LT1114 Linear Technology Corporation, LT1114 Datasheet - Page 11

• Manufacturer Part Number: LT1114
• Description: Dual/quad Low Power Precision, Picoamp Input Op Amps
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
IN
IN
The concepts of common mode and power supply rejec-
tion ratio match (∆CMRR and ∆PSRR) are best demon-
strated with a numerical example:
Clearly the LT1112/LT1114, by specifying and guarantee-
ing all of these matching parameters, can significantly
improve the performance of matching-dependent
circuits.
–
+
Assume CMRR
and CMRR
then ∆CMRR = 0.25µV/V or 132dB;
if CMRR
then ∆CMRR = 1.75µV/V or 115dB.
1/2 LT1112
1/4 LT1114
1/2 LT1112
1/4 LT1114
+
–
–
+
OR
OR
D
A
Three Op Amp Instrumentation Amplifier
B
= – 0.75µV/V which is still 122.5dB,
B
= + 0.75µV/V or 122.5dB,
A
U
R1
10k
1%
R3
2.1k
1%
R8
200Ω
R2
10k
1%
= + 1µV/V or 120dB,
100Ω
100Ω
0.5%
0.5%
R4
R5
U
C1
33pF
R10
1M
R7
9.88k
0.5%
R9
200Ω
W
LT1097 OR
0.5%
–
1/4LT1114
+
10k
R6
B OR C
GAIN = 1000
TRIM R8 FOR GAIN
TRIM R9 FOR DC
COMMON MODE REJECTION
TRIM R10 FOR AC
COMMON MODE REJECTION
U
LT1112/14 • AI02
OUTPUT
Typical performance of the instrumentation amplifier:
When the instrumentation amplifier is used with high
impedance sources, the LT1114 is recommended because
its CMRR vs frequency performance is better than the
LT1112’s. For example, with two matched 1MΩ source
resistors, CMRR at 100Hz is 100dB with the LT1114, 76dB
with the LT1112.
This difference is explained by the fact that capacitance
between adjacent pins on an IC package is about 0.25pF
(including package, socket and PC board trace capaci-
tances).
On the dual op amp package, positive input A is next to the
V
ground pin adjacent to it, resulting in a 0.25pF input
capacitance mismatch. At 100Hz, 0.25pF represents a
6.4 • 10
higher than the 1MΩ source resistors.
On the quad package, all four inputs are adjacent to a
power supply terminal—therefore, there is no mismatch.
–
Input offset voltage = 35µV
Offset voltage drift = 0.3µV/°C
Input bias current = 80pA
Input offset current = 100pA
Input resistance = 800GΩ
Input noise = 0.42µV
pin (AC ground), while positive input B has no AC
9
input impedance mismatch, which is only 76dB
P-P
LT1112/LT1114
11
111214fb