No 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.

Abstract:The importance of energy-constrained processors continues to grow especially for ultra-portable sensor-based platforms for the Internet-of-Things (IoT). Processors for these IoT applications primarily operate at near-threshold (NT) voltages and have multiple power modes. Achieving high conversion efficiency within the DC-DC converter that supplies these processors is critical since energy consumption of the DC-DC/processor system is proportional to the DC-DC converter efficiency. The DC-DC converter must maintain high efficiency over a large load range generated from the multiple power modes of the processor. This paper presents a fully integrated step-down self-oscillating switched-capacitor DC-DC converter that is capable of meeting these challenges. The area of the converter is 0.0104 mm 2 and is designed in 28 nm ultra-thin body and buried oxide fully-depleted SOI (UTBB FD-SOI). Back-gate biasing within FD-SOI is utilized to increase the load power range of the converter. With an input of 1 V and output of 460 mV, measurements of the converter show a minimum efficiency of 75% for 79 nW to 200 µW loads. Measurements with an off-chip NT processor load show efficiency up to 86%. The converter's large load power range and high efficiency make it an excellent fit for energy-constrained processors.

Timing error detection (TED) microprocessors are able to eliminate large timing margins by operating up to a voltage-frequency point in which intermittent errors occur. The detection of these errors requires an error-detection sequential (EDS) circuit. This paper presents the measurements of an EDS circuit called TEDsc. Using subthreshold source-coupled logic, TEDsc is able to dynamically adapt to system-level requirements. Measurements of TEDsc are presented in terms of a new system level TED definition. TEDsc is implemented in 65 nm CMOS, has an area of 97.5 J.lm 2 , and consumes 79 pW (Vdd=250 mY). TEDsc operates at a clock period (Tc LK) of 150 F04 at Vdd=400 m V with a sufficiently large detection window. By decreasing the size of the detection window, TEDsc can operate to at least TCLK=50 F04.

No abstract