Low-noise lossless feedback double-balanced active mixers

DETAILED DESCRIPTION A lossless feedback double-balanced active mixer circuit with improved intermodulation (IM) and noise figure (NF) performance is described which includes a pair of lossless feedback balanced active mixer circuits, each of which includes a differential pair of switching transistors which divide a controlled current into two paths at a rate determined by an input local oscillator (LO).
A hybrid transformer in each lossless feedback balanced mixer, consisting of a centre-tapped primary winding and a secondary winding, combines the two currents to provide a recombined amplified IF signal and an output radio frequency (RF) signal.
The controlled current is provided by an input intermediate frequency (IF) signal and its relation with the lossless feedback mixer input impedance.
Each lossless feedback active mixer circuit further includes a feedback transformer, comprised of an input winding and a tapped output winding, which compares the input IF signal with the recombined amplified IF signal from the hybrid transformers and applies the difference as a correction to the input current, thereby completing a lossless feedback amplifier circuit which improves the IM performance of the mixer circuit.
Since the feedback transformer is essentially lossless, it introduces no significant sources of noise to the active mixer circuit, and therefore the NF of the of the lossless feedback active mixer circuit remains unimpaired beyond the NF of the transistors themselves.
The NF of the lossless feedback double-balanced active mixer is further improved by minimizing the number of active devices.
The connection of the secondary windings of the hybrid transformers of the lossless feedback active mixer circuits effectively cancels the output LO and IF signals and provides and output RF signal.