Signal processing method for use with an optical navigation system

• US 20060106319A1
• Filed: 11/08/2005
• Published: 05/18/2006
• Est. Priority Date: 11/12/2004
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Silicon Light Machines Corporation (SCREEN Holdings Co., Ltd.)
• Inventors: Todoroff, Brian D., Xu, Yansun
• Granted Patent: US 7,248,345 B2
• Time in Patent Office: Days
• US Class Current: 600/476
• CPC Class Codes: G06F 3/0317 in co-operation with a patterned surface, e.g. absolute position or relative movement detection for an optical mouse or pen positioned with respect to a coded surface

Abstract

A signal processor and method are provided for detecting movement of a surface relative to an optical sensor having an array of photosensitive elements. Generally, the method involves: (i) sampling each of a number (M) of phase signals from the photosensitive elements, each of the M signals having a magnitude (A_i) and including a tracking signal at a frequency being tracked and a background signal at other frequencies that offsets the tracking signal, where i, an index of the signals, is a whole number between 0 and M-1; (ii) eliminating the offset to the tracking signal due to the background signal to generate M non-offset phase signals having a magnitude (A′_i); (iii) adjusting phase angles (θ_i) of the non-offset phase signals to generate M weighted phase signals (A′_iθ′_i); and (iv) combining each of the M weighted phase signals (A′_iθ′_i) to generate an average weighted phase having a phase angle (θ), that when tracked over time indicates a direction and velocity of the movement of an image of the surface mapped to the array.

Claims

1. A method for detecting movement of a surface relative to an optical sensor having an array including a plurality of photosensitive elements, the method comprising steps of:

sampling each of a number (M) of phase signals from the plurality of photosensitive elements, each of the M signals having a magnitude (A_i) and including a tracking signal at a frequency being tracked and a background signal at other frequencies that offsets the tracking signal, where i, an index of the signals, is a whole number between 0 and M-1;

eliminating the offset to the tracking signal due to the background signal to generate M non-offset phase signals having a magnitude (A′

_i);

adjusting phase angles (θ

_i) of the non-offset phase signals to generate M weighted phase signals (A′

_iθ

′

_i); and

combining each of the M weighted phase signals (A′

_iθ

′

_i) to generate an average weighted phase having a phase angle (θ

), that when tracked over time indicates a direction and velocity of the movement of an image of the surface mapped to the array.

2. A method according to claim 1, wherein the array is a periodic array in which the plurality of photosensitive elements are regularly spaced having a periodicity matched to that of the frequency of the signal being tracked.

3. A method according to claim 2, wherein the step of eliminating the offset to the tracking signal due to the background signal comprises the steps of:

selecting a phase signal from among the M phase signals; and

subtracting the selected phase signal from each of the remaining (M-1) phase signals to generate the M non-offset phase signals.

4. A method according to claim 3, wherein the step of selecting a phase signal from among the M phase signals comprises the step of identifying and selecting a minimum phase signal (A_min) having the lowest signal strength from among the M phase signals.

5. A method according to claim 4, wherein the step of adjusting phase angles (θ

_i) of the non-offset phase signals to generate M weighted phase signals (A′

_iθ

′

_i) comprises the step of multiplying each of the M non-offset phase signals post subtraction by predetermined angle values to generate M weighted phase signals (A′

_iθ

′

_i).

6. A method according to claim 5, wherein the step of multiplying each of the M non-offset phase signals by predetermined angle values comprises the step of looking up a predetermined angle value for each of the M non-offset phase signals in a look-up-table (LUT).

7. A method according to claim 3, wherein the step of combining each of the M weighted phase signals (A′

_iθ

′

_i) to generate an average weighted phase angle comprises the steps of;

summing values of the M weighted phase signals (A′

_iθ

′

_i); and

dividing the sum of the M weighted phase signals (A′

_iθ

′

_i) by a sum of the M non-offset phase signals post subtraction to generate the average weighted phase angle.

8. A method according to claim 7, further comprising the step of measuring contrast of the image mapped to the array using the sum of the M non-offset phase signals post subtraction.

9. A method according to claim 8, wherein the optical sensor further comprises a light source to illuminate the surface, the light source adapted to cause at least some light reflected from the surface to be incident on the array;

and

wherein the method further comprises the step of controlling an amount of light output from the light source in response to the measured contrast of the image mapped to the array.

10. A method according to claim 9, wherein the optical sensor further comprises an Automatic Gain Control (AGC) circuit to amplify M phase signals from the plurality of photosensitive elements, and

wherein the method further comprises the step of controlling the AGC circuit in response to the measured contrast of the image mapped to the array.

11. A method for detecting motion of a surface relative to an optical sensor having, a number of comb arrays, each including a plurality of photosensitive elements, the method comprising steps of at a first time (t₀):

(a) sampling each of a number (M) of phase signals from the plurality of photosensitive elements, each of the M signals having a magnitude (A_i), where i, an index of the signals, is a whole number between 0 and M-1;

(b) selecting a phase signal from among the M phase signals;

(c) subtracting the selected phase signal from each of the remaining (M-1) phase signals to generate M post subtraction phase signals (A′

_i);

(d) multiplying each of the post subtraction phase signals (A′

_i) by a predetermined angle value to generate weighted phase signals (A′

_iθ

′

_i);

(e) summing values of the weighted phase signals (A′

_iθ

′

_i); and

(f) dividing the sum of the weighted phase signals by a sum of the post subtraction unweighted phase signals to derive an average weighted phase having a phase angle (θ

) at t₀.

12. A method according to claim 11, further comprising the steps of:

(g) repeating steps (a) to (f) at a second time (t_l) to derive a second average weighted phase angle at t_l; and

(h) determining a delta phase angle from a difference between the first and second phase angle; and

(i) determining from the delta phase angle a direction and velocity of the movement of an image of the surface mapped to the number of comb arrays.

13. A method according to claim 12, wherein the step of selecting a phase signal from among the M phase signals comprises the step of identifying and selecting a maximum phase signal (A_max) having the largest signal strength from among the M phase signals.

14. A method according to claim 12, wherein the step of selecting a phase signal from among the M phase signals comprises the step of identifying and selecting a minimum phase signal (A_min) having the lowest signal strength from among the M phase signals.

15. A method according to claim 11, wherein the optical sensor comprises at least two one-dimensional comb-arrays having photosensitive element arranged along non-parallel axes, and wherein the method comprises the steps of detecting motion along each of two axes to detect motion of the surface relative to the optical sensor in two-dimensions.

16. A method according to claim 11, wherein the optical sensor comprises a two-dimensional comb-array having at least a first plurality of photosensitive elements grouped along a first axis and a second plurality of photosensitive elements grouped along a second non-parallel axis, and wherein the method comprises the steps of detecting motion along each of two axes to detect motion of the surface relative to the optical sensor in two-dimensions.

17. A signal processor for processing signals from an optical sensor having an array of a plurality of photosensitive elements to detect movement of a surface relative to the optical sensor, the signal processor comprising:

sampling means for sampling each of a number (M) of phase signals from the plurality of photosensitive elements, each of the M signals having a magnitude (A_i) and including a tracking signal at a frequency being tracked and a background signal at other frequencies, which offsets the tracking signal, where i, an index of the signals, is a whole number between 0 and M-1;

offset elimination means for eliminating the offset to the tracking signal due to the background signal to generate M non-offset phase signals having a magnitude (A_i);

phase angle adjusting means for adjusting phase angles (θ

_i) of the non-offset phase signals to generate M weighted phase signals (A′

_iθ

′

_i); and

combining means for combining each of the M weighted phase signals (A′

_iθ

′

_i) to generate an average weighted phase having a phase angle (θ

), that when tracked over time indicates the direction and velocity of the movement of an image of the surface mapped to the array.

18. A signal processor according to claim 17, wherein the offset elimination means comprises a circuit to identify from among the M phase signals a minimum phase signal (A_min) having the lowest signal strength, and to subtract A_min from each of the remaining (M-1) phase signals to generate the M non-offset phase signals.

19. A signal processor according to claim 18, wherein the phase angle adjusting means comprises a circuit to multiply each of the M non-offset phase signals post subtraction by predetermined angle values to generate M weighted phase signals (A′

_iθ

′

_i).

20. A signal processor according to claim 19, wherein the combining means comprises:

a summing circuit to sum the values of the M weighted phase signals (A′

_iθ

′

_i); and

a dividing circuit to divide the sum of the M weighted phase signals (A′

_iθ

′

_i) by a sum of the M non-offset phase signals post subtraction to generate the average weighted phase angle.