PUB - Publikationen an der Universität Bielefeld

The demand of low power consumption in microelectronics circuits has increased significantly as submicron technologies scale down. Battery operated portable applications are in high demand across the industries such as automotive, medical, MEMS, telecommunication and so on. Subthreshold operations provides the potential solution to the energy consumption problem. However, it comes at the price of significant degradation of performance. Since, it needs to reduce the maximum operating clock frequency in subthreshold operation. An effective solution proposed to such problem was to have different voltage islands. Here, the non-critical power constrained blocks could run in subthreshold domain with the critical ones operating in above threshold domain. Our work proposes a solution to combat such a problem. Our work consists of three parts; 1) a standard cell library optimized for subthreshold operation, 2) couple of level shifter circuits capable of sub-threshold to above threshold voltage conversion and 3) a subthreshold memory array. We have used the 28nm FD-SOI technology from ST Microelectronics. The standard cell library contains basic design cell units, whose dimensions are optimized for subthreshold operation at a low fixed frequency. The optimization process is based upon a multiobjective optimization methodology. Propagation delay, switching power, static power dissipation and, noise margin are the parameters, chosen for multiobjective optimization. We generated separate sets of dimensions for each cells due to the optimization algorithm, which helped us to design the parametric cell (p-cell). We used the p-cell approach as it helps to standardize the cell design reducing the development time. The library is ready for the synthesis of low power blocks. The library is developed with two different variants of transistors, namely RVT and LVT. They have different threshold voltages. The RVT library has 21 combinatorial logic cells, 4 sequential logic cells and 11 clock circuits. The LVT library has only combinatorial cells. We designed two different level shifter circuits, which are performance optimized with the library cells in terms of voltage and frequency. The leakage current loss was kept in mind while doing the design. We have followed the circuit mirror topology for one of the circuits. This circuit can operate convert an input of 250mV to 1V output. The leakage power of this circuit is 37pW. The second level shifter circuit is a combination of both circuit mirror and cross-coupled PMOS topologies. This particular circuit can operate even at 150mV supply, with the leakage power being 107pW. Memory circuits consume a lot of energy. Although it is difficult to reduce the operating voltage of memory cells, without diminishing the performance. Here, we proposed a 4x8 SRAM array, which can operate with a minimum supply of 250mV and a maximum frequency of 3.3 MHz. During the read operation, the energy consumption of the memory cell is 0.107 fJ at 3.33MHZ.