MOSFET Small-Signal Amplification

In summary, the slide illustrates the maximum achievable amplification of a MOSFET using the parameters gm and gDS. It also shows the derivation of the amplification and the effect of an input voltage change on the drain voltage and current. The equation gm * ΔUGS + gDS * ΔUDS = 0 is obtained by assuming constant current and applying KCL at the drain. This is a common way to derive the pi-model.
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Hi everyone,

I am trying to learn about circuits from some slides I obtained and I am stuck on a slide.

Here is a screenshot of it (it is in German): http://i.imgur.com/HCtWF.png

It says: Example: Illustration of maximum achievable amplification of a MOSFET with the use of the parameters gm (transconductance) and gDS (output conductance).

On the left is the circuit configuration. On the right is the effect of an input voltage change with x-axis drain voltage and y-axis drain current. It also has the derivation for the amplification.

What confuses me is how they obtained:

gm * ΔUGS + gDS * ΔUDS = 0

as a result of I0 being constant. Perhaps I am not understanding the graph completely. Can someone point me in the correct direction?

For reference:
gm = dID / dUG with UD const.
gDS = dID / dUD with UG const.

Many thanks.
 
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  • #3
The change in I0 is represented by the sum of ( gm * change in Vg + gd * change in Vd ). You know this already if you understand the definition of gm and gd. Now they assumed the current to be constant. Thus they had to equate this to zero.
 

1. What is a MOSFET and how does it work in small-signal amplification?

MOSFET stands for Metal-Oxide-Semiconductor Field-Effect Transistor. It is a type of semiconductor device that is commonly used in small-signal amplification due to its ability to control the flow of current. It works by using an electric field to control the movement of charge carriers within the device, thus allowing for amplification of small signals.

2. What are the key components of a MOSFET small-signal amplifier?

The key components of a MOSFET small-signal amplifier include the MOSFET itself, a power supply, input and output coupling capacitors, and resistors. Additionally, a biasing circuit is often used to ensure the MOSFET operates in its desired active region.

3. How does the gain of a MOSFET small-signal amplifier compare to other types of amplifiers?

The gain of a MOSFET small-signal amplifier is typically higher than that of other types of amplifiers, such as BJT or JFET amplifiers. This is due to the high input impedance and low output impedance of MOSFETs, which allows for more efficient amplification of small signals.

4. What are the advantages of using a MOSFET small-signal amplifier?

Some advantages of using a MOSFET small-signal amplifier include high input impedance, low output impedance, low noise, and high linearity. Additionally, MOSFETs are relatively easy to manufacture and can be made very compact, making them suitable for use in a variety of electronic devices.

5. Are there any limitations or drawbacks to using a MOSFET small-signal amplifier?

One potential limitation of using a MOSFET small-signal amplifier is its sensitivity to temperature changes. As the temperature increases, the gain of the amplifier may decrease, leading to distortion in the output signal. Additionally, MOSFETs may be more prone to damage from electrostatic discharge compared to other types of amplifiers.

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