Is it possible to amplify weak lows and weak highs?

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I am in possession of a book that says if the gate of an N-channel MOSFET i
s low (say 0 volts), then the output is high impedance; and that if that ga
te is high (say 5 volts), then the voltage at the drain depends on the volt
age at the source; if the voltage at the source is low, then the voltage at
 the drain is low; but if the voltage at the source is high (say 5 volts),  
then the voltage at the drain is a weak high (say 3.5 volts). For a P-chann
el MOSFET, if the gate is high, then the output is high impedance; and if t
hat gate is low, then the voltage at the drain again depends on the voltage
 at the source; if the voltage at the source is high (5 volts), then the vo
ltage at the drain is high (5 volts); but if the voltage at the source is l
ow (0 volts), then the voltage at the drain is a weak low (say 1.5 volts).  
Does this sound about right?

But I've also heard that a transistor can act as an amplifier. Is it possib
le to design a circuit with such an N-channel transistor that has its sourc
e at 0 volts and its gate at 3.5 volts that results in its drain being at 0
 volts? And to design a circuit with such a P-channel transistor that has i
ts source at 5 volts and its gate at 1.5 volts that results in its drain be
ing at 5 volts?

If so, then couldn't I design a multiplexer with just six transistors?

Assume the inputs to my multiplexer are logical bits , , and a
nd the output is defined as the value of if is low, and alte
rnately if is high. I have N-channel transistors , {am
plifyHigh}, and ; and P-channel transistors , {amplify
Low}, and ; and I have wires , , and {h
ighNegated}.

Then I attach to the gates of each of and ,
 to the source of , to the source of , the drains
 of each of and to , to eac
h of the gates of and , the source of {amplifyHig
h} to ground, the source of to high voltage, the drain of {amp
lifyHigh} to , the drain of to , the  
other end of to the gate of , the other end of {lo
wNegated} to the gate of , the source of to ground,
 the source of to high voltage, and the drains of each of {neg
ateLow} and to .

Will this work? I guess it depends on where the threshold is that determine
s whether the transistors and turn on and off. I
f that threshold is somewhere between 1.5 volts and 3.5 volts, then it seem
s like this circuit should work as a multiplexer.

If it does work, are people aware of such a design? When I've heard of impl
ementations of multiplexers, they usually have involved at least fourteen t
ransistors, not six, three NAND gates with four transistors each and one NO
T gate with two transistors.

Is there a problem with noise? Is it possible that noise can cause a 1.5 vo
lt value to turn on an N-channel transistor? Or that noise can cause a 2.5  
volt value to turn off such a transistor? And vice versa for a P-channel tr
ansistor? If so, is there some way to bundle up the four transistors {pivot
Low}, , , and to reduce the risk of no
ise keeping the multiplexer from functioning correctly?

Re: Is it possible to amplify weak lows and weak highs?
On Sat, 1 Jan 2022 21:15:01 -0800 (PST)

Quoted text here. Click to load it

The operation of a FET depends on the type and external components.  
For more clues goggle "fet transconductance graphs"

Jan Coombs
--  


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