Current Sources and Voltage References

Some op amp characteristics

Creating Precision Current Sources with Op Amps and Voltage References

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the op amp to directly interface with a high-impedance signal source.

There are actually two distinct kinds: (1) the

differential input impedance

is the total impedance when looking from one input terminal to the other,

and (2) the

common-mode impedance

is the common impedance when

measured to ground. Although most manufacturers do not specify the

input impedance per se, some do specify the input

resistance

in either

differential-mode

or

common-mode

. The input resistance in differential

mode is defined as the ratio of small-signal change in input ...