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

#title thyristor, what is finger voltage in terms of thyristor

what is finger voltage in terms of thyristor

Determine about the satellite navigation, Determine about the satellite nav...

Determine about the satellite navigation In motor vehicles system is known as satellite navigation (sat nav). On board computer contains pre-stored road maps. Vehicle's exact

Electric machines, a shunt motor supplied at 230V rms runs at 900rev/min wh...

a shunt motor supplied at 230V rms runs at 900rev/min when the armature current is 30A.the resistance of the armature circuit is 0.4 ohms.find the armature input

Determine the required value of the flux density, Q. A 100-turn coil in the...

Q. A 100-turn coil in the configuration of is rotated at a constant speed of 1200 r/min in a magnetic field. The rms induced voltage across the coil is 1 kV, and each turn has a le

Microprocessor, if (n n=n+1 else n=n-1 n=0 how to write this command

if (n n=n+1 else n=n-1 n=0 how to write this command

Marginal tax rate, Stratos Corporation is a privately held tablet semicondu...

Stratos Corporation is a privately held tablet semiconductor technology firm with bright growth prospects.The past 5 years have seen the firm evolve from a pure startup to a profit

Resistance temperature sensor, A Platinum resistance temperature sensor has...

A Platinum resistance temperature sensor has a resistance of 120 ohm at 0°C and forms one arm of a Wheatstone bridge. At this temperature the bridge is balanced with each of the ot

What is a modem, Q. What is a Modem? Modems are generally used to inter...

Q. What is a Modem? Modems are generally used to interface digital circuits to transmit information on analogue channels such as telephone systems. Modem (from modulator-demodu

Determine the voltages vx using voltage division, Q. Determine the voltages...

Q. Determine the voltages Vx using voltage division and equivalent resistor reductions for the circuits shown in Figure.

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