Jarno Salomaa

A High-Resolution Accelerometer With Electrostatic Damping and Improved Supply Sensitivity

In this paper, a charge-balancing accelerometer is presented. A hybrid interface topology is utilised to achieve high resolution, high linearity and low power supply sensitivity. The accelerometer consists of a micromechanical sensor element, a self-balancing bridge (SBB) open-loop readout, AC force feedback and ΔΣ ADC. The SBB converts acceleration to ratiometric voltage. The ratiometric output of the SBB is converted to the digital domain by the ADC. In order to achieve high resolution, a micromechanical sensor element with a high quality factor, Q, is utilised. The AC force feedback is used for damping the high Q to get a low settling time. The sensor interface is fabricated in a standard 0.35 μm CMOS process. The fabricated chip has an area of 6.66 mm2 and consumes 1 mA at a nominal supply voltage of 3.6 V. The sensor has a maximum DC nonlinearity of 1.3% over the commercial temperature range with an input range of ±1.15 g. The noise floor of the sensor is around 2 μg/√{Hz} and the signal bandwidth is 200 Hz. The bias instability is 13 μ g and the sensor gain variation is less than 5% in the 3-3.6 V supply range.

Energy harvesting ASIC for autonomous sensors

In this paper, we present a blackout and brownout insensitive energy harvesting ASIC for ultra-low power autonomous sensor applications. It utilizes both RF or DC power inputs to deliver a regulated voltage for on-chip and off-chip devices. A voltage limiter has been integrated for overvoltage protection. As the ASIC utilizes two regulators alternately, a kick-start method has been used for switching the operation mode. The ASIC is implemented in a 0.18 μm CMOS process. It is able to use a wide range of input DC voltages (0.8...2 V at -40...85 °C) or input AC powers down to -14 dBm.

Power management system for ultra-low power energy harvesting applications

This paper presents a two-regulator power management system for ultra-low power energy harvesting applications. The system consists of an RF-to-DC converter, an LDO and an SC regulator that are connected in parallel operating alternately, and a voltage detector for choosing the operation mode. The system produces a stable 1.2-V output power supply, using a wide range of input DC voltages (0.7...2 V) or input AC powers down to -14 dBm. The system is implemented in a 0.18 μm CMOS process and it has been characterized with load currents from zero to 100 μA.

A 180-nW static power UWB IR transmitter front-end for energy harvesting applications

This paper presents a versatile, FCC compliant ultra-wideband impulse radio transmitter front-end (TFE) that performs well at a wide range of pulse repetition rates up to 105 MHz. The TFE delivers 2.2 pJ pulses with 6.7 % efficiency at 3.8 GHz center frequency. The leakage power is 180 nW from a 1.2 V supply. The TFE operates robustly with a variety of power sources, including a 6.5 cm2 photovoltaic array in office illumination. Along with the low static power consumption level, this feature makes the TFE suitable for energy harvesting applications. The TFE is fabricated in a 180 nm CMOS process.

A 1.3-μW 12-bit incremental ΔΣ ADC for energy harvesting sensor applications

This paper presents an ultra-low power, incremental ΔΣ ADC for sensor applications. The ADC is integrated in an energy harvesting chip, and its power consumption has to be less than 2 μW at temperatures ranging from −40° C to 85° C. The complete system including the ADC, interfacing sensors, and power management circuit is fabricated in 0.18 μm CMOS technology. The ADC works with a single on-chip reference voltage. The fabricated ADC occupies 0.21 mm2, and consumes 1.3 μW from the 1.2-V supply voltage at room temperature. Power consumption increases almost linearly with temperature and reaches 1.7 μW at 85° C. The sleep current is less than 10 nA. In free-running mode at 40 kS/s, the ADC achieves 68 dB peak SNDR with OSR=200. This corresponds to FoMw=1.58 pJ/conv., which is comparable to the state-of-the-art incremental ADCs, while power consumption is at least 5X lower. Measurements with the on-chip temperature sensor verified the ADCs performance.

45.2% Energy efficiency improvement of UWB IR Tx by use of differential PPM in 180nm CMOS

This paper discusses how Differential Pulse Position Modulation (DPPM) can increase the energy efficiency of an UWB impulse radio transmitter when compared to On-Off Keying (OOK). In DPPM, data words are coded in time intervals between consecutive pulses and it saves energy as less pulses are transmitted per bit. A method is shown for minimizing the energy con sumption per bit of a DPPM transmitter by choosing an optimal data word length. Measurement results show an energy efficiency improvement of 45.2%. The jitter of a low-power, low-performance reference clock used in the modulation could cause an unsatisfactory bit error ratio (BER). However, the measurements show that a 1.4 μW, 10 MHz ring oscillator (RO) can enable a BER better than 10−6. The measured transmitter has been implemented in a 180 nm CMOS technology.

A Switched-Capacitor Voltage Regulator for Ultra-Low Power Energy Harvesting Systems

In this paper, an SC voltage doubler-based voltage regulator for ultra-low power energy harvesting applications is presented. It produces a stable 1.2-V power supply, using inputs from 0.63 V to 1.8 V. External compensation and on-chip output capacitor ensure good performance even with zero load current and any load capacitance. The regulator tolerates arbitrary input ramp-ups, and is immune to blackout and brownout. The regulator ASIC is implemented in a 0.18 μm CMOS process. The measured regulator peak power and current efficiency are 63 % (ideal: 80 %) and 49 % (50 %), respectively. The performance has been characterized with load currents from zero to 100 μA.

462-nW 2-axis gesture sensor interface based on capacitively controlled ring oscillators

This paper presents a 2-axis gesture sensor interface that consumes 462 nW powered by a 0.8 V supply. The system consists of two proximity sensor (PS) interfaces that provide digital data outputs. A single PS interface consists of a capacitively controlled ring oscillator (CCRO) whose frequency is sensitive to the capacitance between two copper plates in a coplanar deployment and additional capacitive load introduced by the presence of a hand. The CCRO in each interface is followed by a modified cascaded integrator comb (CIC) filter that performs the frequency-to-digital conversion, filtering and downsampling. When a total of three sensor plates are arranged in parallel, the middle one acting as a shared ground plate, the location of a users hand can be obtained in two dimensions. Measurement results show that hand sweep gestures at 6-cm distance from the sensing plates can be detected by a lightweight algorithm.