Abstract:
A charged coupled device is disclosed including an asymmetrical split with independent control over the regions on opposite sides of the split. The charge coupled device is configurable for use in multiline or kinetic spectroscopy, and includes two separate horizontal registers with optional charge dump regions for improving efficiency.

Description:
This is division of application Ser. No. 08/965,209 filed Nov. 6, 1997, now U.S. Pat. No. 5,986,267. 
    
    
     TECHNICAL FIELD 
     This invention relates to charge coupled devices, and more specifically, to an improved use of a charge coupled device including an asymmetrical split and for use primarily in spectroscopy applications. The inventive method and apparatus is useful in both kinetic spectroscopy and multiline spectroscopy. 
     BACKGROUND OF THE INVENTION 
     Charged coupled devices (CCDs) have been in use for decades and are well known in the field of spectroscopy. Spectroscopy typically involves illuminating one or more rows of a CCD with the spectrum of a signal and then analyzing the captured spectrum represented by the varying magnitudes of charge which accumulate on the various elements of the CCD. For example, if one row of the CCD is used to capture the spectrum, the varying magnitudes of charge along the row represent the varying amplitudes of different wavelengths which comprise the spectrum. 
     The use of CCDs in spectroscopy may be divided into at least two well known types: multiline spectroscopy and kinetic spectroscopy. Commercially available CCDs are usually extremely application specific, and typically are manufactured for use in either multiline spectroscopy, kinetic spectroscopy, or some other application. Conventional CCDs include little or no ability to adapt to different applications. 
     Kinetic spectroscopy involves obtaining multiple spectra, one at a time, at a relatively high rate, and then reading them from the CCD. FIG. 1 shows a conceptual diagram of a CCD for use in kinetic spectroscopy. The first row of elements  101  is utilized to capture a spectrum by focusing the desired spectrum only on row  101 . After the spectrum is captured at row  101 , it is shifted down to row  102  immediately below row  101  and the next spectrum is captured at row  101 . In one commercially available CCD, all rows except the top row  101  are masked. Thus, once the spectrum is captured and shifted down into row  102 , it is no longer subject to distortion from unwanted light signals and the masked rows operate effectively as a memory. Utilizing, for example, an off the shelf 1024×256 CCD  100  of the type described, approximately 65,000 spectra per second may be collected for subsequent read-out through horizontal register  103  and amplifier  104 . 
     Although the arrangement shown in FIG. 1 has been widely accepted in the prior art for performing kinetic spectroscopy, there are drawbacks to such an arrangement. First, since only one row of CCD elements is typically utilized to capture the spectrum, the device is not very sensitive. If the spectrum is focused on plural rows of CCD elements, the device will be more sensitive, however, the read out time will increase dramatically since a spectrum occupying N rows of elements will require N times the read out time when compared with a spectrum occupying one row. The slower read out time is unacceptable in certain applications. 
     Another problem with the arrangement described is that it is relatively inflexible. Specifically, the CCD with all of its rows except one masked is not suitable for multiline spectroscopy, described below. More particularly, multiline spectroscopy requires several spectra to be captured simultaneously. The availability of only one row of unmasked elements in the arrangement of FIG. 1 is unsuitable. Thus, if the specific application changes, a whole new design is required. 
     In view of the above, it can be appreciated that there exists a need in the art for a more sensitive CCD based device which is able to capture and read out spectra at a fast rate for use in kinetic spectroscopy, and which is flexible enough to be adapted for different uses. 
     Multiline spectroscopy is another branch of spectroscopy which is often implemented using CCD devices. FIG. 2 shows a conceptual diagram of a CCD being utilized to effectuate multiline spectroscopy. 
     In multiline spectroscopy, several separate and distinct spectra are captured by a CCD and read out separately for analysis through horizontal shift register  210 . The plural spectra are usually captured simultaneously, and then later shifted out of the CCD sequentially for storage and analysis. The arrangement in FIG. 2 includes such a charge coupled device  200 , a plurality of exemplary spectra represented by  201  through  204 , and a horizontal register  210  for reading out the spectra. Additionally, the regions  205  through  208  represent separation bands in order to prevent energy from each distinct spectrum from contaminating the energy in the regions storing the other spectra. 
     In operation, the spectra are first captured on the CCD  200 , perhaps with the use of a mechanical shutter. Next, the spectra are read by placing them into horizontal register  210  and then shifting each spectrum from register  210  for later storage, analysis or any other required processing. 
     A problem with the use of arrangements such as that of FIG. 2 to accomplish multiline spectroscopy is that the dark bands  205  through  208  must be independently read into horizontal register  210  and shifted out. Accordingly, the overall operation of the device is much slower than desirable. 
     Another problem with the arrangement of FIG. 2 for multiline spectroscopy is that if it is desired to utilize the same chip for kinetic spectroscopy, a large waste in space and time results. Specifically, FIG. 6 shows a conventional CCD device  601  and includes a representation  602  of a single spectrum stored in one row of the device. In operation, the spectrum  602  is transferred into horizontal register  603  for shifting out. The dark charge from region  603  must then also be shifted out. This results in wasted time and thus, slower throughout. 
     Alternatively, when a device is being utilized to capture single spectrum using the technique described, an arrangement such as that shown in FIG. 7 may be used. The arrangement of FIG. 7 includes a relatively small CCD for capturing a single spectrum and a horizontal register  702  for the read out of such spectrum. However, if it is later desired to do multiline spectroscopy utilizing a larger CCD device, the entire chip would have to be replaced. 
     In view of the above there exists a need in the art for an improved CCD arrangement for performing multiline and kinetic spectroscopy. Additionally, such device should be adaptable easily for either of the foregoing types of spectroscopy and should be efficient when operated in either mode. Finally, there exists a need for improved speed when performing either type of spectroscopy utilizing CCD devices. 
     SUMMARY OF THE INVENTION 
     The above and other problems of the prior art are overcome and a technical advance is achieved in accordance with the present invention which relates to an improved charge coupled device (CCD) which includes an asymmetrical split, independent control over the regions on each side of the asymmetrical split, and two horizontal registers for reading information from the CCD. The horizontal registers, one on each side of the CCD, are also independently controllable like the shifting on each side of the asymmetrical split. 
     In operation, the device may be used for kinetic spectroscopy or for multiline spectroscopy. In either case, a spectrometer, for example, is preferably utilized to capture light, split it into its spectrum, and convey the spectrum to the CCD. 
     When utilized for kinetic spectroscopy, a single spectrum may occupy multiple rows of elements, thereby increasing sensitivity over prior art single row spectroscopy devices. Unlike the prior art however, unacceptable additional read out time is not required because the spectra may be binned at the asymmetrical split, a technique only possible due to the independent control of the regions of the CCD on opposite sides of the split. 
     The inventive device is also capable of rapidly transferring sequentially acquired spectra to a horizontal register for read out while independently transferring dark charge, in the opposite direction, to a different horizontal register. Accordingly, when operating in the kinetic spectroscopy mode, charge in the relatively small region on one side of the asymmetrical split is shifted in the opposite direction from the dark charge on the other side of the asymmetrical split. The additional time required to read out the dark charge through the horizontal register is thus avoided, as any dark charge is read out substantially simultaneous with the reading out of the captured spectrum. 
     When it is desirable to use the inventive device in the multiline spectroscopy mode, plural spectra are captured in the relatively large region of the CCD on one side of the asymmetrical split and binned into a smaller number of rows on the relatively smaller side of the asymmetrical split. The binning is done such that (i) the average binning rate is equal to the ratio of the number of rows in the relatively larger region of the CCD divided by the number of rows in the relatively smaller region of the CCD, and (ii) the separation bands of dark charge are binned into separate rows from those into which spectra are binned. This allows for multiple row spectra, relatively quick read out, and easy configurability of the CCD to be used efficiently for both multiline and kinetic spectroscopy. 
     For purposes herein, an asymmetrically split CCD is a CCD wherein the region controllable on one side of said split is at least twenty percent larger than the region on the other side thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art CCD arranged to implement kinetic spectroscopy; 
     FIG. 2 shows a prior art CCD arranged to implement multiline spectroscopy; 
     FIG. 3 shows an asymmetrically split CCD device in accordance with the present invention; 
     FIG. 4 shows the asymmetrically split CCD device of FIG. 3 when utilized in the multiline spectroscopy mode; 
     FIG. 5 shows an exploded view of a portion of the CCD device of FIG. 3; 
     FIG. 6 shows an example of the prior art CCD device being used to capture a single spectrum; 
     FIG. 7 shows an additional prior art CCD device capturing a single spectrum; and 
     FIG. 8 shows a conceptual view of the inventive apparatus when used in a mode for performing kinetic spectroscopy. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 shows a representation of an exemplary embodiment of the present invention comprising a 1340×400 CCD. The arrangement of FIG. 3 includes a novel CCD  300  including a relatively large lower region  301  and a relatively smaller upper region  302  separated by a split  303 . The split  303  may be located for example, such that there are 80 rows above it and  320  of the 400 rows below it, with each of the regions  302  and  301  being controllable independently of each other. Specifically, rows of charge on one side of split  303  may be shifted up or down independently of rows of charge on the other side of split  303 . Additionally, rows of charge may be shifted across asymmetrical split  303 . 
     While the 320 to 80 ratio in the example of FIG. 3 represents but one workable example, other asymmetrically split arrangements are possible. Importantly, the split is such that the small region  302  is suitable for kinetic spectroscopy while the larger region  301  is suitable for multiline spectroscopy. 
     The CCD  300  includes two horizontal registers  304  and  305  for reading charge from the CCD  300  independently of one another. One or both of horizontal registers  304  and  305  may include a charge dump area  306  for providing parallel dump of all charge within horizontal register  304  or  305  as the case may be. Techniques for manufacturing such charge dumps are known in the art and will not be described in detail herein. 
     The operation of the novel device will first be described in its mode for utilization in performing multiline spectroscopy. In operation of multiline spectroscopy, a plurality of spectra are placed in region  301 , each separated by bands of dark charge in order to prevent interference caused by energy from one spectrum spilling over into another spectrum. FIG. 4 shows a conceptual representation of the device of FIG. 3, utilized in its multiline spectroscopy mode including a plurality of exemplary spectra  401  through  404  included thereon. Spectra  401  through  404  are separated by regions  405  in order to prevent contamination of energy from one spectra to another. 
     For purposes of explanation, we presume that region  302  comprises eighty rows, and region  301  comprises 320 rows. Since the 320 rows of charge from region  301  are to be placed into region  302 , there is a desire to provide for 4 to 1 binning at split  303 . Moreover, we presume that each of spectra  401  through  404  is eight rows high, and that region  405  is eight rows as well. 
     In order to shift out the multiple spectra, the four rows  405   a  are binned into row  406 , the first row above the split  303 . The row  406  would then be shifted one row upward, thereby allowing the binning of the next four rows of dark charge from region  405   a  into row  406 . The process continues to repeat itself in a similar manner such that each set of four rows from region  301  is binned into one row in region  302 . Since both the light and dark alternating areas in region  301  are eight rows high, the resulting arrangement in region  302  would be (i) two rows of a spectrum comprising four binned rows of spectra from below  301 , and (ii) two rows comprising dark charge. 
     FIG. 5 shows an exploded view of region  302  of the CCD device of FIG. 4 after the operation of the binning at the asymmetrical split described above. Each of the rows  501  and  502  include four rows of dark charge from region  301  of the device, and rows  503  and  504  contain the spectrum. The alternating pattern repeats itself as shown in FIG.  5 . 
     The binned spectra in rows  503  and  504  may then be read out through horizontal register  304 . It is also contemplated that an 8 to 1 binning may be used in the foregoing example if the capacity of each CCD element is large enough to hold all required charge. 
     It can be appreciated from the foregoing that the implementation of multiline spectroscopy utilizing the foregoing arrangement allows for more sensitive spectra to be obtained by providing for multiple row spectrum yet the time required to read out such spectra is minimized due to the binning occurring at asymmetrical split  303 . 
     In a further embodiment, the dark charge from rows  501  and  502  may be quickly eliminated from horizontal register  304 . Specifically, improved speed may be achieved by utilizing the charge dump  306  to eliminate the entire dark charge from register  304  in parallel without reading it serially out of horizontal register  304 . 
     It is noted that the binning at the asymmetrical split may not necessarily be constant and need not necessarily divide evenly into the different rows of dark charge and spectra contained in region  301 . For example, consider a situation in which the spectra each occupy ten rows and the dark bands therebetween occupy ten rows. If the binning is still desired to be four to one, binning at the asymmetrical split should be done such that the average ratio of rows in region  301  to rows in region  302  is four to one. Additionally, the averaging should be done such that dark charge rows are not mixed with the rows representing spectra. 
     In the foregoing example, a four to one binning ratio can be used to compress 320 rows in region  301  into 80 rows in region  302  by an arrangement which bins according to the following algorithm: 5 to 1, 5 to 1, 4 to 1, 4 to 1, 2 to 1, 5 to 1, 5 to 1, 4 to 1, 4 to 1, 2 to 1, repeat, etc. In accordance with the foregoing arrangement, the first 10 rows would be binned into two rows of dark charge, and next 10 rows would be binned into three rows of spectrum. Thus, the system provides for efficient multiline spectroscopy by binning, at an asymmetrical split, in such a manner that (i) dark charge and spectra are separated and (ii) the average binning ratio is equal to number of rows in the relatively large portion of the CCD divided by the number of rows in the relatively smaller portion of the CCD. 
     In another embodiment of the present invention, the arrangement of FIG. 3 can be utilized to accomplish kinetic spectroscopy efficiently. Specifically, with reference to FIG. 3, the regions  302  may be utilized to capture a spectrum, and such spectrum may be read out through register  304 . However, the remaining dark charge need not be read out since the dark charge in region  301  may be separately controlled and read out through register  305 . FIG. 8 shows a conceptual representation of the use of the asymmetrically split CCD utilized to sequentially read out numerous spectra stored in the small region  302  while shifting dark charge out of large region  301 . The arrows indicate the direction of charge movement, and the dark charge may be dumped in charge dump  801 . 
     In still another embodiment, kinetic spectroscopy may be accomplished by capturing a single spectrum comprising multiple rows in region  302 , binning such multiple row spectrum into one or more rows in region  301 , and then capturing a subsequent spectrum in region  302 . Thus, plural spectra can be captured sequentially and rapidly, and each one binned into one or more rows in a larger region  301  wherein no light is incident. 
     The device shown in FIG. 3 may be utilized for multiline spectroscopy as previously described, as well as for kinetic spectroscopy by simply controlling it differently. Specifically, in the case where multiline spectroscopy is desired, the spectra are captured in region  301 , binned into region  302 , and read out through register  306 . On the other hand, when kinetic spectroscopy is desired, the spectra to be analyzed are captured one at a time using plural rows in region  302 , and read out through register  304  while the dark charge is dumped through register  305 . 
     By having the ability to shift charge on opposite sides of the asymmetrical split in opposite directions, the larger region of dark charge can be dumped or shifted out through a different register than the spectra, as shown in FIG.  8 . Additionally, the device can be configured to operate as a multiline spectroscopy device or a kinetic spectroscopy device by simply using different control software. 
     While the foregoing describes the preferred embodiment of the invention, it is understood that various enhancements or other embodiments will be apparent to those of skill in the art. These variations are intended to be covered by the following claims.