How to design a 4 input XNOR gate?

Question

I want make this 3 input device 4 input legged. Any suggestions?

You can make it using an inverting 4-to-16 decoder (one where the outputs are active LOW) and a 4-input AND gate... — Majenko, Mar 15 '15 at 11:48
@Majenko: If one and only one input high makes a high output, then a 4-to-16 decoder with active low outputs would have to be followed up with a four input NAND, yes? — EM Fields, Mar 15 '15 at 17:45

EM Fields · Accepted Answer · 2015-03-15T11:48:49.217

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If all of the inputs are the same (all high or all low) the output will go high, otherwise the output will g0 low.

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edited Mar 15 '15 at 11:48

answered Mar 15 '15 at 11:08

EM Fields

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That's correct for the "other" type of XNOR gate, but the one pictured has "=1" in it, so it's a "one and only one input HIGH" style XNOR gate. – Majenko Mar 15 '15 at 11:46
@Majenko: AARGHHHH!!! – EM Fields Mar 15 '15 at 11:57
That's the problem with XNOR / XOR with more than 2 inputs - what does it really mean? – Majenko Mar 15 '15 at 12:06
I was confused, so I went looking for clarification and found [this.](http://www.nxp.com/documents/data_sheet/74LVC1G386.pdf) They use =1 also, but their truth table shows that when A is low, B,C, and Y make an XOR, but when A is high, B,C, and Y make an XNOR, so that: "one and only one input High" rule doesn't seem to be hard and fast. :) – EM Fields Mar 15 '15 at 12:39
We had a big long discussion about it all here not so long back: http://electronics.stackexchange.com/questions/93713/how-is-an-xor-with-more-than-2-inputs-supposed-to-work/93720#93720 – Majenko Mar 15 '15 at 12:40

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