Updated: 9 Jan 2001

CONTENTS.

• Introduction.
• Specs.
• Fig a. Series feedback: THD versus level, various loads.

INTRODUCTION.
The AD797 (Analog Devices) is a single opamp with very low noise and distortion. No dual version is available. This is a remarkable device. My experience with it is limited, but so far as it goes the opamp appears to do all that is claimed for it.
It does, however, appear to be rather difficult to guarantee HF stability.

SPECS.
Here are the vital statistics:
All typical values, for +/-15V supply rails.

Supply voltage	+/-18V abs max
Output range	+/-13V typ (2K load)
CM range	+/-12V
en	0.9 nV/rtHz typ 1 kHz
in	2.0 pA/rtHz typ
Ibias	250 nA typ into inputs from +V
Slew rate:	20 V/us
Supply current	8.2 mA
Unity gain stable	YES (with external compen)
Cost	650p RS Jan 2001

Note: Startlingly low figure for input voltage noise, and high Ibias. However, this is a rather expensive part.

THD into loads down to 500 Ohm, at 7.75 Vrms. Output is virtually indistinguishable from input. Series feedback, but no CM problems. Gain=3.2x