GB1249761A - Transmission device for the transmission of analog signals by means of pulse code modulation - Google Patents

Abstract

1,249,761. Analogue/digital and digital analogue converters. TELECOMMUNICATIONS RADIOELECTRIQUES ET TELEPHONIQUES. 23 Jan., 1970 [28 Jan., 1969], No. 3324/70. Heading G4H. A dual ramp digital voltmeter is modified in that the integrator A 2 , C 1 (Fig. 5) receiving the input signal for a fixed time interval P 1 is discharged by a voltage - V R for a time which is measured by counting clock pulses in a counter K 1 (Fig. 7) to a threshold level E 0 a second integrator A 5 , C 2 then being charged at the start of the next clock pulse by a current proportional to this residual voltage for a fixed time and discharged by a reference voltage - V R /2<SP>6</SP> the time for discharge to a zero level being measured by counting clock pulses in a second counter K 2 . In the embodiment described the application of the input signals and the reference signals to the integrators are controlled by MOS transistor switches. To reconstitute the original analogue signal the complements of the count in the counters K 1 , K 2 are stored in counters (K<SP>1</SP>, K<SP>11</SP>, Fig. 10, not shown) the counter constituting the most significant part being then counted down to zero during which time an integrator (A 7 , C 3 , Fig. 8, not shown) integrates a reference signal, proportional to V 2 , the second counter K<SP>1</SP> 2 then being counted down to zero during which time a second reference signal proportional to - V R /2<SP>6</SP> is applied to the integrator. An operational amplifier A 8 is connected as a voltage follower to the output of the integrator to give an output voltage representing the mean value of the recovered signal.