Parasitic capacitance in electrical circuits can cause problems at higher frequencies. It can be addressed through circuit design, component placement, and using compensating electronic components. Shortening conductors and reducing surface area on PCBs can also help. In digital circuits, parasitic capacitance can increase rise and fall times, requiring higher currents and more DC consumption for compensation.
Parasitic capacitance, in electrical circuits, is the extra effect of conductors acting as plates between a dielectric, which is usually air. It becomes a problem with higher frequencies because the very small distributed capacitances that exist will have lower impedances at these frequencies. This effect can be addressed at the circuit design stage, where component placement can reduce the effects to a point where satisfactory operation can be achieved.
Capacitors are available as lumped or distributed components. As lumped components, these capacitors are considered limited to certain components; for distributed capacity, planning is required in the design of components and circuits. When an inductor is manufactured, there is always a distributed capacitance involved; this can be considered a parasitic capacitance. An ideal inductor will have zero distributed capacitance; therefore, it will resonate at a frequency close to infinity. It is known that most inductors will have a non-infinite resonant frequency due to the distributed capacitance of the winding leading to a measurable resonant frequency.
Parasitic capacitance in radio frequency (RF) amplifiers can cause low gain of these amplifiers due to parasitic loss. In some cases, it could cause these amps to wobble. With parasitic capacitance, the actual circuit in the real world is the circuit drawn at the design stage plus the capacitances to ground or between various points in the circuit. In some cases, the solution is simply to reduce the concentrated capacitance for a given circuit location. For other cases, the solution may be to increase an inductance to maintain a certain frequency passband.
There are cases where the characteristics of the electronic component can compensate for the parasitic capacitance. For example, reduced RF output due to parasitic capacitance can be increased by using a higher gain transistor. In some cases, the strange effects of parasitic capacitance can be compensated for by adding circuit stages.
A parasitic element can exist due to the proximity of the conductors or the lengths of traces, wires or conductors of the components. The common approach to reducing the chance of detecting a parasitic element is to shorten the conductors and reduce the surface area in components and traces on printed circuit boards (PCBs). Based on the mentioned practices to avoid excessive parasitic effects, miniaturization of PCB components and traces has become a standard practice.
In digital switching circuits, the rise and fall time of the digital signal greatly affects the maximum achievable speeds. Parasitic capacitance on digital device inputs and outputs increases rise and fall times. An alternative is to use output devices capable of injecting higher currents to compensate for parasitic capacitance. Unfortunately, this approach increases direct current (DC) consumption. This explains why very high speed digital circuits usually require huge amounts of DC currents.
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