Quick Question, What are Amplification Factors in FET?

[freydawg56]

Homework Statement

A BJT has VA of 50 V and MOSFET has lambda(modulation length) = .02 V^-1, and has VGS-VTN=.5

What are the "amplification factors" of the 2 transistors.

Homework Equations

well, not sure, all i really want to know is what do they mean by amplification factors

The Attempt at a Solution

I'm not asking anyone to solve the problem, but I don't know what amplification factors are, or what they mean by them. I assume* they mean the things that increase the gain Vo/Vin. If anyone knows, would they like to push me in the right direction?

 

[vk6kro]

Amplification factor is a measure of the gain of amplifying devices.
It really only applies to triode valves and was always given in the data sheets for triodes.

If you have a triode valve with 10 mA of plate current flowing, it may only have 50 volts of plate voltage on it to produce this current with zero grid voltage.

Now, you make the grid negative and this current will decrease, but you can bring it up to 10 mA again by increasing the plate voltage.

The change in plate voltage needed to do this, divided by the change in grid voltage that made it necessary is the amplification factor.

For example:
Suppose you had a change from zero to -5 volts on the grid and you had to increase the plate voltage to 200 volts from 50 volts to have a current of 10 mA again.
Amplification factor = (200 volts - 50 volts) / ( 0 - (-5) ) = 150 / 5 = 30

It is not the same as voltage gain, although it is convenient as a tool for calculating voltage gain in triodes. It is a property of the valve and does not depend on the circuit components.

It is not applicable for BJTs and Mosfets as these tend to draw much the same collector or drain current regardless of the supply voltage.

 

[Mene]

I can provide a response to your question. Amplification factors in FET (Field Effect Transistors) refer to the parameters that affect the amplification or gain of the transistor. In the case of BJT (Bipolar Junction Transistor), the amplification factor is known as beta (β) and is typically in the range of 50-300. This value represents the ratio of collector current (Ic) to base current (Ib). In the case of MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the amplification factor is known as transconductance (gm) and is typically in the range of 0.1-10 mS (millisiemens). This value represents the ratio of output current (Id) to input voltage (Vgs).

In your homework problem, the VA and λ values for BJT and MOSFET respectively, are related to the amplification factors. The VA value for BJT is the Early voltage, which is a measure of the output resistance of the transistor and affects the amplification factor. The λ value for MOSFET is the channel length modulation parameter, which also affects the amplification factor. The VGS-VTN value for MOSFET represents the difference between the gate-source voltage and the threshold voltage, which also plays a role in determining the amplification factor.

In summary, amplification factors in FET refer to the parameters that determine the amplification or gain of the transistor. They are important in understanding the behavior and performance of these devices. I hope this helps in your understanding of the concept.