PCM encoder-decoder apparatus

• US 3,877,028 A
• Filed: 02/22/1974
• Issued: 04/08/1975
• Est. Priority Date: 02/22/1974
• Status: Expired due to Term

• Current Assignee: Microtel Limited-Microtel Limitee
• Original Assignee: Robert M. Thomas
• Inventors: Thomas, Robert M.
• Primary Examiner(s): Botz, Eugene G.
• Assistant Examiner(s): Sunderdick, Vincent J.
• Application Number:
  US05/444,891
• Time in Patent Office: 410 Days
• Field of Search: 340/347C,347AD 179/15BD 325/38R
• US Class Current: 341/108
• CPC Class Codes: H03M 1/02 Reversible analogue/digital converters
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp
• CPC Class Codes: H03M 1/74 Simultaneous conversion

Abstract

PCM encoder-decoder having a digital code generator which counts through a digital count during a comparison period. An analog voltage waveform generator sweeps in a non-linear manner from a maximum negative to a maximum positive voltage during the same period. The digital code generator and analog voltage waveform generator are synchronized so that during each instant of each comparison period they have corresponding values. At the start of each comparison period a sample of an audio voice signal to be encoded is trapped in a capacitor. During a comparison period the sample is compared with the output of the waveform generator. When equality is detected the count of the digital count generator at that instant is stored as a PCM digital signal for transmission with other PCM signals in accordance with known TDM techniques. A pcm digital signal which is received in accordance with known TDM techniques is stored in a register prior to the start of a comparison period. During a comparison period the stored digital signal is compared with the output of the digital code generator. When equality is detected, the voltage of the analog voltage waveform generator at that instant is trapped in a capacitor. At the end of the comparison period the trapped charge is released as a pulse to a low-pass filter. A series of pulses is converted to a continuous audio signal by the low-pass filter.

Claims

1. Apparatus for encoding a continuous analog signal into digital signals and for decoding digital signals to a continuous analog signal including in combination digital code generating means for producing a sequence of digital code signals;

analog voltage generating means for producing an analog voltage waveform and being synchronized with said digital code generating means whereby for each digital code signal a corresponding analog voltage signal is produced at the same instant;

means for receiving a continuous analog input signal;

sampling means for sampling the analog input signal received by said means;

analog comparison means coupled to the sampling means and to the analog voltage generating means for comparing a sample of the analog input signal with said analog voltage waveform and for producing an output signal when the voltage of the analog voltage waveform is equal to the sample;

digital storage means coupled to the digital code generating means and to the analog comparison means for storing a digital signal equal to the digital code signal being produced by the digital code generating means in response to an output signal from the analog comparison means whereby a digital signal corresponding to the voltage of the samples is stored in the digital storage means;

means for receiving digital input signals;

digital input signal storage means for storing a digital input signal received by said means;

digital signal comparison means coupled to the digital input signal storage means and to the digital code generating means for comparing the stored digital input signal with said sequence of digital code signals and for producing an output signal when the two digital signals are equal;

analog storage means coupled to the analog voltage generating means and to the digital signal comparison means for storing an analog signal equal to the analog signal being produced by the analog voltage generating means in response to an output signal from the digital signal comparison means whereby an analog signal corresponding to the received digital input signal is stored in the analog storage means;

low-pass filter means; and

gating means coupled between the analog storage means and the low-pass filter means for permitting an analog signal stored in the analog storage means to be applied to the low-pass filter means;

said low-pass filter means being operable to produce a continuous analog signal in response to a series of analog signals applied thereto from the analog storage means by the gating means.

2. Apparatus for encoding a continuous analog signal into digital signals and for decoding digital signals to a continuous analog signal including in combination digital code generating means for producing a sequence of digital code signals during a first period of each operating cycle;

analog voltage generating means for producing an analog voltage waveform during the first period of each operating cycle and being synchronized with said digital code generating means whereby for each digital code signal a corresponding analog voltage signal is produced at the same instant during the first period of each operating cycle;

analog signal receiving means for receiving a continuous analog input signal;

sampling means for sampling the analog input signal received by said analog signal receiving means at the same point during each operating cycle;

analog comparison means coupled to the sampling means and to the analog voltage generating means for comparing a sample of the analog input signal with said analog voltage waveform during the first period of each operating cycle and for producing an output signal when the voltage of the analog voltage waveform is equal to the sample;

digital storage means coupled to the digital code generating means and to the analog comparison means for storing a digital signal equal to the digital code signal being produced by the digital code generating means in response to an output signal from the analog comparison means whereby a digital signal corresponding to the voltage of the sample is stored in the digital storage means during the first period of each operating cycle;

digital signal receiving means for receiving digital input signals;

digital input signal storage means for storing a digital input signal received by said digital signal receiving means prior to the first period of each operating cycle;

digital signal comparison means coupled to the digital input signal storage means and to the digital code generating means for comparing the stored digital input signal with said sequence of digital code signals during the first period of each operating cycle and for producing an output signal when the two digital signals are equal;

analog storage means coupled to the analog voltage generating means and to the digital signal comparison means for storing an analog signal equal to the analog signal being produced by the analog voltage generating means in response to an output signal from the digital signal comparison means whereby an analog signal corresponding to the received digital input signal is stored in the analog storage means during the first period of each operating cycle;

low-pass filter means; and

analog output gating means coupled between the analog storage means and the low-pass filter means for permitting an analog signal stored in the storage means to applied to the low-pass filter means at the same point during a second period of each operating cycle;

said low-pass filter means being operable to produce a continuous analog signal in response to a series of analog signals applied thereto from the analog storage means by the analog output gating means.

3. Apparatus in accordance with claim 2 wherein said digital code generating means produces a sequence of digital code signals each of which varies from the preceding signal by an equal digital amount;

and said analog voltage generating means produces an analog voltage waveform of continuously increasing voltage.

4. Apparatus in accordance with claim 3 wherein said digital code generating means includes clock pulse generating means for producing periodic clock pulses;

and counting means coupled to the clock pulse generating means for counting clock pulses during the first period of each operating cycle and for producing a sequence of digital code signals representing the number of pulses counted; and

said analog voltage generating means produces a non-linear analog voltage waveform of continuously increasing voltage.

5. Apparatus in accordance with claim 2 including control means operable to produce a first control signal condition during the first period of each operating cycle and to produce a second control signal condition during the second period of each operating cycle, the first period and second period of each operating cycle being of equal time duration;

6. Apparatus in accordance with claim 5 wherein said sample gating means is operable to provide a conductive path therethrough while the control means is producing the second control signal condition and is operable to provide an open circuit while the control means is producing the first control signal condition whereby the voltage of the analog input signal at the start of the first period of each operating cycle becomes the sample stored in the sample storage means;

and said analog output gating means is operable to provide an open circuit while the control means is producing the first control signal condition and is operable to provide a conductive path therethrough while the control means is producing the second control signal condition whereby an analog signal stored in the storage element is applied to the low-pass filter means at the start of the second period of each operating cycle.

7. Apparatus in accordance with claim 6 wherein said digital code generating means produces a sequence of digital code signals each of which varies from the preceding signal by an equal digital amount;

and said analog voltage generating means produces an analog voltage waveform of continuously increasing voltage.

8. Apparatus in accordance with claim 7 wherein said digital code generating means includes clock pulse generating means for producing periodic clock pulses, and counting means coupled to the clock pulse generating means for counting clock pulses during the first period of each operating cycle and for producing a sequence of digital code signals representing the number of pulses counted;

and said analog voltage generating means produces a non-linear analog voltage waveform of continuously increasing voltage.

9. Apparatus in accordance with claim 8 wherein said conting means counts through a recurring sequence of states during each period of each operating cycle;

said control means is coupled to said counting means and is operable to change from producing one control signal condition to the other in response to completion of each sequence of states.

10. Apparatus in accordance with claim 9 wherein said analog storage gating means includes a gating element connected between the analog voltage generating means and the storage element;

and gate control means coupled to the gating element, said digital signal comparison means, and said control means;

said gate control means having a first operating state during which said gating element provides a conductive path therethrough and a second operating state during which said gating element provides an open circuit;

said gate control means being maintained in said second operating state by said second control signal condition from the control means;

said gate control means being operable to be switched from said second operating state to said first operating state in response to the control signal condition from the control means changing from the second control signal condition to the first control signal condition; and

said gate control means being operable to be switched from said first operating state to said second operating state in response to an output signal from said digital signal comparison means.