Isolation control circuit for an electronic contact lens
An electronic contact lens. In some embodiments, the electronic contact lens includes: a power management circuit; and a first cell, the power management circuit including an active switch, the active switch being configured to isolate the first cell from other contact lens elements when the power management circuit is powered down.
1. An electronic contact lens, comprising:
a power management circuit; and
a first cell,
the power management circuit comprising an active switch,
the active switch being configured to isolate the first cell from other contact lens elements when the power management circuit is powered down,
wherein:
the power management circuit comprises:
a first switching circuit in a first voltage domain defined by the power management circuit, and
a second switching circuit in a second voltage domain defined by the first cell;
the second switching circuit comprises the active switch;
the first switching circuit and the second switching circuit are connected in series between the first cell and the power management circuit;
the first switching circuit comprises a first series switch, connected between the power management circuit and a common node;
the second switching circuit comprises a second series switch, connected between the power management circuit and the common node;
the second series switch is the active switch;
the first switching circuit further comprises a first shunt switch, connected between the common node and ground; and
the second switching circuit further comprises a second shunt switch, connected between the common node and ground.
2. The electronic contact lens of claim 1 , wherein:
the first shunt switch is configured to be turned off when the first series switch is turned on, and
the second shunt switch is configured to be turned off when the second series switch is turned on.
3. The electronic contact lens of claim 1 , wherein:
the first series switch is a field effect transistor;
the first shunt switch is a field effect transistor; and
the gate of the first series switch is connected to the gate of the first shunt switch.
4. The electronic contact lens of claim 3 , wherein the first series switch is a field effect transistor of a first channel type; and
the first shunt switch is a field effect transistor of a second channel type, different from the first channel type.
5. The electronic contact lens of claim 4 , wherein the first series switch is a p-channel field effect transistor; and
the first shunt switch is an n-channel field effect transistor.
6. The electronic contact lens of claim 3 , further comprising a first control circuit, the first control circuit being configured to:
pull down the gate of the first series switch and the gate of the first shunt switch when a first control signal is high and a second control signal is low.
7. The electronic contact lens of claim 6 , wherein the first control circuit comprises a transistor and an inverter, the transistor being connected between an input of the inverter and ground, and the output of the inverter being connected to the gate of the first series switch and the gate of the first shunt switch.
8. The electronic contact lens of claim 6 , further comprising a pulldown circuit for generating the second control signal, the pulldown circuit being configured:
to generate a high signal when the power management circuit is powered down and any charged cell, of a plurality of cells including the first cell, is connected to the power management circuit; and
to generate a low signal otherwise.
9. The electronic contact lens of claim 8 , wherein the pulldown circuit comprises:
a diode-OR circuit having:
a plurality of inputs each connected to a respective cell of a plurality of cells including the first cell, and
an output; and
a resistor connected in series between:
the output of the diode-OR circuit and
a first transistor connected to ground,
a gate of the first transistor being connected to a ready signal, the ready signal being:
high when the power management circuit is powered up, and
low otherwise.
10. The electronic contact lens of claim 9 , wherein the ready signal is an output of a bandgap voltage reference circuit of the power management circuit.
11. The electronic contact lens of claim 9 , further comprising a diode-connected field effect transistor connected in parallel with the first transistor.
12. The electronic contact lens of claim 9 , further comprising a buffer having an input connected to the resistor and to the first transistor.
13. The electronic contact lens of claim 1 , wherein:
the second series switch is a field effect transistor;
the second shunt switch is a field effect transistor; and
the gate of the second series switch is connected to the gate of the second shunt switch.
14. The electronic contact lens of claim 13 , further comprising:
a second control circuit comprising:
a transistor, and
an inverter; and
a level shifter,
the transistor being connected between an input of the inverter and ground,
the output of the inverter being connected to the gate of the second series switch and the gate of the second shunt switch, and
the level shifter being connected between an input for the first control signal and the input of the inverter.