Datasheet

AD797
Rev. H | Page 16 of 20
Differential Line Receiver
The differential receiver circuit of Figure 46 is useful for many
applications, from audio to MRI imaging. The circuit allows
extraction of a low level signal in the presence of common-
mode noise. As shown in Figure 47, the AD797 provides this
function with only 9 nV/√Hz noise at the output. Figure 48
shows the AD797 20-bit THD performance over the audio band
and the 16-bit accuracy to 250 kHz.
**
**
AD797
00846-046
6
2
3
1kΩ
DIFFERENTIAL
INPUT
1kΩ
1kΩ
1kΩ
20pF
50pF*
20p
F
–V
S
+V
S
4
7
8
V
O
U
T
OPTIONAL
USE THE POWER SUPPLY BYPASSING
SHOWN IN FIGURE 35.
*
**
Figure 46. Differential Line Receiver
00846-047
6
10M10010 1M100k10k1k
16
12
8
10
14
FREQUENCY (Hz)
OUTPUT VOLTAGE NOISE (nV/√Hz)
Figure 47. Output Voltage Noise Spectral Density
for Differential Line Receiver
00846-048
FREQUENCY (Hz)
THD
(dB)
THD (%)
–
90
300k
–120
–130
300100
–110
–100
100k30k10k3k1k
0.003
0.0003
0.001
0.0001
WITHOUT
OPTIONAL
50pF C
N
WITH
OPTIONAL
50pF C
N
MEASUREMENT
LIMIT
Figure 48. Total Harmonic Distortion (THD) vs. Frequency
for Differential Line Receiver
A General-Purpose ATE/Instrumentation I/O Driver
The ultralow noise and distortion of the AD797 can be
combined with the wide bandwidth, slew rate, and load drive
of a current feedback amplifier to yield a very wide dynamic
range general-purpose driver. The circuit shown in Figure 49
combines the AD797 with the AD811 in just such an application.
Using the component values shown, this circuit is capable of
better than −90 dB THD with a ±5 V, 500 kHz output signal.
The circuit is, therefore, suitable for driving a high resolution
ADC as an output driver in automatic test equipment (ATE)
systems. Using a 100 kHz sine wave, the circuit drives a 600 Ω
load to a level of 7 V rms with less than −109 dB THD and a
10 kΩ load at less than −117 dB THD.
*
7
*
*
*
+V
S
+V
S
–V
S
AD797
00846-049
22p
F
2kΩ
649Ω
649Ω
1kΩ
R2
6
3
4
2
7
AD811
6
2
4
3
–V
S
*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.
V
OUT
V
IN
Figure 49. A General-Purpose ATE/Instrumentation I/O Driver