OP293 - open loop gain

Document created by analog-archivist Employee on Feb 23, 2016
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Inquiry Description:

Hello,
We encounter a problem with this component on the AV0 parameter.
Indeed we find that the values are lower than those of the datasheet in the
following configurations:
- VS = + / - 15 V with RL = 2kohms, RL = 10 ohms and RL = 100Kohms for -10 V ≤
VOUT ≤ 10 V
- VS = 5V with RL = 10 ohms and RL = 100Kohms 0.03 V to 4.0 V ≤ VOUT ≤ 4.0 V
Is it possible that we did not use the same principle as you, which would
explain these differences. Can you give us your measuring principle parameter
AV0?
Thank you for your feedback

 

The open-loop gain Avo is not constant. It varies with temperature, output
loads and voltages. The following are some of the details which help you get
better understanding about the change and the measurement of the change in Avo.

1.Changes in the output voltage level and output loading are the most common
causes of changes in the open-loop gain of op amps. A change in open-loop gain
with signal level produces a non-linearity in the closed-loop gain transfer
function. This non-linearity cannot be removed during calibration.

2.Most of the op amps have fixed loads. Therefore, the changes in  AVO with
respect to the load are not generally important. However, the sensitivity of
AVO to output signal level may increase for higher load currents.

3.The severity of the non-linearity varies widely from one device type to
another, and generally is not specified on the data sheet. The minimum AVO is
always specified, and choosing an op amp with a high AVO will minimize the
probability of gain non-linearity errors.

4.Gain non-linearity can come from many sources, depending on the design of the
op amp. One common source is thermal feedback (for example, from a hot output
stage back to the input stage). If temperature shift is the sole cause of the
non-linearity error, it can be assumed that minimizing the output loading will
help.

5.To verify this change in Avo, the non-linearity should be  measured with no
load, and then compared to the loaded condition.


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