Video Intermediate Frequency Amplifier with Intermediary Audio for Intercarrier Speech and Automatic Fine Synchronization

摘要

In a television receiver, a down-stream converter responsive to a selected television signal supplies respective first and second output signals as input signals to the first and second intermediate frequency amplifiers, respectively. The down frequency converter includes a local oscillator that generates an oscillation at a controlled frequency in response to the AFT signal. The first intermediate frequency amplifier includes a first adjacent channel voice carrier trap and an in-channel voice carrier trap, wherein the first intermediate frequency amplifier response is substantially reduced for a down-converted frequency image carrier. In response to the first intermediate frequency amplifier response, the video detector generates a composite video signal in which the voice bits are suppressed to a relatively low level by the first adjacent channel voice carrier trap. The second intermediate frequency amplifier includes a second adjacent channel voice carrier trap. The second intermediate frequency amplifier response in which the in-channel voice carrier is not trapped therefrom is determined such that the first intermediate frequency amplification is performed by the second adjacent channel voice carrier as much as the response is reduced by the first adjacent channel voice carrier trap, But is not reduced for an image carrier. From the second intermediate frequency amplifier response, the intercarrier detection circuit detects the inductor carrier speech intermediate frequency response, which is amplified by the intercarrier voice intermediate frequency amplifier, and is then detected by the FM speech detector. In response to the second intermediate frequency amplifier response, the automatic fine tuning detector generates an AFT signal that is used to control the frequency generated by the local oscillator included in the down frequency converter.