Cardiac Pacemakers, Inc.

Terrence L Marshall

William J Linder

Keith R Maile

Michael W Dooley

Suneel Arora

A bandgap voltage reference circuit implemented on an integrated circuit chip in which a proportional-to-temperature current is controlled by a current controlling resistor and converted to a voltage by a voltage controlling resistor, with either or both of the resistors being an integrated on-chip digitally trimmable resistor. The reference circuit is particularly suitable for application to circuitry used in implantable medical devices where off-chip resistors provide a channel by which noise can interfere with the operation of the circuit. The on-chip digitally trimmable resistor is implemented in accordance with the invention by a programmable switch matrix connected to a resistor network.

Digitally trimmable resistor for bandgap voltage reference

A current and temperature compensated voltage reference circuit uses a power supply voltage as low as 1.3 Volts. A folded-cascode amplifier measures the temperature dependent voltages provided by first and second bias circuits, each including two series-coupled diodes or diode-connected bipolar junction transistors (BJTs), and provides a resulting proportional to absolute temperature (PTAT) current through a cascode-protected output transistor. A voltage reference circuit uses a PTAT current through a resistor to create a PTAT voltage in series with a diode-voltage. The resistor value is adjusted until the sum of these voltages is equal to the bandgap voltage of silicon, providing a temperature compensated voltage reference. The reference circuit is suitable for use with an implantable cardiac rhythm management system having a battery that provides a power supply voltage varying approximately between 1.3 Volts and 3.25 Volts. Cascode-protected current mirrors further improve rejection of such variations in the power supply voltage.

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Minneapolis, MN, United States of America

Terrence L Marshall