A leakage reduction methodology for distributed MTCMOS

Multithreshold CMOS (MTCMOS) circuits reduce standby leakage power with low delay overhead. Most MTCMOS designs cut off the power to large blocks of logic using large sleep transistors. Locally distributing sleep devices has remained less popular even though it has several advantages described in this paper. However, locally placed sleep devices are only feasible if sneak leakage currents are prevented. This paper makes two contributions to leakage reduction. First, we examine the causes of sneak leakage paths and propose a design methodology that enables local insertion of sleep devices for sequential and combinational circuits. A set of design rules allows designers to prevent most sneak leakage paths. A fabricated 0.13-μm, dual V_T test chip employs our methodology to implement a low-power FPGA architecture with gate-level sleep FETs and over 8× measured standby current reduction. Second, we describe the implementation and benefits of local sleep regions in our design and examine the interfacing issues for this technique. Local sleep regions reduce leakage in unused circuit components at a local level while the surrounding circuits remain active. Measured results show that local sleep regions reduce leakage in active configurable logic blocks (CLBs) on our chip by up to 2.2× (measured) based on configuration.