A-D encoder and D-A decoder system

An encoder-decoder system for converting an analog input signal to a digital signal and for generating an analog output signal from the digital signal wherein said analog output signal is similar to said analog input signal, said system comprising:

• means for deriving, from the analog input signal, a first control signal with a selected rise time and indicative of the desired step-size;
• a first converter for converting said analog input signal to the digital signal, said converter responsive to said first control signal so that the digital signal will be generated in accordance with the desired step-size;
• means for introducing time delay to said analog input signal before it reaches the first converter to compensate for the rise time of the first control signal;
• means for deriving a second control signal from the first control signal so that the second control signal is substantially similar to the first control signal;
• and
• a second converter responsive to the second control signal for generating from said digital signal the analog output signal.

A circuit receiving through a medium an input digital signal, a step-size control signal and a spectral control signal, said circuit for converting the input digital signal into an analog signal to provide an output analog signal and for altering the spectral content of said output analog signal, said circuit comprising:

• means for limiting the bandwidths of the step-size and spectral control signals;
• adaptive delta demodulator means for converting the input digital signal into an analog signal to provide the output analog signal in accordance with the bandwidth limited step-size control signal;
• and
• means for altering the spectral content of the output signal in accordance with the bandwidth limited spectral control signal, said step-size and spectral control signals having such limited bandwidths that substantially the same output signal is obtained irrespective of the order in which the delta demodulation and spectral altering of the input signal are performed.

An A-D encoder for use in an encoder-decoder system, said system including a decoder for generating analog output signals from digital signals received through a medium, said decoder also receiving through the medium step-size information related to the digital signals, said decoder comprising first means for bandwidth limiting said step-size information and a D-A converter for converting digital signals received into analog signals in response to the bandwidth limited step-size information related to such digital signals, said encoder comprising:

• means for deriving, from an analog input signal, a control signal indicative of a desired step-size;
• a first A-D converter for converting said analog input signal to a digital signal, said converter responsive to said control signal so that the digital signal will be generated in accordance with the desired step-size;
• and
• means for introducing time delay to said analog input signal before it reaches the first A-D converter, said time delay being such that the control signal is available to the medium by a substantially fixed time interval before the digital signal is available to the medium;
• wherein said substantially fixed time interval compensates for the rise time of the first bandwidth limiting means in the decoder so that the bandwidth limited step-size information is available to the D-A converter in the decoder when the digital signal related to such information arrives at such D-A converter, and wherein the effects of errors introduced by the medium are reduced.