POWER

What are the types of power ?

Static

Dynamic

What is IR drop?

The drop in supply voltage we refer it as IR drop and required voltage is not reached to the standard cells.

How can we overcome the IR drop?

By placing the macros towards the boundary

By spreading the standard cells

By increasing the width of power stripes

By increasing the no of power stripes

What is electromigration ?

When constant amount of current is flowing through a wire and if that exceeds the current density capacity of that particular wire. than movement of atom occurs. Which leads to either shorts or opens in the wires. This effect is called electromigration.

How can we overcome the electromigration?

By increasing the width of the power stripes and by reducing the input transition.

For power planning why we use higher layer metals ?

As in higher layers thickness and width of the metals is large, it exhibits less resistance so it results in less IR drop.

What are the power reduction techniques ?

Clock gating

operand isolation

Multi vdd

Multi VT

What is clock gating ?

Clock signal is the highest switching signal in the entire design. Depending on the enable signals clock signal is feed to the sequential cells. So the technique through which the required clock pulses are feed to the sequential circuits is called clock gating.

What is ICG ?

ICG is an integrated clock gating cell which is an active low latch followed by an AND gate.

What is operand isolation?

Operand isolation technique is used in combinational circuits. Let us consider there is a 2:1 mux which is getting inputs from the 2 separate adders and it will give the output based on only one adder. As adders consists of lot of xor gates which exhibits more switching actions, they are very power hungry. So it leads to huge power consumption. So need to design it in such a way that at a time only one adder is processing. This technique we call it as operand isolation.

Which is less leaky among standard VT and high VT and why ?

High VT cells are less leaky. Let us consider in SVT threshold voltage is 1v and in HVT threshold voltage is 1.3v. Suppose 1000 electrons are there in the channel  before the device is getting on. So for SVT at 1v 1000 electrons are there and for HVT at 1.3v 1000 electrons are there, that means for HVT at 1v case less than 1000 electrons are present.
SVT : 1v : 1000 electrons

HVT : 1V : < 1000 electrons

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So less current flows in HVT so it is less leaky.