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What is the effect of capacitance in high frequency circuits and how it is getting added?
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.
What is diffusion capacitance in pn junction?
A capacitor is a device that stores charge. Therefore any device that stores charges( static or dynamic) can be said to have capacitance. When a PN diode is forward biased, a current flows due to the majority charge carriers. At a particular instant there will be charges in motion. This is dynamic charge. The capacitance due to storage of dynamic charge is called the diffusion capacitance. We know that C = Q * V. That is capacitance is directly proportional to charge stored. Since the diode current increases exponentially with the voltage applied across it, the dynamic charge also increases exponentially . Hence the diffusion capacitance increases exponentially with the increasing diode voltage.
What is 220uF?
It is unit of capacitance. 220 micro farad.
Difference between stray and parasitic capacitance?
Parasitic capacitance is unavoidable and usually unwanted capacity between two or more conductors which exists due to close proximity and which typically causes non-ideal circuit behavior. Stray capacitance, as it is typically thought of, is a type of parasitic capacitance. It is the capacity from a conductor to its surroundings which is the aggregate of the conductors in its environment inversely weighted by the distance to each of the environmental conductors.
How does one reduce stray capacitance?
You can reduce stray capacitance by avoiding having long wires running parallel in circuits. Keep wires as short as possible. Long wires running along each other can exhibit stray capacitance effects. Another way is to cut long leads of components such as capacitors and inductors to make them as short as possible. If best, use SM components, as they have no leads which can cause this stray capacitance effect.
