Showing papers on "Effective number of bits published in 2013"

A Fully Integrated 8-Channel Closed-Loop Neural-Prosthetic CMOS SoC for Real-Time Epileptic Seizure Control

Abstract: An 8-channel closed-loop neural-prosthetic SoC is presented for real-time intracranial EEG (iEEG) acquisition, seizure detection, and electrical stimulation in order to suppress epileptic seizures. The SoC is composed of eight energy-efficient analog front-end amplifiers (AFEAs), a 10-b delta-modulated SAR ADC (DMSAR ADC), a configurable bio-signal processor (BSP), and an adaptive high-voltage-tolerant stimulator. A wireless power-and-data transmission system is also embedded. By leveraging T-connected pseudo-resistors, the high-pass (low-pass) cutoff frequency of the AFEAs can be adjusted from 0.1 to 10 Hz (0.8 to 7 kHz). The noise-efficiency factor (NEF) of the AFEA is 1.77, and the DMSAR ADC achieves an ENOB of 9.57 bits. The BSP extracts the epileptic features from time-domain entropy and frequency spectrum for seizure detection. A constant 30- μA stimulus current is delivered by closed-loop control. The acquired signals are transmitted with on-off keying (OOK) modulation at 4 Mbps over the MedRadio band for monitoring. A multi-LDO topology is adopted to mitigate the interferences across different power domains. The proposed SoC is fabricated in 0.18- μm CMOS and occupies 13.47 mm2. Verified on Long Evans rats, the proposed SoC dissipates 2.8 mW and achieves high detection accuracy (> 92%) within 0.8 s.

A 2.8 GS/s 44.6 mW Time-Interleaved ADC Achieving 50.9 dB SNDR and 3 dB Effective Resolution Bandwidth of 1.5 GHz in 65 nm CMOS

Abstract: This paper presents a power- and area-efficient 24-way time-interleaved successive-approximation-register (SAR) analog-to-digital converter (ADC) that achieves 2.8 GS/s and 8.1 ENOB in 65 nm CMOS. To minimize the power and the area, the capacitors in the capacitive DAC are sized to meet the thermal noise requirements rather than the matching requirements, leading to the LSB capacitance of 50 aF. An on-chip digital background calibration is used to calibrate the capacitor mismatches in individual ADC channels, as well as the inter-channel offset, gain and timing mismatches. Measurement results at the 2.8 GS/s sampling rate show that the ADC chip prototype consumes 44.6 mW of power from a 1.2 V supply while achieving peak SNDR of 50.9 dB and retaining SNDR higher than 48.2 dB across the entire first Nyquist zone with a 1.8Vpp-diff input signal. The prototype chip occupies an area of 1.03 × 1.66 mm2, including the pads and the testing circuits. The figure of merit (FoM) of this ADC, calculated with the minimum SNDR in the first Nyquist zone, is 76 fJ/conversion-step.

A 10b/12b 40 kS/s SAR ADC With Data-Driven Noise Reduction Achieving up to 10.1b ENOB at 2.2 fJ/Conversion-Step

Abstract: This paper presents a power-efficient 10/12 bit 40 kS/s SAR ADC for sensor applications. It supports resolutions of 10 and 12 bit and sample rates from DC up to 40 kS/s to accommodate a variety of sensor applications. A Data-Driven Noise-Reduction method is introduced to selectively enhance the comparator noise performance. In this way, a higher ADC resolution can be achieved with a small increase of the power consumption. A self-oscillating comparator is used to generate the bit-cycling clock internally. In this way, the ADC only requires an external clock at the sample-rate frequency. A segmented capacitive DAC with 250 aF unit elements is applied to save power and to reduce DNL errors at the same time. The implemented prototype in 65 nm CMOS occupies an area of 0.076 mm 2. For the two supported resolutions (10/12 bit), the ADC achieves an ENOB of 9.4 and 10.1 bit while consuming 72 and 97 nW from a 0.6 V supply at 40 kS/s. This leads to power efficiencies of 2.7 and 2.2 fJ/conversion-step for 10 bit and 12 bit resolution, respectively. Furthermore, the leakage power, which is below 0.4 nW, ensures that the efficiency can be maintained down to very low sample rates.

A 2.2/2.7fJ/conversion-step 10/12b 40kS/s SAR ADC with Data-Driven Noise Reduction

Abstract: Low-power sensor applications e.g. for environmental monitoring, bio-potential recording, and wireless autonomous sensor networks require highly power-efficient ADCs, typically with resolutions of at least 10b. SAR ADCs are generally beneficial in terms of power efficiency. However, the most power-efficient designs currently lack the required accuracy for these applications [1, 2], as they are limited to 9b ENOB. Other designs that have sufficient accuracy (10b) are limited to power efficiencies above 10fJ/conv-step [3]. The aim of this work is to increase the accuracy of highly efficient SAR ADCs beyond 10b, while further improving the efficiency to 2.2fJ/conv-step. To do so, this work introduces a Data-Driven Noise-Reduction method to efficiently suppress comparator noise, applies a segmented capacitive DAC with 250aF unit elements for better efficiency and accuracy, and implements a self-oscillating comparator to locally generate the internally required oversampled clock.

A 0.45 V 100-Channel Neural-Recording IC With Sub- $\mu {\rm W}$ /Channel Consumption in 0.18 $\mu{\rm m}$ CMOS

Abstract: Neural prosthetics and personal healthcare have increasing need of high channel density low noise low power neural sensor interfaces. The input referred noise and quantization resolution are two essential factors which prevent conventional neural sensor interfaces from simultaneously achieving a good noise efficiency factor and low power consumption. In this paper, a neural recording architecture with dynamic range folding and current reuse techniques is proposed and dedicated to solving the noise and dynamic range trade-off under low voltage low power operation. Measured results from the silicon prototype show that the proposed design achieves 3.2 μVrms input referred noise and 8.27 effective number of bits at only 0.45 V supply and 0.94 μW/channel power consumption.

A Sub-Microwatt Asynchronous Level-Crossing ADC for Biomedical Applications

Abstract: A continuous-time level-crossing analog-to-digital converter (LC-ADC) for biomedical applications is presented. When compared to uniform-sampling (US) ADCs LC-ADCs generate fewer samples for various sparse biomedical signals. Lower power consumption and reduced design complexity with respect to conventional LC-ADCs are achieved due to: 1) replacing the n-bit digital-to-analog converter (DAC) with a 1-bit DAC; 2) splitting the level-crossing detections; and 3) fixing the comparison window. Designed and implemented in 0.18 μm CMOS technology, the proposed ADC uses a chip area of 220 × 203 μm2. Operating from a supply voltage of 0.8 V, the ADC consumes 313-582 nW from 5 Hz to 5 kHz and achieves an ENOB up to 7.9 bits.

A Digital-Domain Calibration of Split-Capacitor DAC for a Differential SAR ADC Without Additional Analog Circuits

Abstract: A digital-domain calibration method is proposed for a split-capacitor DAC (split-CDAC) used in a differential-type 11-bit SAR ADC. It calibrates the nonlinearities of SAR ADC due to the DAC capacitance mismatch as well as the two parasitic capacitances connected in parallel with each of the bridge capacitor and the LSB bank of split-CDAC. The proposed ADC does not require any additional analog circuits for calibration, because it utilizes one of the two split-CDACs to measure the error codes of the other split-CDAC. During the normal A/D conversion step, the 11.5-bit raw SAR code output of ADC is added to the pre-measured error codes to generate the 11-bit calibrated output code. The analog block of the ADC was fabricated in a 0.13- μm CMOS process, and the digital block was implemented in a FPGA. The measured SNDR and SFDR are 61.6 dB (ENOB 9.93 bits) and 78 dB at the Nyquist rate with a 5 kHz sine wave input. INL and DNL are measured to be +0.96/-0.98 LSB, and +0.96/-0.97 LSB, respectively. This work extends the prior work by utilizing an additional 0.5-bit raw SAR code to eliminate the missing code, and by employing a temporal averaging with a FIR LPF to measure the error code reliably in spite of the supply noise.

A 9-Bit 150-MS/s Subrange ADC Based on SAR Architecture in 90-nm CMOS

Abstract: This paper presents a 9-bit subrange analog-to-digital converter (ADC) consisting of a 3.5-bit flash coarse ADC, a 6-bit successive-approximation-register (SAR) fine ADC, and a differential segmented capacitive digital-to-analog converter (DAC). The flash ADC controls the thermometer coarse capacitors of the DAC and the SAR ADC controls the binary fine ones. Both theoretical analysis and behavioral simulations show that the differential non-linearity (DNL) of a SAR ADC with a segmented DAC is better than that of a binary ADC. The merged switching of the coarse capacitors significantly enhances overall operation speed. At 150 MS/s, the ADC consumes 1.53 mW from a 1.2-V supply. The effective number of bits (ENOB) is 8.69 bits and the effective resolution bandwidth (ERBW) is 100 MHz. With a 1.3-V supply voltage, the sampling rate is 200 MS/s with 2.2-mW power consumption. The ENOB is 8.66 bits and the ERBW is 100 MHz. The FOMs at 1.3 V and 200 MS/s, 1.2 V and 150 MS/s and 1 V and 100 MS/s are 27.2, 24.7, and 17.7 fJ/conversion-step, respectively.

915-MHz FSK/OOK Wireless Neural Recording SoC With 64 Mixed-Signal FIR Filters

Abstract: A system-on-chip (SoC) neural recording interface with 64 channels, 64 16-tap programmable mixed-signal FIR filters and a fully integrated 915 MHz OOK/FSK PLL-based wireless transmitter is presented. Each recording channel has a fully differential amplifier with 54 dB gain and utilizes a tunable low-distortion subthreshold MOS-resistor to reject DC offsets with an input-referred noise of 6.5 μV and a CMRR of 75 dB. Each channel contains a modified 8-bit SAR ADC with an ENOB of 7.8-bits and can provide analog-digital multiplication by modifying the the sampling phase of the ADC. It is used in conjunction with 12-bit digital adders and registers to implement 64 programmable transposed FIR filters. The 915 MHz FSK/OOK transmitter offers data rates up to 1.5 Mbps and a maximum output power of 0 dBm. The 4×3 mm2 chip fabricated in a 0.13 μm CMOS process dissipates 5.03 mW from a 1.2 V supply. Experimental measurements characterize the electrical performance of the wireless SoC. In vivo measurement results from freely moving rats are also presented.

An 8-bit 450-MS/s single-bit/cycle SAR ADC in 65-nm CMOS

Abstract: A low-energy 8-bit 450-MS/s single-bit/cycle SAR ADC is presented. The design combines top-plate sampling, small unit capacitances (0.75 fF), symmetric DAC switching, and judicious delay optimization around a single high-speed comparator to achieve an ENOB of 7.6 at Nyquist, translating into an FOM of 76 fJ/conversion-step. The converter occupies an active area of 0.035 mm2 in 65-nm CMOS.

A Compressed Sensing Analog-to-Information Converter With Edge-Triggered SAR ADC Core

Abstract: This paper presents the design and implementation of an analog-to-information converter (AIC) capable of Nyquist and compressed sensing modes of operation. The core of the AIC is a 10-bit edge-triggered charge-sharing SAR ADC with a figure of merit (FOM) of 55 fJ/conversion-step and Nyquist-sampling rate of 9.5 Msample/s. The integration of a pseudorandom clock generator enables compressed sensing operation via random sampling and subsequent asynchronous successive approximation conversion by the core ADC. The AIC allows complete reconstruction of a spectrum consisting of sparse single tones or sparse frequency bands using compressed sensing algorithms based on l1-minimization as well as l1,2 regularization, which exploits group sparsity. Implemented in 90 nm CMOS, the prototype SAR ADC core achieves a maximum sample rate of 9.5 MS/s, an ENOB of 9.3 bits, and consumes 550 μW from a 1.2 V supply. Measurement results of the AIC demonstrate an effective bandwidth of 25 MHz, which is 5 × greater than Nyquist-sampling rate with an improved effective FOM of 12.2 fJ/conversion-step for signals with sparse frequency support.

An 8.6 ENOB 900MS/s time-interleaved 2b/cycle SAR ADC with a 1b/cycle reconfiguration for resolution enhancement

Abstract: By taking advantage of the merits of the low power consumption and hardware simplicity of SAR ADCs, 2b/cycle conversion structures in SAR ADCs have been actively studied in recent years for enhanced conversion rates and excellent FoM [1-3]. However, many error sources in the 2b/cycle SAR ADCs, such as mismatches between DACs and comparators, and the signal-dependent errors from comparators, namely kickback noise and offset, make it difficult to achieve high resolution. To date, pure 2b/cycle structures operating above hundreds of MS/s have shown a somewhat limited resolution with an ENOB lower than 7 at Nyquist rates [1,2]. As a derivation of the structure, a sub-ADC could be implemented using the 2b/cycle SAR ADC structure for high resolution as in [4], at the cost of increased circuit complexity and static current flow. In this work, we present a resolution-enhancing design technique for 2b/cycle SAR ADCs with negligible hardware overhead, while relieving the requirements for the aforementioned errors: Reconfiguration from a 2b/cycle structure to a normal 1b/cycle SAR ADC with error-correction capability achieves an 8.6 ENOB from a 9b ADC.

Advances in high-speed ADCs, DACs, and DSP for optical transceivers

Abstract: We discussed DAC, ADC, and DSP in the context of coherent transceivers We reviewed DAC and ADC technology. We discussed ENOB as a figure of merit. We discussed DAC/ADC performance implications. We showed how the technology can be extended if needed We discussed DSP functions: Equalization; Pulse shaping to increase spectral efficiency and the impact of jitter; Frequency offset compensation, carrier recovery, polarization recovery We explained cycle slips and some possible remedies We showed examples of commercial DACs/ADCs as well as DAC/ADC + DSP monolithic ASICs We looked at forward error correction and how it can affect reach Finally, we put all the above in the context of flexible transceivers to meet increased networks capacity.

Why Analog-to-Information Converters Suffer in High-Bandwidth Sparse Signal Applications

Abstract: In applications where signal frequencies are high, but information bandwidths are low, analog-to-information converters (AICs) have been proposed as a potential solution to overcome the resolution and performance limitations of high-speed analog-to-digital converters (ADCs). However, the hardware implementation of such systems has yet to be evaluated. This paper aims to fill this gap, by evaluating the impact of circuit impairments on performance limitations and energy cost of AICs. We point out that although the AIC architecture facilitates slower ADCs, the signal encoding, typically realized with a mixer-like circuit, still occurs at the Nyquist frequency of the input to avoid aliasing. We illustrate that the jitter and aperture of this mixing stage limit the achievable AIC resolution. In order to do so, we designed an end-to-end system evaluation framework for examining these limitations, as well as the relative energy-efficiency of AICs versus high-speed ADCs across the resolution, receiver gain and signal sparsity. The evaluation shows that the currently proposed AICs have no performance benefits over high-speed ADCs. However, AICs enable 2-10X in energy savings in low to moderate resolution (ENOB), low gain applications.

Resolution upgrade toward 6-bit optical quantization using power-to-wavelength conversion for photonic analog-to-digital conversion

Abstract: We demonstrate a resolution upgrade toward 6 bit optical quantization using a power-to-wavelength conversion without an increment of system parallelism. Expansion of a full-scale input range is employed in conjunction with reduction of a quantization step size with keeping a sampling-rate transparency characteristic over several 100 sGS/s. The effective number of bits is estimated to 5.74 bit, and the integral nonlinearity error and differential nonlinearity error are estimated to less than 1 least significant bit.

A 4-Bit, 1.6 GS/s Low Power Flash ADC, Based on Offset Calibration and Segmentation

Abstract: A low power 4-bit, 1.6 GS/s flash ADC is presented. A new power reduction technique which masks the unused blocks in a semi-pipeline chain of latches and encoders is introduced. The proposed circuit determines the unused blocks based on a pre-sensing of the signal. Moreover, a reference voltage generator with very low static power dissipation is used. Novel techniques to reduce the sensitivity to dynamic noise are proposed to suppress the noise effects on the reference generator. The proposed circuit reduces the power consumption by 20 percent compared to the conventional structure when a Nyquist rate OFDM signal is applied. The INL and DNL of the converter are smaller than 0.3 LSB after calibration. The converter offers 3.8 effective number of bits (ENOB) at 1.6 GS/s sampling rate with a low frequency input signal and more than 1.8 GHz effective resolution bandwidth (ERBW) at this sampling rate. The converter consumes mere 15.5 mW from a 1.8 V supply, yielding an FoM of 695 fJ/conversion.step and occupies 0.3 mm2 in a 0.18 μm standard CMOS process.

A 5GS/s 4-bit time-based single-channel CMOS ADC for radio astronomy

Abstract: A 4-bit 65nm time-based analog-to-digital converter (ADC) targeting the next-generation Square Kilometre Array (SKA) is presented. This ADC is composed of an analog voltage-to-time converter (VTC) front end and a digital time-to-digital converter (TDC) back end. The two components can be physically separated to minimize the impact of digital noise from the ADC on high-gain, high-sensitivity receiver chains common in radio telescopes. At a sampling rate of 5 GS/s the ADC consumes 35 mW from a 1 V supply. After calibration, the ADC achieves a peak SNDR of 22.9 dB, SFDR of 34.0 dB and ENOB of 3.5. At the ERBW of 2100 MHz, SNDR is 18.4 dB, SFDR is 22.3 dB and ENOB is 2.8. The resulting worst-case figure of merit is 1.0 pJ/conversion. This is the highest reported sampling rate for a time-based ADC to date.

A 2.3 mW 10-bit 170 MS/s Two-Step Binary-Search Assisted Time-Interleaved SAR ADC

Abstract: This paper presents the architecture of a 10b 170 MS/s two-step binary-search assisted time-interleaved SAR ADC. The front-end stage of this ADC is built with a 5b binary-search ADC, which is shared by two time-interleaved 6b SAR ADCs in the second-stage. The design does not use any static component such as op-amp or preamplifier that causes large dissipation of static power. DAC settling speed and power are also relaxed thanks to this architecture. Besides, the process insensitive asynchronous logic further reduces the delay of SA loop rather than using worst case delay cells to compensate the process variation problem. The ADC was fabricated in 65 nm CMOS and achieves 54.6 dB SNDR at 170 MS/s with only 2.3 mW of power consumption, leading to a FoM of 30.8 fJ/conversion-step.

A 0.5-V 5.2-fJ/Conversion-Step Full Asynchronous SAR ADC With Leakage Power Reduction Down to 650 pW by Boosted Self-Power Gating in 40-nm CMOS

Abstract: This paper presents an ultralow-power and ultralow-voltage SAR ADC. Full asynchronous operation and boosted self-power gating are proposed to improve conversion accuracy and reduce static leakage power. By designing with MOSFET of high threshold voltage (HVt) and low threshold voltage (LVt), the leakage power is reduced without decrease of maximum sampling frequency. The test chip in 40-nm CMOS process has successfully reduced leakage power by 98%, and it achieves 8.2-bit ENOB and while consuming only 650 pW at 0.1 kS/s from 0.5-V power supply. The power consumption is scalable up to 4 MS/s and power supply range from 0.4 to 0.7 V. The best figure of merit at 0.5 V is 5.2 fJ/conversion-step at 20 kS/s.

A Time-Domain High-Order MASH $\Delta\Sigma$ ADC Using Voltage-Controlled Gated-Ring Oscillator

Abstract: In this paper, a time-domain high-order ΔΣ analog-to-digital converter (ADC) using voltage-controlled gated-ring oscillator (VC-GRO) and time-domain multi-stage-noise-shaping (MASH) is introduced. To implement the high-order noise transfer function (NTF), a voltage-controlled oscillator (VCO) and VC-GRO quantizers are cascaded. Unlike conventional high-order ΔΣ ADC using feedback loop, the proposed ADC has advantages that the architecture is open-loop and the quantizer resolution depends on the time resolution, thus making it attractive for deep submicron CMOS process. The performance of the proposed ADC is theoretically analyzed and simulated, including non-ideal conditions such as nonlinearity, mismatch, propagation delay of logic gates, phase noise, and sampling clock jitter.

A 3-nW 9.1-ENOB SAR ADC at 0.7 V and 1 kS/s

Abstract: This paper presents a 10-bit SAR ADC in 65 nm CMOS for medical implant applications. The ADC consumes 3-nW power and achieves 9.1 ENOB at 1 kS/s. The ultra-low-power consumption is achieved by using an ADC architecture with maximal simplicity, a small split-array capacitive DAC, a bottom-plate sampling approach reducing charge injection error and allowing full-range input sampling without extra voltage sources, and a latch-based SAR control logic resulting in reduced power and low transistor count. Furthermore, a multi-Vt circuit design approach allows the ADC to meet the target performance with a single supply voltage of 0.7 V. The ADC achieves a FOM of 5.5 fJ/conversion-step. The INL and DNL errors are 0.61 LSB and 0.55 LSB, respectively.

Analog-to-digital converter system and method

Abstract: An analog-to-digital converter (ADC) system and method. The ADC system in accord with one embodiment includes a sampling digital-to-analog converter configured to sample a combination of an analog signal value and an analog dither value, and a control circuit comprising a mismatch-shaping encoder. The control circuit is configured to sequentially apply a plurality of digital codes to the sampling digital-to-analog converter during an analog-to-digital conversion operation to derive a digital code representing the combination of the analog signal value and the analog dither value. Several embodiments are presented.

Controllers controlling nonvolatile memory devices and operating methods for controllers

Abstract: An operating method of a controller includes selecting bits of code word to be punctured; detecting locations of incapable bits of an input word based on locations of the bits to be punctured and a structure of a generation matrix calculation unit; refreezing the input word such that frozen bits and incapable bits of the input word overlap; generating input word bits by replacing information word bits with frozen bits based on the refreezing result; generating the code word by performing generation matrix calculation on the input word bits; generating output bits by puncturing the code word based on locations of the bits to be punctured; and transmitting the output bits to a nonvolatile memory device.

Modeling and Measurement of Power Supply Noise Effects on an Analog-to-Digital Converter Based on a Chip-PCB Hierarchical Power Distribution Network Analysis

Abstract: In this paper, a model of power supply noise (PSN) effects on an analog-to-digital converter (ADC) in a hierarchical structure is proposed. The ADC performance is determined by not only on-chip characteristics but also off-chip characteristics. Therefore, chip-package-printed circuit board (PCB) coanalysis and comodeling are required to accurately evaluate the performance of the ADC. We propose the comodel which allows the estimation and analysis of PSN effects on the ADC including off-chip characteristic. The proposed model includes three separate submodels: a power distribution network (PDN) model from the power/ground of the PSN source to the ADC power/ground, an on-chip circuit model from the ADC power/ground to the ADC inputs, and an ADC behavioral model from the ADC inputs to the factor of the effective number of bits (ENOB), which is one of the ADC performance factors. By applying a segmentation method for the PDN model, an analytical model for the on-chip circuit model, and a MATLAB model for the ADC behavioral model, fast, precise, and broadband estimations of the PSN effects are achieved. To validate the proposed models, an ADC was fabricated by a 0.13-μm CMOS process and wire bonded to the designed PCB. The ENOB of the ADC was measured by sweeping the PSN's frequency from 1 MHz up to 3 GHz, which was injected into the PCB to discover which noise frequency is critical to an ADC designed with a chip-PCB hierarchical structure. The results estimated by the proposed model correlated well with the cosimulated and measured results. The proposed modeling procedure saves the chip, package, and PCB designers time and computation resources to achieve high-quality analog devices or mixed-mode systems and provides an intuitive understanding of the noise effect.

A 1.6-Gsps High-Resolution Waveform Digitizer Based on a Time-Interleaved Technique

Abstract: A high-speed and high-resolution Analog-to-Digital Conversion circuit is the crucial part in many physics experiments, data communication, and measurement instrumentation. We present the design and test results on a 1.6-Gsps high-resolution waveform digitizer based on a high-speed AD conversion and time-interleaved technique. Considering the mismatch (gain, offset, and skew) among different ADC channels, we employ real-time correction algorithms integrated in an FPGA to enhance the system performance. In the very high-speed situation, simplification of digital processing algorithms is an important task to guarantee a high processing speed. We proposed a novel correction method based on a fully parallel structure. To achieve good performance, we designed a special jitter-cleaning circuit for the sampling clock and front end coupling circuits for the ADCs, and carefully implemented the hardware circuits to guarantee the signal integrity. Test results indicate that this waveform digitizer achieves a sampling rate of 1.6 Gsps and an ENOB around 11 bits for an input signal from 5 MHz to 150 MHz. The ENOB is still above 10.4 bits for an input up to 300 MHz, with the correction algorithms applied.

An 8-to-1 bit 1-MS/s SAR ADC With VGA and Integrated Data Compression for Neural Recording

Abstract: Low power consumption per channel and data rate minimization are two key challenges which need to be addressed in future generations of neural recording systems (NRS). Power consumption can be reduced by avoiding unnecessary processing whereas data rate is greatly decreased by sending spike time-stamps along with spike features as opposed to raw digitized data. Dynamic range in NRS can vary with time due to change in electrode-neuron distance or background noise, which demands adaptability. An analog-to-digital converter (ADC) is one of the most important blocks in a NRS. This paper presents an 8-bit SAR ADC in 0.13- μm CMOS technology along with input and reference buffer. A novel energy efficient digital-to-analog converter switching scheme is proposed, which consumes 37% less energy than the present state-of-the-art. The use of a ping-pong input sampling scheme is emphasized for multichannel input to alleviate the bandwidth requirement of the input buffer. To reduce the data rate, the A/D process is only enabled through the in-built background noise rejection logic to ensure that the noise is not processed. The ADC resolution can be adjusted from 8 to 1 bit in 1-bit step based on the input dynamic range. The ADC consumes 8.8 μW from 1 V supply at 1 MS/s speed. It achieves effective number of bits of 7.7 bits and FoM of 42.3 fJ/conversion-step.

A 10-bit 50-MS/s SAR ADC with techniques for relaxing the requirement on driving capability of reference voltage buffers

Abstract: A high speed successive approximation (SAR) ADC requires reference voltage buffers with high driving capability. Moreover, the power consumption of the reference buffers is usually several times larger than that of the SAR ADC itself. Three techniques are adopted to mitigate the requirement on driving capability of reference voltage buffers for SAR ADCs. A 10b 50MS/s ADC based on the proposed techniques is presented. The prototype ADC was fabricated in 40nm LP 1P7M CMOS technology. It consumes 0.47 mW at 50 MS/s from 1.1V supply voltage and achieves ENOB of 9.18-bit and figure of merit (FoM) of 16 fJ/conversion-step. The active area is 0.0114 mm2.

A 6-b 1.6-GS/s ADC With Redundant Cycle One-Tap Embedded DFE in 90-nm CMOS

Abstract: ADC-BASED serial link receivers are emerging in order to scale data rates over high attenuation channels. Embedding partial equalization inside the front-end ADC can potentially result in lowering the complexity of back-end DSP and/or decreasing the ADC resolution requirement, which results in a more energy-efficient receiver. This paper presents a 6-b 1.6-GS/s ADC with a novel embedded DFE structure. A redundant cycle technique is proposed for a time-interleaved SAR ADC, which relaxes the DFE feedback critical path delay with low power/area overhead. The 6-b prototype ADC with embedded one-tap DFE is fabricated in an LP 90-nm CMOS process and achieves 4.75-bits peak ENOB and 0.46 pJ/conv.-step FOM at a 1.6-GS/s sampling rate. Enabling the embedded DFE while operating at 1.6 Gb/s over a 46-in FR4 channel with 14-dB loss at Nyquist bandwidth opens a previously closed eye and allows for a 0.2 UI timing margin at a BER=10-9. Total ADC power including front-end T/Hs and reference buffers is 20.1 mW, and the core time-interleaved ADC occupies 0.24 mm 2 area.

A 10.4-ENOB 120MS/s SAR ADC with DAC linearity calibration in 90nm CMOS

Abstract: This paper proposes a DAC linearity calibration and a phase-splitting bit register for a SAR ADC. The calibration corrects the conversion nonlinearity of the bridge DAC structure in the digital domain leading to higher accuracy and insensitivity to comparison offset. Moreover, a phase-splitting bit register is presented to optimize the speed of the digital circuitry. Measurements obtained from a 90nm CMOS prototype operating at 120MS/s and 1.2V supply achieve a SNDR of 64.3dB with 3.2mW power dissipation.

A 281-nW 43.3 fJ/conversion-step 8-ENOB 25-kS/s asynchronous SAR ADC in 65nm CMOS for biomedical applications

Abstract: This paper describes a low-power 25-kS/s successive approximation register (SAR) analog-to-digital converter (ADC) for biomedical applications. The ADC employs a novel low-energy and area-efficient tri-level switching scheme in the DAC. Compared to the conventional SAR ADC, the average switching energy and total capacitance are reduced by 97% and 75%, respectively. Asynchronous design is implemented to eliminate the conventional system clock which is N-time of sampling rate. Furthermore, a delay-based internal clock generator produces a high-speed signal which allows True Single Phase Clock (TSPC) D Flip-flop (DFF) to be used in the low-speed biomedical applications. The ADC can work between 0 to 1 MS/s. The prototype ADC fabricated in UMC 65 nm 1P6M CMOS achieves best performance at 25 kS/s with 50.1 dB SNDR and 55.3 dB SFDR. Operating at 1 V supply and 25 kS/s, the ADC consumes 281 nW and exhibits a FOM of 43.3 fJ/conversion-step. The chip die area is 145 μm × 120 μm.