# Calculation of power dissipation of a MOSFET circuit

As a part of an assignment to design a common source amplifier, I came up with this circuit:

simulate this circuit – Schematic created using CircuitLab

The transistor is a 180nm technology with aspect ratio 2 and early voltage 0.9V for it's dimensions. Also, $$\ \mu_nC_{ox} = 300\mu A/V^2 \$$. after using that information, I obtained current through the drain to be nearly $$\ 80 \mu A\$$, transconductance to be $$\ 120\times10^{-6}\Omega^{-1} \$$, and a small circuit equivalent of:

simulate this circuit

*Please be free to correct any mistakes that I may have done in my calculations. Any help is appreciated in that regard.

My doubt here is how do I calculate the power dissipated in my circuit. Across the resistor R, it is just $$\ I^{2}R\$$ but how do I do the same calculations to determine the MOSFET power dissipation. Can I use the small signal equivalent to determine that or do I need to consider any other factors? Any help is appreciated, and a mathematical expression to determine the value of power is more than appreciated.

*If you can also suggest any improvement in the circuit to improve my gain, you're welcome to do so. Based on my calculations, I obtained it to be nearly 5.53. You may give changes in aspect ratios or resistances in my circuit.

• so you calculated Id (drain current), how calculate Vds (Drain to source voltage) and and then multiply. You will get your power dissipated. There was no need to calculate small signal parameters (but it is good that you did). Don't worry about the power dissipation through gate... just ignore it here. Commented Jan 28, 2022 at 14:42
• So you say to just add power dissipated across the resistor with the product of Id and Vds. If that's what you meant to say, then thanks. Actually I needed to calculate small signal parameters as I wanted to find out the gain of the circuit. Commented Jan 29, 2022 at 6:19