Independent Broadcasting Authority

National Transcommunications Limited

Nds Corporation

Brian H Beech

Simon Moore

The invention concerns a method and apparatus to synthesize a frequency employing digital phase words to represent successive phase values. A digital dither signal generator is used to generate a succession of dither words which are summed with the phase words to form address words. The address words are used to address a store to convert the address words to waveform values. The periodic quantisation noise introduced by the digital process is made more random by means of the dither words thereby reducing the quantisation noise components while accepting an increased total noise power. The synthesizer is of particular advantage when used to generate the reference frequency for a frequency multiplier implemented as a phase lock loop. By making the dither sequence repetition frequency outside the phase lock loop bandwidth, the spurious components are removed from the frequency range of interest.

Digital synthesizer

Compatible non linear pre-emphasis for composite video signals

Method of video noise reduction using non-linear pre/de-emphasis

Noise reduction in high definition television signals

A phase lock loop demodulator has its loop transfer function (F(s)) optimized to: F(s)=A+B/s+CF.sub.1 (s)+DF.sub.2 (s) where CF.sub.1 (s) is a chrominance sub-carrier term DF.sub.2 (s) is a sound sub-carrier term and A, B, C and D are constants whereby to minimize the phase error signal appearing at the output of the phase comparator (10) of the loop. An equalizer circuit (14) may be added at the output of the loop in which case the transfer function (F.sub.T (s)) of the equalizer circuit is as follows: F.sub.T (s)=KoKd+s/F(s) where F(s) is the transfer function of the loop amplifier circuit (12) and A, Ko and Kd are constants.

Demodulator for color television signals including a sub-carrier

Dynamic noise reduction for video

Demodulator for television signals with feedback to correlate frames or

A phase lock loop demodulator has its loop amplifier and filter designed such that the transfer function of the amplifier and filter is optimized for the presence of sound and color subcarriers. An equalizer circuit is included in the demodulator for equalizing the demodulator response and has a transfer function which is independent of the transfer function of the loop filter and amplifier whereby to render the demodulator insensitive to small frequency errors around the subcarrier frequencies.

Phase lock loop television signal demodulator

Growing community of inventors

Bishopstoke, United Kingdom

Brian H Beech