Valentijn De Smedt

Supply-Noise-Resilient Design of a BBPLL-Based Force-Balanced Wheatstone Bridge Interface in 130-nm CMOS

An energy-efficient and supply- and temperature-resilient resistive sensor interface in 130-nm CMOS technology is presented. Traditionally resistive sensors are interfaced with a Wheatstone bridge and an amplitude-based analog-to-digital converter (ADC). However, both the unbalanced Wheatstone bridge and the ADC are highly affected by supply voltage variations, especially in smaller CMOS technologies with low supply voltages. As alternative to ratiometric measuring, this paper presents a force-balanced Wheatstone bridge interface circuit with a highly digital architecture that combines the advantage of energy-efficient sensing with highly improved overall PSRR and temperature resilience in one circuit. The prototyped circuit has a noise-frequency-independent PSRR of 52 dB, even for supply-noise amplitudes up to +10 dB FS. The maximum absolute output error in a supply voltage range of 0.85-1.15 V is only 0.7%, while the maximum absolute output error in a temperature range of 100°C is only 0.56% or 56 ppm/°C. The complete interface is prototyped in 130-nm CMOS and consumes 124.5 μW from a 1-V supply with a 10-kHz input bandwidth and 10.4-b resolution and 8.9-b linearity, resulting in a state-of-the-art sensor figure of merit of 13.03 pJ/bit-conversion.

A 0.4-1.4V 24MHz fully integrated 33µW, 104ppm/V supply-independent oscillator for RFIDs

In RFID-tags with pulse-based UWB communication, accurate supply-independent low-power oscillators are required. The 24 MHz oscillator presented was realized in a 130 nm CMOS technology. It has an ultra-low supply voltage dependency of 104 ppm/V over a voltage range of 1.4 V to 0.4 V. This was achieved by the use of two nested ultra-low-power voltage regulators and a novel circuit technique based on the attraction of two oscillator frequencies. The mean power consumption is 33 µW over the 1 V voltage span. No external biasing and no trimming or calibration was used.

A 0.5 V-1.4 V supply-independent frequency-based analog-to-digital converter with fast start-up time for wireless sensor networks

RF-powered wireless sensor networks demand for ultra-low-energy A/D converters. Such systems have specific requirements, like fast start-up time and supply voltage independence. The presented A/D converter is based on a digital phase locked loop. Two closely matched ring oscillators perform the analog to frequency conversion. The digital output is generated by an in-loop digital proportional-integral filter. The acquisition of the PLL is splitted into coarse and fine tuning to reduce the locking time to less than 30µs. A UMC130 CMOS technology is used to simulate a temperature sensor interface. The energy consumption is maximally 212 pJ per conversion and the effective number of bits is 7 bit in a 0.5 V-1.4 V supply voltage range.

A 0.6V to 1.6V, 46μW voltage and temperature independent 48 MHz pulsed LC oscillator for RFID tags

A low-power oscillator based on a pulsed LC tank is presented in this article. The frequency is determined by a bondwire inductor and a MiM capacitor to obtain a high-Q LC tank. Due to a novel way of driving the LC tank, the power consumption is diminished. Since the driving technique only interacts during a very short period with the LC tank, the frequency mainly depends on the stable LC tank and the temperature and supply voltage dependency is lowered drastically. The samples were measured over a 0.6 to 1.6V supply range and a −40 to 100°C temperature range. A temperature dependency of 92 ppm/°C and a voltage dependency of 73 ppm/V is obtained. The frequency standard deviation over 12 automatically bonded samples is 0.76% (359 KHz).

An energy-efficient BBPLL-based force-balanced Wheatstone bridge sensor-to-digital interface in 130nm CMOS

An energy-efficient time-based sensor interface in 130nm CMOS technology is presented for resistive sensors. Traditionally resistive sensors are interfaced with a voltage divider or a Wheatstone bridge to transform the sensor signal to a voltage. However, both the voltage divider and the unbalanced Wheatstone bridge are highly affected by supply voltage variations, especially in smaller CMOS technologies with low supply voltages. As alternative to ratiometric measuring, this paper presents a force-balanced Wheatstone bridge interface circuit with a highly digital architecture, that offers the advantage of low power consumption with highly improved overall PSRR. It has a noise-frequency-independent PSRR of 52dB for in-band supply noise and supply noise amplitudes up to +10dBFS, which is an improvement of 46dB over the voltage divider and of 26dB over the unbalanced Wheatstone bridge. Apart from the sensor calibration, no other calibration or absolute precise clock or voltage references are needed due to the BBPLL-based architecture. The complete interface consumes only 124.5μW from a 1V supply with 10kHz input bandwidth and 10.4 bit resolution and 8.9 bit linearity, resulting in a state-of-the-art sensor Figure of Merit of 13.03 pJ/conversion.

Development of an open-source smart energy house for K-12 education

Energy consumption in buildings represents about one-third of the world-wide energy consumption. Consumers often are not fully aware of energy-conserving measures they could take. Intelligent control of the heating and lighting systems in buildings is one way to increase energy-efficiency. Children and young adults influence domestic energy consumption, by using appliances such as TV and lighting. Often, they are not aware of the costs incurred. The goal of this research is to develop a educational platform for energy efficiency education aimed towards the full age range of K-12 education. A scaled model of a house is used, to explain the energy flows in the residential setting, well-known by the target audience. A model house is designed, with actual loads, using an Arduino Uno electronics platform as an interface to a PC. A reference program in the integrated development environment S4A allows visualizing the energy consumption in a simple manner. The children control a number of scaled household appliances interactively. A survey with the first 25 children (aged 10-12) suggests higher awareness of energy consumption.

A 40nm-CMOS, 18 μW, temperature and supply voltage independent sensor interface for RFID tags

A fully-integrated, oscillator-based sensor interface for RFIDs and low-power applications is presented in this article. The circuit is processed and tested in a 40 nm CMOS technology. The interface translates the analog sensor signal, coming from a differential sensor, into a Pulse width Modulated (PWM) signal of which the duty cycle is proportional to the sensor value. Due to the high control linearity of the used oscillator, the interface has a low nonlinearity and can be made highly temperature and supply voltage independent. The total power consumption is 18 μW at 1.0 V and the interface works over a 0.8 to 1.5 V supply voltage range and a -20 to 100°C temperature range. The voltage dependency is below 1.42 %/V and the maximum temperature dependency is 79 ppm/°C. The oscillator frequency is slightly above 2 MHz in all circumstances. The measured SNDR of 47.4 dB results in a FOM of 66 fJ/b-conv.

A 127 μW exact timing reference for Wireless Sensor Networks based on injection locking

A low power, fully integrated 130 nm CMOS RC oscillator for RFIDs is presented in this article. By making use of injection locking rather then a power hungry PLL, the RFID clock is locked to an external clock signal. The circuit is able to lock to a -59.3 dBm, 1.9 GHz to 2.3 GHz rf-signal which makes locking to a radiated signal received by an antenna feasible. The oscillator itself is used as a 2-fold frequency divider. This leads to an output frequency of 950 to 1150 MHz and a power consumption of 127 μW. Eight samples of the same batch were tested at different supply voltages (0.7 to 1.6 V) and temperatures (-20 to 100°C). Within the lock range, no frequency deviation was measured. The circuit was also successfully tested when driving an ultra wideband transmitter.

Injection-Locked Oscillators

The first person to notice the phenomenon of injection locking was Christiaan Huygens, the inventor of the pendulum clock (Razavi, IEEE J Solid-State Circuits 39(9):1415–1424, 2004; Siegman in Lasers. University Science Books, Mill Valley, 1986). He was surprised to notice that different pendulum clocks attached to the same wooden beam are running perfectly synchronously. Obviously, these pulling effects between clocks are not limited to mechanical clocks. Electrical oscillators also influence each other, and even the generation of a laser beam can be injection-locked to an accurate reference laser. In literature, also many biological locking phenomena are reported, going from pulsing fireflies to our locking to the day and night rhythm (Niknejad, Injection locking, EECS 242 lecture 26, 2013).

Towards Energy-Efficient CMOS Integrated Sensor-to-Digital Interface Circuits

The ever increasing demand for improved autonomy in wireless sensor devices, drives the search for new energy-efficient sensor interface topologies in CMOS technology. Recently, time-based conversion has gained a lot of interest due to its high potential to implement highly-digital circuitry. While voltage-based analog integrated circuits suffer from the decreased supply voltage and voltage swing in highly-scaled CMOS technologies, time-based processing takes advantage of the increased timing resolution. However, how do these time-based sensor interface circuits compare to their amplitude-based counterparts fundamentally? To answer this question, theoretical limits are derived in this chapter for both implementations, which shows that the sensor itself is actually the dominant factor in limiting the achievable energy efficiency. Time-based topologies, however, enable the implementation of highly-digital interfaces, which are scalable, area-efficient and have low-voltage potential. These observations are illustrated with several practical designs.