Photodetector amplitude linearity
First Claim
1. A method of determining linearity of a photodetector having sequential readouts of signals, each signal correlating with amount of light received during a corresponding readout interval, each readout having a time of readout, and all readout intervals being equal to a predetermined readout period, the method comprising:
- directing a train of light pulses to the photodetector, the light pulses having equal intensity and a variable pulse period between successive pulses, and each light pulse having a variable pulse width equal to a constant fraction of pulse period;
selecting the constant fraction and a maximum pulse period cooperatively so that each pulse width is not greater than the readout period, and further selecting a minimum pulse period not less than two times the readout period;
smoothly changing the pulse period between the maximum pulse period and the minimum pulse period, while reading out and storing sequential signals from the photodetector and corresponding times of readout;
identifying a set of vernier pairs of signals as those pairs of signals occurring in adjacent readout intervals, and establishing a set of non-vernier signals excluding the vernier pairs;
ascertaining occurrence times for the vernier pairs and a corresponding total number of light pulses to each occurrence time;
utilizing the occurrence times to fit an occurrence function of total number of light pulses versus time; and
correlating the non-vernier signals to the occurrence function so as to effect a correlation function of the non-vernier signals versus pulse period as a measure of linearity of the photodetector.
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Accused Products
Abstract
To calibrate a photodetector, a rotating disk with a slot is disposed in a light beam with decreasing speed from a defined maximum rotational speed to a defined minimum speed, while magnitudes and times of signals are read out and stored. Vernier pairs of signals occur in adjacent readout intervals, and non-vernier signals exclude the verniers. Readout times for verniers are used to estimate a preliminary function of rotations versus time. From the function are estimated an occurrence time for each pair and period of disk rotation at the time. Vernier fraction is the ratio of one signal in the pair to the sum of the pair. A time offset is the product of vernier fraction, slot fraction of the disk and the estimated period. Occurrence times corrected with the time offset are utilized to fit a corrected function of disk rotations versus time. Points of time for the non-vernier signals are determined from the corrected function, each point corresponding to disk rotations to a corresponding non-vernier signal. These points of time are employed with corresponding signals for linearly calibrating the photodetector.
10 Citations
17 Claims
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1. A method of determining linearity of a photodetector having sequential readouts of signals, each signal correlating with amount of light received during a corresponding readout interval, each readout having a time of readout, and all readout intervals being equal to a predetermined readout period, the method comprising:
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directing a train of light pulses to the photodetector, the light pulses having equal intensity and a variable pulse period between successive pulses, and each light pulse having a variable pulse width equal to a constant fraction of pulse period; selecting the constant fraction and a maximum pulse period cooperatively so that each pulse width is not greater than the readout period, and further selecting a minimum pulse period not less than two times the readout period; smoothly changing the pulse period between the maximum pulse period and the minimum pulse period, while reading out and storing sequential signals from the photodetector and corresponding times of readout; identifying a set of vernier pairs of signals as those pairs of signals occurring in adjacent readout intervals, and establishing a set of non-vernier signals excluding the vernier pairs; ascertaining occurrence times for the vernier pairs and a corresponding total number of light pulses to each occurrence time; utilizing the occurrence times to fit an occurrence function of total number of light pulses versus time; and correlating the non-vernier signals to the occurrence function so as to effect a correlation function of the non-vernier signals versus pulse period as a measure of linearity of the photodetector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A precision photometric instrument comprising:
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a photodetector having sequential readouts of signals, each signal correlating with amount of light received during a corresponding readout interval, each readout having a time of readout, and all readout intervals being equal to a predetermined readout period; light means for directing a train of light pulses to the photodetector, the light pulses having equal intensity and a variable pulse period between successive pulses, and each light pulse having a variable pulse width equal to a constant fraction of pulse period; changing means for smoothly changing the pulse period between a maximum pulse period and a minimum pulse period as to effect a series of sequential signals, the minimum pulse period being not less than two times the readout period, and the maximum pulse period and the constant fraction cooperatively being such that each pulse width is not greater than the readout period; storing means for storing sequential signals from the photodetector and corresponding times of readout; means for identifying a set of vernier pairs of signals as those pairs of signals occurring in adjacent readout intervals, and establishing a set of non-vernier signals excluding the vernier pairs; means for ascertaining occurrence times for the vernier pairs and a corresponding total number of light pulses to each occurrence time; means for utilizing the occurrence times to fit an occurrence function of total number of light pulses versus time; and means for correlating the non-vernier signals to the occurrence function so as to effect a correlation function of the non-vernier signals versus pulse period as a measure of linearity of the photodetector. - View Dependent Claims (11, 12, 13, 14)
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- 15. The instrument of 10 wherein the photodetector is disposed in a spectrophotometer that includes dispersion means receptive of the light pulses so as to direct spectrally dispersed light pulses to the photodetector.
Specification