An advanced IF amplifier and AFT system suitable for HDTV

A circuit which performs the function of intermediate frequency (IF) amplification AGC (automatic gain control), AFT, and demodulation of a TV IF signal for both positive and negative modulation signals is described. The following techniques were used in developing this device: (a) a new AFT system that eliminates the need for an AFT tuned circuit; (b) a chopper stabilized phase detector which greatly reduces PLL (phase-locked loop) phase offsets and, hence, quadrature distortion; (c) wideband postdetector feedback amplifiers which reduce sound/chroma beat products; (d) a reactance tuned VCO (voltage-controlled oscillator) at half intermediate frequency; and (e) improved demodulation circuits which lower distortion. It is concluded that this system has superior performances and fewer external components and adjustments, requires no shielding, and is much easier to use than existing systems