Passive low pass filter + unity gain buffer clip the sine wave

Thread Starter


Joined Jan 17, 2017
Hi Everyone

I am working in a 0 to 20 amp non contact measurement device.

Before a Delta Sigma converter I would like to insert a passive low pass filter for anti alias

followed by a OP amp as unity gain buffer to drive the converter. The cutoff frequency is around 1.592 kHz.

I am using LM358 with 3.3 v single supply and from a Function generator I am injecting a sine wave of

0.5 Vpp / 60Hz to simulate the output of a CT.

I am attaching the simulation schematic I did and the scope screenshot.

As you can see there is a clipping in spite of there is a virtual ground to refer the low pass filter

and the Function generator signal.

My question is why there is clipping if the virtual ground is at 1.65 v and the signal has 0.5 Vpp.

Thank you in advance



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Joined Jun 4, 2014
The output of the '358 will not go very close to the positive rail but it will go very close to the negative rail (a few mV). Try reducing the virtual ground voltage to, perhaps, 1V.


Joined Mar 30, 2015
Welcome to AAC!

LM358 output can only get to within 1.5V of the positive rail (typical).

Schematic for the convenience of others: