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Join Date: Apr 2010
Posts: 1

# FET Small Signal Analysis

04/20/2010 7:24 PM

Would someone help me solve this problem? Below is a description of a partial circuit. How do you find the resistance looking into the drain of M1? The answer is: Resistance = ro1 (1 + gm1*ro5). Please draw the small signal model you used to get the answer and show all calculations. Thanks

This partial circuit consists of two n-channel fets, M1 and M5. The drain of M1 is not connected to anything. The gate of M1 is grounded. The source of M1 is connected to the drain of M5. The gate of M5 is connected to a voltage called vcmc. The source of M5 is grounded.

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Guru

Join Date: Jan 2007
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#1

### Re: FET Small Signal Analysis

04/20/2010 8:58 PM

Hello xcjameson3,

Why don't you download some free schematic-drawing software, you draw the circuit, convert it to a .jpg, .gif, or .bmp file (Export Schematic Image function in the software), upload it to your post using the button in the CR4 editor, and show us what you have so far?

Mike

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Anonymous Poster
#2

### Re: FET Small Signal Analysis

04/20/2010 9:23 PM

CR4 is not a homework service and we do not do the drafting for students.

But, it is very refreshing to see a student actually register and use good English. Being bombarded by no punctuation texting fragments from people named "Guest" gets old very fast. If you do your own work and show us that you are doing your own work then you will probably find quite a few new friends at CR4.

Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 15113
#3

### Re: FET Small Signal Analysis

04/20/2010 11:50 PM

I agree completely. If this student generates a schematic, and demonstrates as much of this homework as he/she can comprehend, many people like myself will gladly help in understanding. But if all they want is an answer to submit, then this kind of a homework assist will be quickly shutdown.

PS number the components. It helps so much in the descriptive analysis.

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#4

### Re: FET Small Signal Analysis

04/21/2010 10:58 PM

Also agreed! But why didn't YOU register so you could get a GA or two?

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Active Contributor

Join Date: Feb 2010
Posts: 11
#5

### Re: FET Small Signal Analysis

04/22/2010 12:47 AM

IF THEY ARE DEPLETION TYPE

Rds on of M5 will be the resistance if you look from drain side of M1

Guru

Join Date: Dec 2008
Location: Long Island NY
Posts: 15113
#6

### Re: FET Small Signal Analysis

04/22/2010 1:58 AM

Depletion or enhanced, Vgs will have something to do with the impedance. It will also depend if one's in saturation or triode mode. But no transistor of any fabrication will work without other devices attached to it. These just might have a little effect on the circuit impedance.

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