Apparatus And Method For System Identification

• US 20100327183A1
• Filed: 09/03/2010
• Published: 12/30/2010
• Est. Priority Date: 11/10/2005
• Status: Active Grant

• Current Assignee: In-Situ Incorporated
• Original Assignee: In-Situ Incorporated
• Inventors: Danielson, J.D. Sheldon, Baltz, Nathan T.
• Granted Patent: US 8,569,705 B2
• Time in Patent Office: Days
• US Class Current: 250/458.1
• CPC Class Codes: G01N 2021/6432 Quenching
• CPC Class Codes: G01N 21/6408 with measurement of decay time, time resolved fluorescence
• CPC Class Codes: G01N 21/6428 Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" in vivo A61B5/00; immunoassay G01N33/53
• CPC Class Codes: G01N 21/645 Specially adapted constructive features of fluorimeters

Abstract

Methods and apparatus for system identification operate by computing phase and amplitude using linear filters. By digitally processing the linearly filtered signals or data, the phase and amplitude based on measurements of the input and output of a system, are determined.

Claims

1. A down-conversion method for analyzing light emissions from a luminescent sample comprising the following steps:

a. generating excitation light from an excitation signal;

b. passing the excitation light through a sample;

c. detecting the luminescent light after it passes through the sample to provide a detector signal;

d. reducing the frequencies of the excitation and detector signals by mixing those signals with at least one other signal;

e. filtering those mixed signals with linear second-order IIR filters applying at least a portion of a modified Goertzel algorithm to the mixed signals;

f. determining a phase shift between the excitation signal and the detector signal.

2. The down-conversion method of claim 1 wherein the excitation light is generated by at least one light emitting diode.

3. The down-conversion method of claim 1 wherein the excitation light is square wave modulated.

4. The down-conversion method of claim 1 wherein the detector includes at least one photodiode.

5. A down-conversion method for analyzing light emissions from a luminescent sample comprising the following steps:

a. generating an analog excitation signal with a frequency greater than the Nyquist frequency of an excitation ADC;

b. reducing the frequency of the analog excitation signal below the Nyquist frequency;

c. converting the reduced analog excitation signal to a reduced digital excitation signal using the excitation ADC;

d. processing the reduced digital excitation signal to determine a first phase shift,

e. generating an analog detection signal in a system for creating and measuring with luminescent light, the signal having a frequency greater than the detection Nyquist frequency of a detection ADC;

f. reducing the frequency of the analog detection signal below the detection Nyquist frequency;

g. converting the reduced analog detection signal to a reduced digital detection signal using the detection ADC;

h. processing the digital detection signal to determine a second phase shift,

i. subtracting the first phase shift from the second phase shift to compute a phase difference caused by the luminescent sample.

6. The down-conversion method of claim 5 wherein the Nyquist frequency of the excitation and detection ADC are less than 48 kHz.

7. The down-conversion method of claim 6 wherein the excitation and detection ADC are implemented with a stereo Sigma-Delta converter.

8. The down-conversion method of claim 5 where by the excitation signal frequency is greater than 8kHz but less than 100 MHz.

9. A down-conversion method for analyzing light emissions from a luminescent sample comprising the following steps:

a. providing an excitation signal to an excitation light source;

b. providing excitation light to a luminescent sample;

c. detecting emitted luminescence from the luminescent sample;

d. converting the emitted luminescence into a detector signal;

e. mixing the detector signal with a mixer signal;

f. mixing the excitation signal with the mixer signal;

g. filtering the mixed signals to remove high-frequency components;

h. processing the filtered signals with linear second-order digital IIR filters applying at least a portion of a modified Goertzel algorithm; and

i. transforming the linearly-filtered signals using control logic to compute for each signal real portions and imaginary portions to determine the phase shift between the excitation light and the emitted luminescence.

10. The method of claim 9, wherein the real and imaginary portions are used for determining the amplitude of the emitted luminescence.

11. The method of claim 9, wherein the excitation light is generated by at least one light emitting diode.

12. The method of claim 9, wherein the detecting step is performed by at least one photodiode.

13. The method of claim 9, wherein the excitation light varies sinusoidally or as a square wave.

14. A down-conversion method for analyzing light emissions from a luminescent sample comprising the following steps:

a. providing an excitation signal to an excitation light source;

b. providing excitation light to a luminescent sample;

c. detecting luminescence emitted from the luminescent sample;

d. converting the emitted luminescence into a detector signal;

e. combining the detector signal with a mixer signal to form a mixed-detector signal;

f. combining the excitation signal with the mixer signal to form a mixed-detector signal;

g. filtering the mixed-detector and mixed-excitation signals to remove high-frequency components;

h. processing the filtered signals with linear second-order digital IIR filters applying at least a portion of a modified Goertzel algorithm;

i. transforming the linearly-filtered signals using control logic to compute for each signal real portions and imaginary portions to determine a detector phase shift between the detector signal and the excitation signal;

j. providing reference light to the luminescent sample;

k. detecting reference light emitted from the luminescent sample;

l. converting the emitted luminescence into a reference signal;

m. combining the reference signal with the mixer signal to form a mixed-reference signal;

n. filtering the mixed-reference and mixed-excitation signals to remove high-frequency components;

o. processing the filtered signals with the linear second-order digital IIR filters applying at least a portion of the modified Goertzel algorithm;

p. transforming the linearly-filtered signals using control logic to compute for each signal real portions and imaginary portions to determine a reference phase shift between the reference signal and the excitation signal ; and

q. subtracting the detector phase shift from the reference phase shift to determine the phase difference between the excitation light and the emitted luminescence.

15. The method of claim 14, wherein the excitation signal varies sinusoidally or as a square wave.

16. The method of claim 14, wherein the excitation light wavelength is less than the luminescence wavelength.

17. The method of claim 14, wherein the reference light wavelength is greater the excitation light wavelength.

18. A down-converting apparatus for analyzing light emissions from a luminescent sample, comprising:

a. a source of a signal configured to excite a system for generating luminescent light;

b. a detector configured to generate a signal representing the system output;

c. mixers to reduce the frequencies of the source and signal outputs;

d. linear second-order IIR filters for applying at least a portion of a modified Goertzel algorithm to the mixer signals;

e. a processor programmed to determine a phase shift between the excitation signal and the detector signal.

19. The down-converting apparatus of claim 18 wherein the source is modulated at a fixed frequency.

20. The down-converting apparatus of claim 18 wherein the mixers are implemented with two differential amplifiers and two single-pole double-throw switches.

21. The down-converting apparatus of claim 18 wherein the processor is a microcontroller with active current less than 3.6mA.

22. A down-converting apparatus for analyzing light emissions from a luminescent sample, comprising:

a. A pulse width modulation unit configured to provide a digital excitation signal to a system for determining phase shift,

b. an excitation mixer connected to the excitation ADC and configured to provide the excitation ADC with a mixer signal having a frequency that is below the Nyquist limit;

c. an excitation signal source connected to the excitation mixer and having a frequency greater than the Nyquist frequency;

d. a detector configured to generate a detector signal based on the output of a luminescent probe and having a frequency above a detector Nyquist limit of a detector ADC that is configured to provide a digital detector signal to a system for determining phase shift,

e. a detector mixer connected to the detector and configured to provide the detector ADC with a mixer signal having a frequency that is below the Nyquist limit.

23. The down-converting apparatus of claim 22 wherein, the detector is a photodiode.

24. The down-converting apparatus of claim 22 wherein, the Nyquist limit is less than 48 kHz.

25. A down-converting apparatus for measuring luminescent light comprising:

a. an excitation light source configured to receive an excitation signal and transfer excitation light to a fluid medium;

b. a luminescent probe configured to transfer emission light in response to the excitation light;

c. a detector system configured to detect the emission light and generate a detector signal corresponding to the emission light;

d. a detector mixer configured to combine the detector signal with a mixer signal to create a mixed-detector signal;

e. an excitation mixer configured to combine the excitation signal with the mixer signal to create a mixed-excitation signal;

f low-pass filters configured to remove high-frequency components from the outputs of the mixers;

g. linear second-order IIR filters for applying at least a portion of a modified Goertzel algorithm to the filtered signals;

h. a processor programmed to transform the linearly filtered signals using control logic to compute for each signal a real portion and imaginary portion and to determine a phase shift between the excitation light and the emission light.

26. The apparatus of claim 25, wherein the excitation light source includes at least one light emitting diode.

27. The apparatus of claim 25, wherein the detector system includes at least one photodiode to detect the emission light.

28. The apparatus of claim 25 including a processor programmed to implement the linear filter component to determine the amplitude of the digital signal corresponding to the emission light.

29. The apparatus of claim 25, where the excitation light source is modulated sinusoidally or as a square wave.

30. A down-converting apparatus for analyzing light emissions from a luminescent sample, comprising:

a. a luminescent sample comprising first and second surfaces that emanates luminescent light in response to excitation light and reference light in response to reference light;

an excitation light source opposed to the first surface so that luminescent light emanates from the luminescent sample in response to an excitation signal;

c. a reference light source opposed to one surface so that reference light emanates from the luminescent sample in response to the excitation signal;

d. a switch configured to pass the excitation signal to only one of the light sources;

e. a detector of luminescent and reference light opposed to one surface so that luminescent light and reference light are detected depending on the position of the switch, the detector generating a detector signal;

f. a detector mixer configured to combine the detector signal with a mixer signal;

g. an excitation mixer configured to combine the excitation signal with the mixer signal;

h. low-pass filters configured to remove high-frequency components from the outputs of the mixers;

i. filters connected to the low-pass filters, the filters being linear second-order digital IIR filter applying at least a portion of a modified Goertzel algorithm;

j. control logic connected to the filters that computes

(1) real and imaginary portions of the filter outputs corresponding to the luminescent light and then a first phase shift based on those portions;

(2) real and imaginary portions of the filter outputs corresponding to the reference light and then a second phase shift based on those portions;

k. a subtractor connected to the control logic that subtracts the first phase shift from the second phase shift to determine the phase difference between the excitation light and the luminescence light.

31. The system of claim 30 in which the luminescent light source and the reference light source are illuminated sequentially so that only one source is on at a time.

32. The system of claim 30 in which the reference light source is opposed to the first surface of the luminescent sample.

33. The system of claim 30 in which the detector is opposed to the first surface of the luminescent sample.