ICL7642 Maxim, ICL7642 Datasheet - Page 24

• Manufacturer Part Number: ICL7642
• Description: The ICL761X–ICL764X family of monolithic CMOS op amps combine ultra-low input current with low-power operation over a wide supply voltage range
• Manufacturer: Maxim

Single/Dual/Triple/Quad
Operational Amplifiers
24
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
+ I
Figure 11. Pico Ammeter—The response time of this curcuit is
R
output and the inverting terminal of the amplifier.
FB
LEAK(S1
V
IN
x C
______________________________________________________________________________________
CONTROL
INPUT
S/H
FB
, where C
ICL7622
) + I
CURRENT
SOURCE
1
A1
⁄
2
LEAK(S2)
100kΩ
R
FB
1
]/C
is the stray capacitance between the
HOLD
R
FB
+
-
C
- 10
FB
IH5141
.
S1
11
Ω
S2
C
HOLD
ICL7622
1
A2
V
⁄
2
O
= 100mV/pA
BIAS(AZ
V
OUT
)
Figure 10. Long-Time Constant Integrator—With R
the time constant of this integrator is 100,000s. Since the input
voltage is converted to a current by R
far exceed the power-supply range.
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.
V
IN
V
V
IN
IN
Typical Operating Circuit
10MΩ
270pF
(Detailed Circuit Diagram — Figure 10)
LONG TIME CONSTANT INTEGRATOR
5MΩ
R
R
IN
IN
540pF
10MΩ
270pF
+
-
+
-
C
1µF
C
INT
INT
IN
, the input voltage can
-
+
ICL7611
V
V
OUT
OUT
IN
= 1011 Ω ,
OUTPUT