Reversible analog to digital converter

Abstract

A switching arrangement for converting analog signals into digital signals, and vice versa, is described. Conversions between pulse amplitude modulated (PAM) and pulse code modulated (PCM) signals are performed. In telecommunication systems having subscriber stations equipped to transmit and receive analog signals it is necessary to carry out these conversions to facilitate PCM transmission. An analog to digital converter is thus provided at each subscriber station for converting received digital signals into analog signals and analog signals to be transmitted into digital signals; the converter utilizes the iterative principle.

I claim: .[.1. Apparatus for converting analog signals from a source thereof into digital signals for transmission and transmitted digital signals into analog signals for an analog receiver, comprising: 
     
        bistable stages of said intermediate register means..]. 2. The .[.apparatus.]. .Iadd.telecommunication switching system .Iaddend.defined in claim .[.1.]. .Iadd.9 .Iaddend.wherein said bistable stages of said intermediate register means have reset inputs connected to a .[.third.]. .Iadd.first .Iaddend.predetermined output of said .Iadd.multistage 
     
     
        .Iaddend.binary counter. 3. The .[.apparatus.]. .Iadd.telecommunication switching system .Iaddend.defined in claim 2 wherein said reset inputs to said bistable stages are connected additionally to a .[.sixth.]. 
     
     
        .Iadd.fourth .Iaddend.output from said binary counter. 4. The .[.apparatus.]. .Iadd.telecommunication switching system .Iaddend.defined in claim .[.1.]. .Iadd.9 .Iaddend.wherein the outputs of said input register .Iadd.means .Iaddend.are connected to the set inputs of said intermediate register .Iadd.means .Iaddend.by .[.means of second.]. .Iadd.said first .Iaddend.logic means.Iadd., said first logic means .Iaddend.having enabling inputs connected to a .[.fourth.]. .Iadd.second 
     
     
        .Iaddend.predetermined output of said binary counter. 5. The .[.apparatus.]. .Iadd.telecommunication switching system .Iaddend.defined in claim .[.1.]. .Iadd.9 .Iaddend.further comprising switch means operative .[.responsive.]. .Iadd.in response .Iaddend.to a .[.fifth.]. .Iadd.third .Iaddend.predetermined output from said .Iadd.multistage .Iaddend.binary counter for connecting an analog output from said digital .Iadd.converter means .Iaddend.to analog converter to said .[.analog receiver.]. .Iadd.receiving unit of said telephone station. .Iaddend. .Iadd. 6. A method of converting PAM analog signals into PCM digital signals, and of converting PCM digital signals into PAM analog signals in a telecommunication installation having telephone stations, each of said telephone stations comprising a transmitting unit supplying analog signals and a receiving unit accepting analog signals, wherein said telecommunication installation supplies PCM digital signals to a PCM signal receiving unit and receives PCM digital signals from a PCM signal output unit, said telecommunication installation being in communication with said PCM signal receiving unit and said PCM signal output unit for the duration of the pulses of the PCM pulse train, said telecommunication installation comprising an analog-to-digital converter for the conversion of the analog signals from said transmitting unit of said telephone station into PCM digital signals to be supplied to said signal receiving unit, said analog-to-digital converter functioning according to the iterative principle and comprising a counter with a given counting interval, an intermediate register controlled by the outputs of said counter, a digital-to-analog converter following said intermediate register and an analog comparator with one input connected to the output of said digital-to-analog converter and another input connected to receive the analog signals from said transmitting unit, the output signals of said comparator being supplied to said intermediate register, said telecommunication installation further comprising digital signal converting means including said intermediate register and said digital-to-analog converter for converting PCM digital signals from said PCM signal output unit to analog signals to be supplied to said receiving unit of said telephone station, the method comprising the steps of: sharing the counting interval of said counter by converting the PCM digital signals from said PCM signal output unit to analog signals during a first portion of the counting interval of said counter and by converting the analog signals from said transmitting unit of said telephone station to PCM digital signals during a second portion of the counting interval of   
     
     
        said counter. .Iaddend..Iadd. 7.  The method defined in claim 6 wherein the first and second portions of the counting interval of said counter are defined by different counter positions of said counter such that the first portion of the counting interval is of shorter duration than the second portion. .Iaddend..Iadd. 8. The method defined in claim 7 wherein the second portion of the counting interval of said counter starts after the expiration of a no current period following the first portion of the counting interval. .Iaddend. .Iadd. 9. In a telecommunication switching system having telephone stations, each of said telephone stations comprising a transmitting unit for supplying analog signals and a receiving unit for receiving analog signals, a signal conversion circuit connected between said telephone station and a switching unit for converting the analog signals supplied by said telephone station into outgoing digital signals and for converting incoming digital signals into analog signals for said telephone station, said switching unit including a signal output unit for supplying digital signals to said signal conversion circuit and a signal receiving unit for receiving digital signals from said signal conversion circuit, wherein in each pulse frame said signal conversion circuit communicates with said switching unit by supplying digital signals to said signal receiving unit and receiving digital signals from said signal output unit, said conversion circuit comprising: input register means for receiving and temporarily storing digital signals from said signal output unit of said switching unit;   a multistage binary counter with a counting interval less than or equal to the pulse frame;   intermediate register means having a plurality of bistable stages;   first logic means connected to the output of said input register means and actuated by said multistage binary counter for coupling the incoming digital signal from said input register means to said intermediate register means in accordance with a first portion of the counting interval of said multistage binary counter;   digital-to-analog converter means connected to said intermediate register means for converting the digital signal in said intermediate register means to an analog signal within the first portion of the counting interval of said multistage binary counter and supplying the analog signal to said receiving unit of said telephone station;   comparator means with one input connected to receive the analog signal from said transmitting unit of said telephone station and a second input connected to the output of said digital-to-analog converter means;   second logic means connected to the output of said comparator means and actuated by said multistage binary counter for coupling the analog signal from said transmitting unit of said telephone station to said intermediate register means to said digital-to-analog converter means, wherein said digital-to-analog converter means converts the analog signal to an outgoing digital signal in accordance with a second portion of the counting interval of said multistage binary counter to thereby perform both an analog-to-digital and a digital-to-analog conversion within one pulse frame; and   output register means connected to the output of said intermediate register means for coupling the outgoing digital signal to said signal receiving unit of said switching unit. .Iaddend.