I2L Selector Circuit
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-05
Selector circuits are used in many logic applications. The selector function may be expressed as follows: S = CA + CB where A is selected when C is down, and B is selected when C is up. In conventional implementations, two to three stages of logic gates are used. In some logic families, special circuits have been proposed and used to realize this function in one stage. Fig. 1 is an I2L selector circuit implementation. In Fig. 2, input C serves as the variable circuit bias and provides the select function. Fig. 3 is a hazard-free selector circuit. In both Figs. 1 and 2, logic hazard may occur if A=1, B=1, C=0 and C is rising to 1, or C=1 and falling to 0. The hazard is eliminated by employing the circuit of Fig. 3. In Figs. 2 and 3, multiple fanouts of the control signal C are also possible.