Signal processing apparatus and method

• US 6,788,221 B1
• Filed: 12/24/1998
• Issued: 09/07/2004
• Est. Priority Date: 06/28/1996
• Status: Expired due to Term

• Current Assignee: Synaptics (UK) Ltd. (Synaptics Incorporated)
• Original Assignee: Synaptics (UK) Ltd. (Synaptics Incorporated)
• Inventors: Dames, Andrew N., Ely, David T.
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): WONG, ALBERT KANG
• Application Number:
  US09/220,354
• Time in Patent Office: 2,084 Days
• Field of Search: 341/20, 341/5, 341/15, 341/111, 340/870.34, 336/129, 336/130, 324/207.17, 178/18.06, 178/18.07, 178/20.04
• US Class Current: 341/20
• CPC Class Codes: G01D 5/244 influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
• CPC Class Codes: G01D 5/24461 by redundancy or plausibility
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position
• CPC Class Codes: H03M 1/645 for position encoding, e.g. using resolvers or synchros H03M1/485 takes precedence

Abstract

Processing circuitry is provided for processing signals received from, for example, sense coils forming part of a position encoder used to encode the relative positions of two relatively moveable members. The position encoder is such that each of the plurality of signals from the sense coils varies sinusoidally with the relative position of the members but out of phase with respect to each other. The processing circuitry comprises mixers for multiplying each of the received signals with one of a corresponding plurality of periodic time varying signals, each having the same predetermined period and a different predetermined phase, and an adder for adding the signals from the mixers. The phase of the mixing signals are chosen so that the output signals from the adder contains a single periodic component having the predetermined period whose phase varies with the relative position of the two members. Preferably, a reference channel is provided in order to allow for compensation of common phase errors in both channels. The period time varying signals multiplied with each of the signals from the position encoder preferably comprise a two or three level square wave signal having a number of transitions designed to reduce the low order harmonic content of the mixing signals.

Claims

1. A position detector comprising:

first and second members mounted for relative movement in a measurement path, said first member comprising a plurality of sensing circuits, each extending along said measurement path and being offset from each other in said measurement path and said second member comprising generating means for generating, in each of said sensing circuits, a time varying periodic carrier signal whose amplitude varies sinusoidally with the relative position between said generating means and the respective sensing circuit and wherein, due the offset between said sensing circuits, the sinusoidal variation of the amplitude of the signals generated in said sensing circuits are out of phase with respect to each other;

means for combining a first periodic time varying signal having the same period as said carrier signal with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said carrier signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;

means for multiplying each of the signals generated in said plurality of sensing circuits with a respective one of the plurality of combined signals generated by said combining means; and

means for adding the signals from said multiplying means to provide an output signal;

wherein said predetermined phases of said plurality of second periodic time varying signals are determined so that said output signal from said adding means contains a single periodic component having the same predetermined period as said second periodic time varying signals and whose phase varies with the relative position between said first and second members.

2. A position detector according to claim 1, wherein the predetermined phases of said plurality of second periodic time varying signals are determined such that their magnitude equals the phase of the corresponding received signal with which it is multiplied.

3. A position detector according to claim 1, further comprising a waveform generator which is arranged to generate said first and second periodic time varying signals.

4. A position detector according to claim 3, wherein said first and second periodic time varying signals are squarewave signals.

5. A position detector according to claim 4, wherein said combining means is arranged to combine the two different periodic time varying signals prior to multiplication with the respective received signals using an XOR gate.

6. A position detector according to claim 4, wherein said multiplying means comprises a CMOS IC switch.

7. A position detector according to claim 1, further comprising means for filtering said output signal to remove components not having the same predetermined period as said second periodic time varying signals.

8. A position detector according to claim 7, wherein the output of said filtering means is substantially sinusoidal having said predetermined period, and wherein said apparatus further comprises means for converting said sinusoidal signal into a squarewave signal having said predetermined period and said phase which varies with said relative position.

9. A position detector according to claim 8, wherein said converting means comprises a comparator for comparing said sinusoidal signal with a reference signal.

10. A position detector according to claim 8, further comprising means for processing said squarewave signal having said predetermined period whose phase varies with said relative position to output a different squarewave signal whose duty ratio varies with said relative phase.

11. A position detector according to claim 10, wherein said processing means comprises a set-reset latch.

12. A position detector according to claim 1, wherein said plurality of sensing circuits are inductively coupled to said generator means.

13. A position detector according to claim 1, wherein said sensing circuits are capacitively coupled to said generator means.

14. A position detector according to claim 1, wherein said sensing circuits extend over a linear path.

15. A position detector according to claim 1, wherein said sensing circuits extend in a rotary path.

16. A position detector according to claim 1, wherein said sensing circuits extend in a radial path.

17. A position detector according to claim 1, wherein the modulus of the phase of said second periodically varying signals is given by (iπ

)/n, where n is the number of sensing circuits.

18. A method of determining the relative position between first and second members which are relatively moveable in a measurement path, said first member comprising a plurality of sensing circuits, each extending along said measurement path and being offset from each other in said measurement path, said method comprising the steps of:

using a generator on said second member to generate, in each of said sensing circuits, a time varying periodic carrier signal whose amplitude varies sinusoidally with the relative position between the second member and the respective sensing circuit on the first member, and wherein, due to the offset between said sensing circuits, the sinusoidal variation of the amplitude of the signals generated in said sensing circuits are out of phase with respect to each other;

combining a first periodic time varying signal having the same period as said carrier signal with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said carrier signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;

multiplying each of the signals generated in said plurality of sensing circuits with a respective one of the plurality of combined signals generated in said combining step; and

adding the signals from said multiplying step to provide an output signal;

wherein said predetermined phases of said plurality of second periodic time varying signals are determined so that said output signal from said adding means contains a single periodic component having the same predetermined period as said second periodic time varying signals and whose phase varies with the relative position between said first and second members.

19. A method according to claim 18, wherein the predetermined phases of said plurality of second periodic time varying signals are determined such that their modulus equals the phase of the corresponding received signal with which it is multiplied.

20. A method according to claim 18, comprising the step of using a signal generator to generate each of said periodic time varying signals.

21. A method according to claim 20, wherein said first and second periodic time varying signals are squarewave signals.

22. A method according to claim 21, wherein said combining step uses an XOR gate to combined said first and second periodic time varying signals prior to multiplication with the respective received signal.

23. A method according to claim 21, wherein a CMOS IC switch is used to multiply said time varying signals.

24. A method according to claim 18, further comprising the step of filtering said output signal to remove components not having the same predetermined period as said second periodic time varying signals.

25. A method according to claim 24, wherein the output of said filtering step is a sinusoidal signal having said predetermined period, and wherein said method further comprises the step of converting said sinusoidal signal into a squarewave signal having said predetermined period and said phase which varies with said relative position.

26. A method according to claim 25, wherein said converting step compares said sinusoidal signal with a reference signal.

27. A method according to claim 25, further comprising the step of processing said squarewave signal having said predetermined period whose phase varies with said relative position to output a different squarewave signal whose duty ratio varies with said relative phase.

28. A method according to claim 27, wherein said processing step uses a set-reset latch.

29. A processing apparatus for processing a plurality of signals received from a position encoder used to encode the relative positions of two relatively movable members, wherein each of said plurality of signals varies sinusoidally with said relative position and out of phase with respect to each other, the apparatus comprising:

means for combining a first periodic time varying signal having a first period with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said first periodic time varying signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;

means for multiplying each of said received signals with a respective one of the plurality of combined signals generated by said combining means; and

means for adding the signals from said multiplying means to provide an output signal, and wherein said predetermined phases of said periodically varying signals are determined so that, in use, the output signal from said adding means contains a single period whose phase varies with the relative position of the relatively moveable members.

30. An apparatus according to claim 29, wherein each of said periodic time varying signals comprises a digital signal having a fundamental frequency component corresponding to said predetermined period and higher order harmonics;

and wherein each period of said periodic time varying signals includes a plurality of transitions between levels within the digital signal which are arranged so that the energy within at least the third harmonic is reduced as compared with that of the third harmonic in a square wave signal having the same fundamental frequency component.

31. An apparatus according to claim 29, wherein each of said plurality of signals received from a position encoder amplitude modulates a periodic time varying carrier signal having a period substantially equal to said first period.

32. An apparatus according to claim 29, further comprising a waveform generator for generating each of said periodic time varying signals.

33. An apparatus according to claim 32, wherein each of said periodic time varying signals are two or three level digital signals.

34. An apparatus according to claim 33, wherein said waveform generator is arranged to combine the two different periodic time varying signals prior to multiplication with the respective input signal.

35. An apparatus according to claim 29, wherein said multiplying means comprises at least one CMOS IC switch.

36. An apparatus according to claim 29, wherein the predetermined phases of said periodic time varying signals are determined such that their magnitude equals the phase of the corresponding received signal with which it is multiplied.

37. An apparatus according to claim 29, further comprising means for filtering said output signal to remove components not having said predetermined period.

38. An apparatus according to claim 37, wherein the output of said filtering means is substantially sinusoidal having said predetermined period and wherein said apparatus further comprises means for converting said sinusoidal signal into a square wave signal having said predetermined period and said phase which varies with said relative position.

39. An apparatus according to claim 38, wherein said converting means comprises a comparator for comparing said sinusoidal signal with a reference signal.

40. An apparatus according to claim 29, wherein the modulus of the phase of each of said periodically varying signals is given by (iπ

/)/n, where n is the number of received signals.

41. An apparatus according to claim 30, wherein said transitions are located within said period in the vicinity where said fundamental component and at least said third harmonic component add together.

42. An apparatus according to claim 29, wherein said periodic time varying signals each comprise a three level digital signal and wherein said multiplying means comprises at least two switches.

43. An apparatus according to claim 42, comprising a digital waveform generator operable for generating at least two control signals for controlling a respective one of said switches based upon said three level digital signal.

44. An apparatus according to claim 29, further comprising processing means for processing said output signal from said combining means to generate another signal having a characteristic different from said phase which monotonically varies with the value of said variable.

45. An apparatus according to claim 44, wherein said processing circuitry comprises:

a comparator for comparing the output signal from said combining means with a reference signal to generate a square wave signal whose phase varies with the value of said variable;

a first circuit responsive to the leading edge of said square wave signal to generate a first signal having a value which monotonically varies with the phase of the output signal from said combining means and hence with the value of said variable over one period of said sinusoidal variation;

a second circuit responsive to the trailing edge of said square wave signal to generate a second signal having a value which monotonically varies with the phase of said output signal from said combining means and hence with the value of said variable over one period of said sinusoidal variation; and

an adding circuit or a subtracting circuit for combining the first and second output signal values from said first and second circuits to provide a resultant output signal having a value which monotonically varies with the value of said variable over one period of said sinusoidal variation.

46. An apparatus according to claim 44, wherein said processing means comprises first processing circuitry for processing said output signal from said combining means to generate said another signal having said characteristic different from said phase which monotonically varies with the value of said variable and second processing circuitry for processing a periodic time varying signal having said predetermined period to generate an output signal having a value which monotonically varies with the phase of the periodic time varying signal being processed;

and

second combining means for combining the output signal value from said first processing circuitry with the output signal value from said second processing circuitry to provide a combined output signal having a value which monotonically varies with the value of said variable over one period of said sinusoidal variation.

47. An apparatus according to claim 29, wherein said combining means is a first combining means and further comprising:

a comparator for comparing said output signal with a reference voltage to generate a square wave signal whose phase varies with said variable;

a first circuit responsive to the leading edge of said square wave signal to generate a first signal having a value which monotonically varies with the phase of the output signal from said first combining means and hence with the value of said variable over one period of said sinusoidal variation;

a second circuit responsive to the trailing edge of said square wave signal to generate a second signal having a value which monotonically varies with the phase of the output signal from said first combining means and hence with the value of said variable over one period of said sinusoidal variation; and

second means for combining the first and second output signal values from said first and second circuits to provide a combined output signal having a value which monotonically varies with the value of said variable over one period of said sinusoidal variation.

48. An apparatus according to claim 47, wherein said first and second circuits each comprise a latch circuit which is operable to output a pulse width modulated time varying signal whose DC level monotonically varies with the value of said variable.

49. An apparatus according to claim 48, further comprising filter means for filtering out the time varying component of said pulse width modulated signal to provide a DC output whose value monotonically varies with the value of said variable.

50. An apparatus according to claim 47, wherein said first and second circuits each comprise a counter which is operable to output a count which monotonically varies with the value of said variable.

51. An apparatus according to claim 29, wherein said combining means is a first combining means and further comprising:

first processing circuitry for processing said output signal from said first combining means to generate an output signal having a value which monotonically varies with the phase of the output signal from said first combining means and hence with the value of said variable over one period of said sinusoidal variation;

second processing circuitry for processing a periodic time varying signal having said predetermined period to generate an output signal having a value which monotonically varies with the phase of the periodic time varying signal processed; and

second means for combining the output signal value from said first processing circuitry with the output signal value from said processing circuitry to provide a combined output signal having a value which monotonically varies with the value of said variable over one period of said sinusoidal variation.

52. An apparatus according to claim 51, wherein said first and second processing circuitry comprises a comparator for comparing the output signal from said first combining means with a reference signal to generate a square wave signal whose phase varies with the value of said variable.

53. An apparatus according to claim 52, wherein each of said first and second processing circuitry comprises pulse width modulation means responsive to the square wave signal output from said comparator, for generating a pulse width modulating signal whose duty ratio varies with the value of said variable.

54. An apparatus according to claim 53, wherein said pulse width modulation means is responsive to the leading edge of said square wave signal to generate a first pulse width modulated signal whose duty ratio varies with the value of said variable, and wherein each of said first and second processing circuitry further comprises a second pulse width modulating means responsive to the trailing edge of said square wave signal output by said comparator for generating a second pulse width modulated signal whose duty ratio varies with the value of said variable.

55. An apparatus according to claim 53, wherein each of said pulse width modulating means comprises a latch.

56. An apparatus according to claim 54, wherein said second combining means is operable to combine the signals from each of said pulse width modulating means to generate a combined output signal having a value which is less sensitive to voltage offsets in said comparator.

57. An apparatus according to claim 46, wherein said signal processed by said second processing circuitry is a reference periodic time varying signal having said predetermined period and a predetermined phase.

58. An apparatus according to claim 46, wherein said signal processed by said second processing circuitry comprises a single periodic component having said predetermined period, the phase of said component varying with the value of said variable and wherein the variation of the phase of the signal processed by the first processing circuitry varies in the opposite sense to the variation in phase of the signal processed by said second processing circuitry.

59. An apparatus according to claim 58, wherein the signal processed by the first and second processing circuits are obtained from different input signals.

60. An apparatus according to claim 58, wherein the signal processed by said first and second processing circuits are obtained using at least one common input signal.

61. An apparatus according to claim 38, further comprising means for processing said square wave signal having said predetermined period whose phase varies with said relative position to input a different square wave signal whose duty ratio varies with said relative phase.

62. An apparatus according to claim 29, wherein said periodic time varying signals comprise a two or a three level digital signal having a number of spaced transitions within the period, the location of the spacings being to arrange to reduce the energy within at least the low order harmonics of the time varying signals.

63. A position detecting method comprising the steps of:

providing first and second members that are movable relative to each other along a measurement path, said first member comprising a plurality of sensing circuits, each extending along said measurement path and being offset from each other in said measurement path and said second member comprising generating means for generating, in each of said sensing circuits, a time varying periodic carrier signal whose amplitude varies sinusoidally with the relative position between said generating means and the respective sensing circuit and wherein, due to the offset between said sensing circuits, the sinusoidal variation of the amplitude of the signals generated in said sensing circuits are out of phase with respect to each other;

combining a first periodic time varying signal having the same period as said carrier signal with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said carrier signal and each having a different predetermined phase, to generate a plurality of combined time varying signals;

multiplying each of the signals generated in said plurality of sensing circuits with a respective one of the plurality of combined signals generated by said combining means;

adding the signals from said multiplying step to provide an output signal; and

determining the relative position of said first and second members using said output signal;

wherein said predetermined phases of said plurality of second periodic time varying signals are determined so that said output signal from said adding step contains a single periodic component having the same predetermined period as said second periodic time varying signals and whose phase varies with the relative position between said first and second members.

64. A method of processing a plurality of signals received from a position encoder used to encode the relative positions of two relatively movable members, wherein each of the plurality of signals varies sinusoidally with said relative position and out of phase with respect to each other, the method comprising the steps of:

combining a first periodic time varying signal having a first period with a respective one of a plurality of second periodic time varying signals, each having the same predetermined period which is greater than the period of said first periodic time varying signal and each having a different predetermined phase to generate a plurality of combined time varying signals;

multiplying each of the received signals with a respective one of the plurality of combined signals generated in said combining step; and

adding the signals from said multiplying step to provide an output signal, and wherein said predetermined phases of said periodically varying signals are determined so that the output signal from said adding step contains a single periodic component having said predetermined period whose phase varies with the relative position of the relatively movable members.