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I am looking for the logical equation that describes the given circuit below.

Unfortunately I don't have information whether \$U_b\$ is positive or negative - would that make a difference?

Circuit

I derived my current result from a truth table I created.

\$f(a,b,c)=\bar{a}*\bar{bc}\$

Truth Table

I think, my logical term might be right, but I would like to know whether this would also be possible by just looking at the circuit and identifying NAND and NOR constellations in PMOS there.

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  • \$\begingroup\$ Do you think parallel is OR and series is AND? and obviously polarity of Vcc matters. \$\endgroup\$ – Sunnyskyguy EE75 Oct 8 '17 at 16:10
  • \$\begingroup\$ I learned that parallel PMOS is NAND and series is NOR, but using that I can't come to senseful results. Is it possible to derive the Vcc polarity from 'the arrows of the transistors'? \$\endgroup\$ – trizzou Oct 8 '17 at 16:15
  • \$\begingroup\$ Nobody uses Pch FETs like this with -Vdd ( but may exist) and Parallel is OR inverting so NOR. It is just an academic question. \$\endgroup\$ – Sunnyskyguy EE75 Oct 8 '17 at 16:20
  • \$\begingroup\$ Negative Vdd was only used for ECL. and not CMOS or even Pch FETs so this question is kind of useless. \$\endgroup\$ – Sunnyskyguy EE75 Oct 8 '17 at 16:30
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    \$\begingroup\$ This is not really helping, I don't even know what you're talking about. This was one of the exercises that was chosen in a previous exam and I have issues solving it. That's it. \$\endgroup\$ – trizzou Oct 8 '17 at 16:45
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Since you have connected gate of the PMOS to \$U_b\$, this voltage should be negative for the current to flow.
It seems to me some kind of a ratioed logic, so I believe whenever the lower transistors are OFF we will get a logical one.
This happens for: $$f = a + bc$$

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