Signal-enhancement system for photodetector outputs

Abstract

A light scattering photometer signal-enhancement systems includes an adaptive sample and subtract circuit controlled by a computer or microcontroller (MCU). The MCU controls the gain of a programmable-gain amplifier (PGA) cascade that is used to amplify the raw photometer signal. In order to maintain the DC accuracy, the DC offset contained in the raw signal from the photometer is estimated by an algorithmic within the MCU and then subtracted from the raw signal before allowing it to be amplified by the PGA cascade. In addition to DC estimation and adaptive cancellation, the MCU applies a digital filtering scheme to compensate irrelevant frequency bands in the amplified signal and offers user determined averaging functions for additional signal conditioning. Moreover, hardware filters are used to prevent signal aliasing by the analog to digital converters (ADC) and a 60 Hz notch filter suppresses general electrical noise.

1 . A method for enhancing electronic signals from a photodetector comprising:
 at least one of starting and resetting the photodetector;   initializing digital-to-analog converters (DACs), analog-to-digital converters (ADCs) programmable gain amplifiers (PGAs) and filter parameters;   subtracting a voltage increment from the output of a filter until the output of the filter is at least one of less than and equal to a predetermined coarse threshold voltage;   subtracting a voltage increment from the output of the filter until the output of the filter is at least one of less than and equal to a predetermined fine threshold voltage;   filtering and signal processing the output of the filter; and   outputting the filtered and signal processed output of the filter until receiving at least one of a power down and reset command.   
   
   
       2 . The method of  claim 1 , wherein initializing further comprises setting the output voltages of the DACs to 0V; setting the PGA gain to zero; initializing the ADCs; and setting the corner frequencies of the filters. 
   
   
       3 . The method of  claim 1 , wherein subtracting a voltage increment in accordance with the predetermined coarse threshold voltage further comprises reading the ADC value, determining when the ADC value is at least one of less than and equal to the coarse threshold, and incrementing the coarse DAC voltage when the ADC value is at least one of less than and equal to the coarse threshold. 
   
   
       4 . The method of  claim 1 , wherein subtracting a voltage increment in accordance with the predetermined fine threshold voltage further comprises reading the ADC value, determining when the ADC value is at least one of less than and equal to the fine threshold, and incrementing the fine DAC voltage when the ADC value is at least one of less than and equal to the fine threshold. 
   
   
       5 . The method of  claim 1 , wherein sampling by the ADC is performed at regular time intervals of at least two (2) times a highest frequency component in the filter output. 
   
   
       6 . The method of  claim 1 , wherein the filtering and signal processing includes at least one of digital filtering, pattern recognition, or predictive control algorithms. 
   
   
       7 . The method of  claim 2 , wherein the filtering and signal processing further includes at least one of Proportional Integral, Least Mean Square or Kalman Filtering. 
   
   
       8 . The method of  claim 2 , wherein outputting the filtered and signal processed output is provided via at least one of an output DAC, serial output port, parallel output port, USB output port and radio link.