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Method and Apparatus for Finding the Midpoint of a Rising or Falling Ramp in a Data Waveform and for Adjusting the Phase of a Clock with Respect to the Midpoint

IP.com Disclosure Number: IPCOM000037491D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Corti, W: AUTHOR [+2]

Abstract

A waveform of an electrical signal that represents binary data varies between two voltage levels and is commonly called a square wave. When a data waveform is viewed on a fast oscilloscope, its leading and trailing edges appear as rising and falling ramps. The half way point in the falling ramp is a timing reference point for establishing a clock signal that is used by a data waveform detector.

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Method and Apparatus for Finding the Midpoint of a Rising or Falling Ramp in a Data Waveform and for Adjusting the Phase of a Clock with Respect to the Midpoint

A waveform of an electrical signal that represents binary data varies between two voltage levels and is commonly called a square wave. When a data waveform is viewed on a fast oscilloscope, its leading and trailing edges appear as rising and falling ramps. The half way point in the falling ramp is a timing reference point for establishing a clock signal that is used by a data waveform detector.

A known data detector circuit produces the true and the complement of an incoming data waveform. When the true and complement signals are viewed simultaneously on an oscilloscope, the rising ramp of each waveform crosses the falling ramp of its complement. This crossing point is detected and used as the timing reference point. Successive pulses are not exactly synchronized and the waveforms jitter on an oscilloscope so that the crossover point cannot be selected visually. A conventional data waveform detector circuit is set up to receive a test waveform and to produce true and complement outputs. A conventional interval timer is connected to start a timing interval when the falling ramp of the true waveform reaches a selected voltage and to stop when the rising ramp of the complement waveform reaches the same selected voltage. For example, when the selected voltage is near the maximum voltage of the waveform, the f...