Phase detector

• US 6,539,316 B1
• Filed: 01/06/2000
• Issued: 03/25/2003
• Est. Priority Date: 01/06/2000
• Status: Expired due to Fees

• Current Assignee: Transoma Medical, Inc.
• Original Assignee: Data Sciences U K Limited (International Business Machines Corporation)
• Inventors: Patton, Ronald E., Doten, Gregory P.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): SUAREZ, FELIX E
• Application Number:
  US09/478,486
• Time in Patent Office: 1,174 Days
• Field of Search: 738/612--86, 327/3-4, 327/6, 327/9, 327/18, 327/22, 327/23, 327/91, 327/94, 327/174-175, 327/536, 702/33, 702/38-39, 702/45-48, 702/50, 702/54-56, 702/72, 702/100, 702/103
• US Class Current: 702/48
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: G01F 1/66 by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: H03L 7/085 concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal H03L7/10 takes precedence; circuits for comparing the phase or frequency of two mutually-independent oscillations H03D13/00

Abstract

A method for detecting a phase difference between first and second input signals is provided. The method includes modulating a duty cycle of first and second intermediate signals from a first duty cycle based on the phase difference between the first and second input signals. The method further includes creating a differential output signal based on the modulated duty cycles of the first and second intermediate signals that is related to the phase difference between the first and second input signals.

Claims

1. A transit time flow meter, comprising:

a first pair of transducers;

a second pair of transducers;

wherein the first and second pair of transducers are placeable in relation to a conduit to transmit ultrasonic signals through a fluid;

a phase detector, coupled to the first and second pairs of transducers, the phase detector using duty cycle modulation to determine a first phase difference between signals received from the first pair of transducers and a second phase difference between signals received from the second pair of transducers, the phase detector being responsive to an enable signal for selectively sampling portions of the signals received from the first pair of transducers and the second pair of transducers at selectable sampling start times for a selectable number of pulses in the signals; and

a data processing circuit, responsive to the phase detector, that generates a measure of fluid flow in the conduit based on the first and second phase differences.

2. The flow meter of claim 1, wherein the phase detector comprises first and second phase detectors each coupled to one of the first and second pair of transducers.

3. The flow meter of claim 2, wherein each phase detector comprises:

a first stage that receives first and second input signals, modulates the duty cycle of first and second intermediate signals based on a phase difference between the first and second input signals and selects a number of pulses in the first and second intermediate signals; and

a second stage that receives the selected pulses of the first and second intermediate signals and charges first and second capacitors using the first and second intermediate signals, respectively, to create a differential signal that is based on the phase difference between the first and second input signals.

4. The flow meter of claim 3, wherein the second stage includes:

a first current source coupled to the first capacitor through a first switch, the first switch responsive to the first intermediate signal; and

a second current source coupled to the second capacitor through a second switch, the second switch responsive to the second intermediate signal.

5. The flow meter of claim 4, wherein the first and second current sources comprise current mirrors.

6. The flow meter of claim 4, wherein:

the first switch comprises a differential amplifier with a first input coupled to the first intermediate signal and a second input coupled to a complement of the first intermediate signal; and

the second switch comprises a differential amplifier with a first input coupled to the second intermediate signal and a second input coupled to a complement of the second intermediate signal.

7. The flow meter of claim 3, wherein the second stage includes a circuit that clears the voltage on the first and second capacitors.

8. The flow meter of claim 3, wherein the second stage includes an instrumentation amplifier with first and second inputs coupled to the differential signal.

9. The flow meter of claim 8, wherein the instrumentation amplifier includes a reference voltage offset.

10. The flow meter of claim 3, wherein the first stage includes a logic circuit that increases the duration of the high logic level pulses of the first intermediate signal based on the phase difference between the first and second input signals and reduces the duration of the high logic level pulses of the second intermediate signal based on the phase difference between the first and second input signals.

11. The flow meter of claim 4, wherein the second stage includes a switch that decouples the first capacitor from the first switch and a switch that decouples the second capacitor from the second switch when reading the differential signal.

12. The flow meter of claim 1, wherein the data processing circuit includes a transmitter for transmitting data to a remote processor.

13. A method for detecting flow in a fluid, the method comprising:

transmitting ultrasonic signals between first and second transducers;

receiving time-shifted ultrasonic signals at the first and second transducers;

sampling the time-shifted ultrasonic signals from the first and second transducers using a first enable signal, wherein the sampled time-shifted ultrasonic signals are capable of including selectable portions of the time-shifted ultrasonic signals from the first and second transducers beginning at selectable sampling start times for a selectable number of pulses in the ultrasonic signals;

determining a first phase difference between the sampled time-shifted ultrasonic signals from the first and second transducers using duty cycle modulation;

transmitting ultrasonic signals between third and fourth transducers;

receiving time-shifted ultrasonic signals at the third and fourth transducers;

sampling the time-shifted ultrasonic signals from the third and fourth transducers using a second enable signal, wherein the sampled time-shifted ultrasonic signals are capable of including selectable portions of the time-shifted ultrasonic signals from the third and fourth transducers beginning at selectable sampling start times for a selectable number of pulses in the ultrasonic signals;

determining a second phase difference between the sampled time-shifted ultrasonic signals from the third and fourth transducers using duty cycle modulation; and

generating a flow measurement based on the first and second phase differences.

14. The method of claim 13, wherein determining the first phase difference comprises:

modulating a duty cycle of first and second intermediate signals from a first duty cycle based on a phase difference between the time-shifted ultrasonic signals from the first and second transducers; and

creating a differential signal based on the modulated duty cycles of the first and second intermediate signals that is related to the phase difference between the time-shifted ultrasonic signals from the first and second transducers.

15. The method of claim 14, and further comprising selecting a number of pulses in the first and second intermediate signals.

16. The method of claim 14, wherein modulating the duty cycle comprises modulating the duty cycles of the first and second intermediate signals from nominal, fifty percent duty cycles.

17. The method of claim 14, wherein creating a differential signal comprises creating a differential output signal that is proportional to twice the phase difference between the time-shifted ultrasonic signals from the first and second transducers.

18. The method of claim 14, and further comprising converting the time-shifted ultrasonic signals from the first and second transducers to fifty percent duty cycles prior to modulating the duty cycles of the first and second intermediate signals.

19. The method of claim 14, wherein determining the second phase difference comprises:

modulating a duty cycle of first and second intermediate signals from a first duty cycle based on a phase difference between the time-shifted ultrasonic signals from the third and fourth transducers; and

creating at least one additional differential signal based on the modulated duty cycles of the first and second intermediate signals that is related to the phase difference between the time-shifted ultrasonic signals from the third and fourth transducers.

20. The method of claim 14, wherein generating a flow measurement based on the first and second phase differences comprises generating a volumetric flow measurement.

21. A transit time flow meter, comprising:

a pair of transducers;

wherein the pair of transducers are placeable in relation to a conduit to transmit ultrasonic signals through a fluid;

a phase detector, coupled to the pair of transducers, the phase detector using duty cycle modulation to determine a phase difference between signals received from the pair of transducers, the phase detector being responsive to an enable signal for selectively sampling portions of the signals received from the pair of transducers at selectable start times for a selectable number of pulses of the signals; and

a data processing circuit, responsive to the phase detector, that generates a measure of fluid flow in the conduit based on the phase difference.

22. The flow meter of claim 21, wherein the phase detector comprises:

a first stage that receives first and second input signals, modulates the duty cycle of first and second intermediate signals based on a phase difference between the first and second input signals and selects a number of pulses in the first and second intermediate signals; and

a second stage that receives the selected pulses of the first and second intermediate signals and charges first and second capacitors using the first and second intermediate signals, respectively, to create a differential signal that is based on the phase difference between the first and second input signals.

23. The flow meter of claim 22, wherein the second stage includes:

a first current source coupled to the first capacitor through a first switch, the first switch responsive to the first intermediate signal; and

a second current source coupled to the second capacitor through a second switch, the second switch responsive to the second intermediate signal.

24. The flow meter of claim 23, wherein the first and second current sources comprise current mirrors.

25. The flow meter of claim 23, wherein:

the first switch comprises a differential amplifier with a first input coupled to the first intermediate signal and a second input coupled to a complement of the first intermediate signal; and

the second switch comprises a differential amplifier with a first input coupled to the second intermediate signal and a second input coupled to a complement of the second intermediate signal.

26. The flow meter of claim 22, wherein the second stage includes a circuit that clears the voltage on the first and second capacitors.

27. The flow meter of claim 22, wherein the second stage includes an instrumentation amplifier with first and second inputs coupled to the differential signal.

28. The flow meter of claim 27, wherein the instrumentation amplifier includes a reference voltage offset.

29. The flow meter of claim 22, wherein the first stage includes a logic circuit that increases the duration of the high logic level pulses of the first intermediate signal based on the phase difference between the first and second input signals and reduces the duration of the high logic level pulses of the second intermediate signal based on the phase difference between the first and second input signals.

30. The flow meter of claim 23, wherein the second stage includes a switch that decouples the first capacitor from the first switch and a switch that decouples the second capacitor from the second switch when reading the differential signal.

31. The flow meter of claim 21, wherein the data processing circuit includes a transmitter for transmitting data to a remote processor.

32. A method for detecting flow in a fluid, the method comprising:

transmitting ultrasonic signals between first and second transducers;

receiving time-shifted ultrasonic signals at the first and second transducers;

sampling the time-shifted ultrasonic signals using an enable signal, wherein the sampled time-shifted ultrasonic signals are capable of including selectable portions of the time-shifted ultrasonic signals beginning at selectable sampling start times for a selectable number of pulses in the ultrasonic signals;

determining a phase difference between the time-shifted ultrasonic signals from the first and second transducers using duty cycle modulation; and

generating a flow measurement based on the phase difference.

33. The method of claim 32, wherein determining the phase difference comprises:

modulating a duty cycle of first and second intermediate signals from a first duty cycle based on a phase difference between the time-shifted ultrasonic signals from the first and second transducers; and

creating a differential signal based on the modulated duty cycles of the first and second intermediate signals that is related to the phase difference between the time-shifted ultrasonic signals from the first and second transducers.

34. The method of claim 33, and further comprising selecting a number of pulses in the first and second intermediate signals.

35. The method of claim 33, wherein modulating the duty cycle comprises modulating the duty cycles of the first and second intermediate signals from nominal, fifty percent duty cycles.

36. The method of claim 33, wherein creating a differential signal comprises creating a differential output signal that is proportional to twice the phase difference between the time-shifted ultrasonic signals from the first and second transducers.

37. The method of claim 33, and further comprising converting the time-shifted ultrasonic signals from the first and second transducers to fifty percent duty cycles prior to modulating the duty cycles of the first and second intermediate signals.

38. The method of claim 33, wherein generating a flow measurement based on the phase difference comprises generating a volumetric flow measurement.