Timing-Error Detection Design Considerations in Subthreshold: An 8-bit Microprocessor in 65 nm CMOS

Abstract

This paper presents the first known timing-error detection (TED) microprocessor able to operate in subthreshold. Since the minimum energy point (MEP) of static CMOS logic is in subthreshold, there is a strong motivation to design ultra-low-power systems that can operate in this region. However, exponential dependencies in subthreshold, require systems with either excessively large safety margins or that utilize adaptive techniques. Typically, these techniques include replica paths, sensors, or TED. Each of these methods adds system complexity, area, and energy overhead. As a run-time technique, TED is the only method that accounts for both local and global variations. The microprocessor presented in this paper utilizes adaptable error-detection sequential (EDS) circuits that can adjust to process and environmental variations. The results demonstrate the feasibility of the microprocessor, as well as energy savings up to 28%, when using the TED method in subthreshold. The microprocessor is an 8-bit core, which is compatible with a commercial microcontroller. The microprocessor is fabricated in 65 nm CMOS, uses as low as 4.35 pJ/instruction, occupies an area of 50,000 μm 2 , and operates down to 300 mV.

Implementing Minimum-Energy-Point Systems With Adaptive Logic

“…In [11], this requires two extra pipeline stages. TED has also been proven to work in subthreshold [12], where a 28% reduction in energy was achieved for an 8-bit microprocessor. …”

Ultra-Low-Voltage Design of Energy-Efficient Digital Circuits

“…Body biasing has been extensively used to compensate for variations after manufacturing of sub-and near-threshold designs, e.g. in [10,12,14,18,21,44]. However, as shown in Sect.…”

Variation-Resilient Building Blocks for Ultra-Low-Energy Sub-Threshold Design

“…Therefore, this is not the optimal manner of coping with the increased variations. Recently, [4] has also proposed an alternative method that utilizes timing error-detection circuits in sub-threshold to account for both local and global variations. Both issues can be overcome by careful circuit design, resulting in building blocks for a robust sub-threshold system.…”