TLV320ADC3101EVM-K: TLV320ADC3101EVM-K

Kiran Ajjevadimath

Hi,

We are using TLV320ADC3101EVM-K in our solution. Please find below questions on same:

1) What is the maximum input impedance that can be interfaced to single ended input of ADC. as we would like to connect a low pass filter.

2) We are connecting Arbitrary waveform generator as source to ADC, do you recommend any filters for 1KHz frequency. As we see bit higher noise floor and amplitude reduction of fundamental frequency (1Khz) as attached below:

over 1 year ago

0 Daveon Douglas over 1 year ago

TI__Genius 15680 points

Hi Kiran,

In section 10.3.0 of the datasheet, there is a chart that lists the impedance and explains how the technology changes depending on how you program the front end attenuation and set the MIC PGA gain. The maximum being 92kΩ at -6dB attenuation & 40dB PGA gain.

Also, I don't believe you need to implement a low pass filter. Due to the input impedance and required AC-coupling capacitor a high pass filter is created. I suggest manipulating the capacitor you select paired with your input level to filter out the noise you're seeing.

Regards,

Daveon Douglas

0 Kiran Ajjevadimath over 1 year ago in reply to Daveon Douglas

Prodigy 70 points

Hi Daveon,

Thanks for the response.

As you can see in screenshot, the fundamental frequency being 1Khz and there are unwanted harmonics following that(2k,3k,5k). I would ideally need a low pass filter with cut off frequency at 1Khz to clear all other harmonics.

Let me know for more inputs.

0 Daveon Douglas over 1 year ago in reply to Kiran Ajjevadimath

TI__Genius 15680 points

Hi,

Ok I see, ultimately it is not an issue cascading the two filters together.

The datasheet doesn't explicitly outline a 'maximum' impedance for an analog input pin in SE configuration, so as long as the combined impendence of both filters doesn't exceed the local max (40dB PGA gain) for its respective mixer gain it should be ok.

I have sent a note to our internal design team to see if they can provide some insight, I will respond here when possible.

Regards,

0 Kiran Ajjevadimath over 1 year ago in reply to Daveon Douglas

Prodigy 70 points

Hi Daveon,

Any update on above query.

0 Daveon Douglas over 1 year ago in reply to Kiran Ajjevadimath

TI__Genius 15680 points

Hi Kiran,

Apologies for the delay, I have sent another note to our design team and will update you once I get an answer.

Best regards,

0 Daveon Douglas over 1 year ago in reply to Daveon Douglas

TI__Genius 15680 points

Hi Kiran,

An update to our conversation:

There shouldn’t be any limit on the maximum impedance you can put in series with the input pins. However, note that this series impedance will form a divider with the internal impedance and lead to gain error (for eg. For 0dB gain, input impedance is ~35Kohm. If customer puts a 35Kohm in series with the input pins, the ADC will see an effective gain of -6dB). With changing gain, as the input impedance changes, this gain error will also change.

Hope this helps!

Regards,

0 Kiran Ajjevadimath 12 months ago in reply to Daveon Douglas

Prodigy 70 points

Hi Daveon,

Thanks for the response on impedance.

Could you please, respond on 2nd point (noise floor and reducing harmonics) in the query.

0 Daveon Douglas 12 months ago in reply to Kiran Ajjevadimath

TI__Genius 15680 points

Hi Kiran,

From the analog input side we only recommend AC coupling the input to reduce harmonics as suggested in the datasheet.

This app note also addresses methods to improve noise performance: Common Noise Issues in Audio Codecs

Regards,

Audio

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TLV320ADC3101EVM-K: TLV320ADC3101EVM-K