Technique for minimizing decision feedback equalizer wordlength in the presence of a DC component

• US 7,277,481 B2
• Filed: 04/23/2004
• Issued: 10/02/2007
• Est. Priority Date: 11/03/1998
• Status: Expired due to Fees

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Tan, Loke Kun, Liu, Tian-Min, Hung, Hing “Ada” T.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US10/830,827
• Publication Number:
  US 20040196897A1
• Time in Patent Office: 1,257 Days
• Field of Search: 375/229, 375/232, 375/233, 375/346, 375/348, 375/350, 708/322, 708/323
• US Class Current: 375/233
• CPC Class Codes: H04B 1/68 for wholly or partially suppressing the carrier or one side band
• CPC Class Codes: H04L 2025/03382 Single of vestigal sideband
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/03503 as a combination of feedback and prediction filters
• CPC Class Codes: H04L 2027/0032 at baseband and passband
• CPC Class Codes: H04L 2027/0042 the equaliser providing the offset correction per se
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 2027/0067 Phase error detectors
• CPC Class Codes: H04L 2027/0087 Out-of-band signals, (e.g. pilots)
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 27/066 Carrier recovery circuits H04L27/2271 takes precedence
• CPC Class Codes: H04L 27/2273 associated with quadrature demodulation, e.g. Costas loop
• CPC Class Codes: H04L 27/3427 in which the constellation is the n - fold Cartesian product of a single underlying two-dimensional constellation
• CPC Class Codes: H04L 27/3827 in which the carrier is recovered using only the demodulated baseband signals
• 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 5/21 Circuitry for suppressing or minimising disturbance, e.g. moiré or halo
• CPC Class Codes: H04N 5/211 Ghost signal cancellation H04N23/81 takes precedence
• CPC Class Codes: H04N 5/44 : Receiver circuitry for the reception of television signals according to analogue transmission standards H04N5/14 takes precedence
• CPC Class Codes: H04N 5/46 : for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27

Abstract

A system for reducing the complexity of an adaptive decision feedback equalizer, for use in connection with a dual-mode QAM/VSB receiver system is disclosed. QAM and VSB symbols, which are expressed in two'"'"'s compliment notation, include an extra bit required to compensate for a fixed offset term introduced by the two'"'"'s compliment numbering system. A decision feedback equalizer includes a decision feedback filter section which operates on symbolic decisions represented by a wordlength which excludes the added bit representing the offset. The vestigal word is convolved with the decision feedback filter'"'"'s coefficients, while a DC component, corresponding to the excluded bit, is convolved with the same coefficient values in a correction filter. The two values are summed to provide an ISI compensation signal at the input of a decision device such as a slicer. A DC component representing a pilot tone in VSB transmission systems also introduces a DC component, and additional bits, to a VSB wordlength. These additional bits are similarly excluded and the vestigal representation convolved with coefficient values in a decision feedback filter. The DC component, including the pilot tone representation, is convolved with the same coefficient values in a correction filter.

Claims

1. A method for improving the quality of a digital signal evaluated by a digital decision circuit that produces an output signal and an error signal, the digital signal including a pilot for carrier recovery, the method comprising:

applying the digital signal to a feed forward filter (FFF) to produce a partially compensated signal;

applying the output signal to a decision feedback filter (DFF);

adjusting coefficients of the DFF responsive to the error signal;

adjusting coefficients of the FFF responsive to the error signal;

forming a DC offset signal representative of the coefficients of the DFF;

modifying the DC offset signal with a signal representative of the pilot;

forming a feedback signal by combining the output of the DFF and the modified DC offset signal;

combining the feedback signal and the partially compensated signal to form an input signal; and

applying the input signal to the decision circuit.

2. The method of claim 1, additionally comprising modifying the input signal with the signal representative of the pilot before application of the input signal to the decision circuit.

3. The method of claim 2, in which the digital signal is in twos-complement format.