REV. C

AD704

–8–

Table I. Resistance Values for Various Gains

Circuit Gain

Bandwidth

(G)

R1 and 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

CIRCUIT TRIMMED

USING CAPACITOR Ct

WITHOUT CAPACITOR Ct

TYPICAL MONOLITHIC IN AMP

Figure 4. Common-Mode Rejection vs. Frequency with

INSTRUMENTATION AMPLIFIER GAIN = 1 +

+

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

R2

2R2

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

OUTPUT

C3

C4

R8

1M

C5, 0.01 F

C2

R7

1M

R6

1M

C1

0.1 F

GAIN TRIM

(500k

POT)

R2

49.9k

R1

6.34k

R3

6.34k

OPTIONAL

AC CMRR TRIM

R5

2.4k

R4

47.5k

DC

CMRR

TRIM

(5k

POT)

R1

RG

=

R8

C3C4

ω

1

R8 = R9

Q2 =

C3

4C4

R6 = R7

=

R6

C1C2

ω

1

Q1 =

C1

4C2

R10, 2M

–

+

–

+

0.1 F

R9

1M

C6, 0.01 F

R11, 2M

Figure 3. Gain of 10 Instrumentation Amplifier with Post Filtering

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:

R2 = R4 + R5 = 49.9 k

Ω

R1

= R3 =

49.9 k

Ω

0.9 G

−1

Max Value of R

k

G

G

=

Ω

99 8

006

.

.

C

1

2