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OPA171: Open Loop Gain for OPA171

Part Number: OPA171
Other Parts Discussed in Thread: TLV171-Q1


I have a design with fairly large closed-loop gain where I want to use OPA171.

Upon checking open loop gain specification I noticed figure 21 which seems weired to me (3 curves shown but "5 typical units shown", suspicious unit , seemingly contradictive to specification in section 6.7). Also I noticed that the same graph is given for OPA171 and TLV171-Q1 who differ in their respective specification however.

Could you shed some light onto this and explain, how to interpret the figure?

Best Regards

Norman Werner

  • Hello Norman,

    I see two errors in the chart. This is one measured sample. The Y axis scale is incorrect; it should be uV/V 

  • Hello Ron,

    thank you for your answer. This was my (uneducated) guess as well. Additionally this measured sample seems to have lower Aol than given in section 6.7.

    so the question arises : was temperature dependence of Aol measured for OPA171 and is it possible to have a look at the corresponding data?

    Best Regards

    Norman Werner

  • So actually, aside from the scaling error this plot looks pretty good. 

    1. They only show one curve at each supply voltage, but probably averaging the measured results for 5 units for that curve

    2. The spec table line is for 4V to 36V so the 2.7V curve is a bonus. That line is 130dB typ or 0.32uV/V - pretty close to the 4V curve, the min number is 110dB or 1.8uV/V which is a full pdk simulation limit not shown really in the plot but used for outgoing ATE limits. 

    3. The Q1 datasheet is adapted from the 171 and shows a min 4.5V limit with the same specs as the original part, 

    And it used the same typ curve. I read this to mean the outgoing ATE on a Q1 part looked for a min 1.8uV/V Aol at 4.5V supply instead of 4V supply. 

  • You are right - I did the wrong math mixing up uV/V and V/uV

    thanks for the clarification