Power management subsystem with bi-directional DC to DC converter for μ-power biomedical applications

This paper presents a power management subsystem for μ-power biomedical applications. The power management subsystem is embedded in a wireless sensor SoC that requires 1.5V to operate, with the exception of the sensor bias and RF transmitter which require 3V. The proposed power management block can accept a 3V coin cell or 1.5V button cell battery to operate the entire IC. A bi-directional DC/DC converter is implemented such that 3V can be generated from a 1.5V battery, or, alternately, a 1.5V power supply, can be generated from a 3V battery. When using a 1.5V battery the forward mode DC/DC converter generates a 3V supply with 97% efficiency, while in the reverse mode the 3V supply generates a 1.5V supply with 95% efficiency. The circuit is specially designed to be highly efficient with micro-power loads up to 60μW. The power management circuit is comprised of a bi-directional DC/DC converter or Charge Pump, Charge Pump Startup Circuit, Real Time Clock (RTC), Power On reset (POR), micro power bandgap, analog temperature circuit, 6 degree C temperature comparator, LDO, ADC reference and sensor reference. The circuit is fabricated in a 0.35μm BCD technology and occupies an area of 1.125 mm².