DAC IV stage schematic

mahen.jnk · 10th August 2010, 04:47 PM

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 · 12th August 2010, 03:59 PM

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

10th August 2010, 04:47 PM	#1
mahen.jnk diyAudio Member Join Date: Jan 2010	DAC IV stage schematic The schematic at the link below is from analog's AD1955 DAC reference schematic with IV stage using opamps. Picasa Web Albums - mahen.jnk - Temp 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

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12th August 2010, 03:59 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	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

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