Television – Receiver circuitry – Demodulator
Reexamination Certificate
1998-07-13
2002-02-26
Eisenzopf, Reinhard J. (Department: 2614)
Television
Receiver circuitry
Demodulator
C348S536000, C455S204000
Reexamination Certificate
active
06351293
ABSTRACT:
The invention generally relates to digital television signal receivers and, more particularly, the invention relates to a phase detector for a vestigial sideband (VSB) signal receiver.
BACKGROUND OF THE DISCLOSURE
To accurately extract data from a vestigial sideband (VSB) signal as used, for example, in a high definition television (HDTV) transmission system, the phase error of the VSB signal with respect to the phase of the sampling signal for the quantizer (slicer) must be detected and tracked.
FIG. 1
depicts a block diagram of a conventional phase tracking loop
100
for a digital television receiver. This conventional loop is defined in the “Guide To The Use Of The ATSC Digital Television Standard” Document A/54, Advanced Television Systems Committee, Apr. 12, 1995. The standard suggests using a phase tracking loop that operates only upon a real signal (e.g., the in-phase signal). As such, to determine a phase error of the VSB signal, the quadrature phase (Q) signal is derived from the I signal. Because the I and Q components of a VSB signal are related by a filter function that is approximately a Hilbert transform, a filter
104
is used to derive a Q signal from the I signal. The filter is a finite impulse response (FIR) filter having fixed anti-symmetric coefficients and with every other coefficient equal to zero. The I signal is delayed in delay
102
for a period equal to the length of the filter
104
.
To compensate for the phase error, the I and Q signals are coupled to a complex multiplier
106
that is driven by an oscillator (e.g., a numerically controlled oscillator (NCO))
112
that is, in turn, controlled by an error signal from a phase detector
108
. The phase of the NCO output signal is modulated to correct the phase error and produce phase adjusted I and Q signals (I′ and Q′). The phase detector
108
compares the I′ signal to the derived Q′ signal and produces a phase error detection signal (e) that represents the phase error of the VSB signal. A loop filter
110
(a low pass filter) is used to filter the higher order components from the error signal e. In effect, the combination of the oscillator signal and the I and Q input signals within the complex multiplier
102
creates derotated I and Q signals. The depicted circuit
100
is a closed loop phase tracking circuit that compensates for carrier phase error in the I and Q signals such that a relatively stable in-phase (I) signal is created that can be sampled within a demodulator to extract the data from the VSB signal. One example of a phase tracking circuit that uses a derived Q component is described by Lee et al. in “A Hardware Efficient Phase/Gain Tracking Loop For The Grand Alliance VSB HDTV Receiver,” IEEE Trans. on Consumer Electronics, pp. 632-639, Vol. 42, No. 3, Aug. 1996.
Since the Q signal is derived from the I signal to synthesize a complex signal for phase tracking, the derived signal may not always accurately represent the Q signal, i.e., multipath and phase distortion may cause cross-coupling of the I and Q components of the VSB signal such that the derived Q signal misrepresents the actual Q component. When the Q signal is misrepresented, the phase tracking loop will produce an erroneous phase error that will cause the loop to distort the quantized I data. Consequently, the information carried by the I data may not be recoverable.
Therefore, a need exists in the art for a decision directed phase detector that compares the I and Q signals to produce a phase error and uses symbol decision information to enhance the accuracy of the phase error signal.
SUMMARY OF THE INVENTION
The disadvantages heretofore associated with the prior art are overcome by a decision directed phase detector that uses the data output from a slicer (quantizer) to aid the phase error detection process to determine a phase error of a complex signal such as a vestigial sideband VSB) signal containing in-phase (I) and quadrature phase (Q) components (I and Q signals). The phase detector comprises a subtractor having one input coupled to the I signal and a second input coupled to the data output of the slicer representing the magnitude of a sample point within a symbol. The quantized signal is subtracted from the I signal to produce &Dgr;I signal. The Q signal is processed to determine its sign and magnitude. The sign and magnitude values are multiplied together and the result is multiplied with the &Dgr;I signal to produce the phase error of the VSB signal. This phase error signal is used in a digital television receiver to extract a data signal from a VSB signal for demodulation.
REFERENCES:
patent: 5128966 (1992-07-01), Bang
patent: 5471508 (1995-11-01), Koslov
patent: 5533070 (1996-07-01), Krishnamurthy et al.
patent: 5588025 (1996-12-01), Strolle et al.
patent: 5602601 (1997-02-01), Kim et al.
patent: 5673293 (1997-09-01), Scarpa et al.
patent: 5692013 (1997-11-01), Koslov et al.
patent: 5706057 (1998-01-01), Strolle et al.
patent: 5796786 (1998-08-01), Lee
patent: 5799037 (1998-08-01), Strolle et al.
patent: 5805242 (1998-09-01), Strolle et al.
patent: 5835532 (1998-11-01), Strolle et al.
patent: 5872815 (1999-02-01), Strolle et al.
patent: 5894334 (1999-04-01), Strolle et al.
patent: 5933460 (1999-08-01), Lee
patent: 5943369 (1999-08-01), Knutson et al.
patent: 6005640 (1999-12-01), Strolle et al.
patent: 6148037 (2000-11-01), Abe
patent: WO95/26105 (1995-09-01), None
W. Lee, K. Cheun, S. Choi, “A Hardware Efficient Phase/Gain Tracking Loop for the Grand Alliance VSB HDTV Receiver”, IEEE Transactions on Consumer Electronics, vol. 42, No. 3, Aug. 1996, pp. 632-639.
International Search Report concerning PCT/US99/10825; our reference SAR 12881 PCT; filing date May 18, 1999.
Burke William J.
Eisenzopf Reinhard J.
Sarnoff Corporation
Yenke Brian P.
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