate usually set multiples of 2, or maybe i misunderstand.

thanks !

Sincerely,JcWu.

9 months ago

0 Kristien Everett 9 months ago

TI__Expert 7155 points

Hey Juncheng,

Thanks for reaching out over E2E regarding the end range bin discontinuity. One of our signal processing experts will get back to you around next Tuesday, but I would highly recommend reviewing the Programming Chirp Parameters in TI Radar Devices application note which discusses many of the effects of chirp configurations on system parameters. It is possible that this is an issue of maximum range which is affected by the ADC sampling rate as shown in Section 2.1.1 of the previously mentioned app note.

Regards,

Kristien

0 juncheng Wu 9 months ago in reply to Kristien Everett

Prodigy 30 points

Thanks!
I look forward to your next reply

0 Kristien Everett 9 months ago in reply to juncheng Wu

TI__Expert 7155 points

Hey Juncheng,

No problem! We will get back to you around Tuesday, but let us know if you do not hear anything back from one of our experts.

Regards,

Kristien

0 zigang Yang 9 months ago

TI__Mastermind 36485 points

HI, there:

Sorry for the late reply. I was on vacation.

For AWR6843 chirp configuration, you can use the rampTimingCalculator (a tab inside mmwave studio 2.1.1.0) for see how to set the ADC start time and total ramp time. These settings are related to the ADC sampling rate. A larger ADC sampling rate will be helpful to reduce the minimum ADC start time and reduce total ramp time. Note that 99% of settling is usually preferred. Let me know if this is helpful.

Best,

Zigang

0 juncheng Wu 9 months ago in reply to zigang Yang

Prodigy 30 points

Hi zigang,

Follow your advice, I use rampTimingCalculator to check chirp config.

shown this figure

the adc start time set 11us, ramp end time set 41us

and the bandwidth seems still in scope

if there is some weird value in this picture ,please let me know !

so back to previous issue which is range bin 64 discontinuous ,
consider this config bandwidth, does the issue might be cause by maximum range which is affected by the ADC sampling rate that Kristien mentioned ?
or other possibilities

ps : Programming Chirp Parameters in TI Radar Devices mentioned the IF bandwidth is limited to 0.9*(ADC sampling)/2 <- complex2x

0 zigang Yang 9 months ago in reply to juncheng Wu

TI__Mastermind 36485 points

Hi, there:

I am not sure that reduce the ramp time manually will be a good idea. I would rather take the 99% settling column. I will double check with our design team and get back to you.

Best,

Zigang

0 juncheng Wu 9 months ago in reply to zigang Yang

Prodigy 30 points

OK , if consider the previous ADC result ,It maybe is a bad idea.

Waiting for your next reply ! thanks

Sincerely,

JcWu.

+1 zigang Yang 9 months ago in reply to juncheng Wu

TI__Mastermind 36485 points

Hi, JcWu:

Here is the reply from our expert:

It is not recommended to reduce the ramp end time at the last column. Recommendation would be to start with 95% and increase ADC start time and ramp end time uniformly.

Best,

Zigang

0 juncheng Wu 9 months ago in reply to zigang Yang

Prodigy 30 points

ok ! I will follow your advice.

thanks

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AWR6843: ADC sampling rate