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TLV320ADC6140: garbled samples during Input overdrive

Jagdish Patange
Prodigy 250 points
Part Number: TLV320ADC6140

Sir,

I have interfaced ADC6140 with TI DSP C6747.

Configured ADC6140  for word len of 16 bits, single ended ac coupled input. PGA gain to 6 dB.

McAsp0 RFMT register at DSP is set to 0x00018078 // no rotation, 16 bits len, pad with 0, msb first.

Normally I give 250 mV rms inp and I am getting proper sine wave.

To test a input overdrive case, I am giving 600 mV input (i.e. 600 mV at ADC input with pga gain of 6 dB= 1.2V rms ).

I was expecting samples shall be clipped (saturated) during peaks but instead these samples are garbled (i.e. +ve peak is coming as -ve value).

How do I ensure samples are saturated(clipped) during input overdrive condition?

  • +1
    TI__Intellectual 2030 points

    Hi Jagdish

    1) What input freq?  analog? what's the Fs set to?

    2) Can you provide the sampled output for both conditions?

    3) do you have a scope shot of the input?

  • 0
    Prodigy 250 points

    Sir, Thank you for your response and sorry for my delayed reply as was on personal leave.

    1. max analog audio frequency is 6 kHz, Fs is set to 16 kHz.

    3. Scope shot are attached

    Following is for 1 kHz input, 500 mV rms input to ADC6140 with internal PGA gain set to 5dB. Output of AIC3106 codec is captured.

    Following is for 1 kHz input, 600 mV rms input to ADC6140 with internal PGA gain set to 5dB. Output of AIC3106 codec is captured.

  • 0 in reply to Jagdish Patange
    Prodigy 250 points

    Sir,

    Found the bug, I was negating incoming signal on int16 samples, this was creating problem.

    While capturing samples this bug was found, thanks for your suggestion.