As the demand of safety-critical applications (e.g., automobile electronics) increases, various radiation-hardened flip-flops are proposed for enhancing design reliability. Among all flip-flops, Delay-Adjustable D-Flip-Flop (DAD-FF) is specialized in arbitrarily adjusting delay in the design to tolerate soft errors induced by different energy levels. However, due to a lack of testability on DAD-FF, its soft-error tolerability is not yet verified, leading to uncertain design reliability. Therefore, this work proposes Delay-Adjustable, Self-Testable Flip-Flop (DAST-FF), built on top of DAD-FF with two extra MUXs (one for scan test and the other for latching-delay verification) to achieve both soft-error tolerability and testability. Meanwhile, a built-in self-test method is also developed on DAST-FFs to verify the cumulative latching delay before operation. The experimental result shows that for a design with 8,802 DAST-FFs, the built-in self-test method only takes 946 ns to ensure the soft-error tolerability. As to the testability, the enhanced scan capability can be enabled by inserting one extra transmission gate into DAST-FF with only 4.5 area overhead.
