Power scheme for implant stimulators on the human or animal body

1. A compliance monitoring circuit to monitor and control compliance voltage of an electrode suitable to contact a tissue of a human or animal body, the electrode being connected with an electrode driver, comprising:

a connection to the electrode providing an electrode voltage (Ve);

a predetermined reference voltage at a desired voltage level (Vr);

a switching signal Vs;

a predetermined threshold voltage (Vt) chosen to be a maximum voltage variation;

an array of MOSFET transistors including:

a first MOSFET transistor having a source connected to the electrode therefore having the voltage Ve, a gate connected to the switching signal Vs and a drain having a voltage Vds;

a second MOSFET transistor having a source connected to the reference voltage Vr, a gate connected to the switching signal Vs and, a drain;

a third MOSFET transistor having a source connected to the predetermined threshold voltage Vt, a gate and a drain, wherein the gate of the third MOSFET is electrically coupled to the drain of the third MOSFET and the drain of the second MOSFET therefore providing a voltage Vgs on the gate of the third MOSFET, the drain of the third MOSFET and the drain of the second MOSFET;

and a fourth MOSFET transistor having a source connected to the predetermined threshold voltage Vt, a gate electrically coupled to the gate of the third MOSFET therefore containing the voltage Vgs; and a drain that is electrically coupled to the drain of the first MOSFET, therefore containing the drain voltage Vds;

and a comparator configured to compare the voltages Vgs, Vds and Vt, according to the condition:

Vgs−Vds>Vt

and the compactor further configured to generate an alert signal when such condition is met.

2. The compliance monitoring circuit of claim 1 , comprising:

a subtractor, to subtract Vds from Vgs.

3. A compliance monitoring arrangement to monitor and control compliance voltage of a plurality of electrodes adapted to contact a tissue of a human or animal body, each electrode being connected with a respective electrode driver, the compliance monitoring arrangement comprising a plurality of compliance monitoring circuits in accordance with claim 1 .

4. The compliance monitoring arrangement of claim 3 , wherein alert signals of the compliance monitoring circuits are OR-ed together.

5. The compliance monitoring circuit of claim 3 , wherein each driver is a constant current type electrode driver.

6. The compliance monitoring arrangement of claim 1 , further comprising communication means for communicating said alert signal.

7. The compliance monitoring circuit of claim 1 , further comprising a hermetic implantable housing around the compliance monitoring circuit.

8. The compliance monitoring circuit of claim 7 , wherein the compliance monitoring circuit forms part of a neural stimulator.

9. The compliance monitoring circuit of claim 7 , wherein the compliance monitoring circuit forms part of a retinal implant.

10. The compliance monitoring circuit of claim 7 , being coupled with an external unit.

11. The compliance monitoring circuit of claim 7 , wherein coupling between the compliance monitoring circuit and the external unit is obtained through an inductive power link.

12. The compliance monitoring circuit of claim 11 , wherein the inductive power link comprises an implant coil.

13. The compliance monitoring circuit of claim 11 , further comprising a data link to allow exchange of information between the compliance monitoring circuit and the external unit.

14. The compliance monitoring circuit of claim 1 , wherein the electrode is configured to stimulate the tissue by way of biphasic current pulses.

15. The system of claim 14 , wherein the biphasic current pulses comprise anodic pulses and cathodic pulses.

16. A power control system for an implant on a human or animal body, comprising:

a charging circuit to provide power to deliver controlled stimulation currents to a tissue of the human or animal body;

a capacitive storage arrangement connected with the charging circuit and charged by the charging circuit;

an electrode driver array configured to transfer charges from the capacitive storage arrangement to the tissue;

an electrode array connected with the driver array and the tissue;

a connection to an electrode of the electrode array providing an electrode voltage (Ve);

a predetermined reference voltage at a desired voltage level (Vr);

a predetermined threshold voltage (Vt) chosen to be a maximum voltage variation; and

a plurality of compliance monitoring circuits connected to a respective electrode of the electrode array to monitor and control compliance voltage of each electrode of the electrode driver array, wherein each compliance monitoring circuit comprises an array of MOSFET transistors including:

a first MOSFET transistor having a source connected to the respective electrode therefore having the voltage Ve, a gate connected to the switching signal Vs and a drain having a voltage Vds;

a second MOSFET transistor having a source connected to the reference voltage Vr, a gate connected to the switching signal Vs and, a drain;

a third MOSFET transistor having a source connected to the predetermined threshold voltage Vt, a gate and a drain, wherein the gate of the third MOSFET is electrically coupled to the drain of the third MOSFET and the drain of the second MOSFET therefore providing a voltage Vgs on the gate of the third MOSFET, the drain of the third MOSFET and the drain of the second MOSFET;

and a fourth MOSFET transistor having a source connected to the predetermined threshold voltage Vt, a gate electrically coupled to the gate of the third MOSFET therefore containing the voltage Vgs; and a drain that is electrically coupled to the drain of the first MOSFET, therefore containing the drain voltage Vds;

and a comparator configured to compare the voltages Vgs, Vds and Vt, according to the condition:

Vgs−Vds>Vt

and the comparator further configured to generate an alert signal when such condition is met.

17. The system of claim 16 , further comprising a shunting arrangement to limit voltage on the capacitive storage arrangement.

18. The system of claim 16 , wherein the implant is a retinal implant.

19. The system of claim 1 , the system being coupled with an external unit including means to communicate the alert signal to the external unit.