Coding device selectively connected to a transmission line

• US 4,807,250 A
• Filed: 10/06/1986
• Issued: 02/21/1989
• Est. Priority Date: 10/04/1985
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tanaka, Susumu
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/915,351
• Time in Patent Office: 869 Days
• Field of Search: 375/25, 375/26, 375/28, 375/34, 455/31, 340/347 AD, 332/11 D, 370/110.1, 370/110.4, 370/111, 381/41, 381/46
• US Class Current: 375/247
• CPC Class Codes: H03M 3/042 with adaptable step size, e.g. adaptive differential pulse code modulation [ADPCM]

Abstract

In a predictive coding device which is for coding an input signal into a coded signal, such as a PCM signal, and for use in combination with a transmission line having an on and an off state wherein the coding device is selectively connected to the transmission line and disconnected therefrom, a code converter (16) operatively coupling the transmission line to produce a mute signal of a predetermined code as a first local output signal and the coded signal as a second local output signal when the transmission line is in the off and the on states, respectively. A local decoder (15) locally decodes either the first or the second local output signal into a local decoded signal for use in coding the input signal into the coded signal. Preferably, the predetermined code is a code which the coded signal has when the input signal carries no information. Usually, the coding device is selectively connected to the transmission line and disconnected therefrom through a digital speech interpolation (DSI) device.

Claims

1. A coding device for coding for coding an input signal into a coded signal which is transmitted through a connection control circuit to a transmission line while said coding device is connected to said transmission line through said connection control circuit, said coding device comprising subtracting means for subtracting a local signal from said input signal to produce a difference signal, coding means for coding said difference signal into said coded signal, and local decoding means for locally decoding an internal code signal related to said coded signal into said local decoded signal, said coding device being selectively connected to said transmission line under control of said connection control circuit, wherein the improvement comprises:

code producing means for producing a predetermined code;

selecting means, coupled to said connection control circuit and responsive to a control signal provided by said connection control circuit, for selecting said coded signal as a selected code signal when said control signal indicates connection of said transmission line to said coding device, and said predetermined code as said selected code signal when said control signal indicates disconnection of said transmission line from said coding device; and

means for supplying said selected code signal to said local decoding means as said internal code signal.

2. In a communication system for enabling communication between a coding device and a decoding device through a transmission line by selectively connecting said coding device to said transmission line by a digital speech interpolation technique, said coding device coding an input signal into a coded signal by predictive coding and comprising subtracting means for subtracting a local decoded signal from said input signal to produce a difference signal, coding means for coding said difference signal into said coded signal, and local decoding means for locally decoding an internal code signal related to said coded signal into said local decoded signal, the coding device being selectively connected to said transmission line under control of a connection control circuit, the improvement wherein said coding device comprises:

code producing means for producing a predetermined code;

selecting means, responsive to a control said coded signal as a selected code signal when said control signal indicates connection of said transmission line to said signal when said control signal indicates disconnection of said transmission line from said coding device; and

means for supplying said selected code signal to said local decoding means a said internal code signal.