AD706BQ Analog Devices, AD706BQ Datasheet - Page 7

• Manufacturer Part Number: AD706BQ
• Description: Dual Picoampere Input Current Bipolar Op Amp
• Manufacturer: Analog Devices

Figure 23b. Unity Gain Inverter Large
Signal Pulse Response, C
REV. C
Figure 24 shows an in-amp circuit that has the obvious advan-
tage of requiring only one AD706, rather than three op amps,
with subsequent savings in cost and power consumption. The
transfer function of this circuit (without R
Input resistance is high, thus permitting the signal source to
have an unbalanced output impedance.
Furthermore, the circuit gain may be fine trimmed using an
optional trim resistor, R
Figure 24. A Two Op-Amp Instrumentation Amplifier
V
V
IN#2
IN#1
*OPTIONAL INPUT PROTECTION RESISTOR FOR GAINS GREATER
49.9k
THAN 100 OR INPUT VOLTAGES EXCEEDING THE SUPPLY VOLTAGE.
R1
1k
1k
R
R
P
P
*
*
V
FOR R1 = R4, R2 = R3
OUT
V
2
3
OUT
+V
+
–
= (V
S
for R1 = R4 and R2 = R3
A1
8
AD706
1/2
R2
IN#1
0.1 F
G
(V
– V
. Like the three op-amp circuit, CMR
R
IN #1
G
1
IN#2
L
(OPTIONAL)
= 1,000 pF
) (1+
V
R3
R4
R3
IN #2
) + (
) 1
2R4
R
G
5
6
V
G
SQUARE
WAVE
INPUT
)
IN
Figure 23a. Unity Gain Inverter Connection
) is:
–
+
–V
R4
R3
49.9k
A2
S
Figure 23c. Unity Gain Inverter Small
Signal Pulse Response, C
R4
AD706
4
1/2
10k
7
0.1 F
OUTPUT
+
–
AD706
1/2
+V
–V
–7–
10k
8
4
S
S
increases with gain, once initial trimming is accomplished—but
CMR is still dependent upon the ratio matching of Resistors R1
through R4. Resistor values for this circuit, using the optional
gain resistor, R
Table I provides practical 1% resistance values. (Note that
without resistor R
Circuit Gain
1.10
1.33
1.50
2.00
10.1
101.0
1001
For a much more comprehensive discussion of in-amp applica-
tions, refer to the Instrumentation Amplifier Applications Guide—
available free from Analog Devices, Inc.
0.1µF
+
Practical 1% Resistor Values for the Circuit of Figure 24
Table I. Operating Gains of Amplifiers A1 and A2 and
L
0.1 F
= 100 pF
2.5k
R
L
G
, can be calculated using:
Gain of A1 Gain of A2
11.00
4.01
3.00
2.00
1.11
1.01
1.001
where G = Desired Circuit Gain
G
V
C
, R2 and R3 = 49.9 k /G–1.)
OUT
L
Figure 23d. Unity Gain Inverter Small
Signal Pulse Response, C
R1 R4 49.9 k
R2 R3
R
G
99.8 k
0.06 G
1.10
1.33
1.50
2.00
10.10
101.0
1001
0.9 G 1
49.9 k
R2, R3
499 k
150 k
100 k
49.9 k
5.49 k
499
49.9
AD706
L
= 1000 pF
R1, R4
49.9 k
49.9 k
49.9 k
49.9 k
49.9 k
49.9 k
49.9 k