AD704AQ AD [Analog Devices], AD704AQ Datasheet - Page 7

• Manufacturer Part Number: AD704AQ
• Description: Quad Picoampere Input Current Bipolar Op Amp
• Manufacturer: AD [Analog Devices]

REV. A
The instrumentation amplifier with post filtering (Figure 24)
combines two applications which benefit greatly from the
AD704. This circuit achieves low power and dc precision over
temperature with a minimum of components.
The instrumentation amplifier circuit offers many performance
benefits including BiFET level input bias currents, low input
offset voltage drift and only 1.2 mA quiescent current. It will
operate for gains G
the fact that there is no output amplifier offset and noise
contribution as encountered in a 3 op amp design. Good low
frequency CMRR is achieved even without the optional AC
CMRR trim (Figure 25). Table I provides resistance values for
3 common circuit gains. For other gains, use the following
equations:
100
Figure 23b. Unity Gain Inverter
Large Signal Pulse Response,
C
0%
90
10
L
= 1,000 pF
2V
–V
+V
INSTRUMENTATION AMPLIFIER GAIN = 1 +
(5k POT)
IN
IN
CMRR
2.4k
TRIM
R5
AC CMRR TRIM
DC
Max Value of R
OPTIONAL
R2 = R4 + R5 = 49.9 k
C
47.5k
R1 R3
2, and at lower gains it will benefit from
t
R4
C t
2 (R3) 5 10
Figure 24. Gain of 10 Instrumentation Amplifier with Post Filtering
ALL RESISTORS METAL FILM, 1%
50µs
+V
AD704
6.34k
0.9 G 1
R3
49.9 k
1/4
1
S
G
0.1 F
R
0.06 G
99.8 k
G
5
GAIN TRIM
(500k POT)
R2 ___
6.34k
__
R1 RG
R1
+
2R2
Figure 23c. Unity Gain Inverter
Small Signal Pulse Response,
C
100
0%
90
10
L
= 100 pF
(FOR R1 = R3, R2 = R4 + R5)
AD704
20mV
–V
49.9k
1/4
R2
S
0.1 F
1M
R6
–7–
Circuit Gain
(G)
10
100
1,000
1M
R7
Figure 25. Common-Mode Rejection vs. Frequency with
and without Capacitor C
C2
R6 = R7
Q =
1
OPTIONAL BALANCE RESISTOR
NETWORKS CAN BE REPLACED
WITH A SHORT
=
5µS
R10
_________
R6
Table I. Resistance Values for Various Gains
C1
AD704
4C2
C1
__
C5
1/4
160
140
120
100
1
C1C2
80
60
40
20
0
0.01 F
R1 & R3
6.34 k
526
56.2
1
2M
TYPICAL MONOLITHIC IN AMP
GAIN = 10, 0.2V p-p COMMON-MODE INPUT
1M
R8
Figure 23d. Unity Gain Inverter Small
Signal Pulse Response, C
10
100
0%
90
10
R
of Trim Potentiometer) (–3 dB), Hz
166 k
16.6 k
1.66 k
1M
R9
G
C4
FREQUENCY – Hz
t
(Max Value
Q =
R8 = R9
20mV
WITHOUT CAPACITOR C t
CAPACITORS C2 AND C4 ARE
SOUTHERN ELECTRONICS MPCC,
POLYCARBONATE, 5%, 50 VOLT
2
= _________
100
R8
R11
C3
4C4
AD704
C3
__
C6
1/4
C3C4
1
USING CAPACITOR C t
0.01 F
CIRCUIT TRIMMED
2M
1k
OUTPUT
AD704
L
5k
Bandwidth
50k
0.5k
= 1,000 pF
5µS
10k