Input impedance matching with fully differential amplifiers

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Input impedance matching with fully differential amplifiers [复制链接]

Introduction
Impedance matching is widely
used in the transmission of
signals in many end applications
across the industrial,
munications, video, medical,
test, measurement, and
military markets. Impedance
matching is important to
reduce reflections and preserve
signal integrity. Proper
termination results in greater
signal integrity with higher
throughput of data and fewer
errors. Different schemes have
been employed; source termination,
load termination, and
double termination are the
most monly used. Double
termination is generally recognized
as the best method to
reduce reflections, while
source and load termination
have the advantage of
increased signal swing. With
source and load termination,
either the source or the load
(not both) is terminated with
the characteristic impedance of
the transmission line. With
double termination, both the
source and the load are terminated
with that impedance. No matter what impedancematching
scheme is chosen, the termination impedance to
implement must be accurately calculated.
In the last few years, fully differential amplifiers (FDAs)
have grown in popularity; and, while similar in theory to
inverting operational amplifiers, they have important differences
that need to be understood when input impedance
matching is considered. This article shows how to analyze
the input impedance of an FDA. Circuit analysis is performed
to aid understanding of the key design points, and
a methodology is presented to illustrate how to approach
the design variables and calculate ponent values. A
spreadsheet and TINA-TI? SPICE models are available as