Optical encoder using sufficient inactive photodetectors to make leakage current equal throughout

An optical encoder comprising:

• a plurality of active photodiodes in an array on a semiconductor chip;
• a code member having alternating areas for alternately illuminating and not illuminating the active photodiodes in response to movement of the code member;
• means connected to the active photodiodes for measuring current from the active photodiodes;
• and
• sufficient inactive photodiode area on the semiconductor chip at each end of the array of active photodiodes to make the leakage current from the inactive photodiode area to each end active photodiode of the array substantially the same as the leakage current from the other active photodiodes in the array.

An optical encoder comprising:

• a plurality of active photodiodes in an array on a semiconductor chip;
• a code member having alternating areas for alternately illuminating and not illuminating the active photodiodes in response to movement of the code member;
• means connected to the active photodiodes for measuring current from the active photodiodes;
• and
• sufficient inactive photodiode area on the semiconductor chip at each end of the array of active photodiodes that each active photodiode in the array has substantially symmetrical boundary conditions in each direction along the length of the array.

An optical encoder comprising:

• a plurality of active photodiodes in an array on a semiconductor chip;
• a code member having alternating areas for alternately illuminating and not illuminating the active photodiodes in response to movement of the code member;
• means connected to the active photodiodes for measuring current from the active photodiodes;
• and
• a sufficient plurality of inactive photodiodes at each end of the array of active photodiodes to make the leakage current to each active photodiode of the array substantially equal.