ABSTRACT
Bistable circuits exhibit two stable states representing logic one and logic zero. These include latches and flip-flops,1-4 which are useful in a number of applications that require the temporary retention of one or more bits. Some examples are counters, shift registers, and memories. Bistable circuits can also perform signal shaping functions, e.g., the Schmitt trigger, which exhibits hysteresis and is useful in this regard.5,6
The two requirements for realization of bistable operation are amplification (gain greater than unity) and positive feedback. A circuit meeting these requirements can be built using two cross-coupled inverters, as shown in Figure 15.1. There are two stable states for this circuit: state 0 is characterized by Q = 0 and
— Q = 1 and state 1 is characterized by Q = 1 and
— Q = 0. Either
state is stable and will be maintained as long as the system power is on; therefore, this circuit can retain 1 bit of information.
