What is the frequency and capacitance?

What is the effect of capacitance in high frequency circuits and how it is getting added?

• Answer:

  First, capacitance is the resistance of something to a change in voltage. And capacitance exists anywhere there is a conductor that is insulated from another conductor. With that definition, anything has capacitance. And that's correct. It is also the key to understanding the capacitance in high frequency (radio frequency or RF) circuits. The fact that a circuit had conductive pathways and component leads and such means that there is a lot of little bits of capacitance distributed around the circuit. The capacitance is already there; it isn't "added" later as might be inferred. Normally, this bit of capacitance isn't a problem. But at higher and higher frequencies, it is. Remember that the higher the frequency of an AC signal, the better it goes through a given cap. So at higher and higher frequencies, the distributed capacitance in the circuit "shorts the signal to ground" and takes it out of the circuit. The RF is said to be coupled out of the circuit through the distributed capacitance in that circuit. The higher the frequency a given circuit is asked to deal with, the more signal will be lost to this effect. It's just that simple. Design considerations and proper component selection minimize the distributed capacitance in a circuit.