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.
C206/C207 help to reduce common mode interference but C210 will help to reduce differential interference i.e. interference which generates a signal between the positive and negative electrode terminals. I assume the important measurement is between the electrodes, not from the electrodes to ground. C210 will be low impedance at RF so will reduce the interference in combination with the electrode series resistors.
First of all thank you for your reply, however how does it help to reduce the interference? my confusion is, why don' we have two identical capacitor, with each of them connect between either positive or negative terminal and the ground?
There are already two identical capacitors to ground C206 & C207. They will only affect noise on each individual terminal. Noise between the two terminals needs a capacitor between the two terminals.
The C210 capacitor may be fairly ineffective at lower
to mid frequencies, after all the series capacitance of
the C206/C207 pair is still 5X larger. However the larger
the capacitor, generally the lower its self-resonant
frequency and the point where it quits doing its job so
well. Perhaps the C210, 10pF is more effective than
the C206/C207 path at the very high end. That, or a
simple "mobetta" design philosophy at work.