Timing recovery using the pilot signal in high definition TV

• US 6,411,659 B1
• Filed: 10/20/2000
• Issued: 06/25/2002
• Est. Priority Date: 11/03/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Tan, Loke Kun, Liu, Tian-Min, Jaffe, Steven T.
• Primary Examiner(s): Ghebretinsae, Temesghen
• Application Number:
  US09/692,805
• Time in Patent Office: 613 Days
• Field of Search: 375/326, 375/316, 375/355, 375/324, 375/321, 348/725
• US Class Current: 375/326
• 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 5/455 : Demodulation-circuits
• CPC Class Codes: H04N 5/46 : for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27

Abstract

Improved carrier recovery and symbol timing systems and methods suitable for use in connection with a dual-mode QAM/VSB receiver system is disclosed. Carrier and symbol timing acquisition and tracking loops are phase/frequency locked to an inserted pilot signal provided in an input VSB spectrum at a given frequency. An input spectrum is centered about baseband and the pilot is extracted by an equivalent filter which functions as a bandpass filter having pass bands centered about the pilot frequency. Since the pilot signal'"'"'s frequency is given, its position in the frequency domain for any sampling frequency, is deterministic. The receiver'"'"'s sampling frequency is provided such that the relationship is expressed as f_C=f_S4. When tracked by a phase-lock loop, the pilot signal will appear at the correct location in the spectrum if the sampling frequency f_S is correct, and will be shifted in one direction or the other if the sampling frequency f_S is too high or too low.

Claims

1. A method for operating a receiver having a particular sampling frequency related to a symbol rate to recover carrier and timing information from a received spectrum including a pilot signal, wherein the pilot signal is provided at a predetermined frequency, the method comprising:

centering the received spectrum at a known position relative to baseband;

tracking the pilot signal with a phase-lock-loop;

evaluating the frequency of the pilot signal with respect to the particular sampling frequency; and

adjusting the centering of the received spectrum until the evaluated frequency of the pilot is in integral relationship with the particular sampling frequency.

2. The method according to claim 1, further comprising:

filtering the received spectrum in a low pass filter having a cut-off frequency related to the sampling frequency;

processing the filtered signal in a high pass filter having a cut-off frequency related to the sampling frequency; and

wherein the low pass and high pass filters define an equivalent bandpass filter, the equivalent bandpass filter defining upper and lower sideband regions each centered at an expected position of the pilot signal.

3. The method according to claim 2, wherein the received spectrum exhibits a raised cosine response characteristic, the upper and lower sideband regions of the equivalent filter including transition regions of the spectra defined by the high pass and low pass filters.

4. The method according to claim 3, wherein the receiver'"'"'s sampling frequency is determined such that the pilot frequency is equal to about one-fourth the sampling frequency.

5. The method according to claim 4, wherein the high pass filter is a Nyquist prefilter having a lower cut-off frequency at about one-fourth the sampling frequency, the high pass filter centering the spectrum at a frequency about one half the sampling frequency.

6. The method according to claim 5, wherein the low pass filter is a square root Nyquist filter having an upper cutoff frequency at about one-fourth the sampling frequency, the square root Nyquist filter centering the spectrum at about baseband.

7. The method according to claim 6, the desired position of the pilot signal being substantially centered in each transition region, thereby causing the desired position of the pilot signal to be centered in each of the upper and lower sideband regions of the equivalent filter at a frequency substantially equal to one-fourth the sampling frequency, thereby augmenting a signal occurring at one-fourth the sampling frequency.

8. The method according to claim 7, further comprising:

receiving a sideband region from the equivalent filter in a tracking loop;

sweeping the sideband region to identify an augmented frequency component;

comparing the augmented frequency component to the expected frequency of the pilot signal; and

shifting the sampling frequency in a direction and an amount such that the augmented frequency component coincides with the expected frequency of the pilot signal.

9. The method according to claim 8, further comprising the step of using the shifted sampling frequency to define a symbol timing reference signal.

10. In an integrated circuit communication device, a method for synchronizing a receiver'"'"'s timebase to a remote transmitter'"'"'s comprising:

receiving an input spectrum including a pilot signal, wherein the pilot signal is provided at a predetermined frequency;

providing a sampling frequency having a fixed relationship with the pilot frequency;

evaluating the position of the pilot signal in the frequency domain with respect to the sampling frequency; and

adjusting the sampling frequency when the pilot signal is at a location in the spectrum different from its expected frequency location.