Phase detectors in carrier recovery for offset QAM and VSB

The present invention relates to systems for, and methods of, recovering digitally modulated television signals and, more particularly, to a dual mode QAM/VSB receiver system for recovering quadrature amplitude modulated or vestigial sideband modulated signals. Improved carrier recovery, symbol timing, and carrier phase tracking systems and methods suitable for use in connection with a dual-mode QAM/VSB receiver system are disclosed. Carrier and phase recovery systems operate on complex signals representing symbols having the same time stamp for each phase error term. in-phase signals are sampled twice a symbol at the in-phase symbol sampling time and at the quadrature-phase symbol sampling time. The signals are de-multiplexed to generate I and Xdata streams, where I represents the in-phase sampling time signals and Xrepresents mid-symbol point sample times. A similar procedure is carrier out on quadrature-phase signals. When the in-phase signal is de-multiplexed to generate a symbol I, the quadrature-phase signal is de-multiplexed to generate its mid-symbol point X. Both I and Q are decoded in a decision device to define a symbol error term, which is combined with the opposite mid-symbol signal to define a phase error term Pand Pfor each rail. In both cases, the symbol (I) decision (Î), and mid-symbol (X) in each phase error term (P) computation will have the same prime index.