Selective digital integrator

Details Selective digital integrator Selective digital integrator

1999-01-27

2001-01-23

Wamsley, Patrick (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Detecting analog signal peak

C341S155000

Reexamination Certificate

active

06177895

ABSTRACT:

This invention pertains to apparatus and methods for acquiring and processing experimental data at high rates of data flow.
There is an unfilled need for improved, more accurate, and less expensive apparatus and methods for acquiring and processing experimental data over short or long times at high rates of data flow, for example 20 MSPS (mega samples per second), 25 MSPS, 100 MSPS, 500 MSPS, 1 GSPS (giga samples per second) or higher. Such apparatus might be used, for example, to monitor rotational, vibrational, and electronic spectra under varying conditions. Such improved apparatus and methods would be used by chemists, biologists, materials scientists, medicinal chemists, physicists, and others. Currently available electronic and optical measurement instruments and devices have limited applications. There is a trade-off: some current instruments are aimed at very fast data acquisition, while others focus on data processing formats yielding high accuracy; or aim at both if only a few parameters are of interest and the signal waveform is known (or presumed) in advance to have a particular shape, e.g., sinusoidal or square wave. But it has not previously been possible to do both simultaneously for data signals of arbitrary or unknown waveform.
N. Purdie, “Characterization of Biomolecules Using Circular Dichroism Spectroscopy,”
Spectroscopy,
vol. 12, no. 2, pp. 45-55 (1997) reviews the use of circular dichroism measurements in biomolecules such as carbohydrates, peptides, and proteins.
J. Scott et al., “Molecular Rydberg Transitions: Field Effects in the Vacuum Ultraviolet,”
Nuclear Instruments and Methods,
vol. 152, pp. 231-234 (1978) reviews an earlier state of the art, and describes certain magnetic circular dichroism and electric linear dichroism measurements of Rydberg transitions using apparatus that included a lock-in-amplifier to acquire data.
K. Rupnik et al., “The Simulation of an Unusual Magnetic Circular Dichroism Spectrum: The 5p→6s
1
&Sgr;
0
+
→
3
Π
2
transition of HI,”
Journal of Physical Chemistry
, vol. 103, pp. 7661-7663 (1995), representative of the previous state of the art, presents both measured absorption and magnetic circular dichroism spectra, and a model of those spectra for a particular electronic transition of HI.
U.S. Pat. No. 4,807,146 discloses a digital lock-in amplifier.
Stanford Research Systems,
Scientific and Engineering Instruments,
pp. 56-81(1992) describe more-or-less state-of-the-art lock-in amplifiers.
References by the inventors disclosing portions of the present work, all of which are either unpublished as of the original filing date of the present application, or were published less than twelve months prior to the original filing date of the present application, include the following: K. Rupnik et al., “A New Modulated-Polarization Spectroscopy (MPS) Study of Electronic Structures of Molecules,” Slides, Joint Meeting of the American Physical Society et al. (Apr. 18-21, 1997) and
Bull. Amer. Phys. Soc.,
vol. 42, p. 987 (1997); A Vrancic et al., “A Selective Digital Integrator for Modulated-Polarization Spectroscopy: An Evaluation using (+)-3-Methylcyclopentanone,” accepted for publication in
Review of Scientific Instruments
(1998); and A. Vrancic,
A Selective Digital Integrator—The New Device for Modulated Polarization Spectroscopy,
PhD Dissertation, Louisiana State University, Baton Rouge (May 1998).
We have discovered a new device and method for the acquisition of data at high flow rates and with high accuracy. We initially designed the device for use in polarization and field-dependent spectroscopy, but it has much wider application. The novel device, called a “Selective Digital Integrator” (SDI), provides many improved features relative to older techniques, and for some applications it provides a less-expensive replacement for lock-in amplifiers while affording greater functionality and versatility. The device can be integrated into existing instrumentation and technology for high-resolution measurements using various radiation sources (e.g., lamps, lasers, synchrotrons), various polarizations (e.g., linear, circular, elliptical), and various detectors (e.g., photo multipliers, diodes). Unlike the case with conventional lock-in amplifiers, the signal need not be known (or presumed) in advance to have a particular shape, but instead may have an arbitrary or unknown waveform.
Other new capabilities of the novel Selective Digital Integrator (SDI) include the ability for the first time to measure circular dichroism by separating out the left circular and right circular components of that spectrum; and the ability for the first time to make polarization-selective measurements that simultaneously measure both linear and circular dichroism.
The novel device has a substantially better signal-to-noise ratio than those of previous systems. It has the ability to perform over wide (and continuous) ranges of signal strength. It has a wide dynamic range (~10 orders of magnitude). It is particularly good at separating and discriminating small signal components. It has high time-, spectral-, polarization-, and average-value-of-detector-current resolution (~1 part in 10
10
).
The new device can accurately measure very small signals, e.g., where the AC component of interest has a signal strength less than 10
−3
the strength of the DC component, even if the signal is buried in substantial noise. The SDI was originally designed for use with detectors that produce pulsed signals, for example a photo-multiplier tube (PMT). When used in such a configuration, the device had a wide gain-switching-free dynamic range, and can detect light intensities ranging from about 1 photon per second up to the PMT saturation point, a range of 10 orders of magnitude or greater.
In molecular spectra that have been measured with a prototype embodiment, the SDI has performed at higher specifications than any previously described devices. For example, the resolution of vibronic spectra in a standard test molecule, 3-methylcyclopentanone, is higher than has been reported in any previously published studies of this molecule, including prior spectra measured at ostensibly much higher spectral resolution, and with substantially higher light (i.e., synchrotron) intensities.
Applications where the SDI device will be useful include, for example, the following areas: chemistry (e.g., analysis); pharmaceuticals (e.g., molecular structures and configurations); electronics (e.g., as replacements for lock-in amplifiers as part of data acquisition systems); materials science (e.g., crystal structures, optical and magneto-optical properties, films, thin layers, etc.); medicinal chemistry and physics (e.g., structures and properties of molecules in molecular medicine); environmental measurements and studies (e.g., data acquisition for environmental studies); and physics and chemistry (research pertaining to electronic and nuclear structures).
An SDI can be used, among other things, as a replacement for the lock-in amplifiers that are a standard part of many instrumentation setups, such as those used in modulation spectroscopy. A principal application of SDI is the extraction of time-resolved signal from background noise.
Measurements made with SDI are qualitatively and quantitatively better than those obtained with a lock-in amplifier, because the SDI requires no a priori assumption about particular waveforms for a signal (e.g., sinusoidal or square-wave). The signal-to-noise ratio for SDI is considerably better than that for a lock-in amplifier for many types of waveforms. SDI is far superior to a lock-in amplifier in measuring asymmetric or multi-phase modulated signals.
Advantages of the novel SDI include the following: It can provide an average time-resolved profile of a modulated signal. As compared to prior lock-in amplifiers, it virtually eliminates errors associated with non-sinusoidal signals, even where the signal shape is not known in advance. It permits the separate measurement of different phases of a modulated signal. It permits

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