Circuit for driving a load

1. A circuit for driving a load, the circuit comprising:

output circuitry for connecting the circuit to the load, the output circuitry comprising one or more energy-storing components;

switching circuitry arranged to supply power from a power supply to the load by supplying a current through at least one of the energy-storing components of the output circuitry that resists a change in current, or applying a voltage across at least one of the energy-storing components of the output circuitry that resists a change in voltage; and

control circuitry arranged to control the switching circuitry, to cause said current or voltage to oscillate between an upper envelope and a lower envelope;

wherein the control circuitry is configured to modulate data into said current or voltage by shifting the upper envelope between at least a first amplitude level and a second amplitude level, and by shifting the lower envelope by the same amount in the same direction at the same time;

wherein the control circuitry comprises a first comparator and a second comparator, the first comparator being arranged to bound the oscillation to the upper envelope by comparing feedback of said current or voltage to an upper reference signal, and the second comparator being configured to bound the oscillation to the lower envelope by comparing feedback of said current or voltage to a lower reference signal.

2. The circuit of claim 1 , wherein the upper envelope is above zero for each of said levels, and the lower envelope is below zero for each of said levels.

3. The circuit of claim 1 , wherein: the one or more energy-storing components comprise at least an inductor, the switching circuitry being arranged to supply power to the load by supplying said current through the inductor, and the control circuitry being arranged to cause said current to oscillate between the upper and lower envelope and to modulate the data into said current by said shifting of the upper and lower envelopes.

4. The circuit of claim 1 , wherein: the one or more energy-storing components comprise at least a capacitor, the switching circuitry being arranged to supply power to the load by supplying said voltage across the capacitor, and the control circuitry being arranged to cause said voltage to oscillate between the upper and lower envelope and to modulate data into said voltage by said shifting of the upper and lower envelopes.

5. The circuit of claim 3 , wherein the one or more energy-storing components comprise the inductor and a capacitor arranged together in a filter formation to smooth the current supplied to the load.

6. The circuit of claim 4 , wherein the one or more energy-storing components comprise the capacitor and an inductor arranged together in a filter formation to smooth the voltage applied across the load.

7. The circuit of claim 1 , wherein said shifting of the upper and lower envelopes is controlled by software.

8. The circuit of claim 7 , wherein the software controls the shifting by controlling the upper and lower reference signals.

9. The circuit of claim 1 , wherein the switching circuitry comprises a high side switch for connecting the output circuitry to a higher voltage supply rail of said power supply, and a low side switch for connecting the output circuitry to a lower voltage supply rail of said power supply; the control circuitry being configured to cause the oscillation to ramp up towards the upper envelope by asserting the high side switch, and to cause the oscillation to ramp down to towards the lower envelope by asserting the low side switch.

10. The circuit of claim 1 , wherein the load comprises a light source and the output circuitry is connected to drive the light source.

11. The circuit of claim 10 , wherein the light source comprises at least one LED.

12. The circuit of claim 1 , wherein the circuit takes the form of a buck converter.