On the noise properties of balanced amplifiers
Kerr, A.R.
Microwave and Guided Wave Letters, IEEE
Volume 8, Issue 11, Nov 1998 Page(s):390 - 392
Digital Object Identifier 10.1109/75.736255
Summary:The balanced amplifier is used in applications requiring a better
input match than is possible with a single-ended amplifier. While the
impedance matching property of the balanced amplifier is well known, its
noise behavior appears not to be widely understood. It is shown that the
outgoing noise waves at the input and output of a balanced amplifier are
uncorrelated even though they originate in the same components. Hence, a
sliding short-circuit at the input produces no variation in the output
noise of the amplifier. The properties of a balanced amplifier are
similar to those of an amplifier preceded by an isolator, although the
noise wave emerging from inputs of the two circuits originates in
different elements. The noise theory of the balanced amplifier applies
also to balanced mixers based on quadrature hybrids
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