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
The power transferred across the air gap of a two pole inductionmotor is 24 kW. If the electromag netic power developed is 22 kW, find the slip. Calculate the output torque if the

Q. Determine the armature current and torque angle? A 1500-hp, 6600-V, six-pole, 60-Hz, three-phase, wye-connected, synchronous motor, with a synchronous reactance of 36 , neg

what is the reason of low meagger result of dc motor

Starting Methods for Polyphase Induction Motors When high starting torques are required, a wound-rotor induction motor, with external resistances inserted in its rotor circuits

Q. Illustrate working of Differential Amplifier? Figure shows a weighted differencing amplifier, where "weighted" refers to the fact that the output voltage has the form v o =

Q. A two-winding, single-phase transformer rated 3 kVA, 220:110 V, 60 Hz is connected as an autotransformer to transform a line input voltage of 330 V to a line output voltage of 1

Q. Explain about Common Channel Signalling? Common Channel Signalling (CCS), centralized maintenance and automatic faultdiagnosis and interactive human-machine interface are so

Interpret the Assembly Output of the LC - 3 Compilers Goals to understand the stack convention of the LC3 compiler: How the stack pointer and frame pointer are managed


Service standards: The forum of regulators (constituted through the central government for consistency in regulation in the area of distribution) will decide the basic framewo