Can an OR gate be implemented using 4 CMOS transistors? The circuit would have two n-type transistors in parallel in the pull-up network, and two p-type transistors in series for the pull-down network. Every implementation I've seen uses 6 transistors, with the output of a NOR circuit used as the input to an inverter circuit.
EDIT Added diagram created with Logisim. The boxes represent input pins, and the circle is an output pin. My knowledge of electronics is very limited, so I'm sorry I can't produce a detailed schematic. I'm a CS guy.
Answer
No. OR requires 6 transistors. NOR can be implemented with 4.
You can't put NMOS on top in a simple digital circuit because there is no voltage available to turn it on.
You can put NMOS on top on a linear analog circuit, but you will not be able to drive to the upper rail, unless there is some higher voltage available to drive the gate. If you need to drive all the way to the upper rail, you need PMOS on top.
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