Tuner input filter with electronically adjustable response for adapting to antenna characteristic
View Patent ↗A system, apparatus and/or method provides frequency response adjustment of an RF input filter of an RF tuner based on impedance of an antenna system that is providing reception of RF signals to the RF tuner. The frequency response adjustment is preferably accomplished dynamically and/or with respect to each frequency tuned. Particularly, the system, method and/or apparatus provides compensation at the RF tuner level for mistuning effects produced on the RF tuner by antenna system impedance presented at the antenna input that is other than a designed for impedance. Frequency response of an RF input filter for the RF tuner is electronically adjustable with an independent or semi-independent control voltage signal based on one or more measured parameters of a tuning frequency. Frequency response adjustment may include adjustment of a center frequency of the RF input filter bandpass frequency range and/or altering the bandpass frequency range of the RF input filter. The subject invention expands the capability of an RF signal receiver, particularly one using at least one electronically adjustable RF filter at the input of an electronic alignment type tuner.
1. An electronically tunable input filter for a television channel tuner, comprising:
an input adapted to receive a television signal from an antenna;
an output adapted to provide a filtered television signal;
a first varactor connected at the output;
a second varactor coupled in series with the input and the first varactor;
a third varactor coupled to the input and ground; and
an electronically tunable inductor coupled to ground and between the first and second varactor;
the electronically tunable inductor operative to receive an inductor control voltage for causing a passband frequency bandwidth of the electronically tunable input filter to encompass an expected frequency of the television channel to be tuned; and
the second and third varactors operative to receive a first control voltage for adjusting the passband frequency bandwidth of the electronically tunable input filter.
2. The filter of claim 1 , wherein the first control voltage is applied to the third varactor through a voltage scaling circuit that is operative to provide a fixed increase in the passband frequency bandwidth of the electronically tunable input filter upon receipt of a scaling signal.
3. The filter of claim 1 , wherein the third varactor is operative to receive a second control voltage for adjusting the passband frequency bandwidth of the electronically tunable input filter in conjunction with the first control voltage applied to the second varactor.
4. The filter of claim 3 , wherein the second control voltage is applied to the third varactor through a voltage scaling circuit that is operative to provide a fixed increase in the passband frequency bandwidth of the electronically tunable input filter upon receipt of a scaling signal.