The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> capacitor to suppress radio frequency signal
https://designers-guide.org/forum/YaBB.pl?num=1293502806

Message started by Victor chan on Dec 27^th, 2010, 6:20pm

Title: capacitor to suppress radio frequency signal
Post by Victor chan on Dec 27^th, 2010, 6:20pm

Hi

I have attached a picture of a part of a circuit, with which I dont understand how C210 suppresses radio frequency, because it is connecting between positive and negative terminal of channel 1.

Thanks in advance

Title: Re: capacitor to suppress radio frequency signal
Post by rfmagic on Dec 27^th, 2010, 10:17pm

Hi Victor,

What is this circuit doing??

anyway, I assume that C210 with R204 and 203 act togather a a lowpass filter to suppress high frequency tones. the connection between the positive and negative nodes allows for a virtual ground.

hopes this anwers your question

Title: Re: capacitor to suppress radio frequency signal
Post by Victor chan on Dec 28^th, 2010, 3:36am

First of all, thank you for your reply.

This is a protection circuit between the electrode which is attached to human being and amplifier circuit. The original statement claims that the capacitor suppresses radio frequency, which I think your assumption is right (because I was thinking it is acting like a bypass capacitor).

However, I don understand your statement,
" the connection between the positive and negative nodes allows for a virtual ground"

Can you please explain it further?

Title: Re: capacitor to suppress radio frequency signal
Post by rfmagic on Dec 28^th, 2010, 4:19am

the positive node and negative nodes mean that the AC voltage applied to these nodes is symmetric aroung a common DC voltage (usually VDD/2 ). This symmetry working point it treated as an AC virtual ground. for example, you could replace C210 with two series capacitors with double the capacitance of C210 (each), the common node between the capacitors is the AC virtual ground

Title: Re: capacitor to suppress radio frequency signal
Post by Victor chan on Dec 28^th, 2010, 4:53am

Thank you very much for your reply again, is very well explanation.

If you don't mind, would you please also have a look of my second question?

http://www.designers-guide.org/Forum/YaBB.pl?num=1293540714/0