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

Explain wireless electromagnetic channels, Q. Explain Wireless electromagne...

Q. Explain Wireless electromagnetic channels? Wireless electromagnetic channels are used in wireless communication systems, in which the electromagnetic energy is coupled to th

Determine the maximum value of the voltage, Q. Three waveforms seen on an o...

Q. Three waveforms seen on an oscilloscope are shown in Figure. If the horizontal scale is set to 50 ms per division (500 ms for the entire screen width), and the vertical scale is

What is difference between voltage and potential, Voltage is referred as Po...

Voltage is referred as Potential difference among two points. Potential means its force. I think so.voltage defination is 100% correct.

Show the overflow of arithmetic operations, Q. Show the Overflow of arithme...

Q. Show the Overflow of arithmetic operations? A circumstance takes place because the magnitude of the results of arithmetic operations has become too large for the fixed word

Show noise and stability of operational amplifier, Q. Show Noise and Stabil...

Q. Show Noise and Stability of operational amplifier? Noise This refers to the small, rapidly varying, random spurious signals generated by all electronic circuits. Noise

FSM(finite state machine, A sequential circuit has two inputs w1 and w2, an...

A sequential circuit has two inputs w1 and w2, and an output, z. Its function is to compare the input sequences on the two inputs. If w1=w2 during any four consecutive clock cycl

Show n-channel depletion mode mosfet, Q. For a transistor, when v GS = -2....

Q. For a transistor, when v GS = -2.0 V, find V DSsat if Vp= -4.0 V for an n-channel depletion mode MOSFET. Solution: V p = -(V DSsat + v SG ) but  v SG = -v GS = -(-

Define super scalar architecture, Define super scalar architecture. Su...

Define super scalar architecture. Super scalar architecture: The Pentium microprocessor is organized along with three execution units. Individual executes floating-point inst

Cro, explain the operation of a detector probe

explain the operation of a detector probe

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