A Power-Efficient Sensing Approach for Pulse Wave Palpation-Based Heart Rate Measurement

Heart rate (HR) is an essential indicator of health in the human body. It measures the number of times per minute that the heart contracts or beats. An irregular heartbeat can signify a severe health condition, so monitoring heart rate periodically can help prevent heart complications. This paper presents a novel wearable sensing approach for remote HR measurement by a compact resistance-to-microcontroller interface circuit. A heartbeat’s signal can be detected by a Force Sensing Resistor (FSR) attached to the body near large arteries (such as the carotid or radial), which expand their area each time the heart expels blood to the body. Depending on how the sensor interfaces with the subject, the FSR changes its electrical resistance every time a pulse is detected. By placing the FSR in a direct interface circuit, those resistance variations can be measured directly by a microcontroller without using either analog processing stages or an analog-to-digital converter. In this kind of interface, the self-heating of the sensor is avoided, since the FSR does not require any voltage or bias current. The proposed system has a sampling rate of 50 Sa/s, and an effective resolution of 10 bits (200 mΩ), enough for obtaining well-shaped cardiac signals and heart rate estimations in real time by the microcontroller. With this approach, the implementation of wearable systems in health monitoring applications is more feasible.

A Low-Power CMOS Bandgap Voltage Reference for Supply Voltages Down to 0.5 V

A voltage reference is strictly required for sensor interfaces that need to perform nonratiometric data acquisition. In this work, a voltage reference capable of working with supply voltages down to 0.5 V is presented. The voltage reference was based on a classic CMOS bandgap core, properly modified to be compatible with low-threshold or zero-threshold MOSFETs. The advantages of the proposed circuit are illustrated with theoretical analysis and supported by numerical simulations. The core was combined with a recently proposed switched capacitor, inverter-like integrator implementing offset cancellation and low-frequency noise reduction techniques. Experimental results performed on a prototype designed and fabricated using a commercial 0.18 μm CMOS process are presented. The prototype produces a reference voltage of 220 mV with a temperature sensitivity of 45 ppm/°C across a 10–50 °C temperature range. The proposed voltage reference can be used to source currents up to 100 μA with a quiescent current consumption of only 630 nA.

A 3.0 Gsymbol/s/lane MIPI C-PHY Receiver with Adaptive Level-Dependent Equalizer for Mobile CMOS Image Sensor

A 3.0 Gsymbol/s/lane receiver is proposed herein to acquire near-grounded high-speed signals for the mobile industry processor interface (MIPI) C-PHY version 1.1 specification used for CMOS image sensor interfaces. Adaptive level-dependent equalization is also proposed to improve the signal integrity of the high-speed receivers receiving three-level signals. The proposed adaptive level-dependent equalizer (ALDE) is optimized by adjusting the duty cycle ratio of the clock recovered from the received data to 50%. A pre-determined data pattern transmitted from a MIPI C-PHY transmitter is established to perform the adaptive level-dependent equalization. The proposed MIPI C-PHY receiver with three data lanes is implemented using a 65 nm CMOS process with a 1.2 V supply voltage. The power consumption and area of each lane are 4.9 mW/Gsymbol/s/lane and 0.097 mm2, respectively. The proposed ALDE improves the peak-to-peak time jitter of 12 ps and 34 ps, respectively, for the received data and the recovered clock at a symbol rate of 3 Gsymbol/s/lane. Additionally, the duty cycle ratio of the recovered clock is improved from 42.8% to 48.3%.

A Very Low-phase-noise CMOS Ring VCO Intended for Sensor Interfaces

<p>We describe in the paper a ring voltage-controlled oscillator (VCO) indicating an improved phase noise over a wide range of frequency offsets and an extended frequency/voltage tuning range. The phase noise is improved by leveraging a better linearity approach, while reducing the VCO gain and maintaining wide tuning range. The proposed VCO is a block of a time-domain comparator embedded in a monitoring and readout circuit of an industrial sensor interface. An analytical model is extracted resulting in closed-form expressions for both input-referred noise and phase noise of the VCO. Employing the analytical expressions, the contributed noise and phase noise limitations are fully addressed, and all the effective factors are investigated. The prototype of the proposed VCO was implemented and fabricated in a 0.35 µm CMOS process. The integrated VCO consumes 0.903 mW from a 3.3 V supply, when running at its maximum frequency of 9.37 MHz. The measured phase noise of the proposed VCO is -147.57 dBc/Hz at 1 MHz offset from the 9.37 MHz oscillation frequency, and the occupied silicon area of circuit is 0.005 mm².</p>

A Very Low-phase-noise CMOS Ring VCO Intended for Sensor Interfaces

<p>We describe in the paper a ring voltage-controlled oscillator (VCO) indicating an improved phase noise over a wide range of frequency offsets and an extended frequency/voltage tuning range. The phase noise is improved by leveraging a better linearity approach, while reducing the VCO gain and maintaining wide tuning range. The proposed VCO is a block of a time-domain comparator embedded in a monitoring and readout circuit of an industrial sensor interface. An analytical model is extracted resulting in closed-form expressions for both input-referred noise and phase noise of the VCO. Employing the analytical expressions, the contributed noise and phase noise limitations are fully addressed, and all the effective factors are investigated. The prototype of the proposed VCO was implemented and fabricated in a 0.35 µm CMOS process. The integrated VCO consumes 0.903 mW from a 3.3 V supply, when running at its maximum frequency of 9.37 MHz. The measured phase noise of the proposed VCO is -147.57 dBc/Hz at 1 MHz offset from the 9.37 MHz oscillation frequency, and the occupied silicon area of circuit is 0.005 mm².</p>