COMPONENT TIMING RECOVERY SYSTEM FOR QAM

摘要

A receiver for a transmitted quadrature amplitude modulated (QAM) signal representing successive symbols, and including an in-phase (I) component and a quadrature (Q) component. A timing recovery system includes a source of samples (102) representing the QAM signal produced at a fixed frequency. Processing circuitry for the I component includes a first demodulator (104), coupled to the sample source, for demodulating the I component of the QAM signal to baseband; and a first interpolator (108), responsive to a control signal, for producing I component samples taken at times synchronized to the transmitted symbols. Processing circuitry for the Q component includes a second demodulator (114), also coupled to the sample source, for demodulating the Q component of the QAM signal to baseband; and a second interpolator (118), responsive to a control signal, for producing Q component samples taken at times synchronized to the transmitted symbols. A phase error detector (126) detects the phase error between the sample times of the I and Q component samples from the first and second interpolators and times of the successive transmitter symbols. A summer (130) is coupled to the phase error detector and a source of a nominal delay signal. A numerically controlled delay circuit (132), is coupled to the summer, for producing the respective control signals for the first and second interpolators.