Abstract:
The invention refers to a photoelectric detector device to be used in the atomic absorption spectroscopy. This device is characterized by a photo semiconductor array having a plurality of photo semiconductor devices and a read-out means for jointly reading out the charges generated in the photo semiconductor devices of any continuous portion in the photo semiconductor array by means of impingement of radiation, and for generating electric signals corresponding to the read-out charges.

Description:
TECHNICAL FIELD 
     The present invention refers to a photoelectric detector device to be used in atomic absorption spectroscopy. 
     BACKGROUND ART 
     Photoelectric detector devices of that kind, are known in the field of the atomic absorption spectroscopy, for instance in the form of photo semiconductor devices. 
     The photo semiconductor devices in a detector device of that kind may exist in the form of photo diodes, CCD structures etc. 
     However, the signal/noise ratio of known detector devices of that kind depends on the portion of the detector face that is actually loaded by a radiation to be detected. An aggravated signal/noise ratio in particular results if not the entire detector face but only a small part thereof is loaded by the radiation to be detected. 
     SUMMARY OF THE INVENTION 
     Thus, the object underlying the invention is to improve the known photoelectric detector device. 
     This object is achieved by a detector device which is characterized by a photo semiconductor array having a plurality of photo semiconductor devices and a read-out means for jointly reading out the charges generated by impingement of radiation onto the photo semiconductor device of any continuous portion within the photo semiconductor array, and for generating electric signals corresponding to the read-out charges. 
     By means of a detector device designed in that manner, only the charges generated by impingement of radiation in any continuous portion of the photo semiconductor array can be read out by means of the read-out means. Through this it is possible to only read out charges from that part of the photodetector onto which the radiation to be detected or measured actually impinges. Those portions which in the known detectors make a great contribution to the signal/noise ratio, i.e. those portions that do not deliver a measuring signal but merely lead to a read-out noise are therefore not taken into consideration by the read-out device. 
     In accordance with an advantageous development, the detector device comprises a plurality of inputs each being assigned to a photo semiconductor device of the photo semiconductor array, an output for the generated electric signals which correspond to the read-out charges, a switching means having at least one switch associated to at least one input, each switch being provided downstream each input associated thereto, and by means of each switch each input associated thereto can be coupled to the output of the read-out device. 
     By means of this embodiment, which merely comprises simple electronic components, the invention can be realized in an especially reasonable manner. 
     In accordance with a further embodiment, a switch may be assigned to a plurality of inputs. Since this embodiment requires less components, it is in particular advantageous if the photo semiconductor array is designed symmetrically with respect to an axis, and the face of the detector device shall be enlarged or reduced only symmetrical with respect to this axis. 
     Each switch of the switching means may preferably be electrically operable. In this case each switch can be controlled quickly and reliably by electric signals supplied to the read-out device. 
     In an advantageous embodiment a device may additionally be provided to each switch, said device putting all photo semiconductor devices which are not coupled to the output of the read-out device to a predetermined potential. Thus, possible influences of photo semiconductor devices on the circuit, from which charges are not to be read out, are minimized. 
     For this purpose each device associated to a switch may for instance have a further switch, which is provided between the input associated to the switch and the predetermined potential such that it couples the input—when it is not coupled to the output of the read-out device—to the predetermined potential. Furthermore, the switch and the switch associated thereto may be provided in an operative manner by an electric signal which is supplied to the switch directly and to the associated switch via an inverter. 
     Moreover, a decoding means can be provided, which in response to digital selection signals operates the switch(es). Thereby it is possible to easily control a plurality of switches electronically, i.e. by means of a processor means. 
     According to a further advantageous embodiment, a power limiting means, e.g. in the form of a diode, can be provided directly after each input in the read-out device. Such a power limiting means ensures that the read-out device responds not until reaching a predetermined threshold value. 
     According to an advantageous embodiment, the detector device comprises an amplifier device having an operational amplifier for amplifying the electric signals of the read-out device and a variable capacitance connected in parallel to the amplifier. 
     Thereby the sensitivity range of the detector can be adjusted in a simple manner by varying the capacitance. By selecting the sensitivity range in response to the signal to be measured, the signal/noise ratio can moreover be optimized. 
     Such a variable capacitance can in an especially reasonable manner be composed of arrays connected in parallel each consisting of a capacitor and a switch, the capacitance being variable by operating at least one switch. 
     Furthermore, an additional switch may be provided in parallel to the arrays each consisting of a capacitor and a switch. This measure causes the integrator circuit consisting of the operational amplifier and the variable capacity to be set back in an especially simple and quick manner. 
     In accordance with a further purposeful embodiment, a decoder means may be used for operating the switches of the variable capacitance, said decoder means operating the switches in response to digital selection signals. Through this an especially simple change of the capacitance in a means having a plurality of parallel connected arrays of capacitors and switches is possible by means of few selection signals. 
     Further advantages of the invention can be derived from the following exemplary description of preferred embodiments of the invention with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a detector device according to a first embodiment of the invention, 
     FIG. 2 shows a detector device according to a second embodiment of the invention, 
     FIG. 3 shows a detector device according to a third embodiment of the invention, 
     FIGS. 4A and B show a detector device according to a fourth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment  100  of the detector device. 
     The detector device  100  comprises a photo semiconductor array  110 , a read out means  120  and an amplification means  130 . 
     The photo semiconductor array  110  comprises a plurality of photo semiconductor devices A, B and C for converting light, which impinges onto the photo semiconductor devices, into charges. Photo semiconductor devices that can be used are all known photo semiconductor devices, such as photodiodes, CCD structures and the like. The charges generated in each photo semiconductor device may be read out by means of the read-out means  120  via an output of each photo semiconductor device. 
     The dimensions of the photo semiconductor devices may be adapted in accordance with the respective measuring arrangement. If, for instance, the gap of a monochromator is to be imaged onto the detector device, it is purposeful to form the height of all photo semiconductor devices A, B and C corresponding to the height of the image of the gap which is to be projected onto the detector device. Since in such a design in height direction, the entire detector is irradiated, an optimum signal/noise ratio results in the height direction. The width of the photo semiconductor devices practically also depends on the expected widths of the image projected onto the detector device. 
     The read-out means  120  of the detector device  100  is provided with inputs  121 . One of the photo semiconductor devices A, B and C, is each associated to each input. The inputs  121  are connected in a suitable manner to the respective photo semiconductor devices A, B and C, respectively. Furthermore, the read-out means  120  comprises and output  122  at which electric signals corresponding to the charges read-out by the read-out means are output. 
     The read-out means  120  further comprises a switch means  123  having three switches  124 . In the read-out means  120  each switch  124  is provided between one of the inputs  121  of the read-out means  120  and the output  122  of the read-out means. 
     The switches  124  are operative by means of electric signals. In accordance with FIG. 1, a decoder means  125  is provided for operating the switches, said decoder means controlling switches  124  in response to two selection signals SELL and SEL 2 . As an alternative to the decoder means  125 , the switches  124  may, however, also be directly controlled by appropriate electric signals. 
     As can be taken from FIG. 1, any combination of photo semiconductor devices A, B and C can be connected with the output of the read-out means by appropriately closing the switches  124 . If such a connection with the output  122  is established, the charges generated in the respective photo semiconductor devices are output in the form of an electric signal to the output  122  of the read-out means  120 . 
     In particular, by appropriately positioning the switches  124  the continuous portions A, B, C, A and B as well as A and C can be read-out through the read-out means, wherein the portions B and C, A and C, A and B, C or B, respectively are not taken into consideration. On the whole the signal/noise ratio of the detector device may be improved if only a part of the detector face is required for detecting a radiation. 
     The output  122  of the read-out means is connected to the input of an amplification means  130 . This amplification means comprises an operational amplifier  131  and a variable capacitance  132  connected in parallel to the operational amplifier. 
     In accordance with FIG. 1, the variable capacitance is constructed of arrays composed of one capacitor  133  and one switch  134 , said arrays being connected in parallel to one another. The capacitance of the variable capacitance may be easily changed by operating the switches  134 . For this purpose a further decoder means  135  is provided which controls the switches in response to the selection signals SEL 1 , SEL 2  and SEL 3 . As an alternative to the decoder means  135 , the switches can of course also be controlled directly by appropriately supplied signals. 
     The operational amplifier  131  and the variable capacitance  132  represent a current integrator in the circuit shown in FIG. 1, which integrates the power signal which is supplied by the read-out circuit  120  to a voltage taken can be tapped at the output of the amplifier means  130 . This output voltage is proportional to the charges generated in the photo semiconductor devices which are connected through the switching means with the output  122  of the read-out means. 
     Furthermore, a circuit  136  is connected in parallel to the arrays composed of one capacitor and one switch each is provided in accordance with FIG.  1 . The integrator switch can easily be reset by means of this switch. This switch  136  may also be controlled by the decoder means or as an alternative by an electric signal directly applied. 
     By changing the capacitance, the sensitivity range of the detector device can be easily selected and thus the most favorable signal/noise ratio can be adjusted for the detector device in accordance with the measuring signal. 
     The values of the capacitors of the variable capacitance  132  are selected in a purposeful manner in accordance with the measuring range to be expected. In order to enable for instance a possibly universal use of the detector in various atomic absorption methods, seven capacitors having values 0.1 pF, 0.4 pF, 1 pF, 2.5 pF, 7 pF, 12 pF and 20 pF may be selected in the variable capacitance  132 . By this selection, capacitances in the range of 0.1 to 32 pF can be connected. If the inherent dynamics of a semiconductor detector with 3000 is taken into consideration, a dynamic range of approximately 1×10 6  results for the present circuit composed of photo semiconductor array and amplifier. 
     FIG. 2 shows a second embodiment of a detector device  200  according to the present invention. 
     Compared to the detector device  100  shown in FIG. 1, the detector device  200  has a slightly modified photo semiconductor array  210  and inputs  221  of the read-out means  220  which are adapted appropriately. Moreover, the detector device  100  and  200  correspond to one another. In the following, it is merely referred to the above specified modification, and regarding the components corresponding to each other, it is referred to their description in connection with FIG.  1 . In this respect, it must be noted that the reference numerals of elements corresponding to each other only differ by their first number. 
     In contrast to the photo semiconductor array of the first embodiment, the photo semiconductor array  210  comprises a photo semiconductor device A 1  as well as two photo semiconductor devices B 1  and C 1 . The two photo semiconductor devices B 1  and the two photo semiconductor devices C 1  are each formed identically. Whereas the heights of the two photo semiconductor devices A 1 , B 1  and C 1  are equal, the photo semiconductor devices differ by width. In relation to one another, the photo semiconductor devices BE 1  and C 1  area each arranged symmetrically around the photo semiconductor device A 1 . 
     Corresponding to this symmetric arrangement of the photo semiconductor devices, the read-out means  220  is modified with respect to the read-out means  120  shown in FIG.  1 . 
     The read-out means  220  in particular comprises five inputs  221 , one of the above specified photo semiconductor devices each being assigned to these inputs. 
     Moreover, the photo semiconductor device Al is directly connected to the output  222  of the read-out means  220 . Therefore, the charge generated in the photo semiconductor device Al is read out during each read-out process. Moreover, one switch  224  each, controlled directly according to FIG. 2 by two selection signals sel 1  and sel 2 , respectively, is associated to the two photo semiconductor devices B 1  and C 1 , respectively. 
     By closing the switch  224 , which is assigned to the two photo semiconductor devices B 1 , the photo semiconductor devices B 1  are connected to the output  222  of the read-out means. Thus, the charges in this configuration which are generated in the photo semiconductor device Al and in the two photo semiconductor devices B 1 , are read-out by the read-out means  220  and are supplied to the output  222  in form of an electric signal. 
     If furthermore, switch  224  is closed which is assigned to the two photo semiconductor devices C 1 , all photo semiconductor devices are connected to the output  222 . Consequently, all charges that are generated in the photo semiconductor devices A 1 , B 1 , C 1  are read-out and supplied to the output  222  of the read-out means  220 . 
     FIG. 3 shows a third embodiment of a detector device  300 . 
     This embodiment differs from the embodiment shown in FIG. 2 in that power limiting means  325  provided in the form of diodes, are additionally provided in its read-out circuit  320 , said power limiting means being provided directly downstream the inputs associated to the respective photo semiconductor devices A 1 , B 1  and C 1 . 
     These power limiting means  325  ensure that the read-out circuit starts only after a predetermined threshold value to read-out the charges from the respective photo semiconductor devices. 
     Furthermore a device  326  is provided according to FIG. 3, which puts all photo semiconductor devices to a common predetermined potential which are not coupled to the output  322  of the read-out means  320  because of the position of the switches  324 . 
     According to the embodiment shown in FIG. 3, this device  326  comprises switches  327  and inverters  328 . Each switch  327  is associated to one of switches  324 . Each switch  327  is provided between the input assigned to this switch  324  and the common potential. 
     Each switch  327  may be controlled according to FIG. 3 by means of the same selection signal that is used for controlling the switch  324  associated thereto. If the switches  324  and  327 , as in FIG. 3, are of the same type, i.e. if they are for instance opened by a high-level signal and closed by a low-level signal, the selection signal for controlling one of the switches  324  or  327  is inverted; in case of the arrangement shown in FIG. 3, the selection signal for instance for controlling the switch  327  is inverted by means of an inverter  328 . 
     This structure leads to the fact that a pair of switches  324  and  327  assigned to each other always comprise switch positions opposite to each other, i.e. if one of the switches  324  and  327  is closed, the other one is opened. Therefore, a photo semiconductor device which is not coupled to the output  322  of the read-out means  320  because of an open switch  324 , will be put to the common potential by means of the closed switch  327 . This prevents that a photo semiconductor device from which charges are not to be read out, supplies signals to the output  322  of the read-out circuit. 
     Moreover, external terminals  333  are provided in the variable capacitance  322  according to FIG. 3 with respect to the detector device shown in FIG.  2 . 
     The power limiting means  325 , the means  326  as well as the external terminals  333  in this embodiment are obviously preferred embodiments of the detector device which are independent from one another. Therefore, these three preferred embodiments may be used individually or in any combination with one another. 
     The remaining elements of the embodiment shown in FIG. 3 correspond to the elements shown in FIG.  1  and FIG. 2, respectively. For a detailed description of these element, it may therefore be referred to the respective description in connection with these Figures. In this respect, it must be noted that reference numerals of the respective element only differ from one another by their first number. 
     FIG. 4A and 4B show a further embodiment of a detector device  400 . This detector device may in particular be used as a universal detector for a plurality of applications in the atomic absorption spectroscopy. 
     This detector device  400  comprises a photo semiconductor array  410  having fifteen photo semiconductor devices. These photo semiconductor devices are provided in the form of three groups G 1 , G 2  and G 3 , each having five photo semiconductor devices A 1 , B 1  and C 1 , A 2 , B 2  and C 2 , and A 3 , B 3  and C 3 , respectively. 
     The individual groups of the photo semiconductor devices are structured analogously to photo semiconductor array shown in FIG.  2 . Therefore, one photo semiconductor device A 1 , A 2  and A 3 , respectively, is provided around which two photo semiconductor devices B 1 , B 2  and B 3 , respectively, and two further photo semiconductor devices C 1 , C 2 , and C 3 , respectively are symmetrically arranged. 
     A first read-out means  420   a  is provided for the first and the second group, and a second read-out means  420   b  is provided for the third group. Furthermore a first amplification means  430   a  and a second amplification means  430   b  are provided, respectively. 
     The read-out means  420   a  corresponds to the read-out means  320  of FIG. 3, wherein corresponding to the additional photo semiconductor devices A 2 , B 2  and C 2 , additional elements  424   a ,  425   a  and  426   a  are provided. 
     The read-out means  420   b  corresponds to the read-out means  320  in FIG.  3 . 
     The amplification means  430   a  and  430   b , besides the external terminals described in connection with FIG. 3, are also identical with the amplification means  130 . To describe these circuits, it may be referred to the relevant description of FIG.  1  and FIG.  3 . 
     The arrangement of photo semiconductor devices in the detector array  410  shown in FIG. 4A, enables a universal use of the detector device in a plurality of different applications in the atomic absorption spectroscopy. 
     By means of read-out of groups G 1  and G 3 , two beams which have passed through different optical paths may for instance be simultaneously measured by the detector device and may be evaluated subsequently. 
     When using a gap monochromator, the height of the gap formed onto the photo semiconductor array can be adjusted by selective read-out of groups G 1 , G 2  or G 1  and G 2 . Thus, it is possible, for instance, to adapt by means of the read-out means the gap height to the atomic absorption method used. 
     Furthermore, the width of the photo semiconductor array used as a proof can be adjusted in a simple manner for each group by selecting the respective photo semiconductor devices, as already explained in connection with FIG.  2 .