Bandpass phase tracker that automatically samples at prescribed carrier phases when digitizing VSB I-F signal

摘要

A bandpass phase tracker automatically samples at prescribed carrier phases when digitizing a vestigial-sideband intermediate-frequency signal, which VSB I-F signal is modulated in accordance with a baseband symbol code of a prescribed symbol frequency. Heterodyning circuitry mixes oscillations from a local oscillator with the VSB I-F signal received from the I-F amplifier to generate an analog low-frequency heterodyne signal offset from zero frequency. The heterodyne signal is digitized in accordance with a first sampling clock signal to supply input signal for digital demodulation circuitry that demodulates the VSB I-F signal to supply real and imaginary components of a demodulated signal at baseband. The real component of the demodulated signal is supplied to an equalizer and symbol decoded; the imaginary component controls the frequency and phase of the local oscillator. Envelope variations in the VSB I-F signal envelope close to a submultiple of the prescribed symbol frequency are detected and are used in sample clock generating circuitry to control generation of the first sampling clock signal and a second sampling clock signal, each at a respective controlled rate. A carrier signal generator generates the digital carrier signal the frequency of which is controlled responsive to the second sampling clock signal.