Signal overload protection circuit for varactor tuner

Claim 2

A television tuner comprising: a tunable circuit including a varactor diode providing the variable capacitance therefor; means applying a DC tuning voltage to bias said varactor diode for adjusting the resonance of said tunable circuit to receive and translate broadcast television signals in a given frequency spectrum, the maximum and minimum capacitance exhibited by said varactor diode being such that over a certain portion of said frequency spectrum the magnitude of a received broadcast television signal may significantly exceed the magnitude of said DC tuning voltage; and means limiting distortion of said received television signal whenever its magnitude substantially exceeds said DC tuning voltage by automatically back-biasing said varactor diode.

Claim 3

A television tuner as set forth in claim 1, wherein said means limiting distortion comprise a peak detector circuit developing bias as a function of the maximum excursion of said television signal.

Claim 4

A television tuner as set forth in claim 2, wherein said varactor diode is of the abrupt junction type and wherein said tunable circuit comprises a radio frequency stage.

Claim 5

A television tuner as set forth in claim 3, wherein said peak detector circuit comprises a large magnitude resistance coupled between said means applying a DC tuning voltage and said varactor diode.

Claim 6

A television tuner comprising: an RF amplifying stage, an oscillator stage, and a mixer stage; an abrupt junction varactor diode in each of said stages providing variable tuning capacitance; means applying DC tuning voltages to said varactor diodes for adjusting the resonances of said stages for selectively receiving broadcast television signals in a predetermined frequency band; the minimum and maximum capacitance of said abrupt junction varactor diodes being such that at a certain portion of said tuning band a received television signal of excessive magnitude may significantly exceed the tuning voltage applied to the varactor diode in said RF stage; and means for automatically back-biasing the varactor diode in said RF stage in the presence of an excessive magnitude television signal and thereby limiting distortion of said television signal.

Claim 7

A television tuner comprising: an RF amplifying stage, an oscillator stage, and a mixer stage; an abrupt junction varactor diode in each of said stages providing variable tuning capacitance; means applying DC tuning voltages to said varactor diodes for adjusting the resonances of said stages for selectively receiving broadcast television signals in a predetermined frequency band; the minimum and maximum capacitance of said abrupt junction varactor diodes being such that at a certain portion of said tuning band a received television signal of excessive magnitude may significantly exceed the tuning voltage applied to the varactor diode in said RF stage; and means for automatically back-biasing the varactor diode in said RF stage in the presence of an excessive magnitude television signal and thereby limiting distortion of said television signal.

Claim 8

A television tuner as set forth in claim 5, wherein said last-mentioned means comprise a peak detector circuit for establishing the bias on said varactor diode in said RF stage in accordance with the peak level of said excessive magnitude television signal.

Claim 9

A television tuner as set forth in claim 6, wherein said peak detector circuit includes a large magnitude resistor connected between said means for supplying tuning voltages and the varactor diode in said RF stage.

Claim 10

A television tuner as set forth in claim 7, wherein said certain portion of said frequency band embraces a frequency corresponding to VHF channel 2, and wherein said means for automatically back-biasing said varactor diode tunes said RF stage towards the frequency corresponding to VHF channel 3 in the presence of an excessive magnitude television signal corresponding to channel 2.