The Bypass Capacitor eliminates the effect of voltage spikes on the power supply and also reduce the power supply noise. The name Bypass Capacitor is used as it bypasses the high frequency components of power supply.
It is also called as a Decoupling Capacitor as it decouples one part of the circuit from other usually, the noise from power supply or other ICs is shunted and its effect is reduced on the other part of the circuit. Bypass Capacitors are generally applied at two locations on a circuit: one at the power supply and other at every active device analog or digital IC. The bypass capacitor placed near the power supply eliminate voltage drops in power supply by storing charge and releasing them whenever necessary usually, when a spike occurs.
Coming to the bypass capacitor placed near VCC and GND pins of an IC will be able to instantaneous current demands of a switching circuit digital ICs as the parasitic resistance and inductance delay the instantaneous current delivery.
To understand how a bypass capacitor eliminates noise, you need to first understand how a capacitor works in DC and in AC.
When a capacitor is connected across a DC power supply, like a battery from example, an electric field is developed across the dielectric with a positive charge on one of the conductors and negative charge on the other.
As the capacitor charges, a transient current flows from the supply. Hence, in a DC Circuit, the capacitor charges to the supply voltage and blocks the flow of any current through it. When a capacitor is connected across a time varying AC power supply, the current flows with little or no resistance due to charging and discharging cycles. Keeping this in mind, when a Bypass Capacitor is placed across the power supply, it provides a low resistance path for the noise which is essentially an alternating signal from supply to ground.
Hence, the bypass capacitor shunts the power supply with the nose signals. Since DC is blocked by the capacitor, it will pass through the circuits instead of passing through the capacitor to ground.
This is the reason; this capacitor is also known as Decoupling Capacitor. A circuit without Bypass Capacitor or improper Bypassing can create severe power disturbances and may lead to circuit failure. Hence, an appropriate Bypass Capacitor must be used in the circuit. The following are a few considerations that must be taken into account when selecting a Bypass Capacitor.
In high frequency circuits, the lead inductance of the bypass capacitor is an important factor. This prevents the capacitor to supply the necessary current when needed in order to maintain a stable supply. Hence, when selecting a capacitor for bypassing power supply from internal noise of the device integrated circuit , a capacitor with low lead inductance must be selected.
The placement of a Bypass Capacitor is very simple. Generally, a Bypass Capacitor is placed as close as possible to the power pin of the device. If the distance increases, the extra tack on the PCB can translate into a series inductor and a series resistor, which lowers the useful bandwidth of the capacitor.
Hence, longer PCB traces between the power pin and the bypass capacitor increases inductance and defeats the purpose of introducing the bypass capacitor in the first place. Suggested Test Series. Suggested Exams. More Electronic Devices Questions Q1. BC transistor is made by which material? The forward voltage drop of green colour LED is:. What does G stand for in the mobile technology range of 3G, 4G and 5G? The material which is not a semiconductor is.
With increase in temperature, the electrical resistance of a semiconductor. It is a component in an electric circuit that is placed between the power supply VCC and the ground GND in the circuit. It can be used to reduce the power supply noise. It can also be used to provide current supply to the integrated circuits that require a large supply of current.
It is a type of capacitor which is used to produce a clean DC signal. It can bypass the AC noise to produce a better quality signal. Thus, it is basically a filtering device. After that, the DC can freely pass through the bypassed components. If we add an emitter resistance in a Common Emitter amplifier circuit, the voltage gain of the amplifier is greatly reduced. However, the input impedance of the amplifier increases. When we connect a bypass capacitor and an emitter resistance in parallel connection, the voltage gain of the Common Emitter amplifier increases.
If we remove this capacitor from the circuit, it results in an extreme degeneration in the amplifier circuit and this will lead to the reduction of voltage gain in the amplifier. In the case of a cathode type, the cathode resistor which is present in a triode preamp is bypassed within a very large capacitor.
This eliminates the negative feedback. This is also called cathode degeneration which can greatly increase the voltage gain. If the capacitor used is sufficiently large, it is capable of acting as a short circuit for audio frequencies. It can then eliminate the negative feedback.
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