Reducing Scan Shift Power at RTL

Power consumption during scan-based test becomes a concern in nanometer technologies. Previous test power reduction techniques that insert additional logic in gate-level circuits may result in timing violations. In this paper, we show that the problem can be solved at the RTL instead so that the timing and area constraints will be handled automatically by synthesis tools. Using a signal probabilistic approach proposed previously, we identify power-sensitive scan cells at the prototyping gate level, and we map these cells to their corresponding signal/variable bits at the RT-level. Additional RTL code is added to freeze these power- sensitive bits in order to reduce scan shift power consumption. Experimental results on ITC99 benchmarks show that on average more than 22% power reduction can be achieved when we only freeze the top 1% of power-sensitive bits at RTL. The flow is more practical in terms of timing closure than doing the same at the gate-level.