OP490 Datasheet, PDF (10/16 Pages) Analog Devices – Low Voltage Micropower Quad Operational Amplifier

OP490
Micropower Voltage-Controlled Oscillator
An OP490 in combination with an inexpensive quad CMOS
switch comprise the precision V_CO of Figure 5. This circuit
provides triangle and square wave outputs and draws only 75 mA
from a 5 V supply. A acts as an integrator; S1 switches the
charging current symmetrically to yield positive and negative
ramps. The integrator is bounded by B which acts as a Schmitt
trigger with a precise hysteresis of 1.67 V, set by resistors R5,
R6, and R7, and associated CMOS switches. The resulting
output of A is a triangle wave with upper and lower levels of
3.33 V and 1.67 V. The output of B is a square wave with almost
rail-to-rail swing. With the components shown, frequency of
operation is given by the equation:
( ) ^f_OUT ^=V_CONTROL ^{Volts ¥ 10 Hz /V}
but this is easily changed by varying C1. The circuit operates
well up to a few hundred hertz.
V_CONTROL
R1
200k⍀
R2
200k⍀
R3
100k⍀
C1
75nF
+5V
+5V
2
3
R4
200k⍀
4
1
11
1/4
OP490E
A
TRIANGLE
OUT
R5
200k⍀
6
5
+5V
IN/OUT
1
S1
OUT/IN
2
+5V
V_{DD 14}
CONT
13
R8
200k⍀
R6
200k⍀
OUT/IN
3
IN/OUT
4
CONT
S2
12
IN/OUT
11
CONT
5
CONT
6
7 ^VSS
OUT/IN
S3
10
OUT/IN
+5V
9
S4
IN/OUT
8
7
1/4
OP490E
B
R7
200k⍀
SQUARE
OUT
Figure 5. Micropower Voltage Controlled Oscillator
–10–
REV. C