Telemetry system with phase-locking noise suppressing receiver

• US 6,329,929 B1
• Filed: 12/21/1998
• Issued: 12/11/2001
• Est. Priority Date: 12/21/1998
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Houben, Richard, Weijand, Koen J.
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Edwards, Jr., Timothy
• Application Number:
  US09/217,127
• Time in Patent Office: 1,086 Days
• Field of Search: 340/870.25, 607/30, 607/31, 607/32, 607/60, 128/903, 375/326, 375/340, 375/371, 375/376, 375/373
• US Class Current: 340/870.25
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only
• CPC Class Codes: H04L 27/10 Frequency-modulated carrier systems, i.e. using frequency-shift keying H04L27/32 takes precedence
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

There is provided a telemetry system with a receiver which enables detection of pulsed high frequency data (hf) signals in a manner which suppresses noise which may be present within the high frequency bandwidth. The transmitter carrier, which may be subject to some instability, is encoded at a symbol rate which is generated at a lower frequency than the hf, but which is reliably stable. The receiver detects the phase of each received hf pulse, and generates a phase-locked signal which is synchronized to the transmitter symbol signal. The phase-locked signal in turn is used to demodulate the received pulsed signals. In a specific DSP embodiment, the phase-lock loop has a numerically controlled oscillator which has a center frequency which corresponds to the aliased phase difference between the hf carrier phase and the phase of each pulse, thereby obtaining a signal which carries information as to the exact symbol rate. This information is used either to calculate the timing of a narrow window which gates a pulse detector coincident with each next expected symbol time, or to trigger generation of a replica signal which is used in the detect circuit, thereby providing high resolution detection of the pulses and good noise rejection.

Claims

1. A telemetry system for receiving and demodulating transmitted pulsatile high frequency signals, said signals being modulated by a symbol signal having a data symbol rate much less than said high frequency, comprising:

demodulator means for receiving said high frequency signals and for deriving data symbols from said high frequency signals;

phase means for determining the phase of each of said derived symbols;

symbol means for developing a symbol signal synchronized in phase with said derived symbols; and

feedback means for generating feedback signals in phase with said symbol signal and for connecting said feedback signals to said demodulator for use in demodulating said high frequency signals.

2. The system as described in claim 1, comprising a phase lock loop, said phase lock loop comprising said phase means and said symbol means.

3. The system as described in claim 2, wherein said feedback means comprises carrier replica generator means for generating a replica signal in phase with each symbol of said symbol signal, said replica signal being a replica of the transmitted high frequency signal.

4. The system as described in claim 3, wherein said feedback means comprises storage means for storing said replica signal.

5. The system as described in claim 4, wherein said storage means comprises storage of a sinusoidal carrier.

6. The system as described in claim 4, wherein said storage means comprises storage of a pulsatile monopolar signal.

7. The system as described in claim 4, wherein said storage means comprises storage of a chirp.

8. The system as described in claim 4, wherein said storage means comprises means for storing a replica of a bi-phase shift keyed signal.

9. The system as described in claim 4, wherein said storage means comprises means for storing a replica of an exponentially decaying sinusoidal signal.

10. The system as described in claim 1, wherein said feedback means comprises window means for generating window signals which are substantially time coincident with each symbol period of the transmitted high frequency signals.

11. The system as described in claim 3, wherein said demodulator means comprises comparing means for comparing, said feedback signal with said high frequency signal.

12. The system as described in claim 1, wherein said symbol means comprises a controllable clock generator with a center frequency of about the predetermined symbol generator rate of said implanted device, and means for locking said clock generator to said symbol signal.

13. A telemetry system for transmitting data from a remote device to a receiving device, said system having a transmitter in said remote device and a receiver in said receiving device, said transmitter comprising

a carrier generator for generating a high frequency carrier signal;

data means for providing pulse data;

symbol means for generating a relatively low frequency symbol clock signal;

modulating means for modulating said carrier signal to encode it with said data at a rate corresponding to said clock signal so as to provide pulsatile high frequency signals, and transmitting means for transmitting said pulsatile high frequency signals;

said receiver comprising demodulate means for demodulating said transmitted pulsatile high frequency signals, said demodulate means having, circuit means for receiving a feedback signal carrying information used in demodulating said pulsatile high frequency signals;

phase lock means for deriving from said demodulated signals a synchronized signal which is synchronized with said symbol clock signal; and

symbol feedback means for generating a feedback signal in sync with said symbol clock signal and inputting it to said demodulate means.

14. The system as described in claim 13, wherein said symbol feedback means comprises replica means for providing a signal which is a replica of the transmitted pulsatile high frequency signal, and further comprising timing means for timing said feedback signal to substantially coincide with each received pulsatile high frequency signal.

15. The system as described in claim 14, wherein said phase lock means comprises a phase lock loop circuit, said phase lock loop circuit comprising a phase detector for detecting the phase of each received said pulsatile high frequency signal.

16. A telemetry receiver for receiving and detecting transmitted pulsatile high frequency signals, said pulsatile high frequency signals being in the form of a high frequency signal modulated with a train of data symbols generated coincident with a symbol clock having a symbol rate less than said high frequency, and wherein the presence of a said symbol produces a said high frequency signal, comprising:

High Frequency (hf) means for receiving said high frequency signals;

detection means for detecting the occurrence of said high frequency signals, said detection means having enabling means for enabling its operation substantially coincident with each received pulsatile high frequency signal;

phase means for determining the phase of said high frequency signals at the time of detection of each said signal;

Phase Locked Loop (pll) means for generating a continuous signal which is phase-locked to the determined phase of said signals;

calculating means for determining from said continuous phase-locked signal substantially when the next symbol is due to be generated; and

said enabling means having demodulate means for generating a demodulating signal in phase with each received high frequency signal symbol.

17. The telemetry receiver as described in claim 16, wherein said hf means comprises an analog to digital converter, and comprising a digital signal processor for providing said detection means, said phase means, said pll means, said calculating means and said enabling means.

18. The telemetry receiver as described in claim 17, comprising a quad demodulator for determining the magnitude and phase of each said received high frequency signal.

19. The telemetry receiver as described in claim 18, wherein said phase means comprises a sample and hold circuit which obtains and holds a sampled phase value for each detected high frequency signal.

20. The telemetry receiver as described in claim 19, wherein said detection means comprises a level detector.

21. The telemetry receiver as described in claim 19, wherein said pll means comprises a numerically controlled oscillator with a center frequency which corresponds to the aliased phase advance of said high frequency signal relative to each symbol clock.

22. The telemetry receiver as described in claim 21, wherein said pll means comprises error means for determining an error signal representative of the phase difference between each said sampled signal and the numerically controlled oscillator signal at each said hf signal detection.

23. The telemetry receiver as described in claim 22, comprising control means for controlling said numerically controlled oscillator with said error signal.

24. The telemetry receiver as described in claim 23, wherein said quad demodulator comprises a clock generator for generating sine and cosine signals at said high frequency rate, and sync means for numerically controlling said clock as a function of said error signal.