AD704

REV. A

–7–

__

R2

___

2R2

INSTRUMENTATION AMPLIFIER GAIN = 1 +

+

(FOR R1 = R3, R2 = R4 + R5)

ALL RESISTORS METAL FILM, 1%

1/4

AD704

1/4

AD704

1/4

AD704

1/4

AD704

OPTIONAL BALANCE RESISTOR

NETWORKS CAN BE REPLACED

WITH A SHORT

CAPACITORS C2 AND C4 ARE

SOUTHERN ELECTRONICS MPCC,

POLYCARBONATE,

±5%, 50 VOLT

0.01

µF

C6

R11

2M

Ω

OUTPUT

C3

1M

Ω

R9

C4

1M

Ω

R8

0.01

µF

C5

C2

1M

Ω

R7

1M

Ω

R6

C1

0.1

µF

0.1

µF

GAIN TRIM

(500k POT)

49.9k

R2

6.34k

R1

6.34k

R3

OPTIONAL

AC CMRR TRIM

2.4k

R5

47.5k

R4

DC

CMRR

TRIM

(5k POT)

C t

G

R

+V

IN

R1

RG

=

_________

R8

C3C4

1

R8 = R9

Q =

C3

4C4

2

R6 = R7

=

1

_________

R6

C1C2

Q =

C1

4C2

1

R10

2M

Ω

ω

ω

Figure 24. Gain of 10 Instrumentation Amplifier with Post Filtering

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

≥ 2, and at lower gains it will benefit from

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:

R2 = R4 + R5 = 49.9 k

Ω

R1

= R3 =

49.9 k

Ω

0.9 G

−1

Max Value of R

99.8 k

0.06 G

C

1

2

Table I. Resistance Values for Various Gains

Circuit Gain

Bandwidth

(G)

R1 & R3

of Trim Potentiometer)

(–3 dB), Hz

10

6.34 k

Ω

166 k

Ω

50k

100

526

Ω

16.6 k

Ω

5k

1,000

56.2

Ω

1.66 k

Ω

0.5k

160

140

120

100

80

60

40

20

0

1

10

100

1k

10k

FREQUENCY – Hz

GAIN = 10, 0.2V p-p COMMON-MODE INPUT

TYPICAL MONOLITHIC IN AMP

CIRCUIT TRIMMED

USING CAPACITOR Ct

WITHOUT CAPACITOR C t

Figure 25. Common-Mode Rejection vs. Frequency with

10

0%

50µs

2V

100

90

Figure 23b. Unity Gain Inverter

Large Signal Pulse Response,

10

0%

5µS

20mV

100

90

Figure 23c. Unity Gain Inverter

Small Signal Pulse Response,

10

0%

5µS

20mV

100

90

Figure 23d. Unity Gain Inverter Small