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It is important to recognize the limitations of op-amps so that measurement
errors may be avoided in instrumental applications. We will explore two
important characteristics of several different common integrated circuit
op-amps.
- To measure the input offset voltage
, connect the op-amp as a
voltage follower and connect the non-inverting input to common. The output
voltage equals
. Perform this measurement for the three
different types of op-amps and include the data in the table. Repeat for both
of the LF353 dual op-amps. Note that the pinout of the 741 op-amp is identical to that of the LF351.
- To measure the input bias current, , a 10 M resistor
should be connected between the non-inverting input of the voltage follower and common.
The IR drop across the resistor results from the bias current. The output
voltage is the sum of the offset voltage,
, and the IR
drop across the resistor.
.
Carry out this determination
for each of the op-amps under investigation, tabulate, and comment on the results.
Op-Amp |
, for |
, for M |
, nA |
LF353-1 |
|
|
|
LF353-2 |
|
|
|
LF351 |
|
|
|
A741 |
|
|
|
Next: Advanced op-amp designs
Up: Building circuits with op-amps
Previous: Summing amplifier
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Last revised: 2007-01-05