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CAPACITORS - Coggle Diagram
CAPACITORS
bypass
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are used to force signal currents around elements by providing a low impedance path at the frequency
High frequencies and transient currents flow through a bypass capacitor, in preference to the harder path through the decoupled circuit, but DC cannot go through the bypass capacitor, so it continues onto the decoupled circuit
decoupling
used to filter out noise in power line, they work as the device’s local energy storage
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noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit
functioning
if the voltage level for a device is fixed, changing power demands are manifested as changing current demand
The voltage regulator adjusts the amount of current it is supplying to keep the output voltage constant but can only effectively maintain the output voltage for events at frequencies from DC to a few hundred kHz
The decoupling capacitor works as the device’s local energy storage. The capacitor cannot provide DC power because it stores only a small amount of energy but this energy can respond very quickly to changing current demand
The capacitors effectively maintain power-supply voltage at frequencies roughly from hundreds of kHz to hundreds of MHz
decoupling capacitors between the power pin and ground pin of the device ensure low ac impedance to reduce noise and to store energy
To reach low impedance over a wide frequency range, several capacitors must be used, because a C consists also of a parasitic R and L -> resonant circuit
the capacitive characteristics are only valid up to its self-resonant frequency (SRF). Above the SRF, the parasitic effects dominate, and the capacitor acts as an inductor
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placing
near the device
The goal is to minimize the amount of line inductance and series resistance between the decoupling capacitor and that device. Especially for low-valued capacitors
Connect the pad of the capacitor directly with a via to the ground plane. Use two or three viasto get a low-impedance connection to ground
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microprocessor
problems
a single positive or negative noise pulse on the power pins may propagate through a gate and toggle the contents of an internal register. Variations in operating temperature and manufacturing processes may cause the problem to be extremely difficult to debug. It is better to design defensively and to eliminate these problems at the start
minimizing power supply noise is necessary for reliable operation of the processor, and it also minimizes
electromagnetic interference (EMI) electromagnetic compatibility (EMC) compliance problems
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PCB guard
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on AC circuits, where the guard ring surrounds the surface current with a potential problem or is leaking
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