[DFP] what is Isolation Cells?

so , what is Isolation cells?
how it works?
and where is to use it ?

is there any paper i can refer?
thx.

Isolation cells are used to isolate the outputs at the output of the power domain. Power domain is a block in a design that can be switched off when it is not required.

When a specific block is switched off, the outputs of the block will have X, if this value is propagated to switched on blocks, then it may lead to undesired behavior or chip failure. To avoid this, isolation cells be used to isolate the switched off block outputs. For example, for an AND gate, if you propagate this X value and if you make the other input of the AND gate to 0, then you will get known values at the power domain output, in the same way, if 1 is specified at other input of OR gate, then also we can get known values at the power domain outputs.

In some cases, they will be used at the power domain inputs due to multiple reasons.

This is very basic in power aware designs, just google it you will find lot of information..

Isolation cells are more important than for just preventing unknown values propagating into a block of logic. They are needed to prevent floating inputs, which for some cells can result in VDD and VSS being shorted. (e.g. consider an floating input to a inverter).

HI,

Isolation cells are special cells required at the interface between blocks which are shut-down and always on. They clamp the output node to a known voltage. These cells needs to be placed in an 'always on' region only and the enable signal of the isolation cell needs to be 'always_on'. In a nut-shell, an isolation cell is necessary to isolate floating inputs.
There are 2 types of isolation cells (a) Retain "0″ (b) Retain "1″

It may help you.

Thanks.

HAK.