The feedback solution is simple, straightforward and inexpensive. To provide the necessary hysteresis behavior, the result value is fed back with a weight of one less than the threshold as shown in Figure 10. The rounded gate symbol will represent a gate with the hysteresis behavior. This hysteresis behavior may be provided by feedback internal to the gate or by some inherent behavior of the gate implementation approach.

Figure 10. Threshold gate with weighted feedback of threshold -1.

Beginning in a NULL state with all inputs NULL and asserting a NULL result value, the gate will not assert a DATA result value until its input data set is complete, which in this case is four DATAs. With the feedback weight of three, the gate will not transition to a NULL result value until all of its input values are NULL. As long as at least one input value remains DATA, the gate meets its threshold and will continue asserting a DATA result value. It does not fall below its threshold and transition to NULL output until all inputs are NULL. This behavior is shown in Figure 11.

Figure 11. Hysteresis behavior of NULL Convention Logic gate.

The gate enforces the completeness of input criteria for both data in relation to NULL and for NULL in relation to DATA. A threshold 1 gate does not require the feedback connection because its completeness of input criteria is inherently enforced for both DATA and NULL.