Visvesh S. Sathe

A 32nm fully integrated reconfigurable switched-capacitor DC-DC converter delivering 0.55W/mm 2 at 81% efficiency

With the rising integration levels used to increase digital processing performance, there is a clear need for multiple independent on-chip supplies in order to support per-IP or block power management. Simply adding multiple off-chip DCDC converters is not only difficult due to supply impedance concerns, but also adds cost to the platform by increasing motherboard size and package complexity. There is therefore a strong motivation to integrate voltage conversion blocks on the silicon chip.

Energy-Efficient GHz-Class Charge-Recovery Logic

In this paper, we present Boost Logic, a charge- recovery circuit family that can operate efficiently at clock frequencies in excess of 1 GHz. To achieve high energy efficiency, Boost Logic relies on a combination of aggressive voltage scaling, gate overdrive, and charge-recovery techniques. In post-layout simulations of 16-bit multipliers with a 0.13-mum CMOS process at 1GHz, a Boost Logic implementation achieves 5 times higher energy efficiency than its minimum-energy pipelined, voltage-scaled, static CMOS counterpart at the expense of 3 times longer latency. In a fully integrated test chip implemented using a 0.13-mum bulk silicon process and on-chip inductors, chains of Boost Logic gates operate at clock frequencies up to 1.3 GHz with a 1.5-V supply. When resonating at 850 MHz with a 1.2-V supply, the Boost Logic test chip achieves 60% charge-recovery

Resonant clock design for a power-efficient high-volume x86–64 microprocessor

AMDs 32-nm x86-64 core code-named “Piledriver” features a resonant global clock distribution to reduce clock distribution power while maintaining a low clock skew. To support a wide range of operating frequencies expected of the core, the global clock system operates in two modes: a resonant-clock (rclk) mode for energy-efficient operation over a desired frequency range and a conventional, direct-drive mode (cclk) to support low-frequency operation. This dual-mode feature was implemented with minimal area impact to achieve both reduced average power dissipation and improved power-constrained performance. In Piledriver, resonant clocking achieves a peak 25% global clock power reduction at 75 °C, which translates to a 4.5% reduction in average application core power.

A 225 MHz resonant clocked ASIC chip

We have recently designed, fabricated, and successfully tested an experimental chip that validates a novel method for reducing clock dissipation through energy recovery. Our approach includes a single-phase sinusoidal clock signal, an L-C resonant sinusoidal clock generator, and an energy recovering flip-flop. Our chip comprises a dual-mode ASIC with two independent clock systems, one conventional and one energy recovering, and was fabricated in a micron bulk CMOS process. The ASIC computes a pipelined discrete wavelet transform with self-test and contains over 3500 gates. We have verified correct functionality and obtained power measurements in both modes of operation for frequencies up to 225MHz. In the energy recovering mode, our power measurements account for all of the dissipation factors, including the operation of the integrated resonant clock generator, and show a net energy savings over the conventional mode of operation. For example, at 115MHz, measured dissipation is between 60% and 75% of the conventional mode, depending on primary input activity. To our knowledge, this is the first ever published account of a direct experimentally-measured comparison between a complete energy recovering ASIC chip and its conventional implementation correctly operating in silicon at frequencies exceeding 100MHz.

A 1.1ghz charge-recovery logic

A GHz-class dynamic charge-recovery logic is implemented with an on-chip clock generator and integrated inductor in a 0.13mum CMOS process. The chip operation is verified at clock frequencies up to 1.3GHz. At its natural frequency, the design recovers 60% of total circuit energy every cycle

900MHz to 1.2GHz Two-Phase Resonant Clock Network with Programmable Driver and Loading

A resonant clock network with programmable driver and loading is designed in a 0.13mum CMOS technology. The 2mm times 2mm distribution network has on-chip inductors and performs a forced oscillation at the rate of a reference clock programmable in the 900MHz to 1.2GHz range. Clock amplitude and energy efficiency trade-offs at and off resonance are explored with various driver configurations. Energy efficiency per cycle is 1.39 to 1.56 times greater than previous resonant distribution networks

Energy-Efficient Low-Latency 600 MHz FIR With High-Overdrive Charge-Recovery Logic

This paper presents a 14-tap 8-bit finite impulse response (FIR) test-chip that has been designed using a novel charge-recovery logic family, called Enhanced Boost Logic (EBL), to achieve high-speed and low-power operation. Compared to previous charge-recovery circuitry, EBL achieves increased gate overdrive, resulting in low latency overhead over static CMOS design. The EBL-based FIR has been designed with only 1.5 cycles of additional latency over its static CMOS counterpart, while consuming 21% less energy per cycle, based on post-layout simulations of the two designs. The test-chip has been fabricated in a 0.13 μ m CMOS process with a fully-integrated 3 nH inductor. Correct function has been validated in the 365-600 MHz range. At its resonant frequency of 466 MHz, the test-chip dissipates 39.1 mW with a 93.6 nW/MHz/Tap/InBit/CoeffBit figure of merit, recovering 45% of the energy supplied to it every cycle.

RF2: A 1GHz FIR Filter with Distributed Resonant Clock Generator

In this paper we present the design and experimental validation of RF2, a 1 GHz, two-phase resonant-clocked FIR filter test-chip with a distributed resonant clock generator and an on-chip inductor. RF2 is fabricated in a 0.13 mum CMOS process and dissipates 124mW at resonance, with clock power accounting for only 16% of overall power. Implemented using a fully ASIC design flow, RF2 achieves 84% clock-power efficiency over CV2f, the highest for any fully-integrated resonant-clocked chip. Resonating at 1.01 GHz, RF2 reports the highest operating frequency for a resonant-clocked datapath to date.

A charge-recovery 600MHz FIR filter with 1.5-cycle latency overhead

We present a 14-tap 8-bit FIR chip designed using a novel charge-recovery logic family with only 1.5 cycles of additional latency over the best possible static CMOS design. Fabricated in a 0.13µm CMOS process, the chip operates in the 365—600MHz range with a 3nH on-chip inductor. At its resonant frequency of 466MHz, it dissipates 39.1mW and recovers 45% of the energy supplied to it.

Energy-efficient hybrid stochastic-binary neural networks for near-sensor computing

Recent advances in neural networks (NNs) exhibit unprecedented success at transforming large, unstructured data streams into compact higher-level semantic information for tasks such as handwriting recognition, image classification, and speech recognition. Ideally, systems would employ near-sensor computation to execute these tasks at sensor endpoints to maximize data reduction and minimize data movement. However, near-sensor computing presents its own set of challenges such as operating power constraints, energy budgets, and communication bandwidth capacities. In this paper, we propose a stochastic-binary hybrid design which splits the computation between the stochastic and binary domains for near-sensor NN applications. In addition, our design uses a new stochastic adder and multiplier that are significantly more accurate than existing adders and multipliers. We also show that retraining the binary portion of the NN computation can compensate for precision losses introduced by shorter stochastic bit-streams, allowing faster run times at minimal accuracy losses. Our evaluation shows that our hybrid stochastic-binary design can achieve 9.8x energy efficiency savings, and application-level accuracies within 0.05% compared to conventional all-binary designs.