designing operational amplifier oscillator circuits for sensor applicationsM Author: Jim Lepkowski Microchip Technology Inc. AN866 The ratio oscillator provides an output frequency that is proportional to the square root of the ratio of two capacitors (i.e., freq. ∝ (C 4 / C3)1/2). The ratio oscillator can be used to cancel the effect of a fluid-level sensor with a varying dielectric constant, such as an oil level sensor. An oil level sensor consists of two capacitances that are formed by tubes where the fluid serves as the dielectric media. The measurement capacitor (CMEAS) is partially covered by fluid and detects the level of the oil in the tank. In contrast, the compensation sensor (CCOMP) is completely buried in the fluid. When the ratio CMEAS / C COMP is calculated, the dielectric constant of the oil is canceled. Air pressure and acceleration sensors can a……