Techniques for correcting non-linearity in a photodetector using predefined calibration information
AssigneeBio-Rad Laboratories, Inc.
InventorRaul Curbelo
Life of this patent
Estimating the term…
Abstract
A technique that corrects photodetector non-linearity without increasing the noise level in the detector signal. The detector is coupled to a preamplifier characterized by the absence of positive feedback, and the preamplifier signal is communicated to a linear amplifier whose output signal is then digitized. The digitized signal is then transformed according to stored calibration information that is representative of the non-linear characteristic of the photodetector. The transformed digitized value thus exhibits a linear characteristic as a function of the intensity of the light source. A number of embodiments perform the correction in hardware before digitizing the signal.
Claims28
A method of acquiring interferogram data in a Fourier transform spectrometer, the spectrometer including a detector that provides an output signal that exhibits a non-linear variation as a function of intensity, comprising the steps of:
- providing calibration information representing the non-linear variation;
- coupling the detector to a preamplifier circuit characterized by the absence of positive feedback to provide a preamplified output signal representing the intensity;
- operating the spectrometer to modulate the intensity;
- and
- converting the preamplified output signal to a set of digitized values that have been corrected in accordance with the calibration information;
- said providing step being performed before and independently of said operating step.
In the operation of a Fourier transform spectrometer, a method of correcting for detector non-linearity comprising the steps of:
- providing calibration information representing the non-linearity;
- simultaneously measuring AC and DC components of the detector signal;
- determining a correction factor on the basis of at least the calibration information and the measured DC component;
- and
- applying the correction factor to the AC component;
- said providing step being performed before and independently of said measuring step.
A method of calibrating a detector in a Fourier Transform spectrometer, the detector providing an output signal that exhibits a non-linear variation as a function of intensity, comprising the steps of:
- coupling the detector to a preamplifier circuit characterized by the absence of positive feedback to provide a preamplified output signal representing the intensity;
- coupling the output signal to an adjustable non-linear network having an output terminal;
- providing a first light source characterized by an intensity that exhibits fluctuations about an average value where the amplitude of the fluctuations and the average value are small compared to a defined maximum;
- providing a second light source having an adjustable intensity capable of assuming values between zero and the defined maximum, the intensity, once adjusted, being constant;
- illuminating the detector with only the first source operating at a reference intensity, and measuring the AC component of the voltage at the output terminal of the non-linear network, the measured value being designated a reference value;
- and
- illuminating the detector with both sources at each of a set of conditions with the first source operating at the reference intensity and the second source adjusted to provide a different intensity for each condition, and for each condition, adjusting the non-linear network so that the AC component of the voltage at the output terminal of the non-linear network is equal to the reference value.
A method of calibrating a detector in a Fourier transform spectrometer, the detector providing an output signal that exhibits a non-linear variation as a function of intensity, the spectrometer including an interferometer and circuitry for generating an uncorrected detector signal, comprising the steps of:
- generating a plurality of interferograms at a corresponding plurality of different illumination conditions, the illumination conditions having a known relationship to each other, the spectrometer being adjusted for low chopping efficiency so that the interferograms exhibit fluctuations that are a small fraction of the average value of the interferogram;
- measuring corresponding values of the detector signal for each of the interferograms;
- and
- correlating the measured detector signal values and the known relationship to determine calibration information representing the non-linear variation.
A Fourier transform spectrometer comprising:
- a detector that provides an output signal that exhibits a non-linear variation as a function of intensity;
- a preamplifier circuit, responsive to the output signal and characterized by the absence of positive feedback to provide a preamplified output signal representing the intensity;
- an amplifier circuit, responsive to the preamplified signal, and including a positive feedback element having a voltage-dependent characteristic representing the non-linear variation to provide an amplified output signal that exhibits a variation as a function of intensity that is more linear than the variation exhibited by the detector output signal;
- and
- means for digitizing the amplified output signal to provide measured values representing corrected intensity information.
A Fourier transform spectrometer comprising:
- a detector that provides an output signal that exhibits a non-linear variation as a function of intensity;
- means for providing predefined calibration information representing the non-linear variation;
- an amplifier circuit, responsive to the output signal and characterized by the absence of positive feedback to provide an amplified output signal representing the intensity;
- means for modulating the intensity;
- and
- means for digitizing the amplified output signal to provide measured values representing uncorrected intensity information;
- and
- means for correcting each measured value using the predefined calibration information to provide a corrected value.
A Fourier transform spectrometer comprising;
- a detector that provides an output signal that exhibits a non-linear variation as a function of intensity;
- means for providing predefined calibration information representing the non-linear variation;
- means for measuring AC and DC components of the detector signal;
- means for determining on the basis of the predefined calibration information and a predetermined linear combination of the measured AC and DC components a correction factor appropriate for the measured linear combination;
- and
- means for applying the correction factor to the measured linear combination.
In a Fourier transform spectrometer, apparatus for correcting the AC signal for detector non-linearity comprising:
- means defining an AC signal channel having a controllable gain;
- means defining a DC signal channel;
- means for providing predefined calibration information regarding the detector non-linearity;
- and
- means, responsive to at least the predefined calibration information and signals in the DC channel, for changing the gain in the AC channel to provide at least a partial correction.
Dependencies are inferred from the claim text.