PCM6260-Q1: About input attenuator

Kailyn Chen

Part Number: PCM6260-Q1

Hello，

About PCM6260 input attenuator, I'd like to confirm the DC-Coupled Microphone Differential Input mode is -14dB, what about DC-Coupled Microphone single-ended l Input mode,-8dB?

Differential mode: -14dB=20log(2.828/14.14)，

single-ended mode: -8dB=20log(2.828/7.07)

Our customer's application is as following:

Theoretical calculation: We want no attenuation on the path, considering MIC has intrinsic μV - 10.5dB attenuation, ADC intrinsic μV - 8dB attenuation, so the gain is set to GAIN =8dB, Volume10.5dB actually tested: we used ALSA tinycap recording to get PCM files, The sample value was read through the Au software and a mismatch was found with the theoretical value. If the theoretically calculated ADC intrinsic μC- 8dB is changed to 0dB, it will match the actual test.

In addition, here is the ADC registers configuration, please help to check if they are proper.

12.pdf

Best regards

kailyn

over 3 years ago

0 Sanjay Dixit over 3 years ago

TI__Mastermind 23030 points

Please send me your schematic

0 yingxiao-sun over 3 years ago in reply to Sanjay Dixit

Prodigy 70 points

Hello，

The following attachment is our schematic.

And actually we used single-end mode, R42-R53 is 680ohm, R28-R39 is 0ohm, R1/R4/R7/R10/R13/R16 is NC.

/cfs-file/__key/communityserver-discussions-components-files/6/ADC_9F530674FE56_.pdf

0 Sanjay Dixit over 3 years ago in reply to yingxiao-sun

TI__Mastermind 23030 points

shall respond in a few hours

0 yingxiao-sun over 3 years ago in reply to Sanjay Dixit

Prodigy 70 points

Hello,

How about the above question confirmed, can you share the progress with me?

Thank you!

0 Sanjay Dixit over 3 years ago in reply to yingxiao-sun

TI__Mastermind 23030 points

i shall reply in a few hours. Aploogies for the delay

0 Sanjay Dixit over 3 years ago in reply to Sanjay Dixit

TI__Mastermind 23030 points

I see a pullup of 330 ohms on the Mic. What is the output Impedance of the Mic used?

0 yingxiao-sun over 3 years ago in reply to Sanjay Dixit

Prodigy 70 points

Sorry, actually only one 680ohm is used. The Mic impedance is 680ohm.

The following attachment is newest schematic.

/cfs-file/__key/communityserver-discussions-components-files/6/ADC_C791C6967F675F00_2023_2D00_08_2D00_18.pdf

0 yingxiao-sun over 3 years ago in reply to yingxiao-sun

Prodigy 70 points

Can you firstly tell me how many input attenuation in PGA at DC-Coupled Microphone Differential and Single-end Input mode?

And whether it is fixed that couldn't be ignored.

0 Sanjay Dixit over 3 years ago in reply to yingxiao-sun

TI__Mastermind 23030 points

You can approximate the ADC input as a 20k Resistor.

This means that the circuit mic will make a voltage divider with Input Impedance

VADC=Vmic*20k(680+20k)

0 yingxiao-sun over 2 years ago in reply to Sanjay Dixit

Prodigy 70 points

Does this VADC affects the input attenuation? I can not understand.

PS:ADC input is a 25k resistor from PCM6260 datasheet, I think this small divider could be ignored.

Can you help me to confirm how many input attenuation in PGA at DC-Coupled Microphone Differential and Single-end Input mode?

And whether it is fixed and couldn't be ignored or modify through registers configuration.

0 Kailyn Chen over 2 years ago in reply to Sanjay Dixit

TI__Genius 9560 points

Hi Sanjay，

I think you misunderstand the customer's meaning.

As to the description of the PCM 6260 datasheet, it has input attenuator, if the input is DC coupled differential mode, the attenuator is calculated by the following equation:

Differential mode: -14dB=20log(2.828/14.14)，

That is to say, it has about -14dB attenuator if the input is differential mode.

He'd like to confirm if using DC-Coupled Microphone single-ended l Input mode, what is the attenuation? or how to calculate it?

Best regards

kailyn

0 Sanjay Dixit over 2 years ago in reply to Kailyn Chen

TI__Mastermind 23030 points

Hello Kailyn,

Why is the input attenuator of value for the customer?

The ADC in single ended mode supports a 5Vrms input for 0 DBFS digital output.

This is at 0db PGA Gain

This is sufficant information for customer application

The attenuation is a fixed level inside the Chip and is done in order that the 3.3v chip can handle large signals.

0 yingxiao-sun over 2 years ago in reply to Sanjay Dixit

Prodigy 70 points

Hello,

We have already understand how PCM6260 works.

Thank you for your respond.

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PCM6260-Q1: About input attenuator