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Electronics => Electronics => Topic started by: Ocelot on July 14, 2009, 11:14:57 AM

Title: Analog signal to Axon: Should I AC Couple?
Post by: Ocelot on July 14, 2009, 11:14:57 AM

Hey all,

I've got a question about AC coupling and virtual grounds...

I'm using a diff op-amp with a 9V battery and a +4.5V (or rather Vcc/2) virtual ground so that I don't have to use a dual power supply. (BTW I'm detecting EMG signals). I want to hook up the output signal to my Axon's ADC ports but am not sure the best way to do this.

here's what i think my options are:

1) AC couple the signal and connect the 0V ground to the Axon's ground

2) Don't AC couple and connect the virtual ground to the Axon's ground

What are the pros and cons of both options?

After the coupling, does the reference ground change from the virtual ground to 0V power supply ground? I'm planning on using ac coupling on the op-amp output and then cleaning up the signal with passive RC filters... so in other words, after the ac coupling, would the RC filters ground be the +4.5V virtual ground or 0V power supply ground?

If I use AC coupling, how do I calculate what the value of the ac coupling capacitor should be??

Title: Re: Analog signal to Axon: Should I AC Couple?
Post by: Admin on July 21, 2009, 12:56:28 PM

This is out of my expertise, but this link has some info on differential op-amps and virtual ground that might help:
http://en.wikipedia.org/wiki/Virtual_ground