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2-38 GB1400 User Manual
Applications
Application Note
Method For Very Fast Automatic Receiver Synchronization
And Eye Width Measurement
Two Auto Search Synchronization Methods
This application note describes two Auto Search synchronization methods used
in the GB1400 Bit Error Rate test set - a FAST method and a BER method. The
criteria and sequence of events for the two methods are compared and the
differences are described.
Auto Search is the feature that the GB1400 uses to describe its method of
automatic setup and synchronization. Both methods of Auto Search
synchronization perform the following functions, but in different ways and with
differing results depending on the type of data and its quality.
• Analysis of the input data signal amplitude to select the correct threshold
voltage.
• Determine the timing skew between the clock and data signals and
automatically optimize it.
• Determine the correct data sequence and whether it is inverted.
• Measure the data eye width.
So that the following explanations are clear, let us first define some terms.
V–THRESHOLD
This is the absolute DC level above which GB1400 Receiver will declare a data
bit value of “1” (HIGH). Below this value, it is considered to be a “0” (LOW).
DELAY
This is the timing difference (skew) between ideal timing and actual timing
between the incoming clock and data. Ideal timing will place the falling edge of
the clock signal in the center of the data bit. Any deviation from the ideal should,
when possible, be corrected by delaying either the clock or the data (as in the
GB1400 Receiver) in relation to each other.