Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-03-01
2001-09-18
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S545000
Reexamination Certificate
active
06292050
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to precision voltage and current references and particularly, but not by way of limitation, to a system that includes a temperature dependent current source used to generate a temperature compensated voltage reference in a cardiac rhythm management system.
BACKGROUND
Many integrated circuit functions require precise voltage and current references. For example, an analog-to-digital converter typically requires a precise voltage reference to establish and quantize an analog input voltage range. In another example, many analog filters, such as transconductance-capacitance (g
m
C) filters, have filter gain and rolloff frequency characteristics that depend upon their bias currents. A precise current reference is useful for generating accurate bias currents in such filters and other circuits.
Many battery powered electronics applications, including implantable cardiac rhythm management systems, need current and temperature compensated voltage reference circuits that operate at low power supply voltages and power consumption. There is a critical need for circuits, including reference circuits, that operate at low power supply voltages and draw less current from the low voltage power supply in order to increase battery longevity. There is also a need for such reference circuits in which the value of the reference voltage and reference current are capable of fine adjustment. There is a further need for such reference circuits in which the resulting reference voltage is temperature compensated, i.e. the sensitivity of the reference voltage to temperature variations is reduced. Moreover, the internal impedance of the battery results in variations of the terminal voltage. When significant current is being drawn from the battery, the terminal voltage of the battery can droop significantly. There is a need for a reference circuit that can accommodate such power supply voltage variations.
SUMMARY
The present system provides a system that includes a current and temperature compensated voltage reference that is capable of operating from a power supply voltage as low as approximately 1.3 Volts, and that provides improved power supply rejection. For battery powered electronics applications, operation at lower power supply voltages offers significant advantages; it may eliminate the need for electrically coupling more than one battery in series in order to obtain a higher power supply voltage. Also, in some batteries, an internal battery impedance increases over the course of the battery life, thereby reducing the voltage available at the battery terminals. Thus, the useful life of the battery may be extended by using a reference circuit that is capable of operating from this reduced battery terminal voltage near the end of the battery's life or when significant currents are being drawn from the battery. The reference circuit should be capable of accommodating such variations in the power supply voltage.
These characteristics are particularly desirable for implantable medical devices, including cardiac rhythm management systems, such as pacemakers and defibrillators, in which circuits that are capable of operating at reduced power supply voltages can extend battery life for several years, thereby avoiding surgical explantation and replacement of the implanted device. In elderly patients, such traumatic surgical intervention may be both uncomfortable and risky.
The system, by operating from a power supply voltage as low as approximately 1.3 Volts and providing improved power supply rejection, may significantly increase the longevity of the implanted device. The system also operates with less power consumption, further increasing the longevity of the implanted device. The increased device longevity provides the implanting physician with more options in selecting the most appropriate therapy for the patient. Discomfort and patient mortality due to explantation and replacement of the implanted medical device may be decreased. The system also provides a reference circuit in which the value of the reference voltage and reference current are capable of fine adjustment. The resulting reference voltage is temperature compensated, i.e. the sensitivity of the reference voltage to temperature variations is reduced. Furthermore, improved power supply rejection better accommodates variations in the power supply voltage.
In one embodiment, the system includes a reference circuit. The reference circuit includes first and second bias circuits and a complementary metal oxide semiconductor (CMOS) differential input first amplifier. The first bias circuit includes less than three series-coupled diodes comprising first and second series-coupled diodes biased by at least one first current source, providing a first temperature dependent voltage across the series-combination of the first and second diodes. The second bias circuit includes a resistor and less than three series-coupled diodes comprising third and fourth series-coupled diodes biased by at least one second current source, providing a second temperature dependent voltage across the series-combination of the third and fourth diodes, wherein the second temperature dependent voltage has a different temperature dependence than the first temperature dependent voltage. The first amplifier includes first and second inputs electrically coupled to the respective first and second temperature dependent voltages of the respective first and second bias circuits, and having an output providing a proportional to absolute temperature (PTAT) reference current through the resistor by measuring a difference between the first and second temperature dependent voltages. A power supply voltage provided to the first amplifier is between 1.3 volts and 2.1 volts.
In another embodiment, a cardiac rhythm management system includes a battery, an electronics circuit, for controlling delivery of cardiac therapy to a patient, and a reference circuit. The reference circuit is electrically coupled to the battery for receiving a first power supply voltage therefrom, and electrically coupled to a second power supply voltage. The reference circuit provides a reference voltage to the electronics circuit. The reference circuit operates from the first power supply voltage that is as low as 1.3 Volts. The reference circuit includes an amplifier, a first bias circuit, at least one first current source, a second bias circuit, and at least one second current source. The first bias circuit includes less than three series-coupled diodes comprising first and second series-coupled diodes. The first bias circuit is coupled to the second power supply voltage and includes a first output voltage terminal. The at least one first current source is coupled in series between the first power supply voltage and the first output voltage terminal. The second bias circuit includes less than three-series-coupled diodes comprising third and fourth series-coupled diodes. The second bias circuit is coupled to the second power supply voltage and includes a second output voltage terminal. The at least one second current source is coupled in series between the first power supply voltage and the second output voltage terminal.
In another embodiment, the system includes a reference circuit that includes a first bias circuit, a second bias circuit, a CMOS differential-input folded cascode first amplifier, and a voltage reference circuit. The first bias circuit has a first temperature dependence and includes less than three series-coupled diodes comprising first and second diodes that are series-coupled with each other and biased by at least a first current source. The first bias circuit provides a first temperature dependent voltage across the series combination of the first and second series-coupled diodes. The second bias circuit includes a resistor and less than three series-coupled diodes comprising third and fourth diodes. The third and fourth diodes are series-coupled with each other and biased by at least a second current source. The second bias circuit provid
Arora Suneel
Dooley Michael W.
Linder William J.
Marshall Terrence L.
Cardiac Pacemakers Inc.
Schwegman Lundberg Woessner & Kluth P.A.
Wells Kenneth B.
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