Systems and methods for communicating with an implantable stimulator

1. A system, comprising:

an external device, comprising:

first modulation circuitry for producing from first data a first signal modulated with on-off keying (OOK) modulation, wherein the first modulated signal comprises logic ‘0’ bits of a first pulse width and logic ‘1’ bits of a second pulse width different from the first pulse width, wherein each bit further comprises either an ON state with a signal that varies with a first frequency or an OFF state, wherein a transition between adjacent bits in the first signal is marked by a change in the first modulated signal between the ON and OFF states;

a coil configured to wirelessly transmit the first modulated signal to the implantable medical device; and

an implantable medical device, comprising a first telemetry receiver in the implantable medical device for demodulating the first modulated signal to recover the first data.

2. The system of claim 1 , further comprising:

second modulation circuitry in the external device for producing from second data a second signal modulated with frequency modulation, wherein the coil is further configured to wirelessly transmit the second modulated signal to the implantable medical device;

a second telemetry receiver in the implantable medical device for demodulating the second modulated signal to recover the second data.

3. The system of claim 2 , wherein the frequency modulation comprises frequency shift keying (FSK) modulation.

4. The system of claim 2 , wherein the implantable medical device further comprises a reference clock generation circuit for generating a reference clock signal used by the second telemetry receiver.

5. The system of claim 4 , wherein the first data comprises calibration data used to calibrate the reference clock generation circuit such that the reference clock signal is synchronized with a frequency used to transmit the second modulated signal.

6. The system of claim 2 , wherein the first data comprises a start bit and a number of control bits, the start bit being transmitted before the control bits.

7. The system of claim 6 , wherein the first telemetry receiver comprises:

a bit threshold counter configured to measure a pulse width of the start bit to generate a bit width threshold;

a pulse width counter configured to measure a pulse width of the bits; and

a comparator configured to compare the measured pulse widths with the bit width threshold to determine whether a bit comprises a logic ‘0’ or a logic ‘1’.

8. The system of claim 2 , wherein the implantable medical device comprises an implantable stimulator.