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

Thread Starter

Challenger

Joined Jan 17, 2017
11
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

OpAmpClipCircuit-01_circuit.gif

OpAmpClipCircuit-02_WaveForm.jpg



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Many of our members don't like to open the pdf file, so please upload the file as 800x600 or 1024x768 jpg or gif files next time, the circuit already copied as gif file and the graph copied as jpg form the pdf.
 

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AlbertHall

Joined Jun 4, 2014
8,313
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.
 

dl324

Joined Mar 30, 2015
8,860
Welcome to AAC!

LM358 output can only get to within 1.5V of the positive rail (typical).
upload_2017-2-28_8-37-57.png
upload_2017-2-28_8-38-20.png

Schematic for the convenience of others:
upload_2017-2-28_8-35-39.png
 

Thread Starter

Challenger

Joined Jan 17, 2017
11
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.
I did that and the filter is working.
Thank so much
 
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