British Broadcasting Corporation

Lsi Logic Corporation

Christopher K Clarke

Adrian Paul Robinson

Oliver Paul Haffenden

Jonathan Highton Stott

Philippe Roger Sadot

Jean-Marc Guyot

Justin David Mitchell

Lauret Regis

Andrew J Bower

A demodulator suitable for implementation in a single chip for demodulating digital video broadcast signals including data modulated on a multiplicity of spaced carrier frequencies, wherein an input broadcast signal is converted to a frequency sufficiently low to enable analog digital conversion of the signal. The demodulator includes an analog to digital converter for converting the broadcast signal to a series of digital samples; a real to complex converter for converting each digital sample to a complex number value; Fourier transformer for analyzing the complex number values to provide a series of data symbol values for each carrier frequency; a signal processor for receiving the data symbol values and providing an output for decoding; and a timing synchronizer for synchronizing the Fourier transformer with the symbol periods of the broadcast signal. The synchronizer includes a correlation for receiving the data sample values and including a delay having a time period delay equal to the active symbol period, and a multiplier for receiving the data symbol values and a version thereof delayed by the delay, to form a complex product signal, and a filter for filtering the complex product signal. The timing synchronizer includes a coarse synchronizer employing a subset of the data sample values for providing a course timing synchronization, and a fine synchronizer for providing a fine synchronization within a time period determined by the coarse synchronization.

Demodulating digital video broadcast signals

Apparatus for demodulating digital video broadcast signals with an improved mechanism for automatic frequency control including data modulated on a multiplicity of spaced carrier frequencies. The apparatus includes an analog to digital converter for providing a series of digital samples of the broadcast signal, a Fourier Transformer for analyzing the samples to provide a series of data signal values for each carrier frequency, signal processor for processing the series of data signal values including the phase-error-correcter, and automatic frequency controller for controlling the frequency of the signals input to the Fourier Transformer. The automatic frequency controller includes coarse frequency controller for controlling the frequency in terms of increments of the carrier spacing frequency, and fine frequency controller for controlling the frequency for values less than a single carrier spacing frequency interval. The coarse frequency controller includes a recursive filter for assessing a predetermined number (N) of carrier signals on either side of the nominal position of a predetermined continual pilot signal, to determine which signal best represents the continual pilot signal, whereby to determine the coarse frequency error.

Method and apparatus for secure transmission of video signals

A filter is disclosed for adaptively filtering a PAL or NTSC luminance signal so as to attenuate the high frequency portion of the luminance band, wherein the chrominance information lies, when movement is detected. This reduces cross-color in the reproduced picture. Movement is detected by comparing the undelayed luminance signal with this signal delayed by an integral number of lines corresponding substantially to one field or one picture. The filter may precede a coder or follow a decoder.

Adaptive filter for use in color video signal processing

If an N.T.S.C. signal is to be demodulated using a line-locked sampling rate such as 800 times the line frequency, the ratio between the sampling period and the subcarrier period has the awkward value of 455/1600. Line-locked sampling is nevertheless desirable, e.g. in digital standards conversion. The subcarrier digital signals for digital demodulation are derived with the correct frequency from the sampling rate clock pulses CP by an adder and accumulator into which the number 582 is added modulo-2048 (the register is an 11-bit register) to generate an 11-bit number which represents the subcarrier phase angle at each sampling pulse and which addresses a ROM providing sin and cos values representing subcarrier samples. 582/2048 is not exactly equal to 455/1600 but 2048 is a desirable denominator as it is a power of 2 and implies a ROM of suitable size. ##EQU1## is exactly equal to 455/1600. Another adder and accumulator counts modulo-40960 by increments of 16384 and when this adder overflows, an extra 1 is added in through the carry-in to the first adder. Modulo 40960 is set up by altering 10256 to 40960 when the overflow occurs. Alternative numerical values are disclosed which apply to a system with sampling rate 816 times line rate. Phase lock to the color burst is established by examination of the V output of the main demodulators during the color burst. V=sine .theta. where .theta. is the phase error. This quantity is applied via a negative feedback loop to effect fine adjustment of the numbers 40960 and 16384. Similar provisions for are disclosed as is the generation of a PAL switch signal of the correct phase. The apparatus can also be employed as a modulator.

Apparatus for digital demodulation or modulation of television

A signal processing circuit (10) for color television signals, e.g. PAL signals, has first and second one-line delays (14, 16) connected in series to the input (12), an averager (18) connected across the two delays and a subtractor (20) connected to subtract the averager output from the output of the first delay (14). In this way the circuit provides (i) a first signal at the output of the first delay (14) which is the input signal delayed by one line period and (ii) a second signal at the output of the subtractor (20) which is the resultant of the average of the undelayed input signal and the input signal delayed by two line periods subtracted from the input signal. A band-pass filter (22) covering the chrominance band is connected to the output of the subtractor (20). A second subtractor (24) subtracts the filtered signal from the one-line delayed signal. Separated luminance and chrominance are obtained at the outputs of the second subtractor (24) and the filter (22) respectively, which are especially suitable for line-locked sampling frequencies. Either output may be used on its own. For N.T.S.C. signals, a divide-by-two circuit is included in series with the band-pass filter (22).

Processing circuit for color television signals

Demodulated luminance (Y) and chrominance (U, V) signals are stored in field stores 1 to m each with line outputs 1 to n. Output lines are formed by summing the producs of the line outputs with weighting coefficients which are specified for each line in the output standards. Separate sets of coefficients for luminance and chrominance are stored in respective memories. The chrominance sets are arranged to reduce the vertical and temporal resolution of the chrominance information. This has the beneficial effect of reducing cross-color interference. In the implementation shown the signals are stored as time multiplexed digital samples YYYUV (i.e. with one pair of chrominance samples to three luminance samples) and the luminance and chrominance coefficient sets for the current output line are stored as a.sub.11 to a.sub.mn and b.sub.11 to b.sub.mn respectively in buffer registers. A switching waveform controls electronic switches to apply a.sub.11 to a.sub.mn to multipliers when Y samples are presented and to apply b.sub.11 to b.sub.mn when U or V samples are presented.

Growing community of inventors

Crawley, United Kingdom

Christopher K Clarke