A 95mV-startup step-up converter with V<inf>th</inf>-tuned oscillator by fixed-charge programming and capacitor pass-on scheme

Abstract

Harvesting energy from the environment by using a thermoelectric generator (TEG) or photovoltaic cells provides a solution for battery-free sensor networks or electronic healthcare systems. In these systems, the harvested energy is supplied at a very low voltages, requiring a low-startup-voltage power circuit for kick-start from low voltage. A previous sub-100mV-startup-voltage boost converter [1] was implemented by using a mechanically assisted step-up process that needs vibration at startup and the application is rather limited. In this paper, a 95mV startup voltage step-up converter without any mechanical stimulus extends the applicability of energy harvesting. The circuit converts a 100mV input to a 0.9V output with 72% conversion efficiency without any external clocks or mechanical switches. A capacitor pass-on scheme eliminates an additional external output capacitor that functions only at the startup.The minimum startup voltage of a step-up DC-DC converter in standard CMOS technology is limited by the oscillator since a clock signal is required for a charge pump (CP). Practically, the minimum supply voltage of an oscillator (V DDMIN ) is limited by PMOS-NMOS V TH unbalance caused by within-die and dieto-die V TH variations. The within-die V TH variation issue can be solved by increasing the channel width and thus it is easily solved in this application. The problem is the die-to-die variation, which can usually be adjusted by controlling the body bias of the MOSFET. In the startup circuit, however, the body-biasing circuit is not functional since the body-biasing circuit needs another oscillator, which does not function below V DDMIN . To solve this problem, post-fabrication V TH programming is applied to the oscillator. Figure 12.1.1 compares the conventional and our step-up converter architectures.In the conventional approach, two external capacitors are required. One (C OUT1 ) is used in the charge-pumping startup circuit and the other (C OUT2 ) is for the boost converter. C OUT1 is needed to separate the boost converter from the CP at the start-up. Otherwise the start-up CP needs to drive the boost converter control circuit, which is seen as leakage current (I Leak ) for the CP. In our scheme, C OUT1 is eliminated by using the output capacitor of the booster, C OUT2 , as the charge buffer of the CP as shown in Fig. 12.1.1(b). Once the C OUT is charged without leakage, C OUT is "passed on" with its charge inside to the boost converter. By doing so, the large external capacitor of C OUT1 is eliminated.The detailed block diagram of the proposed step-up converter and the timing chart are shown in Fig. 12.1.2. The capacitor pass-on controller contains a CP for PMOS super cut-off (PSC) and two voltage detectors D1 and D2. The CP for PSC provides the overdrive voltage to the gate of PMOS switch and reduces the leakage current. At startup, C OUT is charged by the CP and V START rises. When V CP1 (=V START ) is pumped to the preset trip voltage of D1, the node Y changes from low to high to pass on the C OUT to ...

Energy extraction from the biologic battery in the inner ear

“…First, transistor-based electronics require hundreds of millivolts to start up in the absence of expensive semiconductor post-processing 18,19 . Second, the maximum extractable power levels are at least an order of magnitude less than the quiescent power of the most efficient energy-harvesting and energy-sensing circuits in the literature 20-22 .…”

“…We overcame the challenges of energy harvesting from the EP with a custom integrated circuit featuring a wireless kick-start energy receiver and energy buffering power electronics that consume at least an order of magnitude lower power than previous work 19-21 . The low-voltage turn-on issue was addressed by delivery of an initial one-time wireless start-up charging packet 23 of less than 2 s between an external radio frequency source and an on-board 3 × 4 mm 2 loop antenna.…”

Fully Integrated, 100-mV Minimum Input Voltage Converter With Gate-Boosted Charge Pump Kick-Started by LC Oscillator for Energy Harvesting

“…In this work, the ultra-low power voltage detectors (VDs) proposed in [9] are used to monitor VM. In the proposed converter, the detection of two different voltages is required, and hence two types of VDs, the low and high VD, are implemented.…”

Review of Charge Pump Topologies for Micro Energy Harvesting Systems

“…While off-the-shelf harvesters such as Photovoltaic (PV) cells (SANYO, 2008) and Piezoelectric (PZT) harvesters (MIDE, 2013) have voltages above the CMOS voltage threshold, V TH , Thermoelectric Generator (TEG) harvesters (CUI, 2012) generally fall in the mV range as low as 26 mV (Lim et al, 2014) at ∆T = 1K when CUI Peltier device is modelled upon. Therefore, efforts to kick-start CMOS based power management circuits for low voltage harvesters ranges from providing an external bias (Carlson et al, 2010;Kim and Kim, 2013;Ahmed and Mukhopadhyay, 2014), mechanical MEMs switch (Ramadass and Chandrakasan, 2010), charge pump based (Chen et al, 2011;Shih and Otis, 2011;Chen et al, 2012a;Liu et al, 2012;Bender et al, 2014;Peng et al, 2014), transformer based (Im et al, 2012;Teh and Mok, 2014;Zhang et al, 2014), oscillator based (Sun and Wu, 2010;Ahmed and Mukhopadhyay, 2014;Bender et al, 2014), one time wireless charging scheme (Bandyopadhyay, 2013) to a fully electrical multi-stage start-up mechanism (Chen et al, 2012b;Weng et al, 2013;Bender et al, 2014). Although these start-up scheme can push input voltage boundaries down to as low as 20 mV, they are either based on large inductors (Weng et al, 2013) and transformers (Ahmed and Mukhopadhyay, 2014;Bender et al, 2014;Teh and Mok, 2014;Zhang et al, 2014) or off-chip components (Carlson et al, 2010;Ramadass and Chandrakasan, 2010;Kim and Kim, 2013) which limits how small the system can be.…”