Ghost cancellation of analog tv signals

Abstract

Ghosts are canceled in received analog TV (for IDTV, EDTV, and HDTV) signals by utilizing the fact that there are short periods of time without the analog signals (the horizontal flyback interval between the lines) to process the received signal on a line-to-line basis using a finite impulse response (FIR) or an infinite impulse response (IIR) equalizer. This line-by-line processing (which can be implemented by periodic cleansing of the equalizer) overcomes the limitations of standard equalizers to allow for 40-50 dB of suppression of ghosts, even with nulls in the spectrum, as long as the ghost delay is less than the period of time without the analog signal. Furthermore, by using time inversion in combination with line-by-line processing, the stability problem of the conventional IIR equalizer is eliminated. The IIR equalizer may be implemented on a single digital integrated circuit. Alternatively, an FIR equalizer can be used which, although it may require multiple chips (i.e., more taps), can acquire and adapt to the ghosted channel more rapidly than an IIR equalizer. With line-by-line processing, FIR and IIR equalizers can eliminate any ghost with delays up to 11 .mu.sec in IDTV or EDTV. For larger delays, a standard IIR or FIR equalizer can be used as a preprocessor to eliminate small ghosts and an adaptive antenna can be used to eliminate large ghosts. Thus, with these techniques, the ghosting problem can be eliminated in all TV receivers.