Sigma-delta Analog-to-digital Converter Research Articles

Research on the design and application of Analog-to-Digital converters

Abstract. In the modern digital era, the conversion of analog signals to digital data is a crucial process for a wide range of applications in industries such as consumer electronics, medical devices, and telecommunications. The accelerated evolution of digital technology is driving a surge in demand for high-performance analog-to-digital converters (ADCs). The paper presents a comprehensive analysis of analog-to-digital converters, emphasizing their types, applications, performance measurements, and most recent developments. In the paper, emphasis is placed on the mechanisms of different ADC architectures, such as Successive Approximation Register (SAR), Sigma-Delta (-), and Flash ADCs, and their respective strengths and weaknesses are evaluated. In terms of technique, it synthesizes and summarizes research results from multiple academic sources and technical papers. In addition to underscoring the pivotal concerns of ADC design, including power consumption, resolution, and sample rate, the research delves into novel approaches that leverage the use of advanced materials and techniques. The research results demonstrate the continued development of ADC technology and its critical function in improving the effectiveness and performance of digital systems.

Analysis and Design of Noise-Shaping SAR ADC with Capacitor Stacking and Buffering

The noise-shaping (NS) successive-approximation-register (SAR) is a promising analog-to-digital converter (ADC) architecture which combines the benefits of SAR and Delta-Sigma (ΔΣ) ADCs. Among the various NS-SAR approaches, the recent emerged one with capacitor stacking and buffering exhibits excellent energy efficiency. This paper presents a tutorial for the design of NS-SAR ADC with capacitor stacking and buffering. The fundamental principle of the NS-SAR loop filter is analyzed, an ADC design example is provided, and the circuit implementation details with considerations on the non-idealities and trade-offs are discussed. This paper can be used as a tutorial for designing high-resolution and high-order NS-SAR ADC.

A 78 dB 0.417 mW Second-Order NS SAR ADC with Dynamic Amplifier-Assisted Integrator

The noise-shaping (NS) successive approximation register (SAR) analog-to-digital converter (ADC) is an innovative hybrid structure that offers performance advantages. The NS-SAR ADC leverages the SAR ADC as its foundation and combines oversampling technology and noise-shaping technology found in Sigma-Delta ADC. This integration effectively combines the strengths of both structures and enhances overall performance. The ADC features a simple circuit structure, compact chip area, and high energy efficiency, which has positioned it as a prominent research area. In this paper, leveraging the TSMC 65 nm GP process, the NS-SAR ADC is designed with a power supply voltage of 1 V. This design adopts an 8-bit differential capacitor structure, operates at a sampling frequency of 16 MS/s, and achieves an oversampling rate of 16 times the desired performance indicators. Through extensive circuit post simulation verification, the SNR obtained reaches 78 dB, providing an effective bit resolution of 12.7 bits. The core chip area of the ADC measures 366 × 333 μm2, while the power consumption is impressively low at 417 μW and FoMs is 168 dB.

Study of a High-Precision Read-Out Integrated Circuit for Bridge Sensors.

Bridge sensors are widely used in military and civilian fields, and their demand gradually increases each year. Digital sensors are widely used in the military and civilian fields. High-precision and low-power analog-to-digital converters (ADCs) as sensor read-out circuits are a research hotspot. Sigma-delta ADC circuits based on switched-capacitor topology have the advantages of high signal-to-noise ratio (SNR), good linearity, and better compatibility with CMOS processes. In this work, a fourth-order feed-forward sigma-delta modulator and a digital decimation filter are designed and implemented with a correlated double sampling technique (CDS) to suppress pre-integrator low-frequency noise. This work used an active pre-compensator circuit for deep phase compensation to improve the system's stability in the sigma-delta modulator. The modulator's local feedback factor is designed to be adjustable off-chip to eliminate the effect of process errors. A three-stage cascade structure was chosen for the post-stage digital filter, significantly reducing the number of operations and the required memory cells in the digital circuit. Finally, the layout design and engineering circuit were fabricated by a standard 0.35 μm CMOS process from Shanghai Hua Hong with a chip area of 9 mm2. At a 5 V voltage supply and sampling frequency of 6.144 MHz, the modulator power consumption is 13 mW, the maximum input signal amplitude is -3 dBFs, the 1 Hz dynamic range is about 118 dB, the modulator signal-to-noise ratio can reach 110.5 dB when the signal bandwidth is 24 kHz, the practical bit is about 18.05 bits, and the harmonic distortion is about -113 dB, which meets the design requirements. The output bit stream is 24 bits.

ЗАВИСИМОСТЬ СПЕКТРАЛЬНЫХ ХАРАКТЕРИСТИК СИГМА-ДЕЛЬТА АНАЛОГО-ЦИФРОВЫХ ПРЕОБРАЗОВАТЕЛЕЙ ОТ ПОГЛОЩЕННОЙ ДОЗЫ ИОНИЗИРУЮЩЕГО ИЗЛУЧЕНИЯ

This paper presents the results of the study of sigma-delta analog-to-digital converters` main spectral parameters` dependence on the total ionizing dose (TID). Within the framework of this study the main parameters of analog-to-digital converters (ADC) (dynamic, static and electrical) were controlled. The main dynamic characteristics of sigma-delta ADC are signal-to-noise ratio (SNR), spurious-free dynamic range (SFDR), signal-to-noise and distortion ratio (SINAD) and total harmonic distortion (THD). Those have been determined from the spectrum of digitized sine signal using the fast Fourier transform (FFT). Static parameters (integrated nonlinearity (INL), offset and gain errors) were determined using a straight line that linearizes the transfer function, according to the method which is described in the IEEE Standard for Terminology and Test Methods for Analog-to-Digital Converters. National Instruments modular measuring equipment was used for testing ADC`s parameters. Comparative data on the dose dependence of static and dynamic parameters of two sigma-delta ADC and one sigma-delta modulator are obtained. Based on the results, it was concluded that the most sensitive parameters of sigma-delta ADC to TID are its dynamic parameters. Therefore, when assessing the sigma-delta ADC`s radiation hardness, the spectral characteristics of absorbed dose should be kept under control.

Analog-to-digital converters: a review of existing architectures and a new proposal for high resolution sensors

PurposeAs technology advances the demand for an analog-to digital converter has increased, as every application demands a converter as per its parameters. Currently, work is done on improvement of data converters at three levels of design – architectural, circuit and physical level. This paper aims to review the work done in the field of analog-to-digital converters (ADCs) at architectural and circuit level and discusses the achievements in this field. Furthermore, a new architecture is proposed, which works at higher resolution and provides optimum design parameters at low power consumption.Design/methodology/approachA hybrid architecture combining the features of synthetic approximation register and sigma-delta ADC is presented. The validity of the proposed design at architectural level is verified using MATLAB SIMULINK simulations.FindingsThe design simulation was tested for a sinusoidal wave of 1 V at the test frequency of 60 Hz. The design consumes least power, and is found to yield an error of the order less than 10–3 V, thus providing highly accurate digital output.Originality/valueThe design is applicable in many applications including biomedical systems, Internet-of-Things and earthquake engineering. This architecture can be further optimized to obtain better performance parameters.

Design and Implementation of Sigma-Delta ADC Filter

This paper presents a digital decimation filter based on a third-order four-bit Sigma-Delta modulator. The digital decimation filter is an important part of the Sigma-Delta ADC and is designed to make the Sigma-Delta ADC (Analog-to-Digital Converter) meets the requirements of Signal-to-Noise Ratio (SNR) not less than 120 dB and Equivalent Number of Bits (ENOB) not less than 20 bits. It adopts a three-stages cascaded structure including a Cascaded Integrator Comb (CIC) decimation filter, a Finite Impulse Response (FIR) compensation filter, and a half-band (HB) filter. This structure effectively reduces about 13% multiplier cells and memory cells. The coefficient symmetry technique and CSD (Canonic Signed Digit) coding technique are used to optimize the parameters of the filter, which further reduces the computational complexity. After optimization, the circuit area is reduced by about 15%, and the logic resources are decreased by about 23%. The Verilog hardware description language is used to describe the behavior of the digital decimation filter, and the simulation is carried out based on the VCS (Verilog Compile Simulator) platform. At the same time, the prototype verification is implemented on the Xilinx Artix-7 series FPGA, and the ADC achieves 113 dB SNR and 18.5 bits ENOB. Finally, the Sigma-Delta ADC is fabricated on SMIC 0.18 μm CMOS process with the layout area of 714.8 μm × 628.4 μm and the power consumption of 11.2 mW. The more tests for the fabricated prototypes will be performed in the future to verify that the Sigma-Delta ADC complies with the design specifications.

Small-Signal Processing Low-Overhead Operational Amplifier for delta-Sigma ADC

Aiming at the fully differential (FD) sensing and high-precision small-signal output characteristics of micro-electromechanical systems (MEMS) gyroscopes, a low area overhead, high-gain, medium-speed, FD operation amplifier (Op-Amp) is designed for building a small-signal processing delta-Sigma analog-to-digital converter (ADC). The Op-Amp is a two-stage cascade structure, which combines folded cascade (FC) and gain-boosted technology to make the low frequency gain up to 129 dB, to meet the high-precision requirements of 18-bit delta-Sigma ADC. The first stage is FC gain-boosted structure, which uses a small bias current to achieve high-gain and low area overhead. In order to reduce the input noise, process smaller signals, the input pair adopts positive channel Metal–Oxide–Semiconductor (PMOS). The second-stage uses a large bias current to achieve a high unity gain bandwidth (UGB). Under the premise that the tail current source of the first stage is PMOS, in order to reduce the area overhead, abandoning the traditional common source (CS) structure of negative channel Metal–Oxide–Semiconductor (NMOS) input and PMOS as the current mirror load, adopting a new CS structure that PMOS input and NMOS used as independent bias current source. In this structure, the large overdrive voltage significantly reduces the size of transistors and greatly reduces the area overhead. The Op-Amp was implemented in SMIC 0.18 μm BCD process, 5 V supply voltage. Its post-layout simulation achieved a low-frequency gain of 129 dB, a UGB of 35 MHz and a phase margin (PM) of 62° for a load capacitance of 2 pF. Output voltage swings are ±3.71 V and including common mode feedback (CMFB), bias voltage generating circuit and filter capacitor, the area of Op-Amp is 167.162 μm × 200.82 μm. Behavioral-level verification shows that the designed Op-Amp meets the requirements of high-precision delta-Sigma ADCs.

A Survey on Analog-to-Digital Converter Integrated Circuits for Miniaturized High Resolution Ultrasonic Imaging System.

As traditional ultrasonic imaging systems (UIS) are expensive, bulky, and power-consuming, miniaturized and portable UIS have been developed and widely utilized in the biomedical field. The performance of integrated circuits (ICs) in portable UIS obviously affects the effectiveness and quality of ultrasonic imaging. In the ICs for UIS, the analog-to-digital converter (ADC) is used to complete the conversion of the analog echo signal received by the analog front end into digital for further processing by a digital signal processing (DSP) or microcontroller unit (MCU). The accuracy and speed of the ADC determine the precision and efficiency of UIS. Therefore, it is necessary to systematically review and summarize the characteristics of different types of ADCs for UIS, which can provide valuable guidance to design and fabricate high-performance ADC for miniaturized high resolution UIS. In this paper, the architecture and performance of ADC for UIS, including successive approximation register (SAR) ADC, sigma-delta (Σ-∆) ADC, pipelined ADC, and hybrid ADC, have been systematically introduced. In addition, comparisons and discussions of different types of ADCs are presented. Finally, this paper is summarized, and presents the challenges and prospects of ADC ICs for miniaturized high resolution UIS.

A 78-MHz BW Continuous-Time Sigma-Delta ADC with Programmable VCO Quantizer

This article presents a high speed third-order continuous-time (CT) sigma-delta analog-to-digital converter (SDADC) based on voltage-controlled oscillator (VCO), featuring a digital programmable quantizer structure. To improve the overall performance, not only oversampling technique but also noise-shaping enhancing technique is used to suppress in-band noise. Due to the intrinsic first-order noise-shaping of the VCO quantizer, the proposed third-order SDADC can realize forth-order noise-shaping ideally. As a bright advantage, the proposed programmable VCO quantizer is digital-friendly, which can simplify the design process and improve anti-interference capability of the circuit. A 4-bit programmable VCO quantizer clocked at 2.5 GHz, which is proposed in a 40 nm complementary metal-oxide semiconductor (CMOS) technology, consists of an analog VCO circuit and a digital programmable quantizer, achieving 50.7 dB signal-to-noise ratio (SNR) and 26.9 dB signal-to-noise-and-distortion ration (SNDR) for a 19 MHz − 3.5 dBFS input signal in 78 MHz bandwidth (BW). The digital quantizer, which is programmed in the Verilog hardware description language (HDL), consists of two-stage D-flip-flop (DFF) based registers, XOR gates and an adder. The presented SDADC adopts the cascade of integrators with feed-forward summation (CIFF) structure with a third-order loop filter, operating at 2.5 GHz and showing behavioral simulation performance of 92.9 dB SNR over 78 MHz bandwidth.

Tunnel Magnetoresistance Based Passive Resistance Replacement in Hybrid MTJ-CMOS Integration

Previous theoretical and experimental works revealed the novel factors that Magnetic tunnel junction (MTJ) can be integrated into novel hybrid circuits except for memory applications. This paper makes exploitation of tunnel magnetoresistacne based replacement in diminishing layout penalty of on-chip passive component during circuit design and takes sigma-delta analog-to-digital converter (SD-ADC), resistor-based temperature sensor (-55 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim 125^{\circ }$</tex-math></inline-formula> C) as two case study where large resistance is needed and restricts the scaling down. Considering the application in MRAM, the mainstream field of MTJ process and dealing with the problems of MRAM in wide temperature write operation, two temperature adaptive write schemes of MRAM are also proposed as the further applications of the proposed MTJ-based temperature sensor. The research of these circuits covers major characteristics of MTJ as the passive component, including area, variation and temperature characteristics. Large CMOS resistance in SD-ADC and bridge transducer in resistor-based temperature sensor are replaced by MTJ-based resistors. Simulation results reveal that the layout area of passive resistors in resistor-capacitor (RC) integrator was greatly reduced by the tunnel magnetoresistacne based replacement, specifically by 94.52% in comparison with fully 28nm CMOS design or 94.13% for wide temperature use. As for other figures of merit (FoM), Effective Numbers of Bits (ENOB) is improved by 0.06 bit along with higher thermal stability, and Signal-to-Noise Ratio (SNR) is decreased by 1.1 dB as design trade-off. In addition, the MTJ based bridge transducer in resistor-based temperature sensor can reduce the resistance layout area by over 90% with better linearity comparing with general CMOS resistor-based temperature sensor designs. Based on the MTJ-based temperature sensor, the two different adaptive write circuits help reduce write power consumption and delay of MRAM respectively for wide temperature use.

Channel Estimation in MIMO Systems With One-Bit Spatial Sigma-Delta ADCs

This paper focuses on channel estimation in single-user and multi-user MIMO systems with multi-antenna base stations equipped with 1-bit spatial sigma-delta analog-to-digital converters (ADCs). A careful selection of the quantization voltage level and phase shift used in the feedback loop of 1-bit sigma-delta ADCs is critical to improve its effective resolution. We first develop a quantization noise model for 1-bit spatial sigma-delta ADCs. Using the developed noise model, we then present a two-step channel estimation algorithm to estimate a multipath channel parameterized by the gains, angles of arrival (AoAs), and angles of departure (AoDs). Specifically, in the first step, the AoAs are estimated using uplink pilots, which excite all the angles uniformly. Next, in the second step, the AoDs are estimated by progressively refining uplink beams through a recursive bisection procedure followed by a weighted least squares path gain estimator. For this algorithm, we propose a technique to select the quantization voltage level and phase shift. Through numerical simulations, we demonstrate that with the proposed parametric channel estimation algorithm, MIMO systems with 1-bit spatial sigma-delta ADCs perform significantly better than those with regular 1-bit ADCs and are on par with MIMO systems having high-resolution ADCs

Linearity Enhancement of VCO-Based Continuous-Time Delta-Sigma ADCs Using Digital Feedback Residue Quantization

A linearity enhancement scheme for voltage-controlled oscillator (VCO)-based continuous-time (CT) delta-sigma (ΔΣ) analog-to-digital converters (ADCs) is proposed. Unlike conventional input feedforwarding techniques, the proposed feedforwarding scheme using digital feedback residue quantization (DFRQ) can avoid the analog summing amplifier, allow intrinsic anti-aliasing filtering (AAF) characteristic, and cause no switching noise injection into the input. A VCO-based CT ΔΣ ADC adapting the proposed DFRQ enables residue-only processing in the quantizer, avoiding the degradation of signal-to-noise and distortion ratio (SNDR) due to VCO nonlinearity. The use of DFRQ also reduces the voltage swing of integrators without the drawbacks caused by conventional input feedforwarding techniques. The performance evaluation results indicate that the proposed VCO-based CT ΔΣ ADC with DFRQ provides 30.3-dB SNDR improvement, reaching up to 83.5-dB in 2-MHz signal bandwidth.

Functional verification of a sigma-delta ADC real number model

ABSTRACT Mixed-signal applications form one of the hottest topics in the semiconductor industry. Considerable effort is required for the creation of designs that consist of both analog and digital blocks with high accuracy and performance. Therefore, mixed-signal verification can be considered as a significant matter. Former conventional verification approaches present very slow verification time, which ultimately increases time-to-market. A circuit of interest in modern systems is the sigma-delta analog-to-digital converter (ADC), which is used for encoding analog signals into digital codes, and many other applications. In this work, an effective functional verification architecture using Universal Verification Methodology (UVM) for a SystemVerilog-based sigma-delta ADC real-number model is proposed. The UVM effectiveness of the presented approach encourages the creation of a verification architecture with increased reusability and robustness, with respect to previous literature. The presented verification environment utilises constrained-random stimuli that exploit a novel sine-wave generator, analog assertions and coverage metrics for improved functional verification. Additionally, a metric for verification quality estimation is introduced for comparisons with other reference verification approaches. In all cases, the presented architecture verified the proper operation of the sigma-delta ADC with coverage of more than 98%, in accordance with the specification parameters that were used for the model.

Design of Low-Power 16-Bit R-2R Digital-to-Analog Converter for Effective Biomedical Signal Processing

Digital-to-analog converter (DAC) is a part of various biomedical signal processing systems. DAC is one of the essential blocks optimizing the performance of various analog-to-digital converters (ADCs) such as SAR-ADC, Delta-Sigma ADC. In this paper, a 16-bit DAC is designed and analyzed that can be used in various applications of ADCs specifically useful in effective biomedical data processing. A design of resistor-2 resistor (R-2R) type DAC based on binary weighted resistors is implemented using 16-bit resolution at sampling rate of 500 MS/s. The main components of the design are R-2R ladder, Switch and operational amplifier. During the design of R-2R DAC op-amp, a current mirror circuit is used that provides a single-ended voltage signal without having any losses. In addition to that, it also uses RC coupling for blocking the DC part of the signal and improves the closed loop stability. All the work was carried out by using cadence virtuoso editor tool. The DAC is designed and simulated at 90 and 45 nm CMOS technology and a comparative analysis is done. The result obtained matches the desired specifications of DAC and it is more efficient and can be used for high-speed applications.

Incremental Delta-Sigma ADCs: A Tutorial Review

In many sensor applications, a high-resolution analog-to-digital converter (ADC) is a key block. The use of an incremental delta-sigma ADC (IADC) is often well suited for such applications. While the energy-efficiency of IADCs has improved by several orders of magnitude over the past decade, the implementation of high performance IADCs, especially in battery-powered systems, is still challenging. This paper presents a tutorial review on energy-efficient IADCs and addresses the progress in this area. This paper describes the fundamentals of IADCs and energy-efficient hybrid IADC architectures. Various design techniques for improving the energy-efficiency of the IADCs are described. This paper is intended to serve as a starting point for the development of a new energy-efficient IADC.

Sigma-Delta ADC on SOI Technology for Working at High Temperatures

We consider the integrated circuit design and the measurement results of test crystals for the 12-bit sigma-delta analog-to-digital converter (ADC) based on 180 nm silicon-on-insulator (SOI) technology from X-FAB. The ADC processes input signals in the frequency range up to 100 kHz in the temperature range of –40…+175 °C with the supply voltage equal to 3.3 V and the modulator clock frequency equal to 10 MHz. The circuit consists of the 5-th order switched-capacitor low-pass pre-filter to limit the input signal spectrum, the cascade connection of the second order sigma-delta modulators, and the digital decimation filter to reduce the clock frequency by 48 times. The main blocks of cutoff filter and modulator are assembled according to the balanced scheme on integrators based on operational transconductance amplifiers with the unity gain bandwidth of 63 MHz. The dynamic element matching circuit is used to expand the dynamic range of converter. It reduces the level of nonlinear distortions in digital-to-analog converters in the feedback circuits of modulator. The value of the SINAD parameter is not worse than 68 dB for converting the signal with the differential amplitude equal to 500 mV at the frequency of 100 kHz.

A power efficient delta-sigma ADC with series-bilinear switch capacitor voltage-controlled oscillator

In low-power VLSI design applications non-linearity and harmonics are a major dominant factor which affects the performance of the ADC. To avoid this, the new architecture of voltage-controlled oscillator (VCO) was required to solve the non-linearity issues and harmonic distortion. In this work, a 12-bit, 200MS/s low power delta-sigma analog to digital converter (ADC) VCO based quantizer was designed using switched capacitor technique. The proposed technique uses frequency to current conversion technique as a linearization method to reduce the non-linearity issue. Simulation result show that the proposed 12-bit delta-sigma ADC consumes the power of 2.68 mW and a total area of 0.09 mm² in 90 nm CMOS process.

A Highly Accurate, Polynomial-Based Digital Temperature Compensation for Piezoresistive Pressure Sensor in 180 nm CMOS Technology.

Recently, piezoresistive-type (PRT) pressure sensors have been gaining attention in variety of applications due to their simplicity, low cost, miniature size and ruggedness. The electrical behavior of a pressure sensor is highly dependent on the temperature gradient which seriously degrades its reliability and reduces measurement accuracy. In this paper, polynomial-based adaptive digital temperature compensation is presented for automotive piezoresistive pressure sensor applications. The non-linear temperature dependency of a pressure sensor is accurately compensated for by incorporating opposite characteristics of the pressure sensor as a function of temperature. The compensation polynomial is fully implemented in a digital system and a scaling technique is introduced to enhance its accuracy. The resource sharing technique is adopted for minimizing controller area and power consumption. The negative temperature coefficient (NTC) instead of proportional to absolute temperature (PTAT) or complementary to absolute temperature (CTAT) is used as the temperature-sensing element since it offers the best temperature characteristics for grade 0 ambient temperature operating range according to the automotive electronics council (AEC) test qualification ACE-Q100. The shared structure approach uses an existing analog signal conditioning path, composed of a programmable gain amplifier (PGA) and an analog-to-digital converter (ADC). For improving the accuracy over wide range of temperature, a high-resolution sigma-delta ADC is integrated. The measured temperature compensation accuracy is within ±0.068% with full scale when temperature varies from −40 °C to 150 °C according to ACE-Q100. It takes 37 µs to compute the temperature compensation with a clock frequency of 10 MHz. The proposed technique is integrated in an automotive pressure sensor signal conditioning chip using a 180 nm complementary metal–oxide–semiconductor (CMOS) process.

An Inverter-Based Continuous Time Sigma Delta ADC With Latency-Free DAC Calibration

This paper presents a wide bandwidth inverter-based continuous time sigma delta (CTSD) analog-to-digital converter (ADC) with a latency-free calibration to suppress the nonlinearity originating from the feedback digital-to-analog converter (DAC). The modulator in the ADC uses a fourth-order architecture with 4-bit quantization. To compensate the excess loop delay (ELD), the proportional-integrating element (PI-element) is employed in the loop filter where the problem of no real solution in conventional PI-element compensation method is solved. In addition, the two-stage inverter-based amplifiers are used in the loop filter to improve power efficiency. To suppress nonlinearity of the 4-bit DAC, a background calibration method based on modified quantizer is proposed which would not introduce additional latency thus ensuring stability of the modulator. The CTSD ADC achieves 64.6 dB SNDR and 71.2 dB SFDR over a 75 MHz signal bandwidth before calibration, and the SNDR and the SFDR can be improved to 67.3 dB and 82.3 dB respectively after calibration. The ADC consumes 38 mW from supply voltages of 1.1/1.8 V with an active area of 0.675 mm2 in 40 nm CMOS.