
91-6 Signal Processing
It is better to model signals with very high-output impedance as current sources (Figure 91.2b). e
current through the detector will be
i i
Z
Z Z
d s
s
d s
=
+
(91.2)
In order for i
d
= i
s
, it is required that Z
d
≪ Z
s
, which is easier to achieve than Z
d
≫ Z
s
. If Z
d
is not low
enough, then there is a shunting eect. Qualitatively, Z
d
/Z
s
should be small enough for the ADC not to
detect that Z
d
is nonzero.
91.4 General Amplier Parameters
A voltage amplier produces an output voltage which is a proportional reproduction of the voltage dif-
ference
at its input terminals, regardless of any common-mode voltage and without loading t