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Structural Design of a CMOS Voltage Regulator for an Implanted Device

There is a great interest in the development of equipment and devices that can accurately and efficiently monitor biological signals such as blood pressure, heart beat and body temperature, among others. It is highly desirable to have those devices operating in an environment free of wires, where the information can be accessed remotely and processed in real time by external equipments. When the equipments are connected to communication network they form a telemedicine system by which the patients can be monitored remotely (biotelemetry), even over the internet, thus indicating the portability of these instruments (Miyazaki, 2003; Puers, 2005; Scanlon et al, 1996). Microelectronics has become a powerful tool when used in this scenario. In recent years, integrated circuits are being fabricated with large densities and endowed with intelligence. The reliability of those systems has been increasing and the costs are lowering. The interaction between medicine and technology, as it is the case of microelectronics and biosensor materials, allows the development of diagnosing devices capable of monitoring pathogens and deceases. The design of sensors, signal conditioners and processing units aims to find solutions in which the whole system can be placed directly in the patient or, more desirable, implanted. It becomes a Lab-on-Chip and Point-of-Care device (ColomerFarrarons, 2009). Since the implanted device becomes part of a biological data acquisition system it must meet few requirements such as reduced size, low power consumption and the possibility of being powered by an RF link, then it operates as a passive RFID tag (Landt, 2005). The low power restriction is extremely important for the patient safety, by avoiding heating due to the increase of current density in the tissues surrounding the implant that could cause tissue damage. The power restrictions mean also limited power of RF transmitter that can, as well, to induce dangerous electromagnetic fields – EMF. The focus in this chapter is to discuss the implementation of a Linear Voltage Regulator – LVR by considering the use of a low cost CMOS process, low-power, low silicon area and simple circuit topology.