Datasheet

LMC660

SNOSBZ3D –APRIL 1998–REVISED MARCH 2013

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(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)

(7)

the feedback capacitor should be:

(8)

Note that these capacitor values are usually significant smaller than those given by the older, more conservative

formula:

(9)

consists of the amplifier's input capacitance plus any stray capacitance from the circuit board and socket. C

compensates for the pole caused by C

and the feedback resistors.

Figure 16. General Operational Amplifier Circuit

Using the smaller capacitors will give much higher bandwidth with little degradation of transient response. It may

be necessary in any of the above cases to use a somewhat larger feedback capacitor to allow for unexpected

stray capacitance, or to tolerate additional phase shifts in the loop, or excessive capacitive load, or to decrease

the noise or bandwidth, or simply because the particular circuit implementation needs more feedback

capacitance to be sufficiently stable. For example, a printed circuit board's stray capacitance may be larger or

smaller than the breadboard's, so the actual optimum value for C

may be different from the one estimated using

the breadboard. In most cases, the values of C

should be checked on the actual circuit, starting with the

computed value.

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