Gunhee Han

A 0.7V 36μW 85dB-DR Audio ΔΣ Modulator Using Class-C Inverter

This paper presents an improved low-power DeltaSigma modulator, exploiting the class-C inverter and the feedforward topology. The measurement results show 14b dynamic range for a 20kHz bandwidth with 36muW power consumption from a 0.7V supply.

Noise Analysis and Simulation Method for a Single-Slope ADC With CDS in a CMOS Image Sensor

Many mixed-signal circuits are nonlinear time-varying systems whose noise estimation cannot be obtained from the conventional frequency domain noise simulation (FNS). Although the transient noise simulation (TNS) supported by a commercial simulator takes into account nonlinear time-varying characteristics of the circuit, its simulation time is unacceptably long to obtain meaningful noise estimation results. Since the single-slope analog-to-digital converter with correlated double sampling (CDS/SS-ADC) in a CMOS image sensor (CIS) is composed of several operation phases in which the circuit topologies are different from each other, the noise cannot be estimated by the conventional FNS. This paper presents a noise estimation method for the CDS/SS-ADC that uses the FNS results while the transient noise behavior is taken into account. The proposed method provides noise estimation results closer to that of the TNS than the conventional FNS, whereas the simulation time is about the same as that of the FNS.

A Single-Chip CMOS Smoke and Temperature Sensor for an Intelligent Fire Detector

A single-chip CMOS smoke and temperature sensor for use as an intelligent fire detector is proposed. The proposed smoke sensor measures smoke density based on the light-scattering method. The temperature sensor is integrated with the smoke sensor not only to sense heat from a fire but also to compensate for the temperature dependency of the smoke sensor. The prototype chip includes an on-chip photodiode (PD), pixel circuit, correlated double sampling (CDS) circuit, and analog-to-digital converter (ADC). The prototype chip was fabricated using a 0.35-mu m CMOS process and was placed inside the smoke detection chamber, while the thermistor for the temperature sensor is placed outside the chamber. The measurement results show plusmn 1% smoke detection accuracy over the range 4% ~ 25% and plusmn1degC temperature-sensing accuracy over the range 25degC ~ 95degC. The power consumption of the prototype chip is 220 nW, excluding the infrared light-emitting diode (IR LED).

Bulk Switching Instrumentation Amplifier for a High-Impedance Source in Neural Signal Recording

Flicker noise is the most crucial issue in an instrumentation amplifier (IA) for neural recordings because low-frequency neural signals overlap with the frequency of the amplifiers flicker noise. A Chopping technique, often used to reduce the flicker noise, is not desirable for high-impedance input sources due to the charge injection and clock feedthrough from the MOSFETs of the input chopper to the signal source, resulting in a significant increase in the total input-referred noise. Whereas MOSFETs have less flicker noise at the moment of turning on, and the intrinsic flicker noise can be then reduced by turning on and off the MOSFETs in the IA. This brief proposes a bulk switching IA, which can avoid the input current noise. A prototype IA is implemented in a 65 nm CMOS occupying 0.053 mm2, and it achieves the input-referred noise of 0.74 μVrms (local field potential) for 100 k Ω source impedance, a 3.3 times reduction compared with that of the chopper IAs, while consuming only 3.96 μW from a 1.2 V supply.

A Low Noise and Low Power CMOS Image Sensor with Pixel-level Correlated Double Sampling

A low noise and low power CMOS image sensor (CIS) with pixel-level correlated double sampling (CDS) is proposed. As the pixel readout circuit using source follower is major readout noise and power consumption source in the conventional CIS structure, the proposed new structure removes the source follower and performs pixel-level CDS and comparing. The proposed CIS is integrated with 240 times 180 pixel array. A pixel fill factor is 32% and its pitch is 8.4 mum. The test chip was fabricated with CMOS 0.35-mum process and its power consumption is 18 mW with 3.3 V occupying 8.1 mm2.

Smart CMOS Image Sensor With High SBR and Subpixel Resolution for Light-Section-Based Range Finding

Light-section (LS)-based range finders are commonly used for obstacle recognition in home service robots and autonomous vehicles. This paper proposes a smart CMOS image sensor for LS-based range finding. The proposed sensor can detect the laser light, even under very strong ambient-illumination levels by using a multiple-capture frame-correlated double sampling (F-CDS), which is realized with an inverter-based switched-capacitor F-CDS accumulator. The proposed sensor also includes on-chip winner-take-all circuits that significantly reduce the software and hardware complexity of interpolation for the subpixel resolution. The prototype chip was fabricated using a 0.35-mum CMOS process. The measurement results show that the proposed sensor can detect a laser line with an intensity that is 56.5 dB lower than that of the ambient illumination, providing a spatial resolution of plusmn0.16 pixels.

A complementary metal-oxide-semiconductor image sensor with analog gamma correction using a nonlinear single-slope analog-to-digital converter

An image sensor has limited dynamic range while the human eye has a logarithmic response over a wide range of light intensity. Although the sensor gain can be set high to identify details in darker areas on an image, this high gain results in saturation in brighter areas. Therefore, gamma correction is essential to match the human eye response. However, the digital gamma correction degrades image quality, especially for darker areas on the image, due to the limited resolution and dynamic range of the analog-to-digital converter (ADC). In this paper, we propose a complementary metal–oxide–semiconductor (CMOS) image sensor (CIS) with a compact nonlinear ADC which performs analog gamma corrections that use the full dynamic range. A CIS with the proposed nonlinear ADC was fabricated with a 0.35-µm CMOS process. The test results show that the analog gamma correction provides a 2.2 dB peak-signal-to-noise-ratio (PSNR) improved image quality, which is better than conventional digital gamma corrections.

An analog front-end of a fire detection SoC for a fire alarm system

An analog front-end of a fire detector, which is comprised of a smoke detector, a heat detector and an ADC, is proposed. The smoke detector with active pixel structure works by optical detection measuring the amount of IR LED light scattered by smoke particles. It achieves the reduction of the mismatch from process variation, the influence of dark current and the reset noise by correlated double sampling scheme. The heat detector is a voltage divider consisting of a negative temperature coefficient thermistor and two resistors. It outputs the voltage corresponding to ambient temperature. Each output voltage from the two detectors is alternately converted into an 8-bit code by a successive approximation ADC every 1 second. The test chip was fabricated in 0.35-mum CMOS process and tested in optical chamber. It can detect smoke density range from 4%/m to 25%/m with plusmn 1%/m accuracy and ambient temperature range from 25degC to 95degC with plusmn 1degC accuracy. Maximum power consumption is 71 muW.

A Low Power Dual-Mode Sigma-Delta Modulator for GSM/WCDMA Receivers

This paper proposes a low power dual-mode sigma- delta (SigmaLambda) modulator for GSM and WCDMA receivers. The proposed modulator satisfies both standards by modifying the transfer function without changing sampling frequency or the loop order. The simulation results show 85 dB dynamic range for a GSM mode and 55 dB for a WCDMA mode. The proposed modulator is designed in a 0.35 mum CMOS process and consumes 5.5 mW of power under 1.8-V supply.

Analysis of 1/ƒ 2 and 1/ƒ 3 noise in the high-pass chopper amplifier with a high-impedance source

Chopper stabilization is the most widely used circuit technique to reduce the influence of the flicker noise in an amplifier. Recently, observation of /f2 input-referred noise in the chopper amplifier with a high-impedance input source was reported. However, the mechanism of this /f2 phenomenon has not been completely analyzed. This paper provides the complete analysis of the noise influence generated by a chopper switch. The analysis suggests that the noise current of a chopper switch is directly fed to the output when the impedance of the input signal source is high. Then, the thermal noise of the chopper switch is reflected to the input showing /f2 characteristic while the flicker noise of the chopper switch is reflected to the input showing /f3 characteristic. This analysis has been verified with the simulation and measurement results.