I have an extremely simple circuit that involves a NMOS, three resistors, and a voltage source. The circuit and info are shown below. Please understand that I could probably analyze this circuit while driving on the interstate, at midnight, before I hit the next mile marker. I should also mention that this is Example problem 3.3 on page 147 of Microelectronics Circuit Analysis and Design: Fourth Edition. It's not homework, its curiosity.
Why does PSpice generate an answer that is 1 Volt higher than the expected VDS voltage and .5mA less than what it should be for the drain current? I assume PSpice is adding a default value model property that is not considered when the author of the book wrote the example. But that brings question two: If the author can write an example by supplying only two values and get the correct 'ideal' answer, why does PSpice &^%*(^ it up? I realize this circuit may never cure cancer, or land me on the moon. But what if I design a clock tree or buffer that is of some importance? 1 volt becomes important. I feel like I am constantly double checking PSpice results, frankly because I don't trust it.
I get the correct results if I double the transconductance parameter (KP/Kn) from .1mA to .2mA. Any clue why?
Are there any suggestions?
Am I missing something?
Any constructive criticism would be much apprecitated.
Problem From Book
Calculate the drain current and Vds or a common source circuit with an n-channel enhancement-mode MOSFET. Find the power dissipated in the transistor. For the circuit shown assume R1=30kOhm, R2=20kOhm, RD=20kOhm, VDD=5V, Vtn=1V, and Kn=0.1 mA/V^2
Answer from Book
ID = .1mA, Vds = 3V, Vg = 2V
The Known MOSFET Parameters
Here is a link to PSPICE Model Parameters