Preventing a False Lock in a Phase Lock Loop

• US 20090224837A1
• Filed: 05/15/2009
• Published: 09/10/2009
• Est. Priority Date: 11/01/2004
• Status: Active Grant

• Current Assignee: St. Jude Medical Luxembourg Holdings Ii S.A.R.L.
• Original Assignee: CardioMEMS Incorporated
• Inventors: Allen, Mark, Ellis, Michael, Pyle, Wilton, Joy, James, Kroh, Jason
• Granted Patent: US 7,932,732 B2
• Time in Patent Office: Days
• US Class Current: 331/15
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G01F 15/066 involving magnetic transmission devices
• CPC Class Codes: G01R 23/12 by converting frequency into phase shift
• CPC Class Codes: G01R 23/145 by heterodyning or by beat-frequency comparison with the harmonic of an oscillator

Abstract

The present invention determines the resonant frequency of a sensor by adjusting the phase and frequency of an energizing signal until the frequency of the energizing signal matches the resonant frequency of the sensor. The system energizes the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. The energizing signal is coupled to the sensor via magnetic coupling and induces a current in the sensor which oscillates at the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is used to calculate the measured physical parameter. The system uses a pair of phase locked loops to adjust the phase and the frequency of the energizing signal.

Claims

1. A method for preventing a false lock, comprising:

receiving a return signal from a stimulated circuit, wherein the return signal is based on an energizing signal;

processing the return signal;

mixing the processed return signal with a reference signal;

determining a phase slope of a resulting baseband signal; and

if the phase slope does not satisfy a predetermined criteria, then preventing a phase lock loop (PLL) from locking.

2. The method of claim 1, wherein the predetermined criteria corresponds to a phase difference between the return signal and the energizing signal increasing over time.

3. The method of claim 1, wherein the predetermined criteria corresponds to a phase difference between the return signal and the energizing signal decreasing over time.

4. The method of claim 1, wherein the predetermined criteria corresponds to an absolute magnitude of the phase difference being less than a predetermined threshold.

5. The method of claim 1, wherein preventing a phase lock loop (PLL) from locking comprises suppressing a signal strength so that the signal strength is below a signal strength threshold.

6. The method of claim 1, wherein determining a phase slope of a resulting baseband signal comprises using points before and after the phase difference goes to zero to determine the phase slope.

7. The method of claim 1, wherein the resulting baseband signal corresponds to a phase difference between the energizing signal and the return signal.

8. A method for communicating with an implanted wireless sensor, comprising:

transmitting an energizing signal to the implanted wireless sensor;

receiving a sensor signal from the wireless sensor, wherein the sensor signal is based on the energizing signal;

processing the sensor signal;

mixing the processed sensor signal with a reference signal;

converting the mixed signal to a baseband signal;

using the baseband signal to determine a phase slope corresponding to a phase difference between the sensor signal and the energizing signal; and

preventing a phase lock loop (PLL) from locking, if the phase slope does not satisfy a predetermined criteria.

9. The method of claim 8, further comprising:

if the PLL is prevented from locking, then adjusting a frequency of the energizing signal.

10. The method of claim 8, wherein the predetermined criteria corresponds to the phase difference increasing over time.

11. The method of claim 8, wherein the predetermined criteria corresponds to the phase difference decreasing over time.

12. The method of claim 8, wherein the predetermined criteria corresponds to an absolute magnitude of the phase difference being less than a predetermined threshold.

13. The method of claim 8, further comprising if the slope does not satisfy a predetermined criteria, then suppressing a signal strength below a signal strength threshold.

14. A system for communicating with an implanted wireless sensor, comprising:

a transmitter for transmitting an energizing signal to the implanted wireless sensor;

a receiver for receiving a sensor signal from the wireless sensor, wherein the sensor signal is based on the energizing signal;

means for processing the sensor signal;

a mixer for mixing the processed sensor signal with a reference signal;

means for converting the mixed signal to a baseband signal;

means for using the baseband signal to determine a phase slope of a signal corresponding to a phase difference between the sensor signal and the energizing signal; and

means for preventing a phase lock loop (PLL) from locking, if the phase slope does not satisfy a predetermined criteria.

15. The system of claim 14, wherein the predetermined criteria corresponds to the phase difference increasing over time.

16. The system of claim 14, wherein the predetermined criteria corresponds to the phase difference decreasing over time.

17. The system of claim 14 wherein the means for preventing a phase lock loop (PLL) from locking suppresses a signal strength so that the signal strength is below a signal strength threshold.

18. The system of claim 14, wherein the means for using the baseband signal to determine a phase slope uses multiple sample points to determine the phase slope.