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From: lansford@tusun2.mcs.utulsa.edu (Wendell Wayne Lansford)
Newsgroups: sci.electronics
Subject: MOSFET Puzzle
Message-ID: <1285@tusun2.mcs.utulsa.edu>
Date: 10 Apr 91 03:51:51 GMT
Reply-To: lansford@tusun2.UUCP (Wendell Wayne Lansford)
Distribution: na
Organization: University of Tulsa,  Tulsa, Oklahoma
Lines: 30

The following problem was recently posed by my professor in Advanced 
Networks:
 
TRANSISTOR IN A BOX PUZZLE
 
               -------------
        +  ----|           |----  +
               |   Black   |
       Vin     |    Box    |    Vout
               |           |
        -  ----|           |----  -
               -------------
 
The black box contains ONLY one depletion-mode MOS transistor and 
NOTHING ELSE.  A sinusoidal voltage source, Vin, is connected to the
box as shown, and a measurement in the steady state reveals that the
magnitude of Vout is greater than the magnitude of Vin (ie |Vout| > |Vin|),
where Vout and Vin are phasors corresponding to ac voltages.  
Find how the transistor is connected and explain how such a voltage gain
is possible.  (Note:  The above is not just a "paper" result and can
be reproduced in the laboratory.)
 
 
Can anyone readily provide some insight into this problem?

Thanks!    

Wendell Lansford
lansford@tusun2.mcs.utulsa.edu