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

Static or electronic energy meters, Static or Electronic Energy Meters ...

Static or Electronic Energy Meters Electronic energy meters are replacing traditional electromechanical meters in several residential, commercial and industrial applications s

Microcontroller, Project Garage door opener with password. Wrong password ...

Project Garage door opener with password. Wrong password "door close" on lcd screen, correct password "door open" on lcd Screen no need the motor. Material used - Microcontroller

What do you mean by frequency response, Q. What do you mean by Frequency re...

Q. What do you mean by Frequency response? Now let us examine the response of a circuit to a sinusoidal source, called an oscillator, whose frequency can be varied.Known as the

What are the application specific instruction processors, What are the appl...

What are the application specific instruction processors? Single purpose processor or ASIP (Application Specific Instruction processor) a. Floating point Coprocessor and Gra

Semiconductor in equilibrium, Semiconductor  in Equilibrium Equilib...

Semiconductor  in Equilibrium Equilibrium in semiconductors implies the following: (i) Steady state: ∂Z / ∂t = 0 In which Z is any physical quantity like charge, volt

Discuss endp assembler directive, Discuss the ENDP assembler directive ...

Discuss the ENDP assembler directive with example ENDP: It is stands for End Procedure, which informs assembler the end of a procedure. Within assembly language programm

Explain the architecture of cellular networks, Wireless and Mobile Communic...

Wireless and Mobile Communication 1. Explain the architecture of Cellular Networks. 2. Discuss the fundamentals of GSM Network. 3. Explain briefly the different interface

Public safety - application of software defined radio, Public safety - Appl...

Public safety - Application of Software Defined Radio During emergency situation such as earthquake, tsunami, terrorist attack, public safety officials from different agencies

Example of clamper circuits, Example of clamper circuits: Example of c...

Example of clamper circuits: Example of clamper circuits are as follow Voltage multiplier circuit: voltage circuit is employed to maintain a relatively low transformer pe

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