Advance Lowe Power Design [ Multi Power Domain with Switchable Domain] - 2

Low Power Technique 

• In this Case, we need Isolation Cells with Level Shifter for desired clamp value to avoid X state of net between switchable and always on domain.

 Below Pic valid ,when Switchable Domain and Always On Domain have save supply. In this case level Shifter is not required. 

• Even Isolation cells can be placed any domain, but preferable ISO Cells should be placed in Always On domain. In case placing in switchable domain , we need to have always on Power Grids in the domain and ISO  Cells should have Backup supply pins to connect Always On Power Net.                                                                                                                                        
• So We can have two types of Isolation cells depending upon placement location i.e.  Input Isolation & Output ISOLATION.   
• Input Isolation when placed in Power Gated domain  i.e. Switchable Domain.
• Output Isolation when placed in Destination Domain i.e. Always On Domain.
• Some of Output will have more than one destination domain i.e. multi fan-out . For these output signals more than one Output Isolation would be required, but in case of Input Isolation only one Output Signal would be required.  So to be more area efficient , Isolation Signal should be placed in source domain.
• On Input of Switchable blocks, no Isolation cells are required.

When Swichable Domain and Always on Domain works at different voltages , we need to have Level Shifter with Isolation Cells.