Difference between N/P –select and n/p - active layers in CMOS layout techniques

[VINAY_RAO]

Hi,
What is the significance of using n/p select layers along with n/p active layers to make a CMOS active device? Why we need to draw extra n/p select layers though we can distinguish P and N regions just by using P/N active regions?



Regards,
Vinay Rao.