This question might seem very basic, but it will help me a lot if someone can answer it from the basics!
I have just finished my first year at college and there was a course on digital design, where we studied the fundamentals of digital systems and also implemented various circuits using ICs in the lab.
When we saw the IC in class, we just focussed on the circuit inside the IC – how everything is connected and what logic gates/ FFs are used. But while implementing circuits in lab, I saw that there were 2 power pins also, on each IC.
Why do they need power pins? Like, all that is present in the IC is a few logic gates (even FFs are logic gates at a very fundamental level) right? Logic gates do not require power when we have to use them right?
Best Answer
simulate this circuit – Schematic created using CircuitLab
Figure 1. Equivalent circuit for the simplified output stage of a CMOS logic gate. As shown in the switch version the output is pulled high. All the other transistors in the gate will also require power connections.
They need power pins because the digital logic needs to supply power from the positive rail to create a logic 1 or sink power to the ground rail to create a logic zero.
Without power connections there could be no pull high or pull low. Logic gates do not source or sink electrical current from nowhere. It has to come from and return to the supply.