
200 Analog Electronics
Impedances and gain
The catalogue of desirable features of an amplifier
is still not complete; in addition to low noise, high
linearity and wide dynamic range, the input and
output impedance need to be well defined, and the
gain also. Further, steps to define these three
parameters should not result in deterioration of
any of the others. Figure 8.10a shows a broadband
RF amplifier with its gain, input impedance and
output impedance determined by negative feed-
back." The resistors used in the feedback network
necessarily contribute some noise to the circuit.
This can be avoided by the scheme known as
lossless feedback,^ ...