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TLV320ADC3101 audio offset

Arnout Diels
Intellectual 730 points
Other Parts Discussed in Thread: TLV320ADC3101

Hi,

We are facing an issue that the audio we sample has a slight (positive) offset . (I am talking 0.015 on a scale of -1..1 in linear scale)

We only connect the signal through a capacitor (AC coupled) to the chip, and we can see that the chip drives the voltage at 1.35V. Grounding the pin clearly clips the measured signal all the way negative, so it seems to be driven sighly higher than the ADC expects.
(Attaching a scope (1Mohm input resistance) already changes the measured offset so significantly, that it is hard to see the exact signal directly on the pin.)

=> Is it possible to calibrate the ADC somehow, to compensate for the offset?

Thank you for your reply!

Arnout

  • 0
    TI__Guru* 84915 points
    Hi, Arnout,

    The TLV320ADC3101 has an internal common-mode voltage. This voltage is applied once the ADC is enabled. This voltage cannot be reconfigured by registers. So, in order to increase or reduce the offset for application purposes, you may use the page 1 / register 26 (Dither Control). This register can be used to modify the DC offset of left or right ADC in 15mV steps.

    Please let me know if you have questions or comments about this.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Intellectual 730 points

    Hi,

    Thank you for your reply.

    This works, and allows me to compensate the offset for a given PBA gain. However, for different settings of PBA gain, a different DC dither offset is required to compensate it. (The digital gain has no effect, other than to amplify the offset at a given PBA gain). In general, a higher PBA gain seems to require a stronger offset.

    Is this to be expected?

    Kind regards,

    Arnout

  • 0 in reply to Arnout Diels
    TI__Guru* 84915 points
    Hi, Arnout,

    Additional DC offsets are not expected during the ADC3101 usage. This could be related with an issue at the analog inputs. So, another way to reduce unexpected offsets is with the biquad filters. You may configure the programmable filters as a DC-removal filter. This will avoid the need of reconfigure the Dither Control register during the ADC3101 usage.

    Please let me know if you have questions or comments.

    Best regards,
    Luis Fernando Rodríguez S.