Local oscillator feedthru cancellation circuit

Details Local oscillator feedthru cancellation circuit Local oscillator feedthru cancellation circuit

1988-06-20

1991-03-19

Eisenzopf, Reinhard J.

Telecommunications

Transmitter

Frequency conversion

455126, 455317, H04B 104, H04B 1506

Patent

active

050017730

ABSTRACT:
Method and apparatus are disclosed for canceling local oscillator feed thru in an IF transmission circuit. The apparatus includes first and second mixers for receiving LO and IF signals. The mixers are operable to upconvert the IF signal while passing an attenuated and phase shifted portion of the LO signal. Bias regulation circuitry is provided for regulating the attenuation and phase shift of the LO signal portion passed by at least one of the mixers such that the LO signal portions are combinable to cancel each other. A coupler circuit is provided for combining the mixer outputs such that the LO signal portions are substantially canceled and an upconverted IF signal remains. The bias regulation circuitry may be self-correcting to optimize cancellation of the LO signal portions.

REFERENCES:
patent: 4355420 (1982-10-01), Ishihara
patent: 4584710 (1986-04-01), Hansen
patent: 4593411 (1986-06-01), Schiller

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