analogoperational-amplifier
I am using Multisim to design the first stage of an analog signal processing block.
I am using the Op-Amp AD797AR from Analog Devices. I am trying to check if the opamp is inverting unity gain stable.
I have the following schematic
My input is a sine wave of 100 KHz peak of 10 mV but the output seems to be unstable.
How do I ensure stability for the AD797AR? What are some things I can check to ensure stability?
I think you've got your opamp "upside down" in your schematic though it's hard to tell for sure due to the coarse resolution of the image. But it does look like your feedback divider is connected to the non-inverting input rather than to the inverting input.
If so, you've got something like a schmitt trigger circuit there rather than the difference amplifier you intended.
This would be better (output left open):
simulate this circuit – Schematic created using CircuitLab
Both inputs are within the common-mode range of the amplifer- see the datasheet which gives the values with a +/-6V supply and translate by adding 6V to the numbers.
Best Answer
The AD797 op amp is not really unity gain stable without adding a capacitor and it isn't really designed for a supply as low as 5 volts. Read the data sheet. I wouldn't use 100 M ohm resistors either. Look at table 7 in the data sheet and note the low ohmic values for the resistors used. The 300 kohm resistors are far too high.