SOP Vs POS

Many of you aspiring electronics engineers might be wondering ‘Why do we prefer SOP over POS when it comes to designing a digital circuit?’.

Let me share the real reason behind it and explain.

The real reason is we prefer NAND based chips over NOR based chips, as the NAND gate consumes less space[chip area during fabrication] than NOR gate though they both demand equal number of CMOS transistors.

We always want to design the chips that consume less area and operate at high speed and therefore we prefer NAND based chips. So, obviously we prefer SOP – Sum Of Products, as it’s the straight forward design approach to design the digital circuit using NAND gate.

We prefer only universal logic gates NAND and NOR primarily to design any circuit and create the chip.

Generally, we prefer SOP to design the digital circuits using NAND gate and POS – Product Of Sums to design the digital circuit using NOR gate. If we want to use any legacy NOR circuit as part of the NAND chips, then we may convert them into NAND circuit through POS to SOP conversion and vice-versa.

Also, generally we use SOP to design the circuit for the functionality [Truth Table] which is defined using positive logic and POS to design the circuit for the functionality [Truth Table] which is defined using negative logic. This is the reason we have two options SOP & POS to design the digital circuits.

Most of the textbooks explain the concepts like SOP & POS separately but they don’t explain why we prefer SOP over POS. I have explained such concepts in detail with real time examples in our online VLSI DM course

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