Differential photodiode integrator circuit for absorbance measurements

A method for measuring a light intensity level using a photodetector comprising:

• receiving a light signal at the photodetector;
• generating a photodetector current having a photodetector current level in response to the light signal intensity from a first photodetector terminal to a second photodetector terminal;
• sensing the photodetector current at a first integrator input at the first photodetector terminal;
• generating a first output signal at a first integrator output, the first output signal indicative of an integral of the photodetector current level;
• sensing the photodetector current at a second integrator input at the second photodetector terminal;
• generating a second output signal at a second integrator output, the second output signal indicative of an integral of the photodetector current level;
• receiving the first output signal at a positive differential amplifier input and the second output signal at a negative differential amplifier input;
• generating a third output signal indicative of the difference between the first output signal and the second output signal;
• and
• outputting the third output signal to an analog-to-digital converter (“ADC”).

A detection system comprising:

• an absorbance detection system configured to generate a light having a light intensity indicative of an absorbance by a sample in response to an excitation light;
• a plurality of optical components configured to provide an optical path from the sample to a measurement
• a photodetector measurement circuit comprising:
• a photodetector configured to receive the light and to generate a photodetector current with a current level indicative of the light intensity, the photodetector having a first terminal and a second terminal where the photodetector current flows through the photodetector from the first terminal towards the second terminal;
• a first integrator coupled along a first signal path to the first terminal of the photodetector, where the first integrator is configured to generate a first voltage signal at a first integrator output indicative of an integral of the photodetector current level;
• a second integrator coupled along a second signal path to the second terminal of the photodetector, where the second integrator is configured to generate a second voltage signal at a second integrator output indicative of an integral of the photodetector current level;
• and
• a differential amplifier configured to receive the first voltage signal at a first differential amplifier input, to receive the second voltage signal at a second differential amplifier input, and to generate a third output signal at a differential amplifier output indicative of a difference between the first voltage signal and the second voltage signal, where the differential amplifier is further configured to output the third voltage signal along a fifth signal path to an analog-to-digital conversion function (“ADC function”) input.