OPA1632 + PCM1804 question

dismirlian · 4th July 2007, 02:54 PM

Hello, I am designing an ADC input stage for the PCM1804, usign the OPA1632 differential opamp. Reading the opamp's datahseet, I found a recommended circuit for this implementation (see attachment). The question is: is it necessary to buffer the VCOM pin of the A/D, or can I connect it directly to the Vocm pin of the opamp (perhaps through an RC filter)? Thanks a lot.

Diego.

Keruskerfuerst · 4th July 2007, 03:57 PM

The datasheet of the PCM1804 does not mention the output impedance of the Vocm pin.

Advantage of the additional op: lower impedance of the Vocm source.
Disadvantage: maybe higher offset.

I would say: just try out both circuits.

dismirlian · 4th July 2007, 04:40 PM

Thanks for your answer. I noticed the lack of information regarding the output impedance of the Vocm pin, but the input impedance of the VCOM pin of the opamp is 34Meg, according to the datasheet.

I'll follow your suggestion and try both circuits.

Diego.

4th July 2007, 03:57 PM	#2
Keruskerfuerst diyAudio Member Join Date: May 2007	The datasheet of the PCM1804 does not mention the output impedance of the Vocm pin. Advantage of the additional op: lower impedance of the Vocm source. Disadvantage: maybe higher offset. I would say: just try out both circuits. __________________ Houston, we have a problem!

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4th July 2007, 04:40 PM	#3
dismirlian diyAudio Member Join Date: Sep 2006	Thanks for your answer. I noticed the lack of information regarding the output impedance of the Vocm pin, but the input impedance of the VCOM pin of the opamp is 34Meg, according to the datasheet. I'll follow your suggestion and try both circuits. Diego.