Raytheon Company

Raymond S Pengelly

Miles E Goff

Jun-ichi Sano

Marc R Sheade

A frequency converter employs a balanced bridge mixer of switching elements such as field-effect transistors (FETs) with a local oscillator supplying control signals to gate terminals of the transistors. A carrier at intermediate frequency (IF) or at radio frequency (RF) is modulated for communication of data, and is applied to alternate nodes of the bridge. The remaining bridge nodes supply output signals to respective branches of an output circuit. Each branch of the output circuit is provided with a bandpass filter having a spectral characteristic corresponding to the spectral characteristic of a specific one of plural output signals to be outputted via the branch. Each branch may contain an active element, such as an amplifier, which is activated for outputting a signal, and which is deactivated for when node signal is to be outputted. A switchable impedance circuit is included within each of the branches to present a substantially constant impedance characteristic to the bridge, independently of whether the bridge amplifier is activated or deactivated. The local oscillator may provide plural frequencies, as by use of a variable-frequency oscillator or by use of plural oscillators, to place an output signal within the frequency band of a specific one of the output branches.

Plural band converter

A mixer circuit is provided which incorporates inductive elements for low voltage applications. The circuit consists of a balanced amplifier and a switch composed of transistor pairs driven by a local oscillator signal for multiplying the signal to produce a circuit output signal having a predetermined intermediate frequency. Inductors are used to provide degenerative feedback in the balanced amplifier portion of the circuit. The inductors generate negligible noise and produce a negligible dc voltage drop. The transistors in the circuit are thereby maintained in saturation regions of operation as desired. In accordance with another aspect of the invention, an inductor or, alternatively, a parallel inductor-capacitor circuit, is used as a constant current source in conjunction with the input transistors in the balanced amplifier portion of the circuit.

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Windham, NH, United States of America

Raymond S Pengelly