Datasheet

LT1630/LT1631
17
16301fa
Typical applicaTions
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 com-
mon 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.
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
filter has a gain of 2, and the notch frequency (f
O
) is set
by 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.
+
1/2 LT1630
V
IN
V
IN
+
OUT1
V
OUT
1630/31 F02
R1
20k
R2
2k
R4
20k
R5
432Ω
R3
2k
+
1/2 LT1630
V
S
BW kHz
A
R
R
R
R
R R
R
V V
V
OUT I
=
= + +
+
=
=
355
4
3
1
2
1
3 2
5
100
NN IN V
V A
+
( )
LOWER LIMIT COMMON MODE INPUT VOLTAGE
V
CML
OUT
V
A
=
VV
R
R
V
+
2
5
0 1
1 0
1 1
.
.
.
UPPER LIMIT COMM
OON MODE INPUT VOLTAGE
V
CMH
OUT
V
S
V
A
R
R
V=
+
2
5
00 15
1 0
1 1
.
.
.
V
WHERE
S
( )
V IS THE SUPPLY CURRRENT
Figure 2. Single Supply, 40dB Gain Instrumentation Amplifier
Figure 3. Frequency Response
+
A2
1/2 LT1630
V
IN
V
OUT
1630/31 F04
5V
5V
R2
1k
R9
1k
R8
5k
R11
10k
R10
10k
R6
1k
R1
500Ω
R5
1k
R7
1k
R
1.62k
R
1.62k
C
1000pF
C
1000pF
+
A1
1/2 LT1630
C2
4.7µF
C5
4.7µF
C1
2.2µF
f kHz V
V R
R R
V
f
RC
A
O O DC
O V
= =
( )( )
+
=
= =
98
5 11
11 10
2 5
1
2
( )
.
π
22
Figure 4. Tunable Q Notch Filter
FREQUENCY (kHz)
40
20
0
–20
–40
GAIN (V
OUT
/V
IN
)(dB)
13630/31 F05
0 20 40 60 140 160 180 20080 100 120
INCREASING R8
DECREASING R8
Figure 5. Frequency Response