Patent ID: 6064872
Filing Date: 2000-05-16
Classification: H03D

Abstract:
A signal mixing device for generating a mixer output signal comprising:a first and a second FET, each having a gate and a drain and a source, said first and second FETs having their gates tied to one another and their sources tied to one another such that said first and second FETs are connected source-to-source in series and have substantially equal magnitude gate-to-source voltages at all times and have substantially equal magnitude but opposite sign drain-to-source voltages at all times, said second FET drain connected to ground;an RF/IF diplexer circuit connected to said first FET drain and having an RF signal coupling port and an IF signal coupling port for communicating RF and IF signals between said first FET drain and external sources and sinks of RF and IF signals;a transformer having a primary and secondary portion, said primary portion having a first terminal connected to a LO input port for receiving an external LO input signal and a second terminal connected to ground, said secondary portion having a third terminal connected to said FET gates and a fourth terminal connected to said FET sources, said secondary winding and said FET gates and sources floating and not tied to ground;said transformer receiving said local oscillator signal and generating a floating drive signal between said joined gate terminals and said joined source terminals to switch the conduction state of said serially connected FETs between a conducting state and a non-conducting state;said diplexer receiving an input signal and coupling said input signal to said first FET drain, said input signal passing through the channel combination formed by said first and second FETs during the time said FETs are conducting and mixing said floating local oscillator signal with said input signal to generate said output signal;said first FET introducing a first component of intermodulation distortion in said output signal related to the change in channel resistance of said first FET during channel conduction, and said second FET introducing a second component of intermodulation distortion in said output signal related to the change in channel resistance of said second FET during channel conduction, said second component being about equal in magnitude but opposite in sign to said first component; said back-to-back serial FET connection being operative to sum and cancel said first distortion component with said second distortion component so that the overall intermodulation distortion introduced in said mixer output signal is suppressed; andsaid diplexer having an output port for extracting said output signal.