A 110 nA voltage regulator system with dynamic bandwidth boosting for RFID systems

This paper describes a voltage regulator system for ultra-low-power RFID tags (also called passive tags) in a 0.15 mu m analog CMOS technology. These tags derive their power supply from the incoming RF energy through rectification instead of from a battery. The regulator is functional with just 110 nA current. Owing to the huge variation of the rectified voltage (by as much as tens of volts), voltage limiters and clamps are employed at various points along the regulation path. A limiter at the rectifier output clamps the rectifier voltage to a narrower range of 1.4 V. A fine-regulator, then, regulates the supply voltage close to a bandgap reference value of 1.25 V. The key aspect of this regulator is the dynamic bandwidth boosting that takes place in the regulator by sensing the excess current that is bypassed in the limter (during periods of excess energy) and increasing its bias current and hence bandwidth, accordingly. A higher bandwidth is necessary for quick recovery from line transients due to the burst nature of RF transmission, with a larger energy burst requiring a higher bandwidth to settle quickly without large line transients. The challenge of compensating such a regulator across various load currents and RF energy levels is described in this paper.