TLV320ADC5120: Signal attenuation with different AP output impedance and ADC input impedance

Shubiao Wang

Part Number: TLV320ADC5120

HI there,

i am working on TLV320adc5120 measurement now.

I have measured the output signal amplitude with different configuration of AP output impedance and TLV320ADC5120 input impedance.

however the measurement results is out of expectation.

for example, when the output impedance of AP is 600Ω， input impedance of ADC is 2.5K Ω；input signal is 1Vrms(0dbV) .

the expected measurement is -7.87dB. while the measurement is only -7.168db. would you kindly help to share your comments here?

test condition:

1. input signal, 0dBV, differential input, ac coupling

2. TLV320ADC5120 configuration. DRE=off, gain =0db; line input

BRs,

Shubiao

over 2 years ago

0 Ore Ogundana over 2 years ago

TI__Genius 10305 points

Hey shubiao,

Thanks for these questions. These would be looked into within the next 24-48 business hours.

Best regards,

Ore.

0 Ore Ogundana over 2 years ago

TI__Genius 10305 points

Hey Shubiao,

Where is the measurement of -7.16db coming from? Is this dbFS? Please explain the measurements you collected and share the circuit diagram of the front end. Thanks

Ore.

0 Shubiao Wang over 2 years ago in reply to Ore Ogundana

TI__Intellectual 1490 points

Hi Ore,

Yes, -7.16 is measured by AP; it is dbFS.

the measurement is operated by AP+ TLV320ADC5120 EVM;

BRs,

Shubiao;

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Thanks for your response.

0 Shubiao Wang over 2 years ago in reply to Ore Ogundana

TI__Intellectual 1490 points

Hi Ore,

Do you have any update here?

BRs,

Shubiao

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Yes Shubiao,

Your configurations were replicated using your AP and TLV320ADC5120 impedance configurations and we got these results:

Please clarify how you came about your expectation for the -7.87dBFS at the 600Ohms(AP) and 2.5Kohms(ADC) impedance configurations? For example was there a formula you were following?

Regards,

Ore.

0 Shubiao Wang over 2 years ago in reply to Ore Ogundana

TI__Intellectual 1490 points

AP output voltage is 1VRMS

adc input voltage is

2500/(2500+600)*1Vrms= 0.8065Vrms;

adc full scale input is 2Vrms;

therefore, output =20lg(0.8065/2)=-7.87dB;

BRs,

Shubiao

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Thanks for the clarification.

Regards,

Ore.

0 Shubiao Wang over 2 years ago in reply to Ore Ogundana

TI__Intellectual 1490 points

please let me know your comments, Thanks.

0 Jeff McPherson over 2 years ago in reply to Shubiao Wang

TI__Mastermind 48845 points

Hi Shubiao,

Today is a TI Holiday. Ore will give you an update within 48 hours.

Please wait to reply unless we have failed to respond to you in a timely manner.

Thank you for your patience,

Jeff McPherson

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Hello Shubiao,

I am investigating these results to come up with a viable explanation. Please practice some patience.

Thank you.

Ore.

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Hello Shibuao,

Some gain variation is expected that is why ADC5120 has programmable channel gain feature explained in section '8.3.6.1 Programmable Channel Gain and Digital Volume Control' and a programmable channel gain calibration feature explained in section '8.3.6.2 Programmable Channel Gain Calibration' of the datasheet. I hope this helps.

Best regards,

Ore

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

Hello Shibuao,

In regards to the impedance of the ADC5120, each input pin share the same impedance value. For example, when the ADC impedances are configured to be 2.5KOhms, IN+ and IN- are each 2.5kOhms, so measuring across both pins would result in two 2.5kOhms in series which add up to 5kOhms. Take that into account when measuring and calculating expected results.

Best regards,

Ore.

0 Shubiao Wang over 2 years ago in reply to Ore Ogundana

TI__Intellectual 1490 points

AP output voltage is 1VRMS

adc input voltage is

2500*2/(2500*2+600)*1Vrms= 0.8929Vrms;

adc full scale input is 2Vrms;

therefore, output =20lg(0.8929/2)=-7.0dB;

is that correct?

0 Ore Ogundana over 2 years ago in reply to Shubiao Wang

TI__Genius 10305 points

yes your calculation is correct.

BR,

Ore.

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TLV320ADC5120: Signal attenuation with different AP output impedance and ADC input impedance