ICL761X_1 Datasheet, PDF (24/26 Pages) Maxim Integrated Products – Single/Dual/Triple/Quad Operational Amplifiers

Single/Dual/Triple/Quad
Operational Amplifiers
S/H
CONTROL
INPUT
100kΩ
R₁
1_⁄2
ICL7622
A1
V_IN
S2
S1
IH5141
1_⁄2
ICL7622
A2
C_HOLD
V_OUT
Figure 9. Low Droop Rate Sample and Hold—S2 improves
accuracy and acquisition time by including the voltage drop
across S1 inside the feedback loop. R1 closes the feedback
loop of A1 during the hold phase. The droop rate is [I_BIAS(AZ)
+ I_LEAK(S1) + I_LEAK(S2)]/C_HOLD.
C_FB
R_FB - 10¹¹â„¦
-
CURRENT
+
SOURCE
V_O = 100mV/pA
C_INT
1µF
R_IN
V_IN
-
+
V_OUT
Figure 10. Long-Time Constant Integrator—With R_IN = 1011Ω,
the time constant of this integrator is 100,000s. Since the input
voltage is converted to a current by R_IN, the input voltage can
far exceed the power-supply range.
-
OUTPUT
10MΩ
10MΩ
+
V_IN
ICL7611
540pF
5MΩ
Figure 11. Pico Ammeter—The response time of this curcuit is
R_FB x C_FB, where C_FB is the stray capacitance between the
output and the inverting terminal of the amplifier.
270pF
270pF
Figure 12. 60Hz Twin “T“ Notch Filter—The low 1pA bias cur-
rent of the ICL7611 allows use of small 540pF and 270pF
capacitors, even with a notch frequency of 60Hz. The 60Hz
rejection is approximately 40dB.
Typical Operating Circuit
R_IN
V_IN
C_INT
-
+
V_OUT
LONG TIME CONSTANT INTEGRATOR
(Detailed Circuit Diagram — Figure 10)
24 ______________________________________________________________________________________