Saturation or active mode, Electrical Engineering

Saturation or active mode

While VGS > Vth and VDS > (VGS - Vth)

The switch is turned on, and a channel has been made that allows current to flow between the drain and source. As the drain voltage is higher than as compared to the gate voltage, the electrons spread out, and conduction is not by a narrow channel but by a broader, two- or three-dimensional current distribution extending away from the interface and deeper in the substrate. The onset of this region is as well termed as pinch-off to point out the lack of channel region near the drain. Now the drain current is weakly dependent on drain voltage and controlled primarily through the gate-source voltage, and modeled very approximately like:

ID = (μn Cox /2) W/L (VGS - Vth) 2 (1 + λVDS)    

The additional factor including λ, the channel-length modulation parameter models current dependence on drain voltage because of the early effect or channel length modulation.

As per to this equation, a key design parameter, the MOSFET trans conductance is:

Gm = 2ID/VGS-Vth = 2ID/Vov

In which the combination Vov = VGS - Vth is called the overdrive voltage. One more key design parameter is the MOSFET output resistance rout described by:

rout = 1/ λID

rout is the inverse of gDS

In which gDS = ∂IDS / ∂VDS. VDS is the expression in saturation region.

If λ is considered as zero, an infinite output resistance of the device results which leads to unrealistic circuit predictions, specifically in analog circuits. Since the channel length becomes extremely short, these equations become quite inaccurate. New physical effects take place. For instance, carrier transport in the active mode may become limited through the velocity saturation. While velocity saturation dominates, the saturation drain current is more nearly linear than as compared to the quadratic in VGS. Even at shorter lengths, carriers transport with near zero scattering, termed as quasi-ballistic transport. Additionally, the output current is influenced by drain-induced barrier lowering of the threshold voltage.

Posted Date: 1/11/2013 1:28:32 AM | Location : United States







Related Discussions:- Saturation or active mode, Assignment Help, Ask Question on Saturation or active mode, Get Answer, Expert's Help, Saturation or active mode Discussions

Write discussion on Saturation or active mode
Your posts are moderated
Related Questions
If a permanent magnet creates the flux in a magnetic circuit, the flux exists without the need for a coil, so how does Amperes Law apply to this case?   In this case the flux is

This is basically a simple senior design project where the professors are giving us a limited budget and providing us with an Arduino Board. (We can use rasberry pi, beagle bone, e

Q. The magnetization curve taken at 1000 r/min on a 200-V dc series motor has the following data: Field current, A: 5 10 15 20 25 30 Voltage, A: 80 160 202 222 236 244 Th

Q. Show DC Generator Characteristics? Figure shows schematic diagrams of field-circuit connections for dc machines without including commutating pole or compensating windings.

Q. Explain digital frequency meter. or Explain principle of digital frequency meter and discuss utility of time base selector with suitable diagrams. Sol. Digital Fr

Explain the NOR GATES - Microprocessor The NOR GATE is an OR gate with the output inverted. Consequently the outputs of a NOR gate would have the opposite states as the outputs o

Q. Given that a silicon n-channel JFET has V P = 5 V and I DSS = 12 mA, check whether the device is operating in the ohmic or active region when v GS =-3.2 V and i D = 0.5 mA.

Hey Dear i have a hw in MATLAB by applying Finite Element Method there(Electromagnetic) and i need your help with it. please take alook at the question and let me know if you can h

Define the Signals in Time Domain? The time domain is the type of visualization that most people are familiar with. This method shows variations of a signal with time. The most

operation of induction motor