Datasheet

LTC6252/LTC6253/LTC6254
18
625234fc
TYPICAL APPLICATIONS
Figure 9. Instrumentation Amplifier
Frequency Response
FREQUENCY (Hz)
10k
GAIN (dB)
40
35
25
15
30
20
10
5
0
100k 10M1M
625234 F09
100M
FREQUENCY (Hz)
10k
CMRR (dB)
120
100
60
20
80
40
0
100k 10M1M
625234 F10
100M
Figure 10. Instrumentation
Amplifier CMRR
INPUT
25mV/DIV
OUTPUT
1V/DIV
0V
0V
625234 F11
100ns/DIV
Figure 11. Transient Response,
Instrumentation Amplifier
Figure 8. High Speed Low Voltage Instrumentation Amplifier
625234 F08
+
–
R4
750Ω
R5
750Ω
R6
750Ω
R7
750Ω
R2
1.2k
R1
60Ω
U1
½ LTC6253
V
S
+
V
S
–
R3
1.2k
A
V
= 41
BW = 15MHz
V
S
= ±1.5V
I
S
= 8.4mA
–
+
U2
½ LTC6253
IN
+
IN
–
V
S
+
V
S
–
+
–
U3
½ LTC6253
V
OUT
stages. See the oscillograph of Figure 7, showing the inputs
V
A
and V
B
, the SEL_B control, and the resulting output.
Note that there are protection diodes across the op amp
inputs, so large signals at the output will feed back into
the upstream off channel through the diodes. R1 and R2
were put in place to reduce the loading on the output,
as well as to reduce the upstream feedback current and
improve reverse isolation. Some reverse crosstalk can be
discerned in the V
A
and V
B
traces during their respective
off times, however, as the reverse current works back into
the 50Ω source impedance of the function generators.
High Speed Low Voltage Instrumentation Amplifier
Figure 8 shows a three op amp instrumentation amplifier
with a gain of 41V/V which can operate on low supplies.
Op amps U1 and U2 are channels from an LTC6253.
Op amp U3 can be an LTC6252 or one channel of an
LTC6253. Figure 9 shows the measured frequency re-
sponse of the instrumentation amplifier for a load of 1kΩ.
Figure 10 shows the measured CMRR of the instrumenta-
tion amplifier, and Figure 11 shows the transient response
for a 50mV
P-P
input square wave applied to the positive
input, with the negative input grounded.
Figure 7. Oscilloscope Traces Showing
Multiplexing Channels
SEL_B
5V/DIV
V
B
V
A
V
OUT
625234 F07
50µs/DIV