Low-power Relaxation Oscillator Research Articles

Low-power Relaxation Oscillator with Temperature-compensated Thyristor Decision Elements

This paper presents a low-power 140 kHz relaxation oscillator (ROSC) for low-frequency clock generators and timers. In voltage-mode ROSCs, unavoidable shunt current consumption results from voltage slewing at the integration capacitor. The proposed circuit employs CMOS thyristor-based decision elements which effectively reduce shunt currents by exploiting internal positive feedback. A complementary-to-absolute temperature (CTAT) current reference compensates for the frequency’s temperature sensitivity. In order to achieve high negative temperature coefficient with small area and power overhead, the circuit reuses parts of the positive-to-absolute temperature (PTAT) bias generation block. Moreover, a modified start-up circuit with 3 times faster oscillator power-on is presented. The 0.09 mm{}^2 oscillator consumes 6.5 nW/kHz at 1.5 V to 2.5 V supply if only the CTAT source is considered, resulting in a power consumption of 907.4 nW at 140 kHz. The measured temperature coefficient of -514.7 ppm/K in the range of −40 °C to 85 °C shows an improvement of 5.5 times compared to the uncompensated case. A supply sensitivity of 2.62 %/V, a frequency resolution of 2.67 kHz/step, and an average clock jitter of 6.02 ns are achieved. The oscillator is embedded in an ultra-low power system-on-chip for autonomous environmental sensing.

Experimental Validation of a Fast-Tracking FOCV-MPPT Circuit for a Wave Energy Converter Embedded into an Oceanic Drifter

Wave Energy Converters (WECs) are an ideal solution for expanding the autonomy of surface sensor platforms such as oceanic drifters. To extract the maximum amount of energy from these fast-varying sources, a fast maximum power point tracking (MPPT) technique is required. Previous studies have examined power management units (PMU) with fast MPPT circuits, but none of them have demonstrated their feasibility in a real-world scenario. In this study, the performance of a fast-tracking fractional open circuit voltage (FOCV)-MPPT circuit (sampling period TMPPT of 48 ms) is compared with a commercial slow-tracking PMU (TMPPT of 16 s) in a monitored sea area while using a small-scale, pendulum-type WEC. A specific low-power relaxation oscillator circuit is designed to control the fast MPPT circuit. The results demonstrate that by speeding up the sampling frequency of the MPPT circuit, the harvested energy can be increased by a factor of three.

Low-power CMOS circuit design of audio frequency shift keying for emergency alert system

Emergency alert systems are highly essential during natural disasters like earthquake, flooding, volcanic eruption, landslides and hurricanes to make the public alert. Existing emergency alert systems use siren, text alert and broadcasting, but they are slow and may not alert at the right time in crucial situations. An Audio Frequency Shift Keying (AFSK) is designed to alert the public in emergency without hearing the text of the alert. It is designed with low power relaxation oscillator and voltage-controlled oscillator using CMOS technology. In this work, a relaxation oscillator is designed with inductor-less circuit for wideband tuning and provides huge area saving in the design. The control unit is designed to select the audio signal with two different oscillation frequencies based on input data. The public would be able to get awareness about the condition of natural disaster based on frequency of audio signal. An AFSK is designed with an operating voltage of 400 mV that consumes only 6.18 µW of power while implementing using 180 nm CMOS technology.

A Low-Power Relaxation Oscillator With Switched-Capacitor Frequency-Locked Loop for Wireless Sensor Node Applications

This letter presents a 600-kHz relaxation oscillator with 2.2- $\mu \text{W}$ power consumption. A low-power frequency-locked loop (FLL) structure is proposed to increase the frequency immunity against process, voltage, and temperature variations. A front regulator is proposed to further enhance the voltage stability and widen the voltage range. A current-injection scheme is proposed to compensate the frequency shift due to the temperature shift of the on-chip resistor. Fabricated with 180-nm technology, this oscillator can operate at an unregulated supply from 1.1 to 3.3 V with 0.046%/V voltage stability. The measured temperature stability is 48.69 ppm/°C from −45 °C to 125 °C and the measured jitterrms is 1.56 ns with 120-k hits.

A low-power relaxation oscillator with high frequency stability for RFID

A low-power relaxation oscillator with a high frequency stability is presented for radio frequency identification (RFID). This oscillator implements an improved self-biased and a comparator multiplexing techniques to reduce the power consumption and chip area. A capacitor resetting delay cancellation technique based on a two-phase operation and a proportional to absolute temperature (PTAT) current with an upward curvature versus the temperature are adopted to maintain the frequency stability. The oscillator is designed in a 65 nm standard CMOS process and occupies a small area of 0.0216 mm2. The post-layout simulation results show that a frequency drift of 0.95% from 0.7 to 1.7 V and a temperature stability of 27 ppm/°C as the temperature varies from − 40 to 85 °C at a typical working frequency of 1.92 MHz. Under a supply voltage of 0.7 V, the maximum power consumption is only 15.4 μW at − 40 °C. At room temperature, the figure of merit (FOM1 and FOM2) are 8 nW/kHz and 89.5 dB, respectively, which makes it more efficient than relaxation oscillators reported to date.

A 1.24 <inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>A Quiescent Current NMOS Low Dropout Regulator With Integrated Low-Power Oscillator-Driven Charge-Pump and Switched-Capacitor Pole Tracking Compensation

Supply regulation using low quiescent current linear regulators helps in extending the battery life of power aware applications with very long standby time. A 1.24 $\mu \text{A}$ quiescent current NMOS low dropout (LDO) that uses a hybrid bias current generator (HBCG) which boosts the bias current dynamically and adaptively to improve the transient response is presented in this paper. A bias-current scalable error amplifier with an on-demand pull-up/pull-down buffer drives the NMOS pass device. The error amplifier is powered with an integrated dynamic frequency charge pump to ensure low dropout voltage. A low-power relaxation oscillator (LPRO) generates the charge pump clocks. A novel switched-capacitor pole tracking (SCPT) compensation scheme is proposed to ensure stability up to maximum load current of 150 mA with a low-ESR 1 $\mu \text{F}$ output capacitor. Designed in a 0.25 $\mu \text{m}$ CMOS process, the LDO has an output voltage range of 1–3 V, a dropout voltage of 240 mV, and a core area of 0.11 mm2.

Synchronization of pairwise-coupled, identical, relaxation oscillators based on metal-insulator phase transition devices: A model study

Computing with networks of synchronous oscillators has attracted wide-spread attention as novel materials and device topologies have enabled realization of compact, scalable and low-power coupled oscillatory systems. Of particular interest are compact and low-power relaxation oscillators that have been recently demonstrated using MIT (metal-insulator-transition) devices using properties of correlated oxides. Further the computational capability of pairwise coupled relaxation oscillators has also been shown to outperform traditional Boolean digital logic circuits. This paper presents an analysis of the dynamics and synchronization of a system of two such identical coupled relaxation oscillators implemented with MIT devices. We focus on two implementations of the oscillator: (a) a D-D configuration where complementary MIT devices (D) are connected in series to provide oscillations and (b) a D-R configuration where it is composed of a resistor (R) in series with a voltage-triggered state changing MIT device (D). The MIT device acts like a hysteresis resistor with different resistances in the two different states. The synchronization dynamics of such a system has been analyzed with purely charge based coupling using a resistive (RC) and a capacitive (CC) element in parallel. It is shown that in a D-D configuration symmetric, identical and capacitively coupled relaxation oscillator system synchronizes to an anti-phase locking state, whereas when coupled resistively the system locks in phase. Further, we demonstrate that for certain range of values of RC and CC, a bistable system is possible which can have potential applications in associative computing. In D-R configuration, we demonstrate the existence of rich dynamics including non-monotonic flows and complex phase relationship governed by the ratios of the coupling impedance. Finally, the developed theoretical formulations have been shown to explain experimentally measured waveforms of such pairwise coupled relaxation oscillators.

All switched-capacitor realized piezoresistive pressure sensor interface chip for automotive TPMS

An all switched-capacitor structure realized piezoresistive pressure sensor interface chip for automotive tire pressure monitoring system is presented. The propose integrated circuit consists of high resolution incremental ADC, low noise switched-capacitor amplifier, high accuracy bangdap reference and low-power relaxation oscillator and other related blocks. Proposed structure was implemented in standard 0.35µm CMOS process with an area of 6.1mm2. The experimental results show that the signal conditioning method provides high accuracy of 1% of the full scale output with a battery voltage from 3.6V to 2.1V over the full military temperature range. The charge consumption results into 25mAh in 10 years, including sleep mode and junction leakage current.