i have a problem that needs solving; What is the minimum feedback resistor for modern opamps like opa2134 ? can it be 100 ohm? Im asking because in lt1028 datasheet its says it cant be <100ohm because it causes distortions ,very heavy by the way. How can this value be found for any given opamp? Does it depend on output current ? The configuration of the setup is DAC I/V with multiple feedback low pass filterDAC I/V multiple feedback Active low pass filter with High Voltage output -6VRMS the stage procceding it is a Voltage follower buffer


Looking at the LT1028: -

Because the inputs are protected by back-to-back parallel diodes (not all op-amps do this), when fast edges are inputted, the output voltage doesn't change quickly enough to follow the fast input and one of these diodes gets forward biased through the feedback resistor. This "corrupts" the input signal and distorts it. Read the explanation on page 14.

Also, if you look at figure 9 it shows two configurations that are acceptable and one has zero ohms feedback resistance. Again, it is because of the input diodes.

Regarding the opa2134 I couldn't find reference to it having input protection diodes in its data sheet.

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