Synchrodyning of VSB and QAM final I-F signals supplied by separate converters in a QAM/VSB digital TV receiver

摘要

A QAM/VSB digital television (DTV) receiver of plural conversion type uses the same circuitry up to a penultimate IF amplifier for receiving DTV signals no matter whether they use QAM or VSB modulation. The converter used for generating final IF signals when QAM modulation is received and the converter used for generating final IF signals when VSB modulation is received have respective mixers and respective local oscillators with separate automatic frequency and phase control. The use of such separate converters avoids a lock-out from VSB reception mode that otherwise can occur during the reception of DTV signals with VSB modulation.