For a globally asynchronous locally synchronous (GALS) system, data transfer mechanisms based on a current-mode multiple valued logic (CMMVL) has been studied to reduce complexity and power dissipation of wires. However, these schemes consume considerable amount of power even in idle states because of the static power caused by their inherent structure. In this paper, new encoder and decoder circuits using CMMVL are suggested to reduce the static power. The effectiveness of the proposed data transfer is validated by comparisons with the previous CMMVL scheme and conventional voltage-mode schemes such as dual-rail and 1-of-4 encodings through simulation with a 0.25-µm CMOS technology. Simulation results demonstrate that the proposed CMMVL scheme significantly reduces power consumption of the previous one and is superior to dual-rail and 1-of-4 schemes over wire length of 2 mm and 4 mm, respectively.

Conventional delay-insensitive (DI) data encodings require 2N+1 wires for transferring N-bit. To reduce complexity and power dissipation of wires in designing a large scaled chip, a DI data transfer mechanism based on current-mode multiple valued logic (CMMVL), where N-bit data transfer can be performed with only N+1 wires, is proposed. The effectiveness of the proposed data transfer mechanism is validated by comparisons with conventional data transfer mechanisms using dual-rail and 1-of-4 encodings through simulation at the 0.25-µm CMOS technology. Simulation results with wire lengths of 4 mm or larger demonstrate that the CMMVL scheme significantly reduces delay-power product values of the dual-rail encoding with data rate of 5 MHz or more and the 1-of-4 encoding with data rate of 18 MHz or more.

New functional surface tunnel transistors (STTs) with multiple interband-tunnel-junctions in a symmetric source-to-drain structure are proposed to reduce the number of fabrication steps and to increase functionality. These devices have p+/n+ interband tunnel junctions in series between a p+ source and a p+ drain through n+ channels. We successfully fabricated GaAs-based multiple-junction STTs (MJ-STTs) using molecular-beam epitaxy regrowth. This fabrication method eliminates the need for two of the photo-masks in the conventional process for asymmetric planar STTs. In the preliminary experiments using multiple-junction p+/n+ diodes, we found that the peak-voltage increment in negative-differential-resistance (NDR) characteristics due to the reverse-biased tunnel junction in negligible, while the first-peak voltage is roughly proportional to the number of forward-biased tunnel junctions. Moreover, the number of NDR characteristics are completely determined by the number of tunnel junctions. The fabricated STTs with multiple junctions, up to eight junctions, exhibited clear transistor operation with multiple NDR characteristics, which were symmetric with the drain bias. These results indicate that any number of gate-controlled NDR characteristics can be realized in MJ-STTs by using an appropriate number of tunnel junctions in series. In addition, as an example of a functional circuit using MJ-STTs, we implemented a tri-stable circuit with a four-junction STT and a load resistor connected in series. The tri-stable operation was confirmed by applying a combination of a reset pulse and a set pulse for each stable point.