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Diffusion capacitance is the capacitance due to transport of charge carriers between two terminals of a device, for example, 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 with a current flowing through it (for example, an ongoing transport of charge by diffusion) at a particular moment there is necessarily some charge in the process of transit through the device. If the applied voltage changes to a different value and the current changes to a different value, a different amount of charge will be in transit in the new circumstances. The change in the amount of transiting charge divided by the change in the voltage causing it is the diffusion capacitance. The adjective "diffusion" is used because the original use of this term was for junction diodes, where the charge transport was via the diffusion mechanism. See Fick's laws of diffusion.
To implement this notion quantitatively, at a particular moment in time let the voltage across the device be . Now assume that the voltage changes with time slowly enough that at each moment the current is the same as the DC current that would flow at that voltage, say (the quasistatic approximation). Suppose further that the time to cross the device is the forward transit time . In this case the amount of charge in transit through the device at this particular moment, denoted , is given by.
Consequently, the corresponding diffusion capacitance:. is.
In the event the quasi-static approximation does not hold, that is, for very fast voltage changes occurring in times shorter than the transit time , the equations governing time-dependent transport in the device must be solved to find the charge in transit, for example the Boltzmann equation. That problem is a subject of continuing research under the topic of non-quasistatic effects.
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What is the type of capacitance effect exhibited in P-N junction when it is reverse biased?
1. Transition capacitance 2. Diffusion capacitance 3. Space charge capacitance 4. Drift capacitance
What is meant by transition and space charge capacitance of a diode?
space charge region in a diode or say a bjt for better understanding is same as the depletion region, both transition capacitance and depletion capacitance are the same c= (epsilon*A)/d ; where ... c is capacitance A is area and d is the depletion width the other type of capacitance is the diffusion capacitance c= (T*I)/(n*V) where ... c is the capacitance T is transition ti me I is the drift current n is emission coefficient ... its value is 1 for germanium and V is thermal voltage .. 26mv
What is the difference between capacitance and stray capacitance?
Capacitance is an ability to store an electric charge. "If we consider two same conductors as capacitor,the capacitance will be small even the conductors are close together for long time." this effect is called Stray Capacitance.
What is the capacitance of parallel plate capacitor?
We know the Electric Field, E, is equal to: E=V/l, where V is voltage, l is distance. V=E*l Capacitance, C=q/V, and C=q/(E*l) Hence capacitance is inversely proportional to the distance separating the plates.
What is pn junction capacitance?
The charge inside of a p-n diode with a connected voltage variety yields a capacitance is need to add circuit model of a p-n diode. The capacitance connected with the charge variety in the exhaustion layer is known as the intersection capacitance, in the same process capacitance connected with the abundance bearers in the semi impartial district is known as the dissemination capacitance.
What is capacitor derive an expression for total capacitance when three capacitors are connected in parallel?
capacitance C=C1+C2+C3
What is the type of capacitance effect exhibited in P-N junction when it is reverse biased?
1. Transition capacitance 2. Diffusion capacitance 3. Space charge capacitance 4. Drift capacitance
Definition of a capacitance in mosfet?
Capacitance in mosfet is of three types: gate capacitance diffusion capacitance routing capacitance Gate capacitance: limits the speed of the device t which it can be operated Diffusion capacitance: It is the capacitance due to charge carriers between drain and source. Routing capacitance: It is the capacitance of the metal which is deposited on the top of oxide layer.
What is meant by transistion and space charge capacitance of a diode?
Diffusion capacitance is the capacitance due to transport of charge carriers between two terminals of a device. - Amog This diffusion capacitance is due to depletion capacitance which is a function of forward bias applied to emitter junction of a transistor and due to diffusion capacitance which a function of transconductance of the transistor. Its value is 100 pF. Tirupanyam B.V
Does the diffusion capacitance exit in forward biased diode?
Yes
What is diffusion capacitance in pn junction?
A capacitor is a device that stores charge. Therefore any device that stores charges( static or dynamic) can be said to have capacitance. When a PN diode is forward biased, a current flows due to the majority charge carriers. At a particular instant there will be charges in motion. This is dynamic charge. The capacitance due to storage of dynamic charge is called the diffusion capacitance. We know that C = Q * V. That is capacitance is directly proportional to charge stored. Since the diode current increases exponentially with the voltage applied across it, the dynamic charge also increases exponentially . Hence the diffusion capacitance increases exponentially with the increasing diode voltage.
What is the difference between diffusion capacitance and transition capacitance?
Transition capacitance : A reverse biased PN-junction has a region of high resistivity (depletion layer) sandwiched in between two regions of relatively low resistivity. The P-N regions act as the plates of a capacitor and the depletion layer acts as the dielectric This is known as the transition capacitance or depletion capacitance. Diffusion capacitance : It is the capacitance due to transport of charge carriers between two terminals of a device like the forward biased PN junction. In a semiconductor device with a current flowing through it (for example, an ongoing transport of charge by diffusion) at a particular moment there is necessarily some charge in the process of transit through the device. If the applied voltage changes to a different value and the current changes to a different value, a different amount of charge will be in transit in the new circumstances. The change in the amount of transiting charge divided by the change in the voltage causing it is the diffusion capacitance. The adjective "diffusion" is used because the original use of this term was for junction http://www.answers.com/topic/diode, where the charge transport was via the diffusion mechanism.
Why transition capacitance called so?
Transition capacitance is the capacitance that is accumulated between two terminals as an electrical charge is carried between them. In a diode, this is the diffusion from anode to cathode of a diode in forward bias mode.
What is meant by transition and space charge capacitance of a diode?
space charge region in a diode or say a bjt for better understanding is same as the depletion region, both transition capacitance and depletion capacitance are the same c= (epsilon*A)/d ; where ... c is capacitance A is area and d is the depletion width the other type of capacitance is the diffusion capacitance c= (T*I)/(n*V) where ... c is the capacitance T is transition ti me I is the drift current n is emission coefficient ... its value is 1 for germanium and V is thermal voltage .. 26mv
Will capacitence be increased with increase in the charges?
Definitely not possible. Capacitance is given by an expression C = epsilon x A / d Since charge is not present the capacitance cannot be increased or decreased by the charge placed
Derive an expression for expression for rise of liquid in a capillary tube?
deduce an expression for height of a liquid in capillary tube. also write practical applications of capillary action.
What is the capacitance formed at forward biased?
to find the diffusion capacitance we first find the minority charge "close" the depletion edges Qd and then differentiate it with respect to the voltage applied Vd. Cd =[dQd/dVd]vd=tT{ Id(@Vd)/VT}
