General Electric Company

Robert K Bell

Roy F Hodsdon

A circuit for use in conjunction with a voltage controlled oscillator (VCO). The circuit introduces modulation into a radio system (to create a substantially flat frequency response) at the same VCO port at which VCO frequency centering and negative bias control signals are introduced. A potentiometer is utilized both for providing an adjustable negative bias to the varactor in the VCO resonant circuit and for setting the VCO to the appropriate center frequency. Modulation compensation circuitry is coupled to the control arm of the potentiometer and to the anode of the varactor (via a choke 4). The modulation compensating circuitry is preferably designed to have a transfer function that is substantially the inverse of the closed loop transfer function of the phase locked loop system with respect to the frequency modulation of the VCO.

Multi-function modulation and center frequency control port for voltage

A two piece zinc die-cast housing and cover assembly includes an internal center wall structure which divides the included space into two electromagnetically isolated cavities. A VCO circuit sub-assembly and a PLL circuit sub-assembly are each removably affixed to respective opposite sides of the center wall while each is electrically interconnected to the other directly through at least one aperture provided in the center wall. A one piece molded plastic header is removably affixed to the assembly so as to close the remaining side of the electromagnetically isolated cavity and includes apertures through which electrical leads extend from the circuit sub-assemblies for self-aligning connection to sockets or other external electrical connectors. An additional internal metallic shield directly affixed to the VCO sub-assembly as well as other features cooperate to provide an overall improved frequency synthesizer module of this general type.

Frequency synthesizer module

The gain margin of a junction FET oscillator is improved by the addition thereto of a bipolar transistor in parallel with the FET for boosting the closed loop circuit gain of the oscillator without degrading the phase noise performance of the FET. The oscillator circuit is formed by a grounded gate JFET with a feedback circuit including the internal impedance of the FET, a capacitor which couples source and drain of the FET, a capacitor which couples the FET source to ground, and a resonant circuit coupled between the drain of the FET and ground including a varactor diode for controlling the oscillating frequency and providing a circuit output. A bipolar transistor is coupled in parallel with the FET by coupling its collector to FET's drain and its emitter to the FET's source. The base of the transistor is coupled via a by-pass capacitor to circuit ground.

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Lynchburg, VA, United States of America

Robert K Bell