DAC IV stage schematic

[mahen.jnk]

The schematic at the link below is from analog's AD1955 DAC reference schematic with IV stage using opamps.

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What is the purpose of R80 and R81 and also R60 and C42 in the feedback path? Appreciate if anyone explains their working and how to calculate those values.

Thanks in advance
Ma.jnk

 

[jcx]

data sheet "analog output" section explains bias offset resistors - needs very quiet Vsupply


C across op amp I/V feedback is good for keeping input Z low to higher frequencies, reducing slew rate, output high frequency noise

but AD797 isn't exactly "unity gain stable" the series R is recommended in its data sheet

I would increase the feedback C to give the desired low pass corner frequency with the feedback R - 100 pF is too small