Diffusion capacitance, Electrical Engineering

Assignment Help:

Diffusion Capacitance

Diffusion capacitance is the capacitance because of transport of charge carriers among the two terminals of a device, for instance, the diffusion of carriers from anode to cathode in forward bias mode of a diode or from emitter to base (forward-biased junction in active region) for a transistor. In a semiconductor device along with a current flowing via it (for instance, an ongoing transport of charge by diffusion) at a specific moment there is essentially a number of charge in the procedure of transit via the device. If the applied voltage modifies to a different value and the current changes to a different value, a different amount of charge will be in transit in the new situations. The change in the amount of transiting charge divided by the change in the voltage that causing it is the diffusion capacitance. The adjective "diffusion" is employed because the original make use of this term was for junction diodes, in which the charge transport was through the diffusion mechanism.

To execute this notion quantitatively, at a specific moment in time let the voltage across the device be V. at present assume that the voltage changes with time slowly enough that at each moment the current is similar like the DC current that would flow at that voltage, say I = I(V) (the quasi static approximation). Assume further that the time to cross the device is the forward transit time TF. In this case the amount of charge in transit via the device at this specific moment, denoted Q, is given by

Q = I (V) τF.

Accordingly, the corresponding diffusion capacitance: Cdiff is

Cdiff = dQ /dV = (dI(V) / dV) TF

In the event the quasi-static approximation does not hold, i.e. for extremely fast voltage changes occurring in times shorter than the transit time τF, the equations governing time-dependent transport in the device have to be solved to find the charge in transit, for instance the Boltzmann equation.


Related Discussions:- Diffusion capacitance

Two-winding distribution transformer, Q. A single-phase, 10-kVA, 2300:230-V...

Q. A single-phase, 10-kVA, 2300:230-V, 60-Hz, two-winding distribution transformer is connected as an auto transformer to step up the voltage from 2300 V to 2530 V. (a) Draw a s

Sketch the phasor diagram, Q. A balanced delta-connected load with a per-ph...

Q. A balanced delta-connected load with a per-phase impedance of 12 + j9  is supplied by a 173-V, 60-Hz three-phase source. (a) Determine the line current, the power factor, th

Gas hazards in the laboratory, GAS HAZARDS IN THE LABORATORY : As mentione...

GAS HAZARDS IN THE LABORATORY : As mentioned in the introduction of this unit, the gas hazards in a laboratory arise from LPG and other compressed gases. Though the use of gas for

Describe about digital communication systems, Q. Describe about digital com...

Q. Describe about digital communication systems fl A digital signal can be deflned as having any one of a finite number of discrete amplitudes at any given time. The signal coul

Explain fourier series, Q. Explain Fourier Series? The phasor method of...

Q. Explain Fourier Series? The phasor method of circuit analysis can be extended (by using the principle of superposition) to find the response in linear systems due to nonsinu

Describe the meaning of standing wave ratio, a. Describe the meaning of sta...

a. Describe the meaning of standing wave ratio. What is the formula for it, if the load is purely resistive? Why is a high value of SWR often undesirable? b. Determine how the c

Briefly explain automotive ignition system, Q. Briefly explain Automotive I...

Q. Briefly explain Automotive Ignition System? Ignition systems in automobiles have been designed as a straightforward application of electrical transients. Figure shows a simp

Metals, Metals, Semiconductors, and Insulators For electrons...

Metals, Semiconductors, and Insulators For electrons to move within an applied electric field there have to be states available to them. A totally filled band ca

Example register to memory , Example  Register  to Memory Example ...

Example  Register  to Memory Example : Write assembly language  statement  to copy 25H  stored  in register D to memory location 3052H. Solution :   Assuming  3050H is s

What are shift registers - sequential logic circuit, What are Shift Registe...

What are Shift Registers - Sequential Logic Circuit? The Shift registers are a type of sequential logic circuit that mainly for storage of digital data and they are a group of

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd