Operational amplifier (op amp) oscillators can be used
to accurately measure resistive and capacitive sen-
sors. Oscillator design can be simplified by using the
procedure discussed in this application note. The deri-
vation of the design equations provides a method to
select the passive components and determine the influ-
ence of each component on the frequency of oscilla-
tion. The procedure will be demonstrated by analyzing
two state-variable RC op-amp oscillator circuits. M AN866
Designing Operational Amplifier Oscillator Circuits
For Sensor Applications
The ratio oscillator provides an output frequency that is
Author: Jim Lepkowski
proportional to the square root of the ratio of two capac-
Microchip Technology Inc.
itors (i.e., freq. ∝ (C 4 / C3)1/2). The ratio oscillator can
be used to cancel the effect of a fluid-level sensor with
INTRODUCTION ……
