
AD600/AD602
APPLICATIONS 
The full potential of any high performance amplifier can only 
be realized by careful attention to details in its applications. The 
following pages describe fully tested circuits in which many 
such details have already been considered. However, as is always 
true of high accuracy, high speed analog circuits, the schematic 
is only part of the story; this is no less true for the AD600/ 
AD602. Appropriate choices in the overall board layout and the 
type and placement of power supply decoupling components 
are very important. As explained previously, the input grounds 
A1LO and A2LO must use the shortest possible connections. 
Rev. E | Page 15 of 28 
The following circuits show examples of time-gain control for 
ultrasound and sonar, methods for increasing the output drive, 
and AGC amplifiers for audio and RF/IF signal processing 
using both peak and rms detectors. These circuits also illustrate 
methods of cascading X-AMPs for either maintaining the 
optimal SNR or maximizing the accuracy of the gain-control 
voltage for use in signal measurement. These AGC circuits can 
be modified for use as voltage-controlled amplifiers in sonar 
and ultrasound applications by removing the detector and 
substituting a DAC or other voltage source for supplying the 
control voltage. 
TIME-GAIN CONTROL (TGC) AND TIME-VARIABLE 
GAIN (TVG) 
Ultrasound and sonar systems share a similar requirement: both 
need to provide an exponential increase in gain in response to a 
linear control voltage, that is, a gain control that is linear in dB. 
Figure 33 shows the AD600/AD602 configured for a control 
voltage ramp starting at 625 mV and ending at +625 mV for a 
gain-control range of 40 dB. The polarity of the gain-control 
voltage can be reversed, and the control voltage inputs C1HI 
and C1LO can be reversed to achieve the same effect. The gain-
control voltage can be supplied by a voltage-output DAC, such 
as the 
AD7244
, which contains two complete DACs, operates 
from ±5 V supplies, has an internal reference of +3 V, and 
provides ±3 V of output swing. As such, it is well suited for use 
with the AD600/AD602, needing only a few resistors to scale 
the output voltage of the DACs to the levels needed by the 
AD600/AD602.  
CONTROLVOLTAGE,
V
G
+625mV
0dB
–625mV
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
REF
A1
A2
C1HI
A1CM
A1OP
VNEG
A2OP
A2CM
C2HI
C1LO
A1HI
A1LO
GAT1
A2LO
A2HI
C2LO
V
G
AD600 OR
AD602
GAT2
+5V
–5V
+
–
+
–
VPOS
VOLTAGE-OUTPUT
DAC
A1
GAIN
40dB
0
Figure 33. The Simplest Application of the X-AMP Is as a TGC or TVG Amplifier 
in Ultrasound or Sonar. Only the A1 connections are shown for simplicity. 
INCREASING OUTPUT DRIVE 
The AD600/AD602’s output stage has limited capability for 
negative-load driving capability. For driving loads less than  
500 Ω, the load drive can be increased by approximately 5 mA 
by connecting a 1 kΩ pull-down resistor from the output to the 
negative supply (see Figure 34). 
DRIVING CAPACITIVE LOADS 
For driving capacitive loads of greater than 5 pF, insert a 10 Ω 
resistor between the output and the load. This lowers the 
possibility of oscillation. 
VPOS
VNEG
V
IN
1k
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
REF
A1
A2
C1HI
A1CM
A1OP
A2OP
A2CM
C2HI
C1LO
A1HI
A1LO
GAT1
A2LO
A2HI
C2LO
GAIN-CONTROL
VOLTAGE
GAT2
+5V
–5V
+
–
+
–
AD600/
AD602
ADDED
PULL-DOWN
RESISTOR
0
Figure 34. Adding a 1 kΩ Pull-Down Resistor Increases the X-AMP’s Output 
Drive by About 5 mA. Only the A1 connections are shown for simplicity.