Index signal amplifier for use in a beam index television receiver

Abstract

An index signal amplifier arrangement is disclosed for use in a beam index color television receiver of a type which includes a picture reproducer having index stripes disposed to be scanned by an electron beam and a photodetector for detecting when respective index stripes are scanned by the beam to produce an index signal. A local oscillator generates a local oscillating signal which is mixed with the index signal produced by the photodetector. The mixed signal is amplified by a band-pass amplifier, the latter preferably being formed of a band-pass filter having a predetermined, limited pass-band characteristic substantially centered on the expected frequency of the mixed signal, and a limiter amplifier coupled to the band-pass filter for removing amplitude modulations from the filtered mixed signal. Another mixer is coupled to the band-pass amplifier and also to the local oscillator for mixing the amplified mixed signal with the local oscillating signal to produce an amplified index signal having the index frequency. If the local oscillating signal frequency can be adjusted to 'match' the particular picture reproducer which is used in the color television receiver, then the frequency of the mixed local oscillating and index signals will be constant from one picture reproducer to the next. Consequently, a standardized, or uniform band-pass amplifier may be provided for all picture reproducers.