Apparatus and method for direct digital measurement of electrical properties of passive components

• US 6,498,471 B2
• Filed: 12/18/2001
• Issued: 12/24/2002
• Est. Priority Date: 05/04/1999
• Status: Expired due to Fees

• Current Assignee: Barker A. Clifford
• Original Assignee: Barker A. Clifford
• Inventors: Barker, A. Clifford
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): Hamdan, Wasseem H.
• Application Number:
  US10/020,206
• Publication Number:
  US 20020084776A1
• Time in Patent Office: 371 Days
• Field of Search: 331/1, 331/48, 331/2, 331/74, 331/18, 324/76.53
• US Class Current: 324/76.53
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors

Abstract

A high-resolution apparatus and method provide direct digital measurement of electrical properties such as resistance, capacitance or inductance. An excitation signal derived from a high-frequency source is applied to a network containing an unknown device to produce a network output signal with an amplitude that corresponds to the electrical property to be measured. Amplitude variations in the network output signal are converted to corresponding phase variations in a third signal by adding the network output signal to a reference signal that is phase shifted by 90-degrees with respect to the excitation. The third signal is then applied to a phaselocked loop that employs the above-mentioned high-frequency source in combination with a pulse delete circuit to produce an output that multiplies phase information contained in the third signal by orders of magnitude. Conventional methods can then be used to measure the resulting greatly magnified phase changes corresponding to minute changes in the electrical properties of the device under test.

Claims

1. Measurement apparatus comprising:

means for providing a first signal of constant frequency and phase;

amplitude changing means for producing amplitude changes in said first signal proportional to a phenomenon, property or condition to be measured;

generating means responsive to said amplitude-changed first signal for generating a second signal having a phase which varies in proportion to said amplitude changes in said first signal,

phaselocked loop means for producing an output signal phaselocked to said second signal, wherein phase changes in said second signal produce phase changes in said phaselocked loop output signal that are substantially greater than corresponding phase changes in said second signal.

2. Apparatus as set forth in claim 1, wherein said generating means consists of mixing said amplitude-changed first signal with a reference signal to generate said second signal.

3. Apparatus as set forth in claim 2 wherein said first signal and said reference signal are both derived from the same constant frequency source.

4. Apparatus as set forth in claim 3, wherein said first signal and said reference signal are identical in frequency and differ in phase by a predetermined, fixed phase angle.

5. Apparatus as set forth in claim 4, wherein said fixed phase angle is exactly 90 degrees.

6. Apparatus as set forth in claim 2, wherein said mixing means comprises a linear summing amplifier.

7. Apparatus as set forth in claim 1, wherein said means for providing first signal and said reference signal includes at least one frequency divider.

8. Apparatus as set forth in claim 1, wherein said amplitude changing means comprises a network containing one or more passive sensors that exhibit changes in electrical properties proportional to the phenomenon, property or condition to be measured.

9. Apparatus as set forth in claim 8, wherein said sensors comprise resistors.

10. Apparatus as set forth in claim 8, wherein said sensors comprise capacitors.

11. Apparatus as set forth in claim 9, wherein said resistors are temperature sensing resistors.

12. Apparatus as set forth in claim 8, wherein said sensors comprise inductors.

13. Apparatus as set forth in claim 9, wherein said resistors are strain gages.

14. Apparatus as set forth in claim 8, wherein said network comprises a Wheatstone bridge.

15. Apparatus as set forth in claim 1, wherein the frequency of said phaselocked loop output signal is a multiple of the frequency of said second signal.

16. Apparatus as set forth in claim 15, wherein said phaselocked loop output signal is subtracted from said constant frequency reference source by means of a pulse deletion circuit.

17. Apparatus as set forth in claim 16, wherein the output of said pulse deletion circuit is applied to a divider to produce a signal at a frequency equal to the frequency of said second signal.

18. Apparatus as set forth in claim 1, further comprising phase measurement means for measuring the relative phase of said phaselocked loop output signal and a constant frequency reference signal.

19. Apparatus as set forth in claim 18, wherein said phase measurement means comprises up/down counting means responsive to full-cycle phase variations between said phaselocked loop output signal and said reference signal.

20. Apparatus as set forth in claim 18, wherein said phase measurement means comprises up/down counting means responsive to fractional cycle phase variations between said phaselocked loop output signal and said reference signal.

21. Apparatus as set forth in claim 1, wherein said first signal and said reference signal are used in combination with a plurality of independent amplitude changing means, combining means, and phaselocked loop means to provide a multi-channel measurement apparatus.

22. A measurement method in which a phenomenon, property, or condition to be measured produces amplitude changes in a fixed-frequency reference signal to produce an amplitude-changed reference signal, and in which the amplitude-changed reference signal is employed to produce another signal that is phase shifted in proportion to amplitude changes in the amplitude-changed signal, and in which the phase-shifted signal is employed to produce corresponding, but substantially greater, phase changes in another signal, that produces an output.

23. A method according to claim 22, wherein amplitude changes are produced by applying the fixed reference signal to a network containing one or more passive sensing elements such as resistors, inductors or capacitors, or a combination thereof.

24. A method according to claim 22, wherein the phase-shifted signal is produced by adding the amplitude-changed reference signal to a second reference signal that has a fixed phase offset with respect to the amplitude-changed signal.

25. A method according to claim 22, wherein a phaselocked loop is used to multiply the phase changes in the phase-shifted signal.

26. A method according to claim 25, wherein phase multiplication is produced by subtracting the phaselocked loop output from a fixed-frequency reference at a substantially higher frequency, and dividing the resulting signal by a factor that produces a signal to be applied to the loop phase detector, which signal is at a frequency exactly equal to the phase-shifted input to the phaselocked loop.