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Abstract

A circuit and method for providing temperature stability in an FM quadrature detector. The circuit includes a feedback branch that feeds a portion of the dc output voltage to a varactor diode that is connected in parallel with a capacitor of an LC circuit in the quadrature detector. When the ambient temperature of the LC circuit of the quadrature detector changes, the resonant frequency shifts from the desired center value and a dc voltage is introduced at the output of the quadrature detector. The dc voltage is input to the varactor diode via the feedback circuit branch, and the capacitance of the varactor diode, which is dependent on the dc voltage applied to it, causes the overall capacitance of the LC circuit to change. The change in overall capacitance of the LC circuit caused by the capacitance of the varactor diode causes the resonant frequency of the quadrature detector to shift to be more closely maintained at the desired center frequency. In this manner, the unwanted dc voltage caused by ambient temperature variations is reduced or eliminated.

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