Time-domain Readout Research Articles

A Time-Domain Readout Technique for Neural Interfaces Based on VCO-Timestamping.

CMOS neural interfaces are aimed at studying the electrical activity of neurons and may help to restore lost functions of the nervous system in the future. The central function of most neural interfaces is the detection of extracellular electrical potentials by means of numerous microelectrodes positioned in close vicinity to the neurons. Modern neural interfaces require compact low-power, low-noise readout circuits, capable of recording from thousands of electrodes simultaneously without excessive area consumption and heat dissipation. In this article, we propose a novel readout technique for neural interfaces. The readout is based on a voltage-controlled oscillator (VCO), the frequency of which is modulated by the input voltage. The novelty of this work lies in the postprocessing of the VCO output, which is based on generating digital timestamps that contain temporal information about the oscillation. This method is potentially advantageous, because it requires mostly digital circuitry, which is more scalable than analog circuitry. Furthermore, most of the digital circuitry required for VCO-timestamping can be shared among several VCOs, rendering the architecture efficient for multi-channel architectures. This article introduces the VCO-timestamping concept, including theoretical derivations and simulations, and presents measurements of a prototype fabricated in 0.18-μm CMOS technology. The measured input-referred noise in the 300 Hz-5 kHz band was 5.7 μVrms, and the prototype was able to detect pre-recorded extracellular action potentials.

An energy autonomous and battery-free measurement system for ambient light power with time domain readout

Internet of Things (IoT) provides more and more adequate infrastructures for many applications and advanced services. This context promotes the ability to satisfy the growing demand for innovative measuring systems, increasingly popular with intelligent nodes, totally wireless, easy to install that require the least possible maintenance. This paper aims to contribute to the state-of-the-art with an energy-autonomous and battery-free measurement platform designed to measure the ambient light power when its level exceeds the Limit of Detection (LoD) threshold. The proposed system consists of a single photovoltaic transducer to harvest energy and simultaneously detect ambient light. The result is a wireless measurement platform, which requires neither a battery nor a specific ambient light sensor, with the immediate advantage of achieving greater energy efficiency and using fewer components. The device implements off-the-shelf components on a printed circuit board (PCB) with a tag size of 2 × 2cm2. Data communication is via Bluetooth Low Energy (BLE) and, the device can acquire energy and detect ambient light from 250lux.

A fully autonomous platform for power measurement of environmental RF sources based on a time domain readout

Abstract The introduction of Internet of Things (IoT) technologies, connected and synchronized devices, and smart solutions have brought tremendous technological advancements in global communication. The increasing demand for innovative measurement systems, smart sensing nodes and battery-less instruments is challenging instrumentation and measurement industries to improve communication, power budget and the efficiency in Wireless Sensor Nodes (WSN). In this context, this paper aims to contribute to the state of the art with an energy autonomous platform for power measurement in RF environments. The architecture is a self-sustained, battery-free Radio Frequency (RF) measurement system with a time domain record that it can transmit to receiving stations through appropriate IoT channels. This paper discusses the viability of a battery-free measuring device capable of initiating measurement activity only when ambient RF power levels rise above set thresholds. The paper presents the working principles through modeling, simulation and experimental characterization in order to demonstrate the validity of the proposed method.

A 1.2V Self-Referenced Temperature Sensor With a Time-Domain Readout and a Two-Step Improvement on Output Dynamic Range

A self-referenced temperature sensor with a time-domain readout and a two-step improvement on output dynamic range is presented in this paper. The proposed temperature sensor utilizes BJTs to generate temperature dependent/independent currents, which are converted to digital bits using a ring-oscillator-based time-domain readout scheme. A novel two-step improvement on output dynamic range is proposed to improve the power-efficiency and simplify the hardware design with a high conversion rate. Furthermore, the adopted process compensation strategy and the self-referenced readout scheme make the whole temperature sensor robust to process and supply variations. Fabricated in a standard 0.13- $\mu \text{m}$ CMOS process, the proposed temperature sensor occupies a die area of 0.06 mm2 and consumes 9.92 nJ per conversion at a conversion rate of 75 kSa/s. After one-point calibration at 20 °C, the sensor achieves inaccuracies of −2.88 °C/+2.71 °C and −1.7 °C/1.36 °C from −20 °C to 100 °C, with and without systematic nonlinearity removal, respectively. It shows an average supply sensitivity of 0.0136 °C/mV from 1.05 V to 1.4 V without any external reference clock or voltage regulators.

Time-Domain Readout of 1T–1C DRAM Cells

The conventional readout of one-transistor–one-capacitor dynamic random-access memories (1T–1C DRAMs) depends on using a sense amplifier to develop the bitline voltage and settle it to the voltage of the power supply, [Formula: see text], or to 0[Formula: see text]V depending on whether the stored data is “1” or “0,” respectively. However, using the sense amplifier makes the reading process sluggish. In this paper, a capacitive-voltage divider-based readout scheme is proposed. According to this scheme, the developed bitline voltage is converted into a pulse with a certain starting time. Specifically, this pulse appears at a later time in case of “0” storage than that if a “1” is stored, thus the proposed scheme is aptly called “time-domain readout.” The effects of parameter and component mismatches and technology scaling on the proposed scheme are investigated. The proposed scheme is analyzed quantitatively with a suggestion given to widen the time gap between the starting times of the pulses corresponding to the “0” and “1” states. The proposed scheme is verified by simulation adopting the 45 nm CMOS technology with [Formula: see text][Formula: see text]V. According to the simulation results, percentage savings of 68.8%, 56.8%, and 32% in the read-access time, the read-cycle time, and the average power-delay product, respectively, are shown. The proposed scheme requires approximately 40% extra area overhead for the reading circuitry. Also, a noise analysis is performed and it is found that the device noise does not affect the proposed scheme significantly.

A Passive RFID Tag Embedded Temperature Sensor With Improved Process Spreads Immunity for a $-{\hbox {30}}^{\circ}{\hbox {C}}$ to 60$^{\circ}{\hbox {C}}$ Sensing Range

We present an ultra-low power temperature sensor embedded in the passive RFID tag using the TSMC 1P6M 0.18 μm standard CMOS process. Substrate parasitic NPN bipolar pair is exploited to generate the temperature dependent current signals for thermal sensing. A time-domain readout scheme which has high immunity to the on-chip resistor, capacitor and clock frequency process-voltage-temperature (PVT) spreads is further proposed. Measurement results of the embedded sensor within the tag system shows a sensing accuracy of ±1.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (3σ) from -30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C to 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C after one-point calibration at 20 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, with a sensing resolution of 0.3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C and a sampling rate of 68 samples per second. The embedded sensor draws 0.35 μA from a 1 V supply at room temperature and occupies a chip area of 0.14 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

A ferrofluid inclinometer with a Time Domain Readout strategy

In this paper a tilt sensor exploiting the effect of the imposed tilt on a mass of ferrofluid free to slide along a glass channel is presented. The proposed inclinometer consists of a 10mm diameter pipe containing a 0.25ml of ferrofluid, an actuation coil to control the ferrofluid mass movement and two sensing coils to monitor its position. The actuation and the sensing coils are wound around the pipe and the length of the actuation/sensing system is 78mm.The novelty of this device, as respect to solutions already presented in the literature, consists in the conversion of the device tilt into the time elapsed between transitions of the ferrofluid mass in two fixed positions inside the channel. This Time Domain Readout strategy allows to implement a device with a frequency output which can be intended as the main advantage of the solution proposed.

A Ferrofluid Inclinometer with a Time Domain Readout Strategy

In this paper a tilt sensor exploiting the effect of the imposed tilt on a ferrofluid drop free to move inside a glass channel is presented. The proposed inclinometer consists of a 10 mm diameter pipe containing a 0.25 ml of ferrofluid, an actuation coil to control the ferrofluid mass movement and two sensing coils to monitor the mass position. The actuation and the sensing coils are wound around the pipe and the length of the actuation/sensing system is 78 mm. The novelty of this device, as respect to solutions already presented in the literature, consists in the conversion of the device tilt into the time elapsed between transitions of the ferrofluid mass in two fixed positions inside the channel. This time domain readout strategy allows to implement a digital form of the device output which can be intended as the main advantage of the solution proposed.