PCM1804: Analog input

Hiroshi Saito

Part Number: PCM1804

Hello experts.

Please tell me about the PCM1804 analog input specifications and the input circuit.

(1) The datasheet states that the input voltage is differential ±2.5V.
For example, if signals are input to VINL+ and VINL- in opposite phase, is the maximum input of VINL+ and VINL- ±2.5V? Or is it ±1.25V?

(2)Give me your advice.
The product I'm designing requires an ATT of about -20dB before the PCM1804.
In the schematic below,
(a) Attenuate with the resistance ratio of R1:R3
(b) Attenuate with R7, R8, and R9
Which one is better?

Best regards.
Saito

over 1 year ago

0 Jeff Julich over 1 year ago

TI__Intellectual 2030 points

Hi Saito,

1) For differential of +-2.5V, each leg of that is 1/2 of that. So yes, max input for each leg is +-1.25V.

2) Does the op amp require to unity gain or above?

Regardless for best noise performance you should just R7-9 for gain reduction as long as your op amps' Vout swing is wide enough to handle it well.

0 Hiroshi Saito over 1 year ago

Prodigy 20 points

Hi Jeff, thank you for your answer.

1) ``each leg is +-1.25V.''
In the following circuit example in the datasheet, when 8.28Vpp is input, it seems that each leg is 2.5Vpp. Which is correct, 2.5Vpp or 1.25Vpp?

2) Thanks for your advice. We will use R7, R8, and R9 to attenuate.

+1 Jeff Julich over 1 year ago in reply to Hiroshi Saito

TI__Intellectual 2030 points

1) I believe you are correct and this example is wrong. 2.5Vp-p for each is too much. The gain would have to be 0.15.

2) No problem! Wish you the best of luck.

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PCM1804: Analog input