Adjustable low current in a sensor network

1. A sensor device coupled to a communication interface bus, the sensor device comprising:

a current source operable to provide a supply current to an operating voltage node;

a voltage clamp coupled between the operating voltage node and a power supply terminal; and

a control circuit coupled to the voltage clamp to receive a current sense signal and coupled to the current source to provide an adjustment signal to adjust the supply current responsive to the current sense signal,

wherein the current source is coupled to a tank capacitor to charge the tank capacitor using the supply current.

2. The sensor device of claim 1 , wherein the current source is configured to charge the tank capacitor to a predetermined operating voltage.

3. The sensor device of claim 1 , wherein the current source is operable to draw the supply current from the communication interface bus.

4. The sensor device of claim 3 , wherein the current source is operable to receive the supply current through the communication interface bus from a master device.

5. The sensor device of claim 4 , wherein the supply current corresponds to a first average current level during a power phase of the master device and corresponds to a second average current level during a communications phase of the master device, and wherein the first average current level is at least one hundred times greater than the second average current level.

6. The sensor device of claim 5 , wherein the communication interface bus has a master device to sensor device data bandwidth of 50 kbit/second during the communications phase of the master device.

7. The sensor device of claim 5 , wherein the communication interface bus has a sensor device to master device data bandwidth of 400 kbit/second during the communications phase of the master device.

8. The sensor device of claim 1 , wherein the voltage clamp includes a Zener diode having a cathode connected to the current source and an anode connected to ground.

9. A sensor node coupled to a communication interface bus, the sensor node comprising:

a receiver circuit operable to receive a first supply current and a first control signal;

a supply circuit operable to receive a second supply current and a second control signal, the supply circuit operable to provide an operating voltage at an output; and

a control circuit operable to provide the first control signal to enable the receiver circuit when the control circuit is operating in a first mode and to disable the receiver circuit when the control circuit is operating in a second mode, and operable to provide the second control signal to the supply circuit to adjust a voltage at the output.

10. The sensor node of claim 9 , wherein the supply circuit further comprises:

a capacitor coupled to a power supply terminal; and

a switch responsive to the second control signal to couple the capacitor to the output and to decouple the capacitor from the output.

11. The sensor node of claim 10 , further comprising:

a transmitter circuit powered by the operating voltage,

wherein the control circuit is operable to provide a third control signal to change an operating mode of the transmitter circuit.

12. The sensor node of claim 11 , wherein the first mode corresponds to a communications phase of a sensory network during which information corresponding to one or more signals detected using the receiver circuit are sent to a master node through the communication interface bus and during which the supply circuit receives current through the communication interface bus.

13. The sensor node of claim 12 , wherein the supply circuit supplies operating voltage based, at least in part, on current received through the communication interface bus and during the communications phase of the sensory network.

14. The sensor node of claim 12 , wherein the second mode corresponds to a power phase of the sensory network during which the transmitter circuit is driven in response to a current received through the communication interface bus and during which a second capacitor coupled to output is charged to the operating voltage by the current received through the communication interface bus.

15. A method of operating a sensor node coupled to a communication interface bus, the method comprising:

receiving a first supply current at a receiver circuit;

receiving a second supply current at a supply circuit;

providing an operating voltage at an output of the supply circuit;

providing a first control signal from a control circuit to enable the receive circuit when the control circuit is operating in a first mode and to disable the receiver circuit when the control circuit is operating in a second mode; and

providing a second control signal from the control circuit to adjust the operating voltage at the output of the supply circuit.

16. The method of claim 15 , further comprising:

using the second control signal to close and open a switch coupled between a capacitor and the output of the supply circuit.

17. The method of claim 16 , further comprising:

using the control circuit to provide a third control signal to a transmitter circuit, the transmitter circuit being powered by the output of the supply circuit,

wherein the third control signal changes an operating mode of the transmitter circuit.