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Abstract

A tuner selects one of channels at different locations in a frequency band used for transmitting VSB HDTV signals including symbol codes descriptive of digital signals. The tuner also includes mixers for performing plural conversion of the selected channel to a final intermediate-frequency signal, which is digitized by an analog-to-digital converter. A phase tracker, operative on narrow-bandpass filtered portions of the digitized final intermediate-frequency signal centering on its carrier frequency, suppresses an imaginary portion of the final intermediate-frequency signal, arising from multipath distortion or from phase incoherence in local oscillations used during frequency conversion(s). A digital controlled oscillator in the phase tracker supplies digital descriptions of the carrier wave for a real portion of the final intermediate-frequency signal to a synchronous detector, which synchronous detector detects the real portion of the digitized final intermediate-frequency signal in accordance with those digital descriptions of the carrier wave. The mixers in the tuner provide for the final-IF signal supplied to the analog-to-digital converter to have its lowest frequencies substantially above zero frequency, to have a vestigial sideband below its carrier frequency, and to have a full sideband above its carrier frequency. Because the vestigial sideband is below the carrier of the final-IF signal in frequency, the carrier is closer to zero frequency, so there are more samples per cycle for given sampling rate. This improves the accuracy of the phase tracking in the digital circuitry for synchrodyning the digitized final intermediate-frequency signal to baseband, particularly when the sampling rate for digitization is chosen close to Nyquist rate.

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First Claim