Search

This work presents high resolution and adaptable frequency measurement techniques for relaxation oscillator based capacitive sensors. The techniques rely on extremely simple hardware such as a 1-bit coarse voltage quantizer to generate a 1-bit data stream and subsequently determine frequencies with resolutions greater than 20 bits from the 1-bit data stream. The proposed readouts are based on two types of 1-bit hardware approaches with Nyquist sampling in one approach and oversampling in the other. The first approach employs a Nyquist rate sampled 1-bit comparator while the second approach relies on an oversampled 1-bit quantizer based delta-sigma modulator (DSM) as a hardware to generate the bit stream. High resolution frequency is estimated from the 1-bit data stream using parametric, non-parametric and compressed sensing approaches. We provide detailed study and measurement results comparing the performance of the proposed techniques for test inputs with different frequencies and amplitudes and multiple signal shapes including sine, square, triangular and sawtooth. We show that the 1-bit comparator along with the CS approach provides the best performance across all input amplitude, frequency and shapes. A capacitive water level sensor was implemented in a PCB and embedded in a conventional square wave relaxation oscillator to verify the proposed technique. Measurement results show that incremental SNRs can be achieved only by increasing the 1-bit data stream length without any change in the hardware thereby demonstrating the adaptability of the technique based on an application requirement. [ABSTRACT FROM AUTHOR]

This brief proposes a novel current output resistor string DAC architecture implemented for a 10-bit resolution. The DAC consists of a 6-bit coarse resistor string DAC followed by a 4-bit multi-input interpolation amplifier, and a voltage to current conversion stage. Use of a multi-input interpolation amplifier with shared resistive load provides accurate fine conversion with reduced resistor count. The current output DAC has high output impedance from the regulated current source architecture. The prototype was fabricated in a 0.18 μm CMOS process technology. The measured integral non-linearity (INL) and differential non-linearity are 0.5 LSB and 0.4 LSB, respectively. The chip consumes static power 0.54 mW at 1.8 V supply and occupies 0.042 mm2 area. [ABSTRACT FROM AUTHOR]

Economical sensing and recording of temperature are important in the transportation and management of fragile goods such as medicine, fish/poultry, and other temperature-sensitive items. Existing approaches measure the entire temperature profile using electronic devices running on a continuous power source. This letter presents a simple, intelligent, and battery-free solution for capturing interesting temperature events using the natural thermo-mechanical state of a shape memory alloy (SMA). Our approach utilizes the temperature variation induced irreversible configuration of SMA, which provides a natural ability to capture the temperature history without the need for electronic data logging. In this letter, SMA is used to record the threshold temperature violation event. A prototype antenna is shown to monitor the temperature at 30  $^\circ$ C with a $\pm$ 1  $^\circ$ C error. A difference of 17 dB in frequency response was observed with and without temperature violation. Detailed design and experimental studies have been performed to validate the proposed approach. [ABSTRACT FROM AUTHOR]

There is a need for economical monitoring of fragile goods that are sensitive to temperature, tilt or vibrations during transit. The mishandling of these goods could permanently alter or damage them. Existing methods rely on electronic devices that need a continuous power source for sensing and data logging. This article introduces a simple battery-free economical solution for recording a singular event of temperature crossing or a tilt activity using liquid metal, namely eutectic gallium indium (EGaIn) coupled to a Radio-Frequency Identification (RFID) tag. The crossing of a threshold of either temperature or tilting angle results in EGaIn flow, which activates or deactivates the RFID tag permanently. This change is irreversible; thus, the sensor memorizes the specific temperature or tilt event. This built-in memory function and wireless communication of the RFID sensor enables economical monitoring of temperature and motion-sensitive goods during transport without the need for a battery. In this paper, we have further reduced cost by fabricating these temperature and tilt sensors on paper substrates. [ABSTRACT FROM AUTHOR]

We present washable smart sensing threads for creation of smart wearable fabrics. More specifically, we report the fabrication of a facile stretchable and washable thread-based strain/force sensor, which can be sewn into wearable textiles and is capable of measuring human physiological motion. We use polybutylene terephthalate (PBT) puffy threads as our substrate which is made strain-sensitive using a simple reel-to-reel coating process. While PBT in itself is not very stretchable, threads made from them have coiled helical filaments. Stretching such threads uncoils these filaments imparting them stretchability. To convert them into strain sensor, we coat these PBT threads with resistive carbon ink. The straightening (uncoiling) of the helical filaments changes its resistance. There is a negligible change in resistance after repeated washing steps. Such washable immunity is achieved by coating thin layer of PDMS on them. The sensor exhibits a constant gauge factor of ~2.5 within its working range (50% strain) and exhibits a linear response to applied strain up to 50% of its initial length. Such strain sensing threads can form the basis of smart fabrics that can track human motion and for use in real-time physiological monitoring. We present promising results on the detection of the human form (seated versus standing) and human motion (running versus walking) using these threads sewn onto trousers. [ABSTRACT FROM AUTHOR]

This paper presents a novel ${\text{32}}\times {\text{64}}$ CMOS image sensor for luminescence imaging with direct lifetime-dependent digital pulse frequency modulated output. Recently reported parasitic insensitive multicycle charge modulation scheme is applied to accumulate photon-generated charges in discrete programmable time windows over multiple exposures. An autoreset pulse serving as the digital output is generated by comparing the multicycle charge integrated output with a reference threshold. The detected luminescence's lifetime is extracted by monitoring the frequency in this digital pulse. To compensate for the background photocurrent generated by ambient light and built-in offset, a charge pump based calibration circuitry is also proposed. Driven by a 10-KHz clock signal with 20-μs pulse width as the integration time window, the proposed circuitry can achieve $\text{93 Hz/}(\mu \text{W/cm}^{2})$ responsivity and ${\text{19 nW/cm}}^{2}$ resolution at 575 nm wavelength. It has lifetime resolution of 8 ns. The proposed sensor chip was applied for lifetime measurement of a Ru(dpp)3(PF6)2 fluorescent sample whose lifetime was estimated to be 4.2 μs. A two-dimensional luminescence intensity and lifetime images of a single white LED have also been obtained to further validate its functionality. [ABSTRACT FROM AUTHOR]

Luminescence plays an important role in many scientific and industrial applications. This paper proposes a novel complementary metal–oxide–semiconductor (CMOS) sensor chip that can realize both luminescence intensity and lifetime sensing. To enable high sensitivity, we propose parasitic insensitive multicycle charge modulation scheme for low-light lifetime extraction benefiting from simplicity, accuracy, and compatibility with deeply scaled CMOS process. The designed in-pixel capacitive transimpedance amplifier (CTIA) based structure is able to capture the weak luminescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated 10-ms time windows and 10-μs pulsewidth. A pinned photodiode on chip with 1.04 pA dark current is utilized for luminescence detection. The proposed CTIA-based circuitry can achieve 2.1-mV/(nW/cm2) responsivity and 4.38-nW/cm2 resolution at 630 nm wavelength for intensity measurement and 45-ns resolution for lifetime measurement. The sensor chip is employed for measuring time constants and luminescence lifetimes of an InGaN-based white light-emitting diode at different wavelengths. In addition, we demonstrate accurate measurement of the lifetime of an oxygen sensitive chromophore with sensitivity to oxygen concentration of 7.5%/ppm and 6%/ppm in both intensity and lifetime domain. This CMOS-enabled oxygen sensor was then employed to test water quality from different sources (tap water, lakes, and rivers). [ABSTRACT FROM AUTHOR]

This paper presents a new inverter-based architecture that implements an asynchronous delta–sigma modulator. Different from the classical architecture, it features an input transconductor that promotes a differential and high input impedance that makes it easier to interface with sensors and other front ends. Furthermore, an inverter-based relaxation oscillator accomplishes the required hysteresis through a charge redistribution process, which exhibits lower time delay than hysteretic comparators, besides saving power from quiescent biasing. The circuit has been implemented in 130-nm CMOS digital process using halo-implanted transistors. In addition, transistors are biased in weak inversion and are implemented using distributed layout to reduce power consumption besides mitigating halo-implants undesired effects. Supplied with 0.25 V, the proposed architecture consumes 20 nW with just −55 dB of third harmonic distortion, making it suitable for wearable biomedical applications where energy consumption, low bandwidth, and moderate resolution are required. [ABSTRACT FROM AUTHOR]