Optical positioning device using different combinations of interlaced photosensitive elements

1 . An optical displacement sensor for sensing relative movement between a data input device and a surface by determining displacement of optical features in a succession of frames of the surface, the sensor comprising:

a detector including a plurality of photosensitive elements organized in first and second arrays;

first circuitry configured to combine signals from every Mth element of the first array to generate M group signals; and

second circuitry configured to combine signals from every M′th element of the second array to generate M′ group signals,

wherein M and M′ are numbers which are different from each other.

2 . The optical displacement sensor according to claim 1 , wherein the first and second arrays include at least one shared photosensitive element.

3 . The optical displacement sensor of claim 2 , further comprising:

a current mirror circuit configured to duplicate photocurrent from the shared photosensitive element.

4 . The optical displacement sensor of claim 2 , wherein the first and second arrays share substantially all of the photosensitive elements.

5 . The optical displacement sensor of claim 4 , further comprising:

current mirror circuitry configured to duplicate photocurrent from substantially all of the photosensitive elements.

6 . The optical displacement sensor according to claim 1 , wherein each said array comprises a linear comb array (LCA) arranged parallel to an axis.

7 . The optical displacement sensor according to claim 6 , further comprising:

circuitry configured to generate a first pair of line signals from the M group signals; and

circuitry configured to generate a second pair of line signals from the M′ group signals.

8 . The optical displacement sensor according to claim 7 , wherein the line signals are oscillatory in form as the data input device is moved in a direction not perpendicular to the axis.

9 . The optical displacement sensor according to claim 8 , further comprising:

circuitry configured to calculate from a line signal a component v of a velocity of movement of the data input device along the axis using equation:

v=f*p/τ

f is a frame rate, p is a detector pitch, and τ is the time between a previous two zero-crossings going in a same direction.

10 . The optical displacement sensor according to claim 7 , wherein the line signal generation circuitry comprises weighting circuitry to weight the group signals.

11 . The optical displacement sensor according to claim 10 , wherein the M group signals are each weighted by one of M in-phase weighting factors and one of M quadrature weighting factors, and wherein the M′ group signals are each weighted by one of M′ in-phase weighting factors and one of M′ quadrature weighting factors.

12 . The optical displacement sensor according to claim 11 , where the in-phase weighting factors (S 1 ) and the quadrature weighting factors (S 2 ) are calculated using equations:

S1

=

cos

⁢

⁢

2

⁢

πj

N

;

and

S2

=

sin

⁢

⁢

2

⁢

πj

N

,

where j goes from 0 to M−1, and N=M, for the M group signals used to generate the first pair of line signals, and

where j goes from 0 to M′−1, and N=M′, for the M′ group signals used to generate the second pair of line signals.

13 . The optical displacement sensor according to claim 1 , further comprising:

circuitry configured to compare a quality of a line signal which is generated from the M group signals with the quality of another line signal which is generated from the M′ group signals; and

circuitry configured to select a higher quality line signal based on the comparison.

14 . The optical displacement sensor according to claim 1 , further comprising:

circuitry configured to weight line signals based on a signal quality characteristic and to combine the weighted line signals.

15 . A method of sensing movement of a data input device across a surface using an optical displacement sensor having a detector including a plurality of photosensitive elements organized in first and second arrays, the method comprising:

receiving on the plurality of photosensitive elements an intensity pattern produced by light reflected from a portion of the surface;

combining signals from every Mth element of the first array to generate M group signals; and

combining signals from every M′th element of the second array to generate M′ group signals,

wherein M and M′ are numbers which are different from each other.

16 . The method of claim 15 , wherein the first and second arrays share photosensitive elements.

17 . The method of claim 15 , further comprising:

generating a first pair of oscillatory line signals from the M group signals; and

generating a second pair of oscillatory line signals from the M′ group signals.

18 . The method of claim 17 , further comprising:

comparing a quality of a line signal which is generated from the M group signals with the quality of another line signal which is generated from the M′ group signals; and

selecting a higher quality line signal based on the comparison.

19 . The method of claim 17 , further comprising:

weighting line signals based on a signal quality characteristic; and

combining the weighted line signals.

20 . An optical positioning apparatus, the apparatus comprising:

a two-dimensional array of photosensitive elements organized as an M×M′ pattern of elements which is repeated to form the array; and

circuitry configured to combine signals from every element in a same position within the pattern so as to generate M×M′ group signals.