Binary registration mark detection using 3-state sensing and matched filtering

A system for detecting a registration mark associated with an object, the registration mark representing a binary code sequence of N bits with each bit having either a first discrete value or a second discrete value, where N is an integer greater than one, the system comprising:

• a sensor for sensing for the registration mark, the sensor having an output, the sensor output taking a first state when a bit having the first discrete value is detected, a second state when a bit having the second discrete value is detected, and a third state when no bit having the first discrete value or the second discrete value is detected;
• a shift register for sampling the sensor output over time to produce a sequence of sensor values, each sensor value taking one of the first state, the second state, or the third state;
• and
• a matching filter operatively connected to the shift register for comparing N of the sensor values with corresponding bits of the binary code sequence, and for generating a detection signal in response to the comparing;
• and
• wherein the matching filter is configured to increase a value of the detection signal for each sensor value which matches its corresponding bit of the binary code sequence, decrease the value of the detection signal for each sensor value which is complementary to its corresponding bit of the binary code sequence, and neither increase nor decrease the value of the detection signal for each sensor value taking the third state, the detection signal indicating detection of the registration mark when the detection signal exceeds a predefined value.