Channel search and selection system for television receiver

A channel search and selection system for a television receiver comprising:

• (1) a channel selection voltage generator circuit for producing a continuously changing control voltage;
• (2) an electronic tuner for receiving said control voltage produced from said channel selection voltage generator circuit to receive a televison signal of a channel corresponding to said control voltage and converting said television signal to an intermediate frequency signal;
• (3) an amplifier for receiving and amplifying said intermediate frequency signal produced from said electronic tuner;
• (4) a frequency discriminator circuit for receiving said amplifier intermediate frequency signal from said amplifier and producing an output voltage according to the degree of deviation of the frequency of said intermediate frequency signal from a predetermined frequency, said output voltage being fed to said channel selection voltage generator circuit for controlling said control voltage produced therefrom;
• (5) a detector for receiving and detecting said amplified intermediate frequency signal from said amplifier;
• (6) a sync separator for receiving the television signal output from said detector circuit and separating a synchronization signal from said television signal output;
• (7) a television signal state discriminator circuit for indirectly detecting the state of the television signal being received by said electronic tuner, said television signal state discriminating circuit receiving the output signal from said sync separator and producing no output signal when said output signal from said sync separator contains said synchronization signal while producing an output signal when said output signal does not contain said synchronization signal;
• and
• (8) voltage holding means connected to said channel selection voltage generator circuit, said voltage holding means receiving the output signal from said television signal state discriminator circuit and preventing variations of said control voltage supplied from said channel selection voltage generator circuit to said electronic tuner during the presence of the output signal from said television signal state discriminator circuit, wherein
• (1) said channel selection voltage generator circuit includes:
• (a) a capacitor for producing said control voltage;
• (b) a first constant current circuit for supplying a first constant current to said capacitor;
• (c) a second constant current circuit connected to said capacitor for causing a second constant current less than said first constant current to flow to discharge said capacitor;
• and
• (d) a control circuit for detecting the level of the output voltage fed from said frequency discriminator and rendering said first constant current circuit conductive or non-conductive by producing a first detection signal when said output voltage is higher than a predetermined first voltage and producing a second detection signal when said output voltage is lower than said first voltage;
• and wherein
• (2) said voltage holding means includes:
• (a) a third constant current circuit connected to said capacitor in said channel selection voltage generator circuit for causing a third current equal to the difference between said first constant current from said first constant current circuit and said second constant current from said second constant current circuit to flow;
• and
• (b) means for rendering said first and third constant current circuits conductive when said television signal state discriminator circuit produces the output signal and rendering said third constant current circuit non-conductive when said output signal vanishes.