Passband equalizer for a vestigial sideband signal receiver

• US 6,680,971 B1
• Filed: 12/07/1998
• Issued: 01/20/2004
• Est. Priority Date: 05/18/1998
• Status: Expired due to Term

• Current Assignee: AmTRAN Technology Co., Ltd., NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.), Sarnoff Corporation (SRI International, Inc.)
• Inventors: Tazebay, Mehmet Vakif, Perlow, Randall Bret
• Primary Examiner(s): Miller, John
• Assistant Examiner(s): NATNAEL, PAULOS M
• Application Number:
  US09/206,477
• Time in Patent Office: 1,870 Days
• Field of Search: 348/914, 348/725, 348/726, 348/555, 348/558, 375/233, 375/235, 364/724.19
• US Class Current: 375/235
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 27/066 Carrier recovery circuits H04L27/2271 takes precedence
• CPC Class Codes: H04L 7/027 extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
• CPC Class Codes: H04N 11/24 High-definition television systems
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 5/211 Ghost signal cancellation H04N23/81 takes precedence
• CPC Class Codes: H04N 5/455 Demodulation-circuits
• CPC Class Codes: Y10S 348/914 Delay for equalization

Abstract

A passband equalizer that performs blind equalization upon a complex signal, e.g., a vestigial sideband (VSB) signal, without using a training sequence. The passband equalizer contains a decision directed equalizer (DFE) that operates upon separate in phase (I) and quadrature phase (Q) signals using a filter for the I signal and a filter for the Q signal without using filters for cross components of the I and Q signals. As such, the DFE contains approximately half of the multipliers and adders that are used in prior art DFEs.

Claims

1. A passband equalizer comprising:

a feed forward equalizer containing at least one equalization filter;

a decision feedback equalizer that is supplied with separate in-phase and quadrature components of a complex signal containing a first adaptive filter for only filtering the in-phase (I) component and a second adaptive filter for only filtering the quadrature (Q) component without filtering a cross-coupled component of the complex signal; and

a summer for summing an output of the feed forward equalizer with an output of the decision feedback equalizer.

2. The passband equalizer of claim 1 wherein the first or second adaptive filters are complex 2T-spaced filters.

3. The passband equalizer of claim 2 wherein the complex 2T-spaced filters further comprise:

a plurality of complex multipliers, where each complex multiplier is separated from each other complex multiplier by a time delay element having a delay of 2T, where T is a symbol period of a symbol within the complex signal, and each complex multiplier multiplies a delayed input signal with a weighting value to produce a weighted signal; and

a combiner for adding the weighted values to produce an equalized signal.

4. The passband equalizer of claim 3 wherein the time delay element contains a first delay element and a second delay element and the complex 2T-spaced equalizer further comprises a switch for bypassing the first delay element to change the complex 2T-spaced filter into a complex T-spaced filter.

5. The passband equalizer of claim 3 wherein the weighting value is generated by a blind equalization algorithm.

6. The passband equalizer of claim 1 wherein said equalization filter is either T-spaced or 2T-spaced.

7. The passband equalizer of claim 1 wherein the equalization filter is T-spaced and the first and second adaptive filters are 2T-spaced.

8. The passband equalizer of claim 1 further comprising:

a I&

Q to complex converter that converts equalized I and Q signals from the decision feedback equalizer (DFE) into a complex DFE signal;

a combiner for combining an output of a feed forward equalizer (FFE) with the complex DFE signal;

a first rotator for derotating the complex signal produced by the combiner;

a carrier recovery circuit for producing a carrier signal that is used to derotate the complex signal from the combiner;

quantizer for quantizing the complex signal from the first rotator;

a subtractor for generating an error signal represented by the difference between the derotated complex signal and the quantized signal;

a second rotator for rotating the error signal using a complex conjugate of the carrier signal, where the rotated error signal is used by a blind equalization algorithm to determine tap weights for the FFE and DFE filters;

a third rotator for rotating the quantized signal using a complex conjugate of the carrier signal to produce a rotated quantized signal; and

a complex to I&

Q converter for producing and the I and Q signals that are equalized are applied to the DFE from the rotated quantized signal.

9. The passband equalizer of claim 8 wherein said first or second adaptive filters are complex 2T-spaced filters having every other delay element capable of being bypassed to form a T-spaced filter.

10. An adaptive filter for filtering vestigial sideband (VSB) signals that have a symbol duration of T, the filter comprising:

a plurality of complex multipliers, where each multiplier is separated from each other complex multiplier by a time delay element having a delay of 2T, where T is a symbol period of a symbol within the complex signal, and each complex multiplier multiplies a delayed input signal with a complex weighting value to produce a weighted signal, wherein the time delay element contains a first delay element and a second delay element and the adaptive filter further comprises a switch for bypassing the first delay element to change the 2T-spaced filter into a T-spaced filter; and

a combiner for adding the weighted values to produce an equalized signal.

11. An adaptive filter for filtering vestigial sideband (VSB) signals that have a symbol duration of T, the filter comprising:

a plurality of complex multipliers, where each multiplier is separated from each other complex multiplier by a time delay element having a delay of 2T, where T is a symbol period of a symbol within the complex signal, and each complex multiplier multiplies a delayed Input signal with a complex weighting value to produce a weighted signal, wherein each complex multiplier contains four real multipliers that are selectively arranged to form a T-spaced real filter by having a first pair of real multipliers connected to a first time delay element and a second pair of real multipliers connected to a second time delay element; and

a combiner for adding the weighted values to produce an equalized signal.

12. A selectable adaptive filter for filtering vestigial sideband (VSB) signals that have a symbol duration of T, the filter comprising:

a plurality of complex multipliers, where each complex multiplier is separated from each other complex multiplier by a time delay element having a delay of 2T, where T is a symbol period of a symbol within the complex signal, and each complex multiplier multiplies a delayed input signal with a weighting value to produce a weighted signal;

a combiner for adding the weighted values to produce an equalized signal; and

where the time delay element contains a first delay element and a second delay element and the adaptive filter further comprises a switch for bypassing the first delay element to change the complex 2T-spaced filter into a complex T-spaced filter.

13. The adaptive filter of claim 12 wherein each complex multiplier contains four real multipliers that are selectively arranged to form a T-spaced real filter by having a first pair of real multipliers connected to a first time delay element and a second pair of real multipliers connected to a second time delay element.

14. A digital television receiver comprising

a tuner for selecting a digital television signal from a plurality of available digital television signals;

an analog to digital converter for digitizing said selected digital television signal to produce a digitized signal;

a pilot recovery circuit for recovering a pilot tone from said digitized signal;

a timing recovery circuit for extracting symbol timing from the digitized signal;

a Nyquist filter for extracting a complex signal from the digitized signal;

a passband equalizer for adaptively filtering said complex signal, where said passband equalizer comprises;

a feed-forward equalizer (FFE); and

a decision feedback equalizer (DFE) that is supplied with separate in-phase and quadrature components of said complex signal containing a first adaptive filter for filtering the in-phase (I) component, a second adaptive filter for filtering the quadrature (Q) component, a combiner for combining the filter Q component with the filtered I component, and a delay for delaying the Q component for a duration equal to a delay through the first filter and the combiner.

15. The digital television receiver of claim 14 wherein the first or second adaptive filters are 2T-spaced filters.

16. The digital television receiver of claim 15 wherein the first or second adaptive filters are either T-spaced or 2T-spaced.

17. The digital television receiver of claim 14 wherein an FFE adaptive filter in the feed-forward equalizer is T-spaced and the first and second adaptive filters are 2T-spaced.

18. The digital television receiver of claim 17 wherein the 2T-spaced filters further comprise:

a plurality of multipliers, where each multiplier is separated from each other multiplier by a time delay element having a delay of 2T, where T is a symbol period of a symbol within the complex signal, and each multiplier multiplies a delayed input signal with a weighting value to produce a weighted signal; and

a combiner for adding the weighted values to produce an equalized signal.

19. The digital television receiver of claim 18 wherein the weighting value is generated by a blind equalization algorithm.

20. The adaptive filter of claim 18 wherein the time delay element contains a first delay element and a second delay element and the adaptive filter further comprises a switch for bypassing the first delay element to change the 2T-spaced filter into a T-spaced filter.

21. The adaptive filter of claim 18 wherein each complex multiplier contains four real multipliers that are selectively arranged to form a T-spaced real filter by having a first pair of real multipliers connected to a first time delay element and a second pair of real multipliers connected to a second time delay element.

22. The digital television receiver of claim 14 wherein the passband equalizer further comprises:

a I&

Q to complex converter that converts the DFE equalized I and Q signals into a complex DFE signal;

a combiner for combining an output of the FFE with the complex DFE signal;

a first rotator for derotating the complex signal produced by the combiner;

a carrier recovery circuit for producing a carrier signal that is used to derotate the complex signal from the combiner;

a quantizer for quantizing the complex signal from the first rotator;

a subtractor for generating an error signal represented by the difference between the derotated complex signal and the quantized signal;

a second rotator for rotating the error signal using a complex conjugate of the carrier signal, where the rotated error signal is used by a blind equalization algorithm to determine tap weights for the FFE and DFE filters;

a third rotator for rotating the quantized signal using a complex conjugate of the carrier signal to produce a rotated quantized signal; and

a complex to I&

Q converter for producing the I and Q signals that are equalized are applied to the DFE from the rotated quantized signal.