Low-power A/D converter for an implantable medical device and method of use

• US 5,052,389 A
• Filed: 07/26/1990
• Issued: 10/01/1991
• Est. Priority Date: 07/26/1990
• Status: Expired due to Fees

• Current Assignee: Cook Pacemaker Corporation (Cook Group Incorporated)
• Original Assignee: Cook Pacemaker Corporation (Cook Group Incorporated)
• Inventors: Henry, Donald A.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US07/558,616
• Time in Patent Office: 432 Days
• Field of Search: 128/419 C, 128/419 D, 128/419 E, 128/419 F, 128/419 G, 128/419 PG, 128/419 PT, 128/903, 128/904, 604/65-67
• US Class Current: 607/32
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators

Abstract

A low-power A/D converter for an implantable medical device. The converter includes a high-frequency oscillator capable of generating clock pulses at a frequency substantially higher than the main clock frequency of the implantable device, and an oscillator-gating circuit for enabling the oscillator for a voltage-dependent variable time interval. The gating circuit includes a voltage-controlled monostable multivibrator for generating a gate control pulse having a pulse width corresponding to the value of an analog signal representative of a physiological parameter sensed by the implantable device. A timing controller, which operates at a low frequency under control of a crystal-controlled clock, supplies a trigger pulse to the voltage-controlled monostable at a predetermined first point in the variable time interval and generates an enable pulse at a predetermined second point in the variable time interval. In response to the enable pulse, the A/D converter enables the oscillator at the second point and, in response to the gate control pulse, disables the oscillator at the end of the variable time interval. A counter coupled to the oscillator counts the clock pulses generated between the second point and the end of the variable time interval.

Claims

1. A low-power A/D converter for an implantable medical device operating with a main clock frequency, comprising:

high-frequency oscillator means for generating clock pulses at a predetermined frequency substantially higher than said main clock frequency;

oscillator gating means for enabling said oscillator means for a voltage-dependent variable time interval, said gating means including voltage-controlled monostable means for generating a gate control pulse having a pulse width corresponding to the value of an analog signal representative of a physiological parameter sensed by said implantable medical device; and

counter means coupled to said oscillator means for counting clock pulses generated during said variable time interval.

2. The low-power A/D converter of claim 1, wherein said oscillator gating means includes means for enabling said oscillator means at a predetermined time after the beginning of said gate control pulse and disabling said oscillator means at the end of said gate control pulse.

3. The low-power A/D converter of claim 2, further comprising:

means for defining an A/D sample period for said A/D converter;

means for triggering said voltage-controlled monostable at least twice per sample period; and

means for latching the current output of said counter means and resetting said counter means once per sample period.

4. A low-power A/D conversion method for an implantable medical device operating with a main clock frequency, comprising the steps:

providing an oscillator capable of generating clock pulses at a predetermined frequency substantially higher than said main clock frequency;

gating said oscillator on for a voltage-dependent variable time interval, said gating step including generating a gate control pulse having a pulse width corresponding to the value of an analog signal representative of a physiological parameter sensed by said implantable medical device; and

counting clock pulses generated by said oscillator during said variable time interval.

5. The low-power A/D conversion method of claim 4, wherein said gating step includes enabling said oscillator at a predetermined time after the beginning of said gate control pulse and disabling said oscillator at the end of said gate control pulse.

6. The low-power A/D conversion method of claim 5, further comprising the steps:

defining an A/D sample period;

generating said gate control pulse at least twice per sample period; and

latching the current count of said clock pulses and initializing said counting step once per sample period.

7. A low-power A/D converter for an implantable medical device operating with a main clock frequency, comprising:

high-frequency oscillator means for generating clock pulses at a predetermined frequency substantially higher than said main clock frequency;

oscillator gating means for enabling said oscillator means for a voltage-dependent variable time interval, said gating means including

voltage-controlled monostable means for generating a gate control pulse having a pulse width corresponding to the value of an analog signal representative of a physiological parameter sensed by said implantable medical device;

a crystal-controlled low-frequency clock;

a timing controller having a clock input connected to said low-frequency clock, said timing controller including means for supplying a trigger pulse to said voltage-controlled monostable at a predetermined first point in said variable time interval and means for generating an enable pulse at a predetermined second point in said variable time interval;

means responsive to said enable pulse for enabling said oscillator means at said second point in said variable time interval;

means responsive to said gate control pulse for disabling said oscillator means at the end of said variable time interval; and

counter means coupled to said oscillator means for counting clock pulses generated between said second point and the end of said variable time interval.