Hi Anizz,
There are other filters in Circle, the main single and dual filter. It is covered in the manual, which is available from the circle download section here:
http://www.futureaudioworkshop.com/circle/downloads
It can be abit daunting at first, but I recommend having a read of Gordon Reids Synth Secrets series. Here is a link to the different parts:
http://www.soundonsound.com/sos/allsynthsecrets.htm
It starts right at the beginning and covers all the main topics, filters, oscillators, mouth filter etc.
Also we need to do some tutorial videos for Circle as well, we'll try and get around to this soon.
If you have any questions just ask!