PULSE CODE MODULATION SYSTEM

• US 3,657,653 A
• Filed: 04/27/1970
• Issued: 04/18/1972
• Est. Priority Date: 04/30/1969
• Status: Expired due to Term

• Current Assignee: Roger Martin Wilkinson
• Original Assignee: Roger Martin Wilkinson
• Inventors: Wilkinson, Roger Martin
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/032,322
• Time in Patent Office: 722 Days
• Field of Search: 325/38R,38B,321,324 340/347AD 178/68
• US Class Current: 375/246
• CPC Class Codes: H03M 3/04 Differential modulation with several bits , e.g. differential pulse code modulation [DPCM] H03M3/30 takes precedence

Abstract

A pulse code telecommunications system in which samples of an analogue signal to be transmitted are each represented by a binary word. In each binary word, one signal bit represents the polarity of the sample with respect to a reference level and one or more further signal bits represent the magnitude of the sample with respect to a second, variable, reference level which is derived from the coded representation of the magnitudes of preceding samples. The system includes a binary signal multiplexer and a transmitter. A receiver for use with the system includes a binary signal demultiplexer, circuits for correctly allocating the polarity and magnitude bit signals to polarity and magnitude signal channels, and decoder circuits for reconstituting the analogue signal from the binary word signal.

Claims

1. Telecommunications apparatus for transmitting analogue signals, comprising an analogue signal input, pulse-coding means connected to said analogue signal input, for generating a stream of digital word signals, wherein each digital word signal will represent a sampled instantaneous value of an analogue signal applied to said analogue signal input and will comprise one polarity-bit signal representing the sign of the difference between the sampled value and a predetermined value and at least one amplitude-bit signal representing the magnitude of the modulus of the said difference, and reference-level deriving means, connected to outputs of the said pulse-coding means, for deriving a variable referencelevel signal dependent on the magnitudes of a plurality of the moduli represented in a sequence comprising a plurality of the said digital word signals which represent successively sampled values of the said analogue signal, the said pulse-coding means including means for generating the amplitude-bit signals, connected to receive the said referencelevel signal from the said reference-level deriving means and controlled thereby, for generating the amplitude-bit signals to represent the magnitudes of the sampled values of the analogue signal quantized in terms of units whose size will vary according to the value of The said reference-level signal.

2. Telecommunications apparatus as claimed in claim 1, wherein the said pulse-coding means comprises means for generating a polarity-bit signal of a predetermined binary kind in response to each sampled instantaneous value of the said analogue signal which is found to be greater than the said predetermined value, and for generating a polarity-bit signal of the converse binary kind in response to each sampled instantaneous value of the said analogue signal which is found to be less than the said predetermined value, and wherein the said means for generating the amplitude-bit signals comprises means for generating a single amplitude-bit signal of a predetermined binary kind in response to each sampled instantaneous value of the said analogue signal whose difference from the said predetermined value is found to have a modulus greater than a magnitude determined by an instantaneous value of the said reference-level signal, and means for generating a single amplitude-bit signal of the converse binary kind in response to each sampled instantaneous value of the said analogue signal whose difference from the said predetermined value is found to have a modulus less than the said magnitude determined by the value of the said reference-level signal.

3. Telecommunications apparatus as claimed in claim 2 wherein the said pulse-coding means comprises an inverter connected to the output of the reference-level deriving means, and first, second and third comparator amplifiers, wherein each of the said comparator amplifiers has a signal input and a reference input, and wherein the signal inputs of the said comparator amplifiers are all connected to the said analogue signal input, the reference input of the first comparator amplifier being connected to receive a predetermined fixed voltage, the reference input of the second comparator amplifier being connected to receive the reference-level signal directly from the reference-level deriving means, and the reference input of the third comparator amplifier being connected to receive an inverted form of the reference-level signal from the said inverter.

4. Telecommunications apparatus as claimed in claim 3 and also comprising an OR-gate circuit connected to pass signals from the said second and third comparator amplifiers, and transmitting means for transmitting signals from the said OR-gate circuit and signals from the said first comparator amplifier through a telecommunications channel.

5. Telecommunications apparatus as claimed in claim 4 and wherein the said transmitting means comprises a first sample-and-hold circuit connected to the output of the said first comparator amplifier and a second sample-and-hold circuit connected to the output of the said OR-gate, and means for transmitting signals from the first and second sample-and-hold circuits sequentially.

6. Telecommunications apparatus as claimed in claim 1 wherein the said reference-level deriving means comprises an integrating circuit having a input connected to receive from the pulse-coding means at least some of the amplitude-bit signals generated to represent a sequence of successive sampled values of the analogue signal, and an output from which the said reference-level signal is derived.

7. Telecommunications apparatus as claimed in claim 6, wherein the said integrating circuit has a time constant of about 10 milliseconds.

8. Telecommunications apparatus, for receiving a continuous stream of pulse code signals formed of word signals wherein each word signal comprises one polarity-bit signal and at least one amplitude-bit signal sequentially transmitted, and represents one sampled instantaneous value of an analogue signal;

the said apparatus comprising receiver means for receiving pulse code signals from a telecommunications channel;

switching means, having a signal input connected to receive said pulse code signals from the said receiver means, and having a control input and at least two outputS, for distributing successive ones of said pulse code signals sequentially to the said at least two outputs of said switching means in a predetermined cyclic order, and causing a single modification to the distribution whenever a signal is applied to the said control input;

threshold detector means, having an input connected to one of the said outputs of the said switching means, and having an output connected to the said control input of the said switching means, for applying a signal to the said control input whenever an average of a sequence of signals successively developed on the said one of the said outputs of said switching means occurs outside a predetermined range of values; and

decoder means, having a polarity-bit signal input and at least one amplitude-bit signal input connected to separate outputs of the said switching means, for reproducing the said analogue signal by generating a sequence of signals having their polarities determined by the signals applied to its polarity-bit signal input and their amplitudes individually dependent on the bit signals applied to the said at least one amplitude-bit signal input and also proportional to an average of the values of a sequence of the signals applied to at least one amplitude-bit signal input of the said decoder means.

9. Telecommunications apparatus as claimed in claim 8 and wherein the said decoder means comprises reference-signal deriving means connected to the said at least one amplitude-bit signal input for deriving a reference signal dependent on an average of the values of a sequence of the signals applied to the said at least one amplitude-bit signal input, potential divider means connected across the output of the said reference-signal deriving means and having output connections on which predetermined fractions of the said reference signal will be developed, and further switching means, having a common output, separate analogue signal inputs connected to separate output connections of the said potential divider means, and control inputs separately connected to the said polarity-bit signal input and the said at least one amplitude-bit signal input, for connecting a predetermined one of the said analogue signal inputs to the said common output in response to each particular combination of binary signals which may be applied to the said control inputs.

10. Telecommunications apparatus as claimed in claim 9 wherein the said reference-signal deriving means comprises a resistance-capacitance integrating circuit.

11. Telecommunications apparatus as claimed in claim 13, wherein the said integrating circuit has a time constant of about 10 milliseconds.

12. Telecommunications apparatus as claimed in claim 8 and wherein the said decoder means comprises reference-signal deriving means connected to the said at least one amplitude-bit signal input for deriving a reference signal dependent on an average of the values of a sequence of the signals applied to the said at least one amplitude-bit signal input;

an amplifier having an input connected to the reference-signal deriving means;

gain-switching means having at least one control input connected to the said at least one amplitude-bit signal input and connected to control the said amplifier, for switching the effective gain of the said amplifier according to the pulse code signals applied to the said at lease one amplitude-bit signal input; and

polarity-switching means, connected to the output of the said amplifier and having a control input connected to the said polarity-bit signal input, for passing the output of the said amplifier without inversion when a binary signal of one predetermined kind is applied to its control input and for inverting the said output of the said amplifier when a binary signal of the converse kind is applied to its control input.

13. Telecommunications apparatus as claimed in claim 12 and wherein the said reference-signal deriving means comprises a resistance-capacitance integrating circuit.

14. Telecommunications Apparatus as claimed in claim 13 wherein the said integrating circuit has a time constant of about 10 milliseconds.

15. Telecommunications apparatus, for receiving a continuous stream of pulse code signals formed of word signals wherein each word signal comprises one polarity-bit signal and at least one amplitude-bit signal sequentially transmitted, and represents one sampled instantaneous value of an analogue signal;

the said apparatus comprising receiver means for receiving pulse code signals from a telecommunications channel;

switching means, having a signal input connected to receive said pulse code signals from the said receiver means, and having at least two outputs, for distributing successive ones of said pulse code signals sequentially to the said at least two outputs in a predetermined cyclic order;

a plurality of threshold detector means, wherein each threshold detector means is connected to a separate one of the outputs of the said switching means, for generating a binary-signal output of a predetermined kind whenever an average of the pulse code signals applied to the one of the outputs of the switching means to which it is connected occurs within a predetermined range;

gate circuit means, comprising a plurality of gate circuits and having pulse code signal inputs separately connected to the said outputs of the said switching means, control inputs separately connected to receive the binary-signal outputs of the said plurality of threshold detector means, a polarity-bit signal output channel and at least one amplitude-bit signal output channel, for passing the pulse code signals developed on the separate outputs of the said switching means to separate output channels in cyclic order so that the pulse code signals applied to the one of the said threshold detector means which has most recently produced a binary signal output of the said predetermined kind will also be applied to a predetermined one of the output channels of the gate-circuit means; and

decoder means, having a polarity-bit signal input connected to the said polarity-bit signal output channel and at least one amplitude-bit signal input connected to the said at least one amplitude-bit signal output channel of the said gate-circuit means, for reproducing the said analogue signal by generating a sequence of signals having their polarities determined by the signals applied to the said polarity-bit signal input and their amplitudes individually dependent on the bit signals applied to the said at least one amplitude-bit signal channel and also proportional to an average of the values of a sequence of the signals applied to at least one amplitude-bit signal channel.