Abstract: Improved digital FSK demodulator methods and circuitry are disclosed. The demodulation method can be implemented using a standard microcontroller such as is usually already present in a telemetry receiving device. The demodulation method is simple and, when a microcontroller is used, easy to implement using standard portions of the microcontroller (e.g., the UART) and/or through programming. In a preferred embodiment, the demodulation circuitry comprises a delay line, preferably a shift register comprising part of the microcontroller's UART. The shift register delays samples of the received FSK modulated signal by a number of cycles so as to introduce a 90-degree delay. The received signal samples, and their delayed counterparts, are input to an XOR gate, whose output reflects whether a logic ‘0’ or ‘1’ has been received by the device, although filtering of this output make this determination more reliable.

Abstract: A method for telemetry between an implantable medical device and an external programming component is disclosed. The telemetry circuitry of the implantable device is initially powered on for only a portion of the time needed to receive the entirety of a wake-up signal from the external component. During that time, only a first portion of the wake-up signal as received form the external component is checked against the implantable device's understanding of that first portion as stored in its memory. If the implantable device does not recognize the received first portion, powering on of the telemetry circuitry is terminated. However, if that first portion is recognized, then the implantable device continues to power on the telemetry circuitry to receive another (second) portion of the wake-up signal. If that received second portion is recognized, then the telemetry circuitry is further powered to receive a next (third) portion of the wake-up signal from the external component, etc.

Abstract: An improved telemetry protocol for an implantable medical device is disclosed. The sending device forms a block of information to be telemetered to the receiving device in a typical fashion, including a header, a message, and an error detection data, such as a Cyclic Redundancy Code (CRC) for that data. This CRC, called CRC1, is preferably computed using a first CRC polynomial. Then, the entirety of the block is divided into smaller packets of a predetermined byte size. Each packet, regardless of its contents, has a CRC computed for it (CRC2) preferably computed using a second CRC polynomial. Each packet with its appended CRC2 is sent to the receiving device, which deduces a CRC2 and compares it with the appended CRC2. If not valid, that packet is again requested to be resent. If valid, the next packet is requested to be sent, its CRC2 checked, etc., until all packets are received and verified. The receiving device then discards the CRC2s to reconstitute the original block.