Patent ID: 7218686
Filing Date: 2007-05-15
Classification: H04B,H04L

Abstract:
1. A decision threshold voltage controlling method to feed an optimum decision threshold voltage to a clock and data recovery circuit which inputs an electric signal converted from an optical input signal and amplified with a predetermined amplitude as an input data signal, extracts a clock frequency component from the input data signal, and identifies 1 or 0 in the input data signal at a timing of the clock, the method comprising: controlling three decision points suitably, by selectively performing, depending on a measurement result of an error pulse, a process of changing differences between the three decision points, a process of moving the three decision points with their differences kept as they are, or a process of changing an error pulse measurement time, the error pulse measurement time being a time period over which error pulses are counted, wherein the process of changing differences between the three decision points is performed upon a first measurement result of the error pulse, the process of moving the three decision points with their differences kept as they are is performed upon a second measurement result of the error pulse, and the process of changing an error pulse measurement time is performed upon a third measurement result of the error pulse.