ad797bn Analog Devices, Inc., ad797bn Datasheet - Page 17

• Manufacturer Part Number: ad797bn
• Description: Ultralow Distortion, Ultralow Noise Op Amp
• Manufacturer: Analog Devices, Inc.

A General Purpose ATE/Instrumentation Input/Output
Driver
The ultralow noise and distortion of the AD797 may 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 of 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 high resolution A/D
converters and 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.
–100
–110
–120
–130
–90
100
16
14
12
10
Figure 48. Total Harmonic Distortion (THD) vs. Frequency
8
6
10
Figure 47. Output Voltage Noise Spectral Density
300
100
for Differential Line Receiver
for Differential Line Receiver
1k
FREQUENCY (Hz)
1k
FREQUENCY (Hz)
3k
MEASUREMENT
10k
10k
OPTIONAL
100k
30k
LIMIT
WITHOUT
OPTIONAL
50pF C
WITH
50C
N
N
100k
1M
300k
10M
0.003
0.001
0.0003
0.0001
Rev. E | Page 17 of 20
Ultrasound/Sonar Imaging Preamp
The AD600 variable gain amplifier provides the time controlled
gain (TCG) function necessary for very wide dynamic range
sonar and low frequency ultrasound applications. Under some
circumstances, it is necessary to buffer the input of the AD600
to preserve its low noise performance. To optimize dynamic
range this buffer should have at most 6 dB of gain. The combi-
nation of low noise and low gain is difficult to achieve. The
input buffer circuit shown in Figure 50 provides 1 nV/√Hz
noise performance at a gain of two (dc to 1 MHz) by using
26.1 Ω resistors in its feedback path. Distortion is only −50 dBc
@ 1 MHz at a 2 V p-p output level and drops rapidly to better
than −70 dBc at an output level of 200 mV p-p.
Figure 49. A General Purpose ATE/Instrumentation Input/Output Driver
INPUT
R2
INPUT
26.1Ω
1kΩ
**Use Power Supply Bypassing Shown in Figure 35
**Use Power Supply Bypassing Shown in Figure 35
Figure 50. An Ultrasound Preamplifier Circuit
2
3
2
3
26.1Ω
AD797
AD797
+V
–V
7
4
–V
+V
S
S
22pF
7
4
2kΩ
S
S
**
6
**
649Ω
**
**
6
649Ω
V
3
2
S
= ±6Vdc
AD600
AD811
+V
–V
7
4
S
S
**
**
6
**
**
V
OUT
AD797