| 摘要 |
An implantable cardiac pacemaker having programmable stimulating pulse amplitudes selectable by means of an external programming unit. The pacemaker includes charge pump circuitry for developing a stimulating pulse voltage on an output capacitor. The output capacitor is charged to a selected level identified by a multiple-bit amplitude value communicated to the implanted device from the external programmer. The pacemaker is also provided with circuitry for monitoring the depletion level of its battery and for generating an indicator signal when the battery has depleted beyond a predetermined level. Associated with the charge pump circuitry is a selectively activated comparator circuit for controlling the charging of the output capacitor. Prior to generation of the indicator signal, the charge pump circuitry remains deactivated for some programmed output amplitudes, the level of output capacitor charging being proportional to the battery voltage. After issuance of the indicator signal, the comparator circuit is activated to control the charging of the output capacitor. When the comparator circuit is activated for charging the capacitor, the resulting voltage established on the capacitor is proportional to a predetermined constant reference voltage. Longevity of the device is optimized by not activating the comparator circuit during early stages of battery depletion when the battery's output voltage is relatively stable. |
