Selectable upper voltage range monitoring circuit

摘要

A battery voltage measuring circuit for an implantable cardiac device is presented. Since the usable battery voltage for the device is limited to an upper range of voltages, the need for measuring lower voltages at which the battery is approaching end of life is of no use. The disclosed invention allows for the measurement of a selectable upper range of battery levels that can be chosen without using a level shifting device such as a zener diode. Multiple voltage ranges with associated measurement resolutions can be achieved without using high current zener diode implementations. This allows for a trade-off between measurement range and resolution while resulting in a lower power and more accurate measurement circuit. Conventional zener diode implementations only allow for a single measurement range and are prone to non-linear error as the voltage measurement range increases.

主权项

1. An implantable cardiac device having a hermetic container including a battery coupled to operational circuitry for providing functionality to the implantable medical device, the operational circuitry including a battery monitoring circuit comprising the following:
a voltage divider to generate a scaled voltage related to a battery voltage; a resistor, Rdiff, having first and second nodes; an amplifier having an output current and taking the scaled voltage and applying the scaled voltage to the first node of the Rdiff resistor; a level shifting reference voltage input coupled to the second node of the Rdiff resistor, such that the current through the Rdiff resistor is related to the difference between the scaled voltage and the level shifting reference voltage at the level shifting reference voltage input; a current mirror coupled to the output of the amplifier driving an output resistance, coupled such that the current mirror uses the current through Rdiff as a reference; and an output generating a battery voltage indicator coupled to the current mirror.