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

Find the bandwidth of the circuit, Q. A simple parallel resonant circuit wi...

Q. A simple parallel resonant circuit with L = 50 µH is used to performthe frequency selection. The circuit is to be tuned to the first station at a frequency of 1000 kHz. In order

A transistor has how many p-n junction, A transistor has (A) One p-n j...

A transistor has (A) One p-n junction.  (B) Two p-n junction. (C) Four p-n junction. (D) Five p-n junction. Ans: A transistor has two p-n junctions.

Derive an expression for the electric force, Q. A two-winding system has it...

Q. A two-winding system has its inductances given by where k 1 and k 2 are constants. Neglecting the winding resistances, derive an expression for the electric force when

There are many advantages of plc - stepper motor , There are many advantage...

There are many advantages of PLC a.The PLC  was specifically designed for harsh  conditions with  electrical  noise magnetic fields vibration  extreme temperatures or humidit

Find the first-null bandwidth, An audiomessage is band-limited to 15 kHz, s...

An audiomessage is band-limited to 15 kHz, sampled at twice the Nyquist rate, and encoded by a 12-bit natural binary code that corresponds to Lb = 212 = 4096 levels, all of which s

Its use in civil engineering, applications of electronics device (bjt,mosfe...

applications of electronics device (bjt,mosfets) in civil engineering

Illustrate procedure of hex to binary conversion, Q. Illustrate procedure o...

Q. Illustrate procedure of Hex to Binary Conversion? It is also simple to convert from an integer hex number to binary. This is achieved by: Convert the Hex number t

Write a note on feedback of emitter follower, Q. Write a note on feedback o...

Q. Write a note on feedback of emitter follower? The emitter follower can be seen to be an example of negative feedback when the relationship is put in the form

Find differential equation & state-space representation, 1. For the followi...

1. For the following network: a. Find the differential equation assuming that v ( t ) is the input and the charge on the capacitor q ( t ) is the output. Hints: i R1= ( i R2

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