Sensor circuit

A method of calculating a corrected data value for a sensor circuit, said method comprising:

• accessing a nominal reset voltage value, wherein said nominal reset voltage value is a first charge collected on a capacitor of said sensor circuit just after reset thereof;
• accessing an output voltage value associated with said photodiode at an end of an integration period of a photodiode of said sensor circuit, wherein a first knee point voltage is asserted, during said integration time, to said photodiode which resets a voltage on said photodiode to said first knee point voltage when said photodiode voltage is below said first knee point voltage;
• measuring a voltage value of said photodiode corresponding to a second knee point voltage, wherein said second knee point voltage is approximately equal to said first knee point voltage;
• determining said corrected data value to be said nominal reset voltage minus said output voltage value when said nominal reset voltage value minus said output voltage value, divided by a gain, is greater than said nominal reset voltage value minus said voltage value of said photodiode;
• and
• determining said corrected data value to be said voltage value of said photodiode minus said output voltage value, multiplied by said gain, plus said nominal voltage value minus said voltage value of said photodiode when said nominal reset voltage value minus said output voltage value, divided by said gain, is less than said nominal reset voltage value minus said voltage value of said photodiode.

A process to measure and correct signals related to a photodiode based sensor, the process configured to:

• measure a nominal reset voltage value of said sensor:
• assert a first knee point voltage to a photodiode of said sensor, wherein said first knee point voltage resets a voltage on said photodiode to said first knee point voltage when said photodiode voltage is below said first knee point voltage;
• measure an output voltage associated with said photodiode at an end of an integration period of said photodiode;
• subsequent to the end of said integration period, assert a second knee point voltage to said photodiode, wherein said second knee point voltage has a value approximately equal to a value of said first knee point voltage;
• measure a voltage value of said photodiode in response to said asserted second knee point voltage;
• determine a corrected data value to be said nominal reset voltage minus said output voltage value when said nominal reset voltage value minus said output voltage value, divided by a gain, is greater than said nominal reset voltage value minus said voltage value of said photodiode;
• and
• determine said corrected data value to be said voltage value of said photodiode minus said output voltage value, multiplied by said gain, plus said nominal voltage value minus said voltage value of said photodiode when said nominal reset voltage value minus said output voltage value, divided by said gain, is less than said nominal reset voltage value minus said voltage value of said photodiode.