Patent ID: 6507626
Filing Date: 2003-01-14
Classification: H04L,H04N

Abstract:
A bandpass phase tracker for automatically sampling at prescribed phases of digital carrier when digitizing a vestigial-sideband intermediate-frequency signal received from an intermediate-frequency amplifier, which said vestigial-sideband intermediate-frequency signal is modulated in accordance with a baseband symbol code of a prescribed symbol rate, said bandpass phase tracker comprising:a local oscillator for generating analog oscillations at a frequency and phase responsive to an automatic frequency and phase control signal; heterodyning circuitry for mixing oscillations from said local oscillator with said vestigial-sideband intermediate-frequency signal received from an intermediate-frequency amplifier to generate an analog low-frequency heterodyne signal with its lowest frequencies offset from zero frequency; analog-to-digital conversion circuitry for sampling said analog low-frequency heterodyne signal in accordance with a first sampling clock signal and converting the resulting samples to a complex digital low-frequency heterodyne signal having real and imaginary components; digital demodulation circuitry for synchrodyning said complex digital low-frequency heterodyne signal with a digital carrier signal to generate real and imaginary components of a demodulated signal at baseband; circuitry responsive to the imaginary component of said demodulated signal for generating an automatic frequency and phase control signal for said local oscillator; an envelope detector for detecting envelope variations in said vestigial-sideband intermediate-frequency signal received from an intermediate-frequency amplifier to supply an envelope detector response; a frequency-selective filter for receiving said envelope detector response as its input signal and selectively responding in its output signal to frequencies in its input signal that are proximate to a submultiple of said prescribed symbol rate; sampling clock signal generating circuitry for responding to said submultiple of said prescribed symbol rate contained in the output signal from said frequency-selective filter to generate said first sampling clock signal and a second sampling clock signal, each at a respective controlled rate that is a rational multiple of said submultiple of said prescribed symbol rate; and a carrier signal generator for generating said digital carrier signal for synchrodyning with said complex digital low-frequency heterodyne signal, with the frequency and phase of said digital carrier being controlled by said second sampling clock signal.