A Low-Power Voltage Limiter/Regulator IC in Standard Thick-Oxide 130？nm CMOS for Inductive Power Transfer Application

This paper presents a novel CMOS low-power voltage limiter/regulator circuit with hysteresis for inductive power transfer in an implanted telemetry application. The circuit controls its rail voltage to the maximum value of 3？V DC employing 100？mV of comparator hysteresis. It occupies a silicon area of only 127？μm × 125？μm using the 130？nm IBM CMOS process. In addition, the circuit dissipated less than 1？mW and was designed using thick-oxide 3.6？V NMOS and PMOS devices available in the process library. 1. Introduction and Circuit Description Wireless inductive transfer of power across air gaps between loosely coupled inductors is of significant interest in remote pickup and telemetry. Voltage control using a limiter/regulator is an essential component of such a system. Also, hysteretic voltage control devices are frequently used in power converters [1, 2]. This paper discusses the design, fabrication, and testing of a hysteretic inductive power limiter/regulator for application in implantable telemetry devices. The schematic diagram of the overall wireless power transfer circuit is shown in Figure 1 with the proposed novel CMOS limiter bounded by the rectangular box. The purpose of the implemented integrated circuit is to control its inductively generated rectified rail-to-rail voltage attained through the wireless power transfer. The current induced on the wireless pickup coil is rectified using the Schottky diode bridge. The rectified current charges a capacitor (power supply capacitor) connected to the load. The voltages on the positive and negative sides of this capacitor are and , respectively, which also forms the rail voltages of the limiter/regulator. The integrated circuit limiter controls the voltage by periodically shorting both sides (terminals) of the pickup coil to the negative terminal of the capacitor ( rail) using triode regime MOSFET switches. The MOSFET switches are driven by a novel hysteresis comparator. The maximum value of the controlled voltage is limited to 3？V by employing 100？mV of comparator hysteresis and a suitable reference voltage, . The comparator output is sufficiently buffered to drive the large shorting switches with reasonably small turn-on and turn-off delays. A capacitor is used at the noninverting terminal for shorting any spurious signal pickups. All transistor size values in all the figures are provided in micrometers. The top number and the bottom number adjacent to the transistors, respectively, denote the values for the channel width and the channel length. Figure 1: Schematic diagram of the overall circuit.