Role of Test Chips
Test chips usually goes before real product to collect the following data:
1. Characterization of key devices, for choosing the right circuit structure.
2. failure density, for redundancy and architecture design reference.
3. to test new ideas of circuit implementation for certain function.
4. to understand device performance distribution, whihc is especially important for memory circuit design.
5. to understand the reliability of cells, see how they degrade with cycling, high temperature and etc.
to design a new test chip, we normally use interpolated model parameters learned from past few generations ( say gm reduced 20% for every generation, and etc). and leave a lot of options to adjust reference voltages, current sources and decide the right value through silicon, not simulation.