LM301A Op-Amp: Why Does 20logA Increase at Unity Gain With 10pF Compensation?

The discussion addresses an observed anomaly in the frequency response of an LM301A operational amplifier compensated with different capacitor values (10pF, 20pF, 30pF) placed in parallel with the feedback resistor (Rf). While 20pF and 30pF capacitors show a decrease in 20logA at unity gain, the 10pF capacitor causes an unexpected increase in 20logA over log(ω) at unity gain, opposite to the other cases. Measurements were taken at multiple frequency points to analyze the compensation effects. The output voltage behavior differs notably with the 10pF capacitor, showing an increase rather than a decrease at unity gain. The measurements were confirmed to be experimental rather than simulated. A suggested explanation involves the capacitive loading effect of the oscilloscope probe, which can cause peaking in the op-amp frequency response due to interaction with the compensation capacitor. To mitigate this, it was recommended to insert a 100-ohm resistor between the op-amp output and the oscilloscope probe to isolate the probe capacitance and obtain more accurate frequency response measurements.
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