Testing of Differential Cascode Voltage Switch One-Count Generators

- Clocked differential cascode voltage switch (DCVS) circuits are dynamic CMOS circuits which can implement both inverting and noninverting functions. They have protection against test-set invalidation due to timing skews at the inputs and circuit delays as well as due to charge distribution. We consider the problem of detecting stuck-at, stuck-open, and stuck-on faults in DCVS implementations of one-count generators. A one-count generator counts the number of one's in its inputs. It is made up of full adders and half-adders. If the number of inputs to the one-count generator is n, then the number of outputs k is given by [log₂(n + 1)]. For a maximal DCVS one-count generator, for which n = 2^k - 1, we show that the size of the test set is only four. For a nonmaximal DCVS one-count generator, for which n ≠ 2^k -1, the upper bound on the size of the test set is 5(k - 1), in other words, the size is O(log₂n). For a DCVS ripple-carry adder, which forms a part of the DCVS one-count generator, the test-set size is four.