We designed, fabricated, and tested a sweat-based conductivity sensor device toward a real-time, non-invasive physiological condition monitoring device for humans. Sweat collector, conductivity sensor, and the interfacing circuit were developed and combined to form a wearable device. Polydimethylsiloxane (PDMS) based sweat collector was fabricated to collect sweat from skin using the hydraulic pumping action of sweat glands. PDMS sweat collectors were prepared using 3D printed plastic molds. The interfacing circuit was designed based on the results of the conductivity sensor that was characterized by the Electrochemical Impedance Spectroscopy. Human testing was performed to prove the feasibility of the proposed sweat sensing system for the real-time non-invasive monitoring of human sweat. The first reading from the device was obtained in 7–20 min depending on the subject and the location of the electrodes. Sweat rate plateaued after a consistent work load of exercise, as was expected. The sweat conductivity decayed after the first readings due to the initial mineral content of the skin. Finally, an increasing trend in sweat conductivity was observed which may be due to subjects’ changing hydration level.

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A wearable conductivity sensor for wireless real-time sweat monitoring

The invention relates to the technical field of analog-digital conversion and discloses a successive approximation fully differential analog-digital converter with a figure correction function and a processing method thereof, in order to correct the mismatch error of a capacitor array and improve the precision of an analog-digital converter. The analog-digital converter is connected to the positive input end and the negative input end of a comparer in a fully differential way by adopting a DAC unit which is composed of two switch capacitor arrays which are mutually matched; a digital correction positive technology is used for removing the mismatch error of a DAC converter; an input signal is subjected to two times of quantization; during the second quantization, a redundancy capacitance replaces a corrected unit capacitance to participate in the quantization, while the corrected unit capacitance is taken as the redundancy capacitance; and the digital weight of the corrected unit capacitance is corrected according to the digital code difference of previous and next two times of quantization, so that the digital weight is increasingly subjected to convergence to a real analog weight. The average value of the digital code obtained by the two times of quantization is used as the output of ADC, and the converter is applicable to high-precision analog-digital conversion application.

Successive approximation fully differential analog-digital converter with figure correction function and processing method thereof

The invention discloses a successive approximation analog-digital converter and a conversion method thereof. The successive approximation analog-digital converter comprises a subsection multi-level capacitor array with a redundancy bit, a comparator, a weight storage circuit, a coding rebuilding circuit and a control logic circuit. The successive approximation analog-digital converter can reduce complexity of circuit design, save the layout area and power consumption, and accurately measure capacitor mismatch errors and conduct capacitor mismatch error correction without auxiliary capacitor arrays, auxiliary switches and control logics.

Successive approximation analog-digital converter and conversion method thereof

Apparatus and methods are provided for a temperature-compensated oscillator adapted to receive an input reference current. The apparatus and methods include or provide a temperature coefficient control circuit adapted to adjust the input reference current based on temperature information, wherein the temperature coefficient control circuit receives a first signal corresponding to the temperature information at a first signal node, and a second signal corresponding to a trimmed bias signal at a second signal node.

Methods and Apparatus for Clock Oscillator Temperature Coefficient Trimming

The invention discloses a digital calibration method for a high-precision SAR ADC (successive approximation register analog to digital converter). The method comprises the following steps of (1) designing of a calibration DAC (digital to analog converter), digitalizing the error voltage of each capacitor in the high segment of a main DAC, and carrying out digital to analog conversion on the processed calibration codes; (2) designing of digital calibration time sequence, obtaining the calibration codes, maintaining sampling, and gradually converting. The method is applied to the high-precision SAR ADC, and a capacitor array of the high segment in the sectional main DAC is subjected to digital calibration, so the mismatch of the capacitors caused by parasitic capacitors and the process manufacturing error is reduced, the problem of unable realizing of precise double relationship due to the mismatch of the adjacent capacitors in the high segment is greatly corrected, and the precision of the SAR ADC is effectively improved.

Digital calibration method for high-precision SAR ADC (successive approximation register analog to digital converter)

Sequential approximation analog to digital converter with digital correction and processing method thereof

The invention provides a relaxation oscillator with a low temperature drift characteristic and a debug method thereof, and relates to an oscillator field. The oscillator circuit comprises a bias module, a register and an oscillation module. The oscillation module is composed of a switching structural circuit, a comparator and a capacitor charging and discharging circuit. The oscillator uses switching structural circuit as a core, and a debug method of a current adjusting mode is combined, such that monolithic integration of the relaxation oscillator is realized while the oscillation frequency of the oscillator obtains excellent temperature stability. The disclosed switching structural circuit in the invention is provided for enable the relaxation oscillator to acquire the good temperature stability. According to a working principle of the circuit, the relaxation oscillator always possesses the good temperature stability no matter threshold voltages with different temperature characteristics are provided to the comparator by components in the switching structural circuit. The relaxation oscillator with the low temperature characteristic in the invention and the debug method thereof are suitable for any standard CMOS technologies.

Relaxation oscillator with low temperature drift characteristic, and debug method thereof

A fully integrated supply voltage and temperature variation-tolerant relaxation oscillator for biomedical systems has been presented. Concepts of dynamic threshold and switched resistors are proposed to improve the frequency stability against power supply and temperature variations, respectively. This design was verified in a 0.35- $\mu{\rm m}$ standard CMOS process with a 3 V supply. Measurement results show the frequency drift of 0.6% from 2.4 to 4.0 V and temperature stability of 53.9 ppm/ $^{\circ}{\rm C}$ as temperature varied from ${-}{30}{}^{\circ}{\rm C}$ to 120 $^{\circ}{\rm C}$ at a typical working frequency of 4 MHz. With the consideration of resistor and transistor matching, the oscillator was implemented in a core area of 0.05 ${\rm mm}^{2}$ .

A Supply Voltage and Temperature Variation-Tolerant Relaxation Oscillator for Biomedical Systems Based on Dynamic Threshold and Switched Resistors

The invention discloses a constant voltage output charge pump circuit. The circuit comprises a pump circuit, a clock generating circuit, a first feedback loop circuit and a second feedback loop circuit. The pump circuit comprises a switching device for switching clock signals when the pump circuit is switched to work between the first stage and the second stage and an adjusting device for adjusting the magnitude of the output voltage of the pump circuit of the second stage. The clock generating circuit is used for generating clock signals enabling the switching device to work. The first feedback loop circuit monitors the output voltage of the pump circuit to generate a corrected voltage to the adjusting device of the pump voltage so as to control the output voltage of the pump circuit. The second feedback loop circuit monitors the output voltage of the pump circuit to generate an enabling signal to the clock generating circuit so as to determine whether the pump circuit works and control the output voltage of the pump circuit. Therefore, the charge pump circuit can keep constant output voltage under the condition of variable input voltage or load so as to prevent the output voltage from changing together with the change of the input voltage or the load.

Constant voltage output charge pump circuit

A relaxation oscillator for high accuracy application is proposed in this paper. A Dynamic-Threshold (DT) concept is introduced to obtain low power-sensitivity characteristics of frequency, Switched-Resistor (SR) is adopted for frequency stability to temperature and current trimming is also utilized to compensate process drift. Simulation with typical frequency of 5MHz was conducted in 0.18μm CMOS process and shows that the peak error of oscillator’s frequency is 0.41% with supply variation of ±10% and temperature drift is only 8.2ppm/°C. The frequency inaccuracy is less than 0.3% via digital trimming for 20% offset of resistances.

Zhentao Xu

Papers

Sequential approximation analog to digital converter with digital correction and processing method thereof

Relaxation oscillator with low temperature drift characteristic, and debug method thereof

A Supply Voltage and Temperature Variation-Tolerant Relaxation Oscillator for Biomedical Systems Based on Dynamic Threshold and Switched Resistors

Constant voltage output charge pump circuit

Design of a Relaxation Oscillator with Low Power-Sensitivity and High Temperature-Stability