Datasheet

AD588
Rev. L | Page 9 of 20
NOISE PERFORMANCE AND REDUCTION
The noise generated by the AD588 is typically less than 6 µV p-p
over the 0.1 Hz to 10 Hz band. Noise in a 1 MHz bandwidth is
approximately 600 µV p-p. The dominant source of this noise is
the buried Zener, which contributes approximately 100 nV/√Hz. In
comparison, the op amp’s contribution is negligible. Figure 7
shows the 0.1 Hz to 10 Hz noise of a typical AD588.
If further noise reduction is desired, an optional capacitor, C
N
,
can be added between the NOISE REDUCTION pin and
ground, as shown in Figure 5.
This forms a low-pass filter with the 4 kΩ R
B
on the output of
the Zener cell. A 1 µF capacitor has a 3 dB point at 40 Hz and
reduces the high frequency noise (to 1 MHz) to about
200 µV p-p. Figure 8 shows the 1 MHz noise of a typical AD588
both with and without a 1 µF capacitor.
Note that a second capacitor is needed in order to implement
the noise reduction feature when using the AD588 in the −10 V
mode (Figure 6). The noise reduction capacitor is limited to
0.1 µF maximum in this mode.
00531-007
1µV
Figure 7. 0.1 Hz to 10 Hz Noise (0.1 Hz to 10 Hz BPF
with Gain of 1000 Applied)
00531-008
C
N
= 1mF
NO C
N
Figure 8. Effect of 1 μF Noise Reduction Capacitor on Broadband Noise