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# MOSFET Analysis

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A) In comparing the behaviour of an n-channel MOSFET with a p-channel device having identical geometry and threshold voltage, it is found that the n-channel FET has a greater drain current than that of the p-channel FET. State why this should be so and give one other characteristic in which the two devices would differ.

B) In order to increase the packing density, or the number of devices per unit area, that can be achieved on an integrated circuit, the supply voltage has been reduced. Very large scale integrated circuits (VLSI) now work at a 3.3 V supply or below. Give two reasons why it has been necessary to reduce the supply
voltage in order to achieve a higher packing density on the 'chip'.

https://brainmass.com/engineering/electrical-engineering/mosfet-analysis-522466

#### Solution Preview

Please find attached with one further reference.

A. , generally produce greater comparable drain currents than similarly specified devices. This is a consequence of the fact that the carriers, which happen to be electrons in devices, have greater surface mobility than the charge carriers, which are holes in devices.

The electron surface mobility and hole surface mobility trends are shown below [1]. In general one can say that the electron surface mobility is twice that for holes for similar dimensioned devices

As drain current is directly proportional to charge carrier surface mobility as shown by equation {1} ...

#### Solution Summary

The solution provides a MOSFET analysis for the given scenarios.

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## NMOS FET and BJT Analysis

Show all logic/work/sources leading up to the conclusions drawn for each problem.

1. In an NMOS FET, why does the drain current reach a maximum value, independent of increasing drain-to-source voltage?

2. Quite frequently, one needs to control a light emitting diode with a microprocessor output pin. A typical LED requires about 15 mA to fully illuminate at which time it will have a voltage drop of about 1.7V, while the microprocessor may only be capable of generating an output current of about 250 μA, while switching between 0 and 5 V. Describe how an NPN transistor like the 2N2222 or 2N3904 could be connected to the microprocessor, the LED, one or more resistors (specify the value(s)), and a 5V power source to turn the LED on and off.

3. Coupling capacitors are often used in the input and output stages of an amplifier. Why? What impact do these components have on the amplifier operation? Why? In a bipolar junction transistor amplifier with a base resistor of about 5 k and a collector resistor of about 500 , roughly estimate these capacitors for an audio amplifier that has a frequency response from 100 Hz to 10 kHz?

4. A standard silicon NPN BJT is to be used as an amplifier. The emitter voltage is biased at 4 volts, the base is biased at 5 volts, and the collector is biased at 10 volts. Will this circuit perform as desired? Why or why not.

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