Adaptive delta modulation system

Details Adaptive delta modulation system Adaptive delta modulation system

1978-12-20

1980-06-17

Griffin, Robert L.

Pulse or digital communications

Repeaters

Testing

332 11D, 370 7, H03K 1322

Patent

active

042087406

ABSTRACT:
An adaptive delta modulation system is disclosed which features an improved digital compandor which may be used with a digital integrating network. The compandor executes a companding algorithm having a nonlinear characteristic to provide a rapid increase in step size to follow the fast rising start or fast decaying end of talkspurts in input signals so as to minimize any slope overload distortions and to provide a small increase or decrease in step size during the smooth portion of the talkspurts in input signals to reduce any granular noise effect. The step size generated by the compandor is directly related to the input signal level, providing a maximum companding range in which good signal-to-noise characteristics are preserved for the soft or low voiced speaker as well as for the loud voiced speaker and providing a fast transient response most suitable for telephone applications. The step size logic of the compandor has a built-in minimum step size circuit which insures that a well behaved idle pattern of alternating ones and zeros will appear at the digital output when the input signal is zero, and which provides a mechanism to rapidly build up the step size when an input signal appears. The step sizes can be integrated with an integrating network to reconstruct the input signal. The compandor may be used in conjunction with a digital integrating network which exhibits, for example, a system function, having either a single pole or a zero and a pair of poles which may be real or complex. The filter constants can be chosen to match any input spectrum to obtain optimum performance. A significantly high signal-to-noise ratio and a wide companding range have been obtained with the disclosed compandor. By providing storage elements in the compandor and in a digital integrating network and storing the calculated intermediate values, a plurality of input for output analog signals can be time division multiplexed and delta modulated with a single delta modulation system.

REFERENCES:
patent: 3899754 (1975-08-01), Brolin
patent: 3971987 (1976-07-01), Carrubba et al.
patent: 4059800 (1977-11-01), Jones, Jr.
"Adaptive Delta Modulation with One Bit Memory" Jayant, Bell Sys. T. J. vol. 49, No. 3, pp. 321-342, (Mar. 1970).
"Overshoot Suppression in ADM Modulator Links for Video Transmission" Weiss et al., 1973 Conference, National Telecommunications Conference vol. I, Atlanta, Ga., (26-28, Nov. 1973).

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