Frequency response modifier for fixed-tuned IF amplifiers

Claim 2

In a television receiver having a fixed-tuned IF amplifier with an IF frequency response characteristic determined by a surface wave integratable filter for selectively amplifying a range of intermediate frequency components of a received television signal associated with a plurality of intermediate frequency carriers therein, a frequency response modifier, comprising: variable bandwidth means coupled to the output of the fixedtuned IF amplifier and having no frequency response characteristics, the first of said frequency response characteristics being relatively non-selectIve and wide-band over the IF frequency range and the second of said frequency response characteristics being relatively more narrow-band with a peak in its frequency response curve at or near the frequency of one of said plurality of intermediate carriers; means for generating a variable control signal; and selector means responsive to predetermined amplitude levels of said control signal for selecting and cascading with said fixed-tuned IF amplifier one of said frequency response characteristics associated with said variable bandwidth means, said wide-band frequency response being selected in response to a first predetermined level of the control signal and said narrowband frequency response being selected in response to a second predetermined level of said control signal.

Claim 3

A frequency response modifier as defined in claim 1 wherein said control signal consists of an AGC voltage developed in the television receiver.

Claim 4

A frequency response modifier as defined in claim 2 wherein said selector means includes means responsive to predetermined amplitude levels in said AGC voltage for causing the wide-band frequency response of said variable bandwidth means to be cascaded with the frequency response of said fixed-tuned IF amplifier for AGC voltage levels corresponding to a relatively great signal strength in the received television signal and for causing the narrow-band frequency response of said variable bandwidth means to be cascaded with the frequency response of said fixed-tuned IF amplifier for AGC levels corresponding to a relatively weak signal strength in the received television signal.

Claim 5

A frequency response modifier as in claim 3 wherein said variable bandwidth means include two independent fixed bandwidth elements to be alternatively coupled to the output of the fixed-tuned IF amplifier in response to appropriate selection by said voltage sensing means, the first element having a wide bandwidth over the IF frequency range and the second element having both a relatively narrow bandwidth and a peak in its frequency response curve at or near the frequency of the IF picture carrier.

Claim 6

A frequency response modifier as in claim 3 wherein said variable bandwidth means includes a tuned circuit exhibiting a condition of antiresonance at or near the frequency of the IF picture carrier and means for damping said tuned circuit with a low or high value resistance in response to predetermined amplitude levels of the AGC voltage, thereby causing said tuned circuit to exhibit a wide-band or narrow-band frequency response according to the level of said AGC voltage.

Claim 7

In a television receiver having a fixed-tuned IF amplifier for selectively amplifying certain predetermined frequency components of a received television signal, the combination comprising: an IF stage including an amplifier and surface wave filter means for determining the frequency response thereof; variable bandwidth means exhibiting a condition of antiresonance at or near the frequency of the If picture carrier and coupled to the IF stage; means for generating a variable AGC signal whose amplitude corresponds to the strength of the received television signal; and voltage sensing means responsive to said AGC signal and coupled to said variable bandwidth means for causing said variable bandwidth means to exhibit a relatively wide-band frequency response over the IF frequency range when the amplitude of said AGC signal corresponds to a relatively great signal strength in the received television signal, and for causing said element to exhibit a more narrow-band response with a peak in its frequency response curve in the vicinity of the IF picture carrier frequency when the amplitude of said AGC signal corresponds to a relatively weak signal strength in the received television signal, thereby causing the cascaded frequency response of the fixed-tuned IF stage and the variable bandwidth means to change in response to Changes in the amplitude of the AGC signal and the corresponding variations in the signal strength of the received television signal.

Claim 8

In a television receiver having a fixed-tuned IF amplifier for selectively amplifying certain predetermined frequency components of a received television signal, the combination comprising: an IF stage including an amplifier and surface wave filter means for determining the frequency response thereof; variable bandwidth means exhibiting a condition of antiresonance at or near the frequency of the If picture carrier and coupled to the IF stage; means for generating a variable AGC signal whose amplitude corresponds to the strength of the received television signal; and voltage sensing means responsive to said AGC signal and coupled to said variable bandwidth means for causing said variable bandwidth means to exhibit a relatively wide-band frequency response over the IF frequency range when the amplitude of said AGC signal corresponds to a relatively great signal strength in the received television signal, and for causing said element to exhibit a more narrow-band response with a peak in its frequency response curve in the vicinity of the IF picture carrier frequency when the amplitude of said AGC signal corresponds to a relatively weak signal strength in the received television signal, thereby causing the cascaded frequency response of the fixed-tuned IF stage and the variable bandwidth means to change in response to Changes in the amplitude of the AGC signal and the corresponding variations in the signal strength of the received television signal.

Claim 9

A frequency response modifier as in claim 6 wherein said variable bandwidth means consists of a parallel tuned circuit, and wherein said voltage sensing means includes a transistor in a common emitter configuration whose base is coupled to said control signal and whose collector is coupled to said parallel tuned circuit, the transistor being so biased as to be in a state of conduction at a predetermined amplitude of said control signal so as to load said tuned circuit with the relatively low output impedance of said transistor and thereby lower its Q, and to be in a state of non-conduction at another predetermined amplitude of said control signal, thereby presenting a relatively high output impedance to the tuned circuit and causing its Q to be at a preselected higher level.