Tuyet Nguyen

A 32-bit PowerPC system-on-a-chip with support for dynamic voltage scaling and dynamic frequency scaling

A PowerPC system-on-a-chip processor which makes use of dynamic voltage scaling and on-the-fly frequency scaling to adapt to the dynamically changing performance demands and power consumption constraints of high-content, battery powered applications is described. The PowerPC core and caches achieve frequencies as high as 380 MHz at a supply of 1.8 V and active power consumption as low as 53 mW at a supply of 1.0 V. The system executes up to 500 MIPS and can achieve standby power as low as 54 /spl mu/W. Logic supply changes as fast as 10 mV//spl mu/s are supported. A low-voltage PLL supplied by an on-chip regulator, which isolates the clock generator from the variable logic supply, allows the SOC to operate continuously while the logic supply voltage is modified. Hardware accelerators for speech recognition, instruction-stream decompression and cryptography are included in the SOC. The SOC occupies 36 mm/sup 2/ in a 0.18 /spl mu/m, 1.8 V nominal supply, bulk CMOS process.

A Distributed Critical-Path Timing Monitor for a 65nm High-Performance Microprocessor

A distributed critical-path timing monitor (CPM) is designed as part of the POWER6trade microprocessor in 65nm SOI. The CPM is capable of monitoring timing margin, process variation, localized noise and VDD droop, or clock stability. It tracks critical-path delay to within 3 FO2 delays at extreme operating voltages with a standard deviation less than frac12 an FO2 delay. The CPM detects DC VDD droops greater than 10mV and tracks timing changes greater than 1 FO2 delay.

Resonant clocking using distributed parasitic capacitance

A resonant-clock generation and distribution scheme that uses the inherent, parasitic capacitance of the clocked logic as a lumped capacitor in a negative-resistance oscillator is described. Clock energy is resonated between inductors and the parasitic, local clock network to save power over traditional clocking methodologies. Theory predicts that the data passing though the clocked logic will change the clock frequency by less than 1.25%. A resonant clock test chip was designed and fabricated in an IBM 0.13-/spl mu/m partially depleted SOI process. Although the test chip was designed to operate in the gigahertz range using integrated inductors, startup difficulties required the addition of external inductance to reduce the resonant frequency so that the effects of the parasitic capacitance could be measured. The parasitic capacitance is approximately 40 pF per clock phase, resulting in a clock frequency between 106 and 146 MHz, depending on biasing. At its most efficient bias point, the clock dissipated 2.09 mW, which is approximately 35% less power than a conventional, buffer-driven clock. The maximum period jitter measured in the resonant clock due to changing data in the clocked latches was 55 ps at 124 MHz, or 0.68% of the clock period.

A 0.9 V to 1.95 V dynamic voltage-scalable and frequency-scalable 32 b PowerPC processor

A 32 b PowerPC/spl trade/ system-on-a-chip supporting dynamic voltage supply and dynamic frequency scaling operates from 366 MHz at 1.8 V and 600 mW down to 150 MHz at 1.0 V and 53 mW in a 0.18 /spl mu/m CMOS process. Maximum supply change without PLL relock is 10 mV//spl mu/s. Processor state save/restore enables a deep-sleep state.

A double precision floating point multiply

A 2.2GHz 53/spl times/54 bit pipelined multiplier is fabricated in 130nm CMOS technology with an area of 0.15mm/sup 2/. The circuit implementation results in a 50% size reduction over the previously reported values. The circuit operates at 2.2GHz and uses 522mW at 80% switching factor, 1.2V supply and 25/spl deg/C.

An 8GHz floating-point multiply

The implementation of the mantissa portion of a floating-point multiply (54/spl times/54b) is described. The 0.124mm/sup 2/ multiplier is implemented using limited switch dynamic logic and operates at speeds up to 8GHz in a 90nm SOI technology. The multiplier dissipates between 150mW and 1.8W as it scales between 2GHz and 8GHz.

On-chip jitter and oscilloscope circuits using an asynchronous sample clock

We demonstrate digital circuits for measuring the jitter histograms of gigahertz clock and data signals. The circuits do not require calibration, and an asynchronous sampling technique alleviates the need for an on-chip sample clock generator with delay control. We combine measurements across swept reference voltages to create statistical clock signal and eye diagram waveforms at 6GHz and 5Gbit/s, respectively. The proposed technique produced RMS jitter measurements of 2.0ps on clock signals and 6.2ps on random data signals.

Design Considerations for PD/SOI SRAM: Impact of Gate Leakage and Threshold Voltage Variation

We present a critical study of the impact of gate tunneling currents on the yield of 65-nm partially depleted/silicon-on-insulator (PD/SOI) SRAM designs. A new gate leakage monitor structure is developed to obtain device-specific gate leakage characteristics of the SRAM cells. This allows us to explore the design space accurately with reliable process information at an early stage. By relying on supply voltage-dependent analysis, it is shown that the gate-leakage impact on the cell yield can be nonmonotonic and substantial even for nondefective devices. It is also shown that design optimizations such as increased operating voltages or shorter hierarchical bitline architecture can help alleviate the gate-leakage impact on yield. Mixture importance sampling is used to estimate yield in terms of cell writability and stability. Threshold voltage variations to model random fluctuation effects are extrapolated from hardware results.

Digital-phase aligner macro for clock tree compensation with 70 ps jitter

This paper describes a digital phase aligner (DPA) that can be used to decrease the chip-to-chip clock skew caused by process and temperature variations of the on-chip clock trees in a multiple-chip synchronous system with multiple clock domains. This method adjusts the delay of a variable-delay line to align an output of the clock tree to the clock input of a chip. Delay is added to make the clock tree latency an integral number of cycles. The goal was to design a delay-locked loop over a 8-25 ns cycle time with low jitter, allow multiple uses per ASIC, have the ability to start and stop the external clock without a long period of initialization and be fully testable by level-sensitive scan design (LSSD).

An on-chip dual supply charge pump system for 45nm PD SOI eDRAM

We present an on-chip word line (WL) dual supply system for server class embedded DRAM (eDRAM) applications. The design consists of switched capacitor charge pumps, voltage regulators, reference and clock circuits. Charge pump engines feature efficient charge transfer and energy conversion, boosting unregulated rails to 1.8x supply. At vdd=1 V, regulated high (1.5 to 1.7 V) and low (-0.3 to -0.6 V) levels ensure WL overdrive and cell turn-off, respectively, with rippling <plusmn35 mV and maintenance power <780 muW/2Mb-DRAM. The system supports >2 GHz AC array access and can endure excessive DC load.