Electronic pressure transducer

Abstract

An electronic pressure transducer for providing a pressure-indicative analog output signal includes a capacitive pressure sensing oscillator having a frequency dependent on an applied pressure. A combining circuit combines the oscillator signal with a constant frequency signal generated by a reference oscillator to generate a difference signal having a duty cycle dependent on the frequency difference between the oscillator signals. The difference signal is applied to an integrating circuit and amplified by a variable-gain output amplifier to develop the pressure-indicative analog output signal. A pair of D-type flip-flops and an EXCLUSIVE OR logic gate in the combining circuit enable the combining circuit to function with oscillator frequency ratios of 1:1 to 2:1, thereby enabling the capacitive pressure sensing element of the pressure sensing oscillator to operate over a wider range of sensitivities. Non-linearities at the output of the integrating circuit are compensated for by a linearizing transistor having main electrodes coupled to a degenerative feedback network in the output amplifier. A second transistor having main electrodes coupled to the control electrode of the linearizing transistor compensates for temperature variations in the conduction level of the linearizing transistor.