Personnel

FICs - Prof. Philip K. T. Mok

Description

Internet-of-Things (IoT) is an emerging trend which is foreseen to bring about the next wave of semiconductor following the smartphone and broadband wireless communication era. Innovative business models based on interconnected smart sensor nodes, with enhanced features such as machine-to-machine communication, and the Big Data generated from these sensor networks are envisaged. Due to the astronomical number of sensor nodes, minimal battery maintenance is critical to low cost. Energy Harvesting (EH) is a key enabling technology to extend battery-life, or even in some cases, make the IoT sensor node entirely battery-free. To power IoT nodes, energy sources deriving electrical power from solar energy, mechanical vibrations, and heat are available. Each type comes with a different physical size and power (current-voltage) profile. Despite the infinitely available energy from these EH sources, the source impedance is generally high and also highly influenced by environmental changes. Therefore, a critical circuit, called a maximum power point tracking (MPPT) circuit is necessary to constantly condition the EH source, in order to produce the optimum possible power output. Comprehensive MPPT circuits require complex signal processing and current sensing, which are power hungry. For low power solutions, fractional open circuit voltage (FOCV) or hill-climbing approaches using sample-and-hold technique are often implemented. Nevertheless, the power consumption of such solution is still in the microwatts ballpark due to the power hungry op-amp based comparators blocks. Although the scaling of CMOS technologies greatly benefits digital circuits, analog circuits built using advanced CMOS processes such as op-amps suffer several problems such as reduced signal swings and small-signal gain, and poor on-off switch function due to leakage currents, etc. Since the narrowed voltage headroom is the root cause, time-domain signal processing (TDSP) is being considered as an alternate solution to conventional voltage-mode processing techniques. The core idea of TDSP is to utilize controllable delay elements instead of voltage values to represent the signal to be processed. This project explores a novel MPPT circuit using FOCV and the hill-climbing algorithm, based on the TDSP technique, which will further reduce the supply voltage of the MPPT to levels lower than an op-amp based voltage domain solution. This will reduce the microwatt power consumption of current MPPT by at least an order of magnitude, down to the nanowatt level. Prototypes of a DC-DC converter, i.e. inductor-based switching converter and capacitor-based charge pump leveraging on the proposed TD-MPPT circuits, will also be developed.

Source: RGC | ITF