OP490
MICROPOWER VOLTAGE-CONTROLLED OSCILLATOR
An OP490 in combination with an inexpensive quad CMOS
switch comprise the precision V
CO
of Figure 2. This circuit pro-
vides triangle and square wave outputs and draws only 75
µA
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 volts, set by resistors R5,
R6, and R7, and associated CMOS switches. The resulting out-
put of A is a triangle wave with upper and lower levels of 3.33
and 1.67 volts. The output of B is a square wave with almost
rail-to-rail swing. With the components shown, frequency of op-
eration 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.
Figure 2. Micropower Voltage Controlled Oscillator
REV. B
–9–
AD [ ANALOG DEVICES ]
