Correcting crossover distortion produced when analog signal thresholds are used to remove noise from signal

• US 5,287,534 A
• Filed: 11/08/1991
• Issued: 02/15/1994
• Est. Priority Date: 01/04/1990
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Reuther, Thomas, Bloomberg, Neil, Welch, Albra M., Gist, William J. Jr.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Treat, William M.
• Application Number:
  US07/775,681
• Time in Patent Office: 830 Days
• Field of Search: 395/800, 328/162, 328/163, 328/165, 307/443, 307/542, 307/555
• US Class Current: 714/819
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296

Abstract

Apparatus for coupling and decoupling a data terminal to a computer system of the kind that continues to interact with a device only while the computer system detects interaction by the device. The apparatus includes switching circuitry for connection between the data terminal and the computer system; the switching circuitry has a first mode in which a path is provided for interaction between the data terminal and the computer system, and a second mode in which the path is disabled and the data terminal may engage in other activities. The apparatus also includes communication circuitry, responsive to the switching circuitry, for interacting with the computer system at times when the path is disabled, in order to cause the computer system to continue to interact with the communication circuitry during those times and then to be immediately available for interaction with the data terminal when the path is again provided. In other aspects, multiple data terminals are served simultaneously from a single bi-phase communications processor of the kind having a RISC processor containing an integral coax interface, and crossover distortion is removed in the course of deriving a processed digital signal from positive and negative digital signal sample components that were formed by positive and negative threshold comparisons and which appear at a given sampling clock rate.

Claims

1. A method utilizing digital circuitry for removing crossover distortion to derive a processed digital signal from positive and negative digital signal sample components that were formed by positive and negative threshold comparisons, said crossover distortion manifested by periods during which both said negative and said positive digital signal sample components have a logic zero value, comprising

A. forming a replica of said positive digital signal sample component which is delayed by a predetermined time period,

B. forming a first intermediate signal represented a logical OR of said replica with said positive digital signal sample component,

C. forming a second intermediate signal representing a negation of said negative digital signal sample component, and

D. forming a logical AND of said first and second intermediate signals, to form said processed digital signal.

2. Apparatus for removing crossover distortion to derive a processed digital signal from positive and negative digital signal sample components that were formed by positive and negative threshold comparisons, said crossover distortion manifested by periods during which both said negative and said positive digital signal sample components have a logic zero value, comprising;

A. digital circuit means for forming a replica of said positive digital signal sample component which is delayed by a predetermined time period,

B. digital circuit means for forming a first intermediate signal representing a logical OR of said replica with said positive digital signal sample component,

C. digital circuit means for forming a second intermediate signal representing a negative of said negative digital signal sample component, and

D. digital circuit means for forming a logial AND of said first and second intermediate signals, to form said processed digital signal.