Switching circuitry

Details Switching circuitry Switching circuitry

1990-02-27

1991-04-30

Isen, Forester W.

Electrical audio signal processing systems and devices

Binaural and stereophonic

Broadcast or multiplex stereo

H04H 500

Patent

active

050125168

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to automatic switching circuitry, particularly but not solely for use in multi-standard television equipment relating to multi-channel audio accompanying conventional television format signals.
There are many television systems in general use throughout the world. In each of these systems, video signals including colour information are modulated on a vision carrier and sound signals are modulated on a sound carrier whose frequency differs from the vision carrier by an amount which depends on the television system and on the local standard of the system. Also, more systems transmit FM sound signals, although one SECAM system transmits AM sound.
With the systems and standards presently in use the spacing between the vision and sound carriers is 4.5 MHz, 5.5 MHz, 6.0 MHz or 6.5 MHz depending on the television system and standard. Also, spacings of 5.7 MHz and 6.2 MHz are coming into use for stereo TV sound. This frequency spacing is preserved during conversion to the intermediate frequency (IF) in a television receiver, and is converted to the sound intercarrier by balanced demodulation of the sound IF signal by the vision carrier signal filtered from the vision IF signal. Thus, the carrier frequency of the sound intercarrier signal supplied to the sound demodulator has one of the values mentioned above.
In conventional television receivers, the sound IF stages and the sound demodulator contain filters and tuned circuits whose resonant frequencies are adapted to the system and standard for which the receiver is designed. Also, the vision IF stages contain resonant traps for preventing sound-on-vision interference, and the resonant frequencies of these traps are similarly adapted to the system and standard in use.
GB 2124060A (SPT Video) discloses a circuit arrangement to provide automatic selection of television sound frequency, such as sound intercarrier frequency, in a television receiver for receiving television signals of different systems or standards. The arrangement comprises a plurality of band pass filters tuned to the different sound intercarrier frequencies. The levels of the outputs of the filters are determined by level detecting means and supplied to a circuit arrangement for detecting the highest level of the detected signals. Selection controlling means then selects the frequency of the highest level and drives the sound demodulator of the television set.
A proposed transmission system for stereo signals to accompany conventional television transmissions, known as NICAM, provides a serial data stream partitioned into 728-bit frames, each transmitted in a millisecond. Each frame has: a first section of eight bits comprising a Frame Alignment Word (FAW) which marks the start of the frame; a second section of five bits which provide control information, being one flag bit (namely C.sub.o, which alternates between 0 and 1 every 8 milliseconds to determine odd and even frames over a 16 frame sequence) and four mode bits (namely C.sub.1, C.sub.2, C.sub.3 and C.sub.4, which indicate the nature of the transmitted signal, e.g. mono, stereo, dual-language, data); a third section of eleven bits of additional data, independent of the control information bits; and finally a fourth section of sixty-four 11-bit words corresponding to the audio (or data if appropriate) being transmitted, this last section having a total of 704 bits.
In each frame as transmitted, interleaving is applied to the block of 720 bits which follow the FAW in order to ensure that adjacent bits are not transmitted sequentially so as to minimise the effect of multiple-bit errors. The interleaving pattern places data bits, which are adjacent in the frame structure as output by the television receiver, in positions at least 16 clock periods apart in the transmitted bit stream (i.e. at least 15 other bits occur between bits which are adjacent in the output frame structure).
In the production of the sound signals, they are sampled at 32 kHz and coded initially with a resolution of 14 bits per sample. For transm

REFERENCES:
patent: 3991374 (1976-11-01), Csicsatka et al.
patent: 4030036 (1977-06-01), Kusano
patent: 4302837 (1981-11-01), Tanaka et al.
patent: 4761814 (1988-08-01), Sugai et al.

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