14

LT1630/LT1631

Figure 2. Single Supply, 40dB Gain Instrumentation Amplifier

V

VR

RR

V

A

ODC

V

()

.

)

+

=

=

511

11

10

25

2

f

kHz

f

RC

O

O

=

=

98

1

2

π

A2

1/2 LT1630

1630/31 F04

5V

5V

R2

1k

R9

1k

R8

5k

R11

10k

R10

10k

R6

1k

R1

500

Ω

R5

1k

R7

1k

R

1.62k

R

1.62k

C

1000pF

C

1000pF

–

+

A1

1/2 LT1630

C2

4.7

µF

C5

4.7

µF

C1

2.2

µF

1/2 LT1630

–

+

OUT1

1630/31 F02

R1

20k

R2

2k

R4

20k

R5

432

Ω

R3

2k

1/2 LT1630

LOWER LIMI

V

A

R

R

V

V

A

R

R

VV

OUT

V

OUT

V

S

T COMMON MODE INPUT VOLTAGE

V

UPPER LIMIT COMMON MODE INPUT VOLTAGE

V

WHERE V IS THE SUPPLY VOLTAGE

CML

CMH

S

=









+

















=









+−

()

















2

5

01

10

11

2

5

015

10

11

.

.

.

.

.

.

BW

kHz

A

R

R

R

R

RR

R

VV

V

A

V

OUT

IN

IN

V

=

=+

+

+









=

=−









+−

355

4

3

1

2

1

32

5

100

•

Single Supply, 40dB Gain, 350kHz

Instrumentation Amplifier

An instrumentation amplifier with a rail-to-rail output

swing, operating from a 3V supply can be constructed with

the LT1630 as shown in Figure 2. The amplifier has a

nominal gain of 100, which can be adjusted with resistor

R5. The DC output level is set by the difference of the two

inputs multiplied by the gain of 100. Common mode range

can be calculated by the equations shown with Figure 2.

For example, the common mode range is from 0.15V to

2.65V if the output is set at one half of the 3V supply. The

common mode rejection is greater than 110dB at 100Hz

when trimmed with resistor R1. The amplifier has a

bandwidth of 355kHz as shown in Figure 3.

Figure 3. Frequency Response

FREQUENCY (Hz)

50

40

30

20

10

0

–10

–20

–30

–40

–50

–60

–70

100

10k

100k

10M

1630/31 F03

1k

1M

COMMON MODE INPUT

DIFFERENTIAL INPUT

Figure 5. Frequency Response

FREQUENCY (kHz)

40

20

0

–20

–40

13630/31 F05

0

20 40 60

140 160 180 200

80 100 120

INCREASING R8

DECREASING R8

Figure 4. Tunable Q Notch Filter

Tunable Q Notch Filter

A single supply, tunable Q notch filter as shown in Figure

4 is built with LT1630 to maximize the output swing. The

the values of R and C. The resistors R10 and R11 set up the

DC level at the output. The Q factor can be adjusted by

varying the value of R8. The higher value of R8 will

decrease Q as depicted in Figure 5, because the output

induces less of feedback to amplifier A2. The value of R7

should be equal or greater than R9 to prevent oscillation.

If R8 is a short and R9 is larger than R7, then the positive

feedback from the output will create phase inversion at the

output of amplifier A2, which will lead to oscillation.