Coulomb counter and battery management for hearing aid
A hearing aid output amplifier additionally outputs a scaled replica of the output battery current, which is integrated and measured by a coulomb counter. The scaled current charges a capacitor. When the capacitor reaches a threshold voltage, a switch is activated. The switch rapidly discharges the capacitor and allows the charging cycle to begin again. The switch also sends a digital pulse to a digital counter, which keeps track of the number of charge/discharge cycles the capacitor has undergone over the lifetime of the device. The amount of charge produced by the battery is proportional to the number of charge/discharge cycles counted. A hearing aid is disclosed, which has different modes that have different dynamic ranges, such as a “sleep” mode, an “active” mode, and/or an “RF communication” mode.
1. A hearing aid for a patient, comprising:
a sensor that converts ambient sound around the patient into an input electrical signal;
an output amplifier that produces a primary output electrical signal in response to the input electrical signal and simultaneously produces a secondary output electrical signal that is a scaled version of the primary output electrical signal;
a driver that receives the primary output electrical signal and stimulates an anatomy of the patient;
an oscillator that receives the secondary output electrical signal and oscillates each time that a predetermined amount of electrical charge is received in the secondary output electrical signal; and
a digital counter that increments each time the oscillator oscillates,
wherein the secondary output electrical signal charges a capacitor and increases a voltage across the capacitor; and
wherein when the voltage exceeds a predetermined threshold, the digital counter is incremented and the capacitor is discharged,
wherein the digital counter tallies the number of charge/discharge cycles of the capacitor; and
wherein when the digital counter reaches a predetermined count, the hearing aid indicates that its battery is running low.
2. The hearing aid of claim 1 , wherein the secondary output electrical signal includes a rectifier that ensures that the secondary output electrical signal is one-sided.
3. The hearing aid of claim 1 , wherein during the each charging phase of the capacitor, the voltage across the capacitor increases generally linearly.
4. The hearing aid of claim 3 , wherein the predetermined threshold for voltage is sufficiently low to avoid roll-off behavior from the capacitor.
5. The hearing aid of claim 1 wherein the capacitor is fully discharged to ground for each charge/discharge cycle.
6. The hearing aid of claim 1 wherein the capacitor is partially discharged to a voltage greater than ground for each charge/discharge cycle.
7. The hearing aid of claim 1 , wherein the secondary output electrical signal is received by only one oscillator and one digital counter.
8. The hearing aid of claim 1 , wherein the secondary output electrical signal is switchably received by more than one oscillator and more than one digital counter.
9. The hearing aid of claim 8 ,
wherein the hearing aid includes more than one operational mode; and wherein the operational modes all use the same oscillator and digital counter.
10. The hearing aid of claim 8 , wherein the hearing aid includes more than one operational mode; and
wherein each operational mode has a corresponding oscillator and a corresponding digital counter.
11. The hearing aid of claim 10 , wherein each oscillator includes a resistor that is matched to typical current levels encountered in the corresponding mode.
12. The hearing aid of claim 10 , wherein the operational modes include active, sleep and/or RF communication.
13. The hearing aid of claim 1 , wherein if a periodic poll determines that a battery of the hearing aid has a remaining charge that is below a predetermined threshold, the driver alerts the patient with an audible signal.
14. The hearing aid of claim 1 , wherein if a periodic poll determines that a discharge rate of a battery of the hearing aid exceeds a predetermined threshold, the driver alerts the patient with an audible signal.
15. The hearing aid of claim 1 , wherein if a periodic poll determines that a hearing aid has undergone a number of telemetry events that exceeds a predetermined threshold, the driver alerts the patient with an audible signal.