Hello,

Bit of an amateur question, but it's been some time since i have worked with op-amps. I am trying to feed an analog signal into an ADC, the ADC can only see a range of 0 to 3.3V. My AC signal as seen in the image floats around a 5V DC-offset, with a minimum value of 2.32. I would like to use a differential amplifier to subtract 2V from this AC signal to pull it closer to 0 so the ADC can actually see it.


This is my differential amplifier, it should subtract the 2V from my 5V signal with an amplitude of 1V. However this is the output i get:


I have used the THS3201 op-amp and other op-amps with significant bandwith that should support the 12.5MHz signal.

 

Why don’t you just AC couple it?

 

Because then the AC mean is at 0 volts, and it will swing below 0 all the way down to -1 even. Which my ADC is not able handle. But i fixed the differential amplfier already

 

Hi Lucky,
Is your query now solved.?
E

 

Because then the AC mean is at 0 volts, and it will swing below 0 all the way down to -1 even. Which my ADC is not able handle. But i fixed the differential amplfier already

Not if you bias it to half supply. Equal value resistors between input and Vss and between input and Vcc, then connect the signal to the input using a capacitor.

 

That could be a possible solution, I think I'll go with the operational amplifier however. I feel like it's a more reliable approach, do you think otherwise?

 

That could be a possible solution, I think I'll go with the operational amplifier however. I feel like it's a more reliable approach, do you think otherwise?

Yes. An amplifier will add phase shift, and could add noise and distortion, may not be linear near the supply rails.

 

I calculated the right values and simulated a model in simulation. It works as intended, thanks, my thread is now answered.