High definition television (HDTV) services will play the most important role in the digital television systems for the future. HDTV is already broadcast daily in Japan and advanced television (ATV) standards will soon be established in the US. The hardware systems for two HDTV systems, the 1125/60 and 1250/50 systems, have already been developed. Their outlines are described in the paper. Signal processing of HDTV is mainly carried out by digital methods on both the studio and receiver sides. The principles of processing are the same as for conventional television but the higher clock frequency and larger quantity of information require more sophisticated hardware. Digital signal processing methods are the key technology in HDTV broadcasting systems regardless of whether modulation is analog or digital. Some broadcasting systems are already practical use while others, are experimental. The author discusses these systems. The aim of the article is to present a global scope of the HDTV technology.>

A motion-compensated interframe coding system for an NTSC color television signal has been developed. The output of a local decoder is used in the form of aY/Cseparated signal. Motion vectors are detected using theYsignal, and theYsignal and both baseband components of theCsignal are motion-compensated. The motion-compensated signals are reencoded into an NTSC signal to provide a motion-compensation interframe prediction in the NTSC format. Real-time experimental hardware has been built. The sampling frequency and bit rate of this system are 10.7 MHz and 1.6 bits/ sample, respectively. This value includes all overhead information such as motion vectors and other control information. An assessment has been made of the picture quality of coded/decoded pictures taken from a variety of broadcast television programs. The quality was good for almost all the programs. A subjective test of picture quality was performed under stringent conditigns. The lowest value for the picture quality of the most difficult scenes at 1.6 bits/sample was 3.3 on a five-grade impairment scale.

A motion-compensated prediction system for interframe coding is proposed. An interframe coding system is developed using this prediction method and second-order temporal prediction. Real-time hardware of reasonable circuit size using this coding system for monochrome TV pictures has been constructed. Assessments have been made of the picture quality of coded/decoded pictures from a variety of broadcast television programs. Quality was good for almost all such programs. A subjective test of picture quality was performed under stringent conditions, using some of the most difficult scenes selected in earlier experiments.

A very high-speed 8 bit A/D converter in which the sampling rate is 100 MHz has been developed. This converter is intended for application to a high-definition television (HDTV) system. The converter maintains high linearity even at high input frequencies. The basic configuration of the converter is a three-stage seriesparallel type. A digital correction system and ac coupling are used. The characteristics of the converter are as follows. At 100 MHz sampling rate, 8 bit/sample and for1 V _{p-p} (75 \omega)input operation, the linearity error is less than 1/2 LSB, DG at 30 percent 24.3 MHz subcarrier less than 1.5 percent.

An A/D converter circuit system with a very high bit-rate has been developed. It is a series-parallel type, and the input of the last A/D stage is equivalently ac-coupled. This can be allowed by the statistical charactertstics of input signals. A prototype of this A/D converter has the following characteristics: 1) dc coupled analog input-able to accept almost all analog signals as well as television signals; 2) sampling frequency up to 20 MHz; 3) linear coding scheme with 10 bits per sample; 4) linearity error of less than one third of quantizing level; 5) differential gain and differential phase of 0.4% and 0.25°, respectively; and 6) operating temperature range of from 0° to 50°C.