Voice encode/decode subsystem in a system for acquisition of test data using pulse code modulation

• US 5,557,635 A
• Filed: 09/28/1994
• Issued: 09/17/1996
• Est. Priority Date: 01/12/1994
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Laird, Daniel T.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): MAY, TIMOTHY
• Application Number:
  US08/313,972
• Time in Patent Office: 720 Days
• Field of Search: 375/238, 375/247, 375/250, 375/251, 341/77, 341/143, 341/61, 381/36, 395/2.79
• US Class Current: 375/250
• CPC Class Codes: H03M 3/024 using syllabic companding, e.g. continuously variable slope delta modulation [CVSD]

Abstract

The encode and decode subsystems use a continuously variable slope delta-modulation (CVSD) approach, with either parallel or serial data transfers. To allow for synchronization with a stable data transfer, the entire subsystem uses the main acquisition systems bit rate clock (BRC) as a basis. All other clocks required are simply divided down versions of the BRC and a request pulse from the main system to transfer the data. The delta-modulator is clocked at a rate commensurate with the word placement in the minor frame of the data acquisition cycle; the NRZ-L bits are clocked into serial-to-parallel registers, then latched into the parallel discrete interface (PDI) unit of the main data system. For a serial feed, a similar situation is possible by clocking the data off the circuit board into a serial discrete interface (SDI) unit. The request pulse that activates, the transfer is synchronized with the BRC to ensure a stable transfer. The decoder uses the same CVSD integrated circuit to decode the digital data. The decoder is able to lock onto the data stream as a parasitic extension of a standard PCM decommutator. To locate the data and establish the necessary clocking, the standard word rate clock (WRC), frame rate clock (FRC), and the BRC of the decommutators are used.

Claims

1. A subsystem to integrate voice into a data acquisition system pulse code modulation (PCM) stream for digital data having bits controlled by a bit rate clock (BRC), with an acquisition format in which the bits are organized into words with a given number of bits per word controlled by a word rate clock (WRC), and the words are organized into frames with a given number of words per frame controlled by a frame rate clock (FRC), words being identified for a type of data by their placement in the frame;

wherein said subsystem uses continuously variable slope delta-modulation (CVSD), comprising a CVSD encoder device operated as an analog-to-digital converter, an analog input of the CVSD encoder device being coupled to a source of voice signals, encoder register means having a data input coupled to a digital output of the CVSD device, and an encoder register clock input for clock pulses to serially shift digital data bits from the digital output of the CVSD encoder device into the encoder register means;

encoder synchronization means comprising an encoder word counter, means for loading the encoder word counter with a selected word value to determine placement of PCM voice words in said frames, the encoder word counter having a clock input coupled to the data acquisition system to receive BRC pulses and controlled to count from said selected word value to a given value and then output a clock pulse at a pulse output, means coupling the pulse output to means for generating encoder clock pulses and supplying them to a clock input of the CVSD encoder device and also to an encoder control gate, the encoder control gate having an enable input coupled to receive request pulses from the data acquisition system, so that when the request pulse is received the CVSD encoder device and the encoder register means are enabled to generate and load a PCM voice word from the CVSD encoder device into the encoder register means, and encoder output control means including means setting the given number of bits per word and means for causing a word which has accumulated said given number of bits to be transferred from the encoder register means to the data acquisition system;

whereby the encoder subsystem uses the bit rate clock (BRC) from said data acquisition system for all timing in said subsystem, with other clocks of the subsystem being divided down from the BRC and a request pulse from said data acquisition system.

2. A subsystem according to claim 1, wherein the encoder synchronization means further includes an encoder bit counter, means for loading the encoder bit counter with a selected bit value to determine said given number of bits per word, the encoder bit counter having a clock input coupled to said pulse output of the encoder word counter and controlled to count from said selected bit value to a given value and then output a clock pulse which enables the transfer from the encoder register means to the data acquisition system.

3. A subsystem according to claim 1, wherein the CVSD encoder device includes means converting the digital output signals back to analog form at an analog output terminal, and means coupling the analog output terminal via amplifier means to sound transducer means, to thereby provide a test of the quality of the digitized signals.

4. A subsystem according to claim 1, which further includes decoder means, including a CVSD decoder device operated as a digital-to-analog converter, decoder register means having data input means, means for selecting a principal decode mode or a built-in-test mode, so that in the principal decode mode the data input means is coupled to receive data from the data acquisition system, and in the built-in-test mode the data input means is coupled to a data output of the encoder register means to provide a test of the encode and decode operations, the decoder register means having a serial data output coupled to a digital input of the CVSD decoder device, an analog output of the CVSD decoder device being coupled via amplifier means to transducer means for reproducing the voice signals;

decoder synchronization means comprising a bit rate divide counter and a decoder word counter, means coupled to the FRC of the data acquisition system for loading the decoder word counter with a selected word value to locate the placement of PCM voice words in said frames, means coupling the WRC of the data acquisition system to a clock input of the word counter to cause the word counter to count the words to a preprogrammed value, and then supply a signal to load control input means for controlling the loading of data words into the decoder register means;

means for loading the bit rate divide counter with said selected word value, the bit rate divide counter having a clock input coupled to the data acquisition system to receive BRC pulses and controlled to count from said selected word value to a given value and then output a clock pulse at a bit rate pulse output to means for generating decoder clock pulses and supplying them to a clock input of the CVSD decoder device and also to the decoder register clock input to serially shift digital data bits from the serial data output of the decoder register means to the digital input of the CVSD decoder device.

5. A subsystem to decode voice from a data acquisition system pulse code modulation (PCM) stream for digital data having bits controlled by a bit rate clock (BRC), with an acquisition format in which the bits are organized into words with a given number of bits per word controlled by a word rate clock (WRC), and the words are organized into frames with a given number of words per frame controlled by a frame rate clock (FRC), words being identified for a type of data by their placement in the frame;

wherein said subsystem uses continuously variable slope delta-modulation (CVSD), including a CVSD decoder device operated as a digital-to-analog converter, decoder register means having data input means coupled to receive data from the data acquisition system, the decoder register means having a serial data output coupled to a digital input of the CVSD decoder device, an analog output of the CVSD decoder device being coupled via amplifier means to transducer means for reproducing the voice signals;

decoder synchronization means comprising a bit rate divide counter and a decoder word counter, means coupled to the FRC of the data acquisition system for loading the decoder word counter with a selected word value to locate the placement of PCM voice words in said frames, means coupling the WRC of the data acquisition system to a clock input of the word counter to cause the word counter to count the words to a preprogrammed value, and then supply a signal to load control input means for controlling the loading of data words into the decoder register means;

means for loading the bit rate divide counter with said selected word value, the bit rate divide counter having a clock input coupled to the data acquisition system to receive BRC pulses and controlled to count from said selected word value to a given value and then output a clock pulse at a bit rate pulse output to means for generating decoder clock pulses and supplying them to a clock input of the CVSD decoder device and also to the decoder register clock input to serially shift digital data bits from the serial data output of the decoder register means to the digital input of the CVSD decoder device;

whereby the decoder subsystem uses the bit rate clock (BRC) from said data acquisition system for all timing in said subsystem, with other clocks of the subsystem being divided down from the BRC.