Re: What's the difference between dummy cell & spare cel
according to my understandings, dummy cell and spare cell apply in different world. The former applies often in analog circuit design world, while the later in digital world.
Normally, spare cells are actually standard cells that are put in the spare areas here and there in a single die. They are used when minor modification of chip is needed. For example, if you want to inverse one signal after chip tape out, and there happens to be a inverter spare cell, then you can simply reconnect the metal layers to get the expected result. No modifications of substrate layers are needed, which could save a lot of money and time.
As for dummy cell, for me, it is rather an analog layout technique. You simply duplicate the devices near the one of the concern. You are doing this for the reason of symmetry. You never gonna activated them. That's why they are called "dummy".
Regards
ceyjey