Jimin Cheon

A 2.1Mpixel 120frame/s CMOS image sensor with column-parallel ΔΣ ADC architecture

Over the last few years, the demands for high-density and high-speed imaging have increased drastically. Since CMOS image sensors have the advantages of low power consumption and easy system integration, they have become dominant over CCDs in the consumer market [1–4]. A column-parallel ADC architecture is the most widely used ADC in CMOS image sensors for high-speed and low-power operation [2–6]. The column-parallel architecture can be classified as: successive-approximation register (SAR) [2], cyclic [3], single-slope (SS) [4], and delta-sigma (ΔΣ) [5,6] ADCs. Although SAR ADCs have been utilized for high-speed imaging, such as UDTV, they require a DAC in a column, whose area is unacceptably large for consumer electronics with a fine pixel pitch. Cyclic ADCs have also been reported in high-speed imaging, but they have high power consumption and high noise levels. Since SS ADCs provide relatively high resolution with minimum area, they have been widely used in CMOS image sensors. However, SS ADCs require very fast clock signals leading to high power consumption in the case of high-speed imaging. Although ΔΣ ADCs have been investigated for low-noise imaging, they have only been applied for low-speed imaging with large pixel pitch because of the complexity of ΔΣ modulators and following decimation filters.

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).

Wide dynamic range CMOS active pixel sensor with sensitivity control gate

This paper proposes a wide dynamic range CMOS APS pixel array using a sensitivity control gate (SCG) without much degradation in optical performance. The proposed method is realized by adding a polysilicon control gate over the photodiode (PD) area, which adds MOS capacitance to the original PD capacitance. While a single control gate over PD can maximize the range of capacitance PD can have, it also has the maximum light absorption in the gate. By using SCG with holes, fringing capacitance of the control gate can be utilized to effectively sustain the total capacitance range while increasing the QE.

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.

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.