power domain 与 voltage area的区别

另外，烦请大家解释下always-on cell，谢谢

另外，烦请大家解释下alway-on cell，谢谢

必须先定义power domain，才有voltage area，
voltage area更偏重物理位置和区域，power domain则先有这个概念才对，

power domain is logical constrain, and voltage area is physical constrain. Each domain need have one area specified.
always-on cell, usually in power-gated design, is relative to the std cell which can be shut down. the rail should be different