OP490
Micropower Voltage-Controlled Oscillator
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:
An OP490 in combination with an inexpensive quad CMOS
switch comprise the precision VCO 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
fOUT =VCONTROL Volts ¥10 Hz /V
(
)
but this is easily changed by varying C1. The circuit operates
well up to a few hundred hertz.
C1
75nF
+5V
+5V
R1
R5
200k⍀
2
3
200k⍀
4
1
6
VCONTROL
7
SQUARE
OUT
1/4
11
5
R2
OP490E
A
200k⍀
1/4
R4
OP490E
B
200k⍀
TRIANGLE
OUT
R3
100k⍀
+5V
R8
200k⍀
+5V
IN/OUT
OUT/IN
R6
R7
VDD
200k⍀
200k⍀
14
1
2
S1
S2
CONT
CONT
13
OUT/IN
IN/OUT
CONT
3
4
12
11
IN/OUT
OUT/IN
OUT/IN
S3
S4
5
6
7
10
9
+5V
CONT
VSS
IN/OUT
8
Figure 5. Micropower Voltage Controlled Oscillator
–10–
REV. C
ADI [ ADI ]
