Other Parts Discussed in Thread: LMV712
Tool/software:
Hi,
I'm struggling to understand the behavior of the LMV712TL/NOPB in various application. When it's configured as a non-inverting amplifier with 101x gain, the output dithers between voltage levels that are separated by ~1 mV. There is no corresponding dithering of the input signal which is evident from Figure A. There is no such dithering of the output signal when the same device is configured for unity gain (i.e., voltage follower) as shown in Figure B. Both figures have the same x-axis and the y-axis is in millivolts in both figures as well. In both figures, I subtracted a DC offset from the output only to bring the input and output plots closer together for the purpose of displaying both with the highest possible resolution.
I also increaed the input voltage to the LMV712 when configured for unity gain to ~80 mV and the output still did *not* dither. So the dithering appears to be a function of the closed loop gain and independent of the input voltage level. I should mention that when the LMV712 was configured as a voltage follower, the 1K resistor from the inverting input to ground was preserved. So, if noise from GND was coupling into the inverting input of the LMV712, it should have manifested in Figure B.
I am also using the LMV712 to drive the gate of an NMOS in a voltage controlled current source circuit. I've observed the same dithering of the output of the LM712 in this circuit as well.
Lastly, I am familiar with the propensity for op amps to oscillate when phase margin is inadequate, but the dithering in Figure A is not periodic which leads me to believe this is *not* oscillation due to instablity. Also, the dithering occurs on a large time scale, which is much lower frequency than I would expect for oscillation.
Any insight you can provide will be much appreciated. Please let me know if you have any questions.
