Ming-Hsien Tu

A Single-Ended Disturb-Free 9T Subthreshold SRAM With Cross-Point Data-Aware Write Word-Line Structure, Negative Bit-Line, and Adaptive Read Operation Timing Tracing

This paper presents a novel single-ended disturb-free 9T subthreshold SRAM cell with cross-point data-aware Write word-line structure. The disturb-free feature facilitates bit-interleaving architecture, which can reduce multiple-bit upsets in a single word and enhance soft error immunity by employing Error Checking and Correction (ECC) technique. The proposed 9T SRAM cell is demonstrated by a 72 Kb SRAM macro with a Negative Bit-Line (NBL) Write-assist and an adaptive Read operation timing tracing circuit implemented in 65 nm low-leakage CMOS technology. Measured full Read and Write functionality is error free with VDD down to 0.35 V ( 0.15 V lower than the threshold voltage) with 229 KHz frequency and 4.05 μW power. Data is held down to 0.275 V with 2.29 μW Standby power. The minimum energy per operation is 4.5 pJ at 0.5 V. The 72 Kb SRAM macro has wide operation range from 1.2 V down to 0.35 V, with operating frequency of around 200 MHz for VDD around/above 1.0 V.

Single-Ended Subthreshold SRAM With Asymmetrical Write/Read-Assist

In this paper, asymmetrical Write-assist cell virtual ground biasing scheme and positive feedback sensing keeper schemes are proposed to improve the read static noise margin (RSNM), write margin (WM), and operation speed of a single-ended read/write 8 T SRAM cell. A 4 Kbit SRAM test chip is implemented in 90 nm CMOS technology. The test chip measurement results show that at 0.2 V VDD, an operation frequency of 6.0 MHz can be achieved with power consumption of 10.4 μW.

40 nm Bit-Interleaving 12T Subthreshold SRAM With Data-Aware Write-Assist

This paper presents a new bit-interleaving 12T subthreshold SRAM cell with Data-Aware Power-Cutoff (DAPC) Write-assist to improve the Write-ability to mitigate increased device variations at low supply voltage under deep sub-100 nm processes. The disturb-free feature facilitates the bit-interleaving architecture that can reduce multiple-bit errors in a single word and enhance soft error immunity by employing error checking and correction (ECC) techniques. The proposed 12T SRAM cell is demonstrated by a 4 kb SRAM macro implemented in 40 nm general purpose (40GP) CMOS technology. The test chip operates from typical VDD to 350 mV ( ~ 100 mV lower than the threshold voltage) with VDDMIN limited by Read operation. Data can be written successfully for VDD down to 300 mV. The measured maximum operation frequency is 11.5 MHz with total power consumption of 22 μW at 350 mV, 25 °C.

8T single-ended sub-threshold SRAM with cross-point data-aware write operation

This paper presents a new 8T SRAM cell with data-aware cross-point Write operation and series connected Read buffer for low power and low voltage operation. The cell features a shared footer device to control the VGND for cell pass-gate (Write) transistors and the Read buffer. The row-based VGND control and the column-based data-aware Write Word-Line form a cross-point Write structure, thus eliminating Write Half-Select Disturb to facilitate bit-interleaving architecture. Replica based timing tracking circuit is used to control the pulse width of Word-Line Enable (WLE) signal to overcome the large timing variation at low voltage and to reduce the Word-Line active power consumption. A 4Kbit SRAM test chip implemented in 90nm HVT CMOS technology operates at 120MHz at 0.6V and 6MHz at 0.38V with measured power consumption of 2.99uW at 6MHz, 0.38V.

A 40 nm 512 kb Cross-Point 8 T Pipeline SRAM With Binary Word-Line Boosting Control, Ripple Bit-Line and Adaptive Data-Aware Write-Assist

This paper presents a cross-point 512 kb 8 T pipeline static random-access memory (SRAM). The cross-point structure eliminates write half-select disturb to facilitate bit-interleaving architecture for enhanced soft error immunity. The design employs boosted word-line (WL) for improving both read performance and write-ability. A ripple bit-line (RiBL) structure provides 30%-44% read access performance improvement and 2 ×-3.5 × variation immunity at 0.7 V compared with the conventional hierarchical bit-line (HiBL) schemes. An adaptive data-aware write-assist (ADAWA) with VCS tracking is employed to further enhance the write-ability while ensuring adequate stability for half-selected cells on the selected bit-lines. An adaptive voltage detector (AVD) with binary boosting control is used to mitigating gate electric over-stress. The design is implemented in UMC 40 nm low-power (40LP) CMOS technology. The 512 kb test chip operates from 1.5 V to 0.65 V, with maximum operation frequency of 800 MHz@1.1 V and 200 MHz@0.65 V. The measured power consumption is 0.5 mW/MHz (active) and 4.4 mW (standby) at 1.1 V, and 0.107 mW/MHz (active) and 0.367 mW (standby) at 0.65 V.

A 0.33-V, 500-kHz, 3.94-

This paper presents an ultra-low-power 72-Kb 9T static random-access memory (SRAM) with a ripple bit-line (RPBL) structure and negative bit-line (NBL) write-assist. The RPBL scheme provides over 40% read access performance improvement for VDD below 0.4 V compared with the conventional hierarchical bit-line structure. A variation-tolerant ripple-initiated NBL write-assist scheme with the transient negative pulse coupled only into the single selected local bit-line segment is employed to enhance the NBL, boosting efficiency and reducing power consumption. The 331 × 385 μm2 72-Kb SRAM macro has been fabricated in UMC 40-nm low-power CMOS technology and was tested with full suites of SRAM compiler qualification patterns. Error-free full functionality without redundancy is achieved from 1.5 V down to 0.33 V. The measured maximum operation frequency is 220 MHz (500 kHz) at 1.1 V (0.33 V) and 25 °C. The measured total power consumption is 3.94 μW at 0.33 V, 500 kHz, and 25 °C .

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This paper presents a digital hearing aid chip designed for Mandarin user to enhance speech quality and intelligibility. The hearing aid consists of an 18 subbands analysis and synthesis filter bank, insertion gain stage, and three channels wide dynamic range control for the new Mandarin-specific auditory compensation algorithm. A noise reduction block based on multiband spectral subtraction and enhanced entropy voice activity detection is also included to enhance quality. We reduce the power consumption of these algorithms through algorithmic and architecture optimization. In addition, for the data storage requirement, a low power SRAM that can operate at 0.6V and below is developed. Moreover, several strategies such as multi-clock domain, bypass mode, and voltage scaling are also adopted for power reduction. The chip measurement shows that the hearing aid consumes 314uW at 0.6V.

40-nm 72-Kb 9T Subthreshold SRAM With Ripple Bit-Line Structure and Negative Bit-Line Write-Assist

This brief presents a two-port disturb-free 9T subthreshold static random access memory (SRAM) cell with independent single-ended read bitline and write bitline (WBL) and cross-point data-aware write structure to facilitate robust subthreshold operation and bit-interleaving architecture for enhanced soft error immunity. The design employs a variation-tolerant line-up write-assist scheme where the timing of areaefficient boosted write wordline and negative WBL are aligned and triggered/initiated by the same low-going global WBL to maximize the write-ability enhancement. A 72-kb test chip is implemented in United Microelectronics Corp. 40-nm low-power (40LP) CMOS. Full functionality is achieved for VDD ranging from 1.5 to 0.32 V without redundancy. The measured maximum operation frequency is 260 MHz (450 kHz) at 1.1 V (0.32 V) and 25 °C. At 0.325 V and 25 °C, the chip operates at 600 kHz with 5.78 μW total power and 4.69 μW leakage power, offering 2× frequency improvement compared with 300 kHz of our previous 72-kb 9T subthreshold SRAM design in the same 40LP technology. The energy efficiency (power/frequency/IO) at 0.325 V and 25 °C is 0.267 pJ/bit, a 23.7% improvement over the 0.350 pJ/bit of our previous design.

A low-power Mandarin-specific hearing aid chip

In this paper, asymmetrical Write-assist cell virtual ground biasing and positive feedback sensing keeper schemes are proposed to improve the Read Static Noise Margin (RSNM), Write Margin (WM), and operation speed of a single-ended Read/Write 8T SRAM cell. A 4Kbit SRAM implemented in 90nm CMOS technology achieves 1uW/bit average power consumption at 6MHz, Vmin of 410mV at 6MHz, and 234MHz maximum operation frequency at 600mV.

A 0.325 V, 600-kHz, 40-nm 72-kb 9T Subthreshold SRAM with Aligned Boosted Write Wordline and Negative Write Bitline Write-Assist

This paper presents a new bit-interleaving 11T subthreshold SRAM cell with Data-Aware Power-Cutoff (DAPC) Write-assist to mitigate the leakage and variation and improve the Write-ability in deep sub-100nm technology. Measurement results from a 4 Kb test chip implemented in 40 nm General Purpose (40GP) CMOS technology operates for VDD down to 0.32 V (~0.69X of threshold voltage) with VDDMIN limited by Read operation. The measured maximum operation frequency is 3.5 MHz (16.5 MHz) at 0.32 V (0.38 V) with total power consumption of 15.2 μW (27.2 μW) at 25 °C.