Z-Voter: a novel high-impedance voter for efficient realization of tristate logic in quantum-dot cellular automata technology

Regardless of the technology, the tristate logic is a crucial concept which facilitate bidirectional shared media access as an essential requirement for development of large-scale systems. Moreover, the tristate circuits significantly contribute to some advanced design topics such as wired logic and construction of basic components. Lack of a straightforward realization for the tristate logic is still a challenge in efficient development of some advanced topics such as shared media, and memory and I/O access mechanism in Quantum-dot Cellular Automata, as a tentative replacement candidate of the digital technology. A two-input tristate voter named as Z-Voter is introduced in this paper whose output is equal to both inputs in case of identical inputs. In case of different inputs, however, it does not enforce a strict ‘0’ or ‘1’ value on its output which resembles a high-impedance state. To demonstrate the Z-Voter correct functionality and applicability, it is utilized to propose a novel stand-alone efficient tristate buffer. Its main advantage with respect to other previous rivals is that it operates just similar to other conventional Quantum-dot Cellular Automata gates and does not rely on a special clocking mechanism. This simplifies its utilization for implementing larger systems. To demonstrate its correct operation as well as simple utilization, the introduced tristate buffer is exploited to implement a simple yet scalable shared media access control scheme. The simulation results of the proposed scheme with two and three simultaneously connected drivers are presented in the paper to demonstrate its scalability. The proposed Z-Voter and tristate buffer are very compact and composed of 4 and 29 cells, respectively. Convenient kink energy proofs, as well as QCADesigner-E tool simulation results, prove the correct functionality and applicability of the proposed gates and circuits. The power analysis results of the circuits are also extracted using QCAPro.