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PWM noise on ADC

CoreyC
Prodigy 10 points

Hello,

 

I am generating a PWM signal that is modulated to produce a 12khz sine wave when filtered. However, when the PWM is turned on, a small 12khz signal appears on the ADC channels when I sample them. Is there a way to reduce this effect or is there inherent to the DSP?

 

Thank you,

Corey

  • 0
    Genius 5170 points

    Hello

    No, it is not inherent to DSP or to any microcontroller. ADC channels shouldn't be corrupted by PWM operations/signals. However, the signal quality will depend on board layout and manufacturing. I believe there are several application notes from Texas Intruments discussing how to make boards noise immune. Also, there are tons general material available on the web.

  • 0
    TI__Guru 57255 points

    Corey,

    As Arefeen mentions, your ADC should not see PWM signals directly, and that board layout can generally fixes the issue.

    However, on the ADC, impulses found on the rising and falling edges of PWM (when the mosfets/mosfet drivers charge/discharge energy to the ground plane) is a very common issue to all ADCs.  If this is what you are seeing, you can limit the effects of this "switching noise" but will have difficulty getting rid of it completely.  The key is instead to sample the ADC as far as you can from switching noise.  On C2000 devices, PWM signal events can directly drive ADC conversion and therefore you may configure the ADC to sample away from switching noise.


    Thank you,
    Brett