Designed Readout Circuit Research Articles

A 16-Channel Impedance-Readout IC With Synchronous Sampling and Baseline Cancelation for Fast Neural Electrical Impedance Tomography

Fast neural electrical impedance tomography (EIT) is a promising method to not only record neural activities but also to localize them in peripheral nerves in a minimally invasive way. A much higher image frame rate is required for this application than conventional impedance measurement applications, which generally adopt the I/Q demodulation technique. To achieve a high enough frame rate to capture neural activities along the peripheral nerve fascicle, this paper proposes synchronous sampling (SS) and fast baseline tracking based on successive approximation (SA). The SS method needs an injection of only a single or a few periods of square-wave current signal for the amplitude measurement by synchronously sampling the received voltage signal. The proposed SA-based baseline tracking provides fast signal recovery from unwanted motion artifacts or baseline drifts. The designed readout circuit uses a two-step conversion where its coarse bits are generated from a current-based baseline cancellation circuit and its fine bits from a following SAR ADC. Thanks to the baseline tracking based on the SS and SA, the proposed IC achieves a faster frame rate of 312 fps with continuous baseline update and 500 fps with constant baseline compared to state-of-the-art works. The implemented IC is validated by measuring a water-filled tank and reconstructing its tomographic image. The results show successful discrimination of varied impedance areas over the tank.

External temperature sensor assisted a new low power photoplethysmography readout system for accurate measurement of the bio-signs.

This study presents an external temperature sensor assisted a new low power, time-interleave, wide dynamic range, and low DC drift photoplethysmography (PPG) signal acquisition system to obtain the accurate measurement of various bio signs in real-time. The designed chip incorporates a 2-bit control programmable transimpedance amplifier (TIA), a high order filter, a 3:8 programmable gain amplifier (PGA) and 2 × 2 organic light-emitting diode (OLED) driver. Temperature sensor is used herein to compensate the adverse effect of low-skin-temperature on the PPG signal quality. The analog front-end circuit is implemented in the integrated chip with chip area of 2008 μm × 1377 μm and fabricated via TSMC T18 process. With the standard 1.8 V, the experimental result shows that the measured current sensing range is 20 nA–100 uA. The measured dynamic range of the designed readout circuit is 80 dB. The estimated signal to noise ratio is 60 dB@1 uA, and the measured input referred noise is 60.2 pA/Hz½. The total power consumption of the designed chip is 31.32 µW (readout) + 1.62 mW (OLED driver@100% duty cycle). The non-invasive PPG sensor is applied to the wrist artery of the 40 healthy subjects for sensing the pulsation of the blood vessel. The experimental results show that for every 1 °C decrease in mean ambient temperature tends to 0.06 beats/min, 0.125 mmHg and 0.063 mmHg increase in hear rate (HR), systolic (SBP) and diastolic (DBP), respectively. Similarly, for every 1 °C increase in mean ambient temperature tends to 0.13 beats/min, 0.601 mmHg and 0.121 mmHg increase in HR, SBP and DBP, respectively. The measured accuracy and standard error for the HR estimation are 96%, and − 0.022 ± 2.589 beats/minute, respectively. The oxygen stauration (SpO2) measurement results shows that the mean absolute percentage error is less than 5%. The resultant errors for the SBP and DBP measurement are − 0.318 ± 5.19 mmHg and − 0.5 ± 1.91 mmHg, respectively.Electronic supplementary materialThe online version of this article (10.1007/s00542-020-05106-y) contains supplementary material, which is available to authorized users.

A low-power self-biased rail-to-rail preamplifier as a readout circuit for a capacitor-type microphone

This study is dedicated to design a readout circuit to extract the output signal of a capacitive-type MEMS microphone. A low-power preamplifier is forged for a capacitive-type microphone to meet the demands on cell phone applications. The design starts with modeling the electro-mechanical behavior of a biased capacitive-type microphone using combination of AV and DC voltages sources. This aims to enable co-simulation of the microphone and the readout circuit design. The output signal of a capacitance-to-voltage converter is normally small and may cause substantial noise in the output signals. Therefore, a preamplifier is designed and applied to amplify the signal to an acceptable level for the convenience of ensuing signal processing. The designed readout circuit consists of two main sub-circuits, responsible for functions in two different stages. One is a newly-designed self-bias circuit in the structure of a capacitance-to-voltage converter at the first stage, while another is a low-voltage low-power two-stage or rail-to-rail MOS operational amplifier at the second stage. The proposed circuit is implemented by using the technology of TSMC 0.35 µm Mixed-Signal MODE (2P4M, 3.3 V/5 V) POLYCIDE. The supply voltage is fixed at low voltage (3 V), the total power dissipation is merely 200 μW. Experiments are finally conducted to validate the performance of the designed readout circuit from 20 to 20k Hz with appropriate add-on high- and low-pass filters.

Novel portable electrical detection system for DNA SENSOR application

A novel, portable, electrical detection system was constructed for DNA sensor application to detect DNA hybridisation. The read-out circuit consists of an analogue circuit and a digital circuit. The analogue circuit with an IC MAX038 generates a sine wave with a constant frequency (10 kHz), which serves as the input for the DNA sensor. The DNA sensor consists of active and reference sensors. DNA hybridisation between the DNA probe and the target sequences causes changes in the conductance of the conductive membrane (DNA/MWCNTs) on the sensor surface, which lead to changes in the amplitude of the sine wave from the sensor output compared with that of the reference signal output (input sine wave). We used a digital circuit with a microprocessor (PIC33FJ256MC710) to determine the change in the amplitude of the sine wave signal of the sensor. From these digital data, the difference in the amplitudes of the active and reference sensors was calculated and displayed on the liquid crystal display. Measurement results show that the portable electrical detection system can detect DNA target concentrations as low as 0.16 µM. The detection of the amplified polymerase chain reaction sample and the reproducibility of the DNA sensor results were also determined using the designed readout circuit. The proposed electrical detection system is suitable for DNA sensor application.

A Z-axis Quartz Cross-fork Micromachined Gyroscope Based on Shear Stress Detection

Here we propose a novel quartz micromachined gyroscope. The sensor has a simple cross-fork structure in the x-y plane of quartz crystal. Shear stress rather than normal stress is utilized to sense Coriolis’ force generated by the input angular rate signal. Compared to traditional quartz gyroscopes, which have two separate sense electrodes on each sidewall, there is only one electrode on each sidewall of the sense beam. As a result, the fabrication of the electrodes is simplified and the structure can be easily miniaturized. In order to increase sensitivity, a pair of proof masses is attached to the ends of the drive beam, and the sense beam has a tapered design. The structure is etched from a z-cut quartz wafer and the electrodes are realized by direct evaporation using the aperture mask method. The drive mode frequency of the prototype is 13.38 kHz, and the quality factor is approximately 1,000 in air. Therefore, the gyroscope can work properly without a vacuum package. The measurement ability of the shear stress detection design scheme is validated by the Coriolis’ force test. The performance of the sensor is characterized on a precision rate table using a specially designed readout circuit. The experimentally obtained scale factor is 1.45 mV/°/s and the nonlinearity is 3.6% in range of ±200 °/s.