Synchronous detection system for multichannel infrared spectroscopy

• US 6,080,983 A
• Filed: 12/21/1998
• Issued: 06/27/2000
• Est. Priority Date: 02/23/1996
• Status: Expired due to Fees

• Current Assignee: Dominion Assets LLC
• Original Assignee: Diasense Inc.
• Inventors: Hartwick, David J., Hendrickson, Mark L., Waczynski, Augustyn
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/125,564
• Time in Patent Office: 554 Days
• Field of Search: 250/231.16, 250/231.13, 250/234, 250/237 R, 250/208.2, 250/214 R, 356/25, 356/375, 356/374, 356/300, 356/310, 356/304, 341/13, 359/241, 359/244, 359/245
• US Class Current: 250/231.16
• CPC Class Codes: G01J 1/0266 Field-of-view determination; Aiming or pointing of a photometer; Adjusting alignment; Encoding angular position; Size of the measurement area; Position tracking; Photodetection involving different fields of view for a single detector
• CPC Class Codes: G01J 1/04 Optical or mechanical part supplementary adjustable parts
• CPC Class Codes: G01J 1/044 using shutters
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4242 Modulated light, e.g. for synchronizing source and detector circuit
• CPC Class Codes: G01J 3/0232 using shutters
• CPC Class Codes: G01J 3/0289 Field-of-view determination; Aiming or pointing of a spectrometer; Adjusting alignment; Encoding angular position; Size of measurement area; Position tracking
• CPC Class Codes: G01J 5/28 using photoemissive or photovoltaic cells
• CPC Class Codes: G01J 5/30 Electrical features thereof

Abstract

Disclosed is a radiation detector which includes at least one photoconductive detector and a modulator, which modulates in an on-off manner radiation passing to the photoconductive detector from a radiation source. A bias source is connected to one terminal of the photoconductive detector. A first amplifier is connected to the other terminal of the photoconductive detector, and a second amplifier receives an output of the first amplifier. A first phase detector detects the phase of modulation of the radiation source by the modulator and generates a reference signal relating thereto. A switch in the second amplifier changes, in response to the reference signal generated by the first phase detector, the second amplifier between an inverting state and a non-inverting state as the modulator changes the phase of modulation of the radiation.

Claims

1. A radiation detector comprising at least one photoconductive detector, a modulator which modulates in an on-off manner radiation passing to said photoconductive detector from a radiation source, a bias source connected to one terminal of the photoconductive detector, a first amplifier connected to the other terminal of the photoconductive detector, a second amplifier which receives an output of the first amplifier, a first phase detector which monitors the phase of modulation of the radiation source by the modulator and generates a reference signal relating thereto, a switch means in said second amplifier which, in response to the reference signal generated by the first phase detector, changes the second amplifier between an inverting state and a non-inverting state as the modulator changes the phase of modulation of the radiation, an analog-to-digital converter which receives an output from the second amplifier, a second phase detector which monitors the operation of the modulator, a control means for controlling, in response to the second phase detector, the operation of the modulator, and a master clock which supplies a control frequency to the control means and to the analog-to-digital converter.

2. The radiation detector of claim 1 further including a low pass filter which receives an output signal from the second amplifier and supplies a filtered signal to the analog-to-digital converter.

3. The radiation detector of claim 1 further including a high pass filter which receives an output signal from the photoconductive detector and supplies a filtered signal to the first amplifier.

4. The radiation detector of claim 1 further including a plurality of photoconductive detectors each receiving radiation from the radiation source as modulated by the modulator, with the bias source connected to each photoconductive detector, and with each photoconductive detector having an associated first amplifier and second amplifier with switch means, with the first phase detector supplying the reference signal to and controlling the switch means in each second amplifier, with an output signal generated by each second amplifier supplied to a multiplexer, and with an output signal generated by the multiplexer supplied to the analog-to-digital converter.

5. The radiation detector of claim 4 further including a low pass filter associated with the output of each second amplifier and supplying a filtered signal to the multiplexer.

6. The radiation detector of claim 4 further including a high pass filter associated with the output of each photoconductive detector and supplying a filtered signal to the associated first amplifier.

7. The radiation detector of claim 4 further including a digital signal processor which receives an output signal from the analog-to-digital converter.

8. The radiation detector of claim 4 wherein the modulator is a chopper wheel having a plurality of evenly spaced radiation beam chopping holes which control the radiation supplied to the photoconductive detectors and wherein the first phase detector is a first optointerrupter associated with the radiation beam chopping holes.

9. The radiation detector of claim 8 wherein the reference signal generated by the first optointerrupter is amplified before it is supplied to the switch means associated with each of the second amplifiers.

10. The radiation detector of claim 8 wherein the chopper wheel includes a plurality of encoder holes evenly spaced along an outer peripheral edge thereof and wherein the second phase detector is a second optointerrupter associated with the encoder holes.

11. The radiation detector of claim 10 wherein the encoder holes are substantially smaller than the radiation beam chopping holes, wherein the chopper wheel includes substantially more encoder holes than radiation beam chopping holes and wherein the ratio of encoder holes to radiation beam chopping holes in the chopper wheel is a whole number.

12. The radiation detector of claim 11 wherein the chopper wheel includes at least ten times as many encoder holes as radiation beam chopping holes.

13. The radiation detector of claim 11 wherein the chopper wheel includes five radiation beam chopping holes and one hundred encoder holes.

14. The radiation detector of claim 11 wherein the chopper wheel includes ten radiation beam chopping holes and one hundred encoder holes.