ad704ar Analog Devices, Inc., ad704ar Datasheet - Page 8

• Manufacturer Part Number: ad704ar
• Description: Quad Picoampere Input Current Bipolar Op Amp
• Manufacturer: Analog Devices, Inc.

AD704
The instrumentation amplifier with post filtering (Figure 3)
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 ≥ 2, and at lower gains it will benefit from
the fact that there is no output amplifier offset and noise contri-
bution as encountered in a 3 op amp design. Good low frequency
CMRR is achieved even without the optional ac CMRR trim
(Figure 4). Table I provides resistance values for 3 common
circuit gains. For other gains, use the following equations:
–V
+V
(5k
INSTRUMENTATION AMPLIFIER GAIN = 1 +
2.4k
IN
IN
CMRR
R5
TRIM
AC CMRR TRIM
DC
OPTIONAL
POT)
47.5k
R4
Max Value of R
R2 = R4 + R5 = 49.9 kΩ
C
R1 = R3 =
C
t
t
≈
2 π (R3) 5 × 10
ALL RESISTORS METAL FILM, 1%
AD704
–
+
1/4
+V
6.34k
S
R3
(500k
0.1 F
GAIN TRIM
0.9 G − 1
49.9 kΩ
G
1
R
=
G
POT)
R2
R1
99 8
0 06
.
6.34k
+
.
2R2
5
R1
RG
k
G
Ω
(FOR R1 = R3, R2 = R4 + R5)
AD704
–
+
49.9k
1/4
–V
R2
S
0.1 F
1M
R6
Circuit Gain
(G)
10
100
1,000
OPTIONAL BALANCE RESISTOR
NETWORKS CAN BE REPLACED
1M
R7
Q 1 =
R6 = R7
160
140
120
100
C2
ω
80
60
40
20
Table I. Resistance Values for Various Gains
0
=
C1
1
R6
+
AD704
–
C5, 0.01 F
R10, 2M
TYPICAL MONOLITHIC IN AMP
WITH A SHORT
1/4
4C2
R1 and R3 of Trim Potentiometer) (–3 dB), Hz
6.34 kΩ
526 Ω
56.2 Ω
C1
1
C1C2
GAIN = 10, 0.2V p-p COMMON-MODE INPUT
10
1M
R8
R
166 kΩ
16.6 kΩ
1.66 kΩ
FREQUENCY – Hz
G
WITHOUT CAPACITOR C t
(Max Value
1M
R9
Q 2 =
R8 = R9
CAPACITORS C2 AND C4 ARE
SOUTHERN ELECTRONICS MPCC,
POL YCARBONATE, 5%, 50 VOLT
ω
100
=
C4
R8
4C4
C3
C3
CIRCUIT TRIMMED
USING CAPACITOR C t
1
C3C4
C6, 0.01 F
AD704
+
–
R11, 2M
1/4
1k
Bandwidth
50k
5k
0.5k
OUTPUT
10k