Datasheet

OP290
Rev. C | Page 11 of 12
VARIABLE SLEW RATE FILTER
The circuit shown in Figure 21 can be used to remove pulse
noise from an input signal without limiting the response rate to
a genuine signal. The nonlinear filter has use in applications
where the input signal of interest is known to have physical
limitations. An example of this is a transducer output where a
change of temperature or pressure cannot exceed a certain rate
due to physical limitations of the environment. The filter consists
of a comparator that drives an integrator. The comparator
compares the input voltage to the output voltage and forces
the integrator output to equal the input voltage. A1 acts as a
comparator with its output high or low. Diode D1 and Diode
D2 clamp the voltage across R3, forcing a constant current to
flow in or out of C2. R3, C2, and A2 form an integrator with the
output of A2 slewing at a maximum rate of
C2R3C2R3
V
rateslewMaximum
D
×
≈
×
=
V6.0
For an input voltage slewing at a rate under this maximum slew
rate, the output simply follows the input with A1 operating in
its linear region.
1/2
A2
OP290GP
1
1/2
A1
OP290GP
3
2
7
5
6
R1
250kΩ
C1
0.1µF
+15V
–15V
V
OUT
R2
100kΩ
R3
1MΩ
D2
D1
DIODES ARE 1N4148
4
R4
25kΩ
C2
4700pF
8
00327-022
Figure 21. Variable Slew Rate Filter
LOW OVERHEAD VOLTAGE REFERENCE
Figure 22 shows a voltage reference that requires only 0.1 V of
overhead voltage. As shown, the reference provides a stable
4.5 V output with a 4.6 V to 36 V supply. Output voltage drift is
only 12 ppm/°C. Line regulation of the reference is under
5 μV/V with load regulation better than 10 μV/mA with up to
50 mA of output current.
The REF43 provides a stable 2.5 V that is multiplied by the
OP290. The PNP output transistor enables the output voltage to
approach the supply voltage.
Resistor R1 and Resistor R2 determine the output voltage.






+=
R1
R2
V
OUT
1
V5.2
The 200 Ω variable resistor is used to trim the output voltage.
For the lowest temperature drift, parallel resistors can be used
in place of the variable resistor and taken out of the circuit as
required to adjust the output voltage.
6
2
4
REF43FZ
V
OUT
V
IN
V
OUT
GND
C1
10µF
C2
0.1µF
V+
R2
2kΩ
1%
R1A
2.37Ω
1%
R1B
200Ω
20-TURN
BOURNS 3006P-1-201
2N2907A
1
1/2
OP290GP
3
2
8
4
00327-023
Figure 22. Low Overhead Voltage Reference