SNOS608C – MAY 1998 – REVISED MARCH 2013
(2)
where
(3)
is the amplifier's low-frequency noise gain and GBW is the amplifier's gain bandwidth product. An amplifier's low-
frequency noise gain is represented by the formula
(4)
regardless of whether the amplifier is being used in inverting or non-inverting mode. Note that a feedback
capacitor is more likely to be needed when the noise gain is low and/or the feedback resistor is large.
If the above condition is met (indicating a feedback capacitor will probably be needed), and the noise gain is
large enough that:
(5)
the following value of feedback capacitor is recommended:
(6)
If
(7)
the feedback capacitor should be:
(8)
Note that these capacitor values are usually significantly smaller than those given by the older, more
conservative formula:
(9)
C
S
consists of the amplifier's input capacitance plus any stray capacitance from the circuit board and socket. C
F
compensates for the pole caused by C
S
and the feedback resistors.
Figure 14. General Operational Amplifier Circuit
8
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