REV. C

OP490

–10–

Micropower Voltage-Controlled Oscillator

An OP490 in combination with an inexpensive quad CMOS

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

1

14

213

312

4

11

5

10

69

78

S3

S4

S2

S1

CONT

IN/OUT

CONT

OUT/IN

OUT/IN

IN/OUT

IN/OUT

OUT/IN

IN/OUT

OUT/IN

CONT

CONT

+5V

+5V

1/4

OP490E

A

+5V

R2

200k

R1

200k

R3

100k

R4

200k

11

4

2

3

1

TRIANGLE

OUT

+5V

R8

200k

6

5

7

+5V

R5

200k

SQUARE

OUT

R6

200k

R7

200k

C1

75nF

1/4

OP490E

B

Figure 5. 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:

fV

Volts

Hz V

OUT

CONTROL

=

but this is easily changed by varying C1. The circuit operates

well up to a few hundred hertz.