NMOS flip-flop sensors: a multipurpose digital-output sensor technique

With the current trend toward digital signal processing, a sensor with a digital output has clear advantages over the conventional analogue types. The paper presents a solution using a flip-flop as a sensing element. The sensor operates by bringing a flip-flop into the unstable state, over a large number of cycles. Any imbalance in the system, introduced by the parameter to be measured, will change the probability of a ´one´ or a ´zero´ and thus the ratio of ´ones´ to ´zeros´ over a large number of cycles. Because of the unstable state, this system is highly sensitive to small perturbations. Although both bipolar and NMOS flip-flop sensors have been successfully fabricated, the paper concentrates on NMOS structures.