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Table 2-8. Voltage and Percent Error For Various
Time Constants
/Time* 1
VM
/ % Error
7
IO.632
Es / 36
%
A. CIRCUIT
h?
0.632
ES
kL
RSCIN
6. EXPONENTIAL RESPONSE
Input amplifier
noise and drift appearing
at the output
can be
calculated
as follows:
Figure 2-28. Input Capacitance Effects
Equation
1.
2.14.7 Source Resistance
Figure 2-29. Simplified Model for Source
Resistance and Source Capacitance
Effects
Table 2-9. Minimum Recommended Source Resis-
tance Values in Amps
Minimum Source
Range I
All pA
1
Resistance
lOOGil
1OOMQ
100 kQ
All mA
100 n
Output
Enoise
RF
= Input En+
X (1 +-)
Rs
As shown in Table 2-9, a minimum
value of source resistance
is recommended
for each AMPS
range.
The reason for this
Thus it is clear that as long as Rs>>
RF, Output
E,,ise = In-
can
be understood
by examining
Figure 2-29. Considering
ef-
put En,,ire. When RF = Rs, output
Enoh = 2 X Input Enoie.
fects
on low frequency
noise
and drift,
Cs and
CF can
momentarily
be ignored.
2-34
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