Patent ID: 8060324

Claim:
A method for estimating parameter variations of transistors that belong to a first circuit, the method comprises: providing the first circuit; providing a test circuit adapted to perform a first function and a stacked test circuit adapted to perform a second function that substantially equals the first function wherein the first circuit, the test circuit, and the stacked test circuit are different circuits; wherein the test circuit, the stacked test circuit and the first circuit are processed under substantially the same processing conditions; determining a relationship between a parameter of the test circuit and a parameter of the stacked test circuit, wherein the parameter of the test circuit is a same type of parameter as the parameter of the stacked test circuit; and estimating parameter variations of transistors that belong to the first circuit in response to the determined relationship; wherein the determining comprises searching for a supply voltage range that when supplied to the first circuit will result in parameter variation difference level that does not exceed an acceptable parameter variation difference.