Pulse or digital communications – Receivers – Amplitude modulation
Reexamination Certificate
1998-08-12
2001-03-06
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Receivers
Amplitude modulation
C375S355000, C348S726000
Reexamination Certificate
active
06198780
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vestigial sideband (VSB) demodulating system; and, more particularly, to a method and apparatus for recovering symbol timing of a VSB television signal transmitted from a transmitter.
BACKGROUND OF THE INVENTION
As is well known, an advanced television (ATV) system is provided with a vestigial sideband (VSB) demodulator for demodulating a VSB television signal transmitted from a transmitter which employs a VSB modulation technique.
Basic components of a VSB demodulator include a tuner module having a tuner, an analog/digital (A/D) converter and an automatic gain controller (AGC), a VSB carrier recovery circuit and a VSB timing recovery circuit. Specifically, a VSB television signal having a plurality of symbol data is received by the tuner via an antenna to selectively receive a VSB signal which corresponds to a channel selected by a user. The VSB signal received by the tuner is then digitized by the A/D converter according to a certain sampling rate to provide a digitized VSB signal to the AGC.
At the AGC, the gain of the digitized VSB signal is adjusted to a predetermined level and the digitized VSB signal so adjusted is then provided to the VSB carrier recovery circuit. At the VSB carrier recovery circuit, a carrier recovery operation on the adjusted digitized VSB signal is carried out. Specifically, a pilot tone is first extracted from the adjusted digitized VSB signal by a band pass filter and then applied to a phase locked loop (PLL) circuit to obtain a recovered carrier signal. The recovered carrier signal is then delivered to a next processor, e.g., an equalizer, for further processing thereof.
In the meantime, the VSB timing recovery circuit receives the VSB television signal and performs, on a symbol data basis, a timing recovery operation thereon so as to control the sampling rate of the A/D converter. By controlling the sampling rate, the symbol rate of the VSB television signal can be synchronized with the rate of a clock in the transmitter.
One of the conventional VSB demodulators incorporating therein a VSB timing recovery circuit is disclosed in U.S. Pat. No. 5,673,293. The VSB timing recovery circuit disclosed therein includes a voltage control oscillator (VCXO), a digital to analog (D/A) converter, and a VSB timing recovery module which has a synchronization (SYNC) detector/locator, a discriminator circuit, a switch and a PLL circuit. Specifically, the SYNC detector/locator receives a real passband VSB signal and detects a timing SYNC signal therefrom. When the timing SYNC signal is detected from the real passband VSB signal received, a switch control signal is issued from the SYNC detector/locator to the switch to close it. In response to the switch control signal, an output from the discriminator is coupled to the PLL circuit through the switch to extract a VSB symbol timing signal therefrom. Thereafter, the VSB symbol timing signal is provided to the A/D converter through the D/A converter and the VCXO for use in digitizing the VSB television signal.
In the conventional VSB timing recovery device, however, the timing recovery operation on each of the symbol data included in the VSB television signal is carried out only when the timing SYNC signal is detected, thereby resulting in a prolonged process time for the whole timing recovery of the VSB television signal.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a method and apparatus, capable of providing an efficient symbol timing recovery operation on a VSB television signal transmitted.
In accordance with one aspect of the invention, there is provided a method for symbol timing recovery of each of sampled data included in a vestigial sideband (VSB) signal transmitted to obtain interpolated data on said each of the sampled data as timing recovered data, which comprises:
(a) filtering said each of the sampled data to output a positive and a negative band edge filtered components thereof;
(b) processing the negative band edge filtered component to obtain a conjugate complex component thereon and multiplying the positive band edge filtered component by the conjugate complex component to extract symbol timing information on said each of the symbol data from the multiplied component;
(c) deriving a phase error value of said each of the sampled data by using the symbol timing information;
(d) calculating a mean phase error value of a set of phase error values out of the phase error values, the set of phase error values corresponding to said each of the sampled data and one or more of its previous sampled data;
(e) adding a predetermined value to the mean phase error value to derive a phase corrected value and comparing the symbol rate of the phase corrected value with a predetermined symbol rate to produce a signal indicating the compared result; and
(f) correcting said each of the sampled data by replacing it with one of a set of predetermined interpolated data on the basis of the phase corrected value and the comparison result signal to obtain the interpolated data thereon.
In accordance with another aspect of the invention, there is provided a symbol timing recovery apparatus for timing recovery of each of sampled data included in a vestigial sideband (VSB) signal to obtain interpolated data on said each of the sampled data as timing recovered data, the apparatus comprising:
means for filtering said each of the sampled data to output a positive and a negative band edge filtered components thereof;
means for processing the negative band edge filtered component to obtain a conjugate complex component thereon and multiplying the positive band edge filtered component by the conjugate complex component to extract symbol timing information on said each of the sampled data from the multiplied component; and
means for correcting said each of the sampled data based on the symbol timing information to obtain the interpolated data thereon.
REFERENCES:
patent: 5588025 (1996-12-01), Strolle et al.
patent: 5673293 (1997-09-01), Scarpa et al.
patent: 5805242 (1998-09-01), Strolle et al.
patent: 5943369 (1999-08-01), Knutson et al.
patent: 0765057 (1997-03-01), None
patent: 9526074 (1995-09-01), None
Daewoo Electronics Co. Ltd.
Le Amanda T.
Pennie & Edmonds LLP
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