Signature Analysis :
Data compression techniques are mainly used in built in self tests systems and consist of making comparisons on compacted test responses. The test compacting scheme currently used most is called signature analysis. In Signature analysis polynomial division of the device under test has been carried out. Here, the data is represented like a polynomial and is divided by the characteristic polynomial. The signature from the device under test is compared with the expected signature to determine if device under test is fault free. The differences between the faulty signature and good signature may also be used to indicate the nature of fault. Signature analysis has been proved to be a reliable and attractive alternative to full compacted testing. Another technique of data compression-transition counting-has been in use for some considerable time. These consist of counting transitions of a specified direction (0 to 1 or 1 to 0) and then comparing this count with the count obtained from the simulation model.