CMOS inverting amp with negative VDD?

[Chad1]

Hi guys,

I'm trying to design a circuit using only an N-FET and a resistor that performs with the basic inverting amp characteristics, but I want it to work with both a + and - VDD. Any suggestions? I'm sure this spec will require more components than an N-FET and a resistor. I tried to come up with a circuit that introduces a diode in series with GND so that when Vin (gate) is pulled low, Vout is VDD (where VDD<0). Below is a truth table of what I want (the last line is the only one that is a problem):

Vin (VDD>0)      Vin (VDD<0)         Vout
------------------------------------------------------
  high                                               0
  low                                              VDD (>0)
                             high                    0
                             low                   VDD (<0)



                 VDD
                   |
                   |
                   /
                   \
                   /
              R   \
                   |
                   |
             -----o----------o Vout
Vin ----|
             -----|
                   |
                   |
                 GND



Thanks a lot!

[ejeffrey]

Are either or both of these analog signals or only digital? Does 'Vdd' really need to be the supply voltage, or can you generate separate rail voltages that are above the maximum input voltage and below the minimum.  If you can have fixed supplies that cover the entire input range an analog switch will do what you want.  Just feed what you call "VDD" to the input and send your "Vin" to the control pin.

[Unclegummers]

http://www.southalabama.edu/engineering/ece/faculty/akhan/Courses/EE334-Fall07/Chap16-1-NMOS-Inverter.pdf

Google is your friend.