Feedback MOSFET


by roeb
Tags: feedback, mosfet
roeb
roeb is offline
#1
Jan19-10, 09:20 PM
P: 107
1. The problem statement, all variables and given/known data


An n-channel enhancement MOSFET for which Vt = 2 V and K = 100 uA/V2 is operated from a 9 V supply using a drain resistor RD of 60kohms and the feedback bias scheme depicted. What drain current results? What is VD What is the largest sine wave output signal for which operation in the saturation region is maintained?


2. Relevant equations



3. The attempt at a solution

I'm able to the first two questions but I'm having difficulty with the last sine wave part.

To find Vd and Id, I simply solved (9 - Vd)/60k = (100uA/V^2)(Vd - 2)^2, where I get Vd = 3 V and Id = .1 mA.

To maintain saturation in a n-channel MOSFET this condition: vds >= vgs - vt has to be satisfied. vds >= 3 - 2 = 1. Since Vd = 3 V at DC, then I would think that the sine wave could be +/-2 volts. Unfortunately, the book states the answer is 1.85 volts peak. I think this has to do with the feedback that I may not be correctly taking into account. Does anyone see what I am doing incorrectly?
Phys.Org News Partner Science news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
The hemihelix: Scientists discover a new shape using rubber bands (w/ video)
Microbes provide insights into evolution of human language

Register to reply

Related Discussions
equation R = K / W mean for mosfets? Engineering, Comp Sci, & Technology Homework 0
Voltage feedback and current feedback. Electrical Engineering 1
MOSFET pinout? Electrical Engineering 1
MOSFET help Electrical Engineering 2
Mosfet Introductory Physics Homework 0