Abstract:
In a multi-element sensor calibration apparatus, an image signal derived from a multi-element sensor installed in a facsimile or a satellite is periodically calibrated based upon a zero level signal and a calibration signal having more than two uniform levels. The multi-element sensor calibration apparatus is arranged by employing a light reception unit for receiving incident light to convert the received incident light into an electric signal; a calibration signal output unit for outputting a calibration signal used to calibrate the electric signal; a transfer unit for transferring the electric signal and the calibration signal; a gate for executing a gating operation of the electric signal in such a manner that when the gate is set to an ON state, the electric signal derived from the light reception unit is outputted to the transfer unit whereas when the gate is set to an OFF state, outputting of the electric signal to the transfer unit is interrupted; and a calibration signal output control unit for performing output control of the calibration signal in such a way that when the gate means is set to an ON state, the calibration signal is not outputted to the transfer unit, whereas when the gate is set to an OFF state, the calibration signal is outputted to the transfer unit. As a result, the image signal of the multi-element sensor can be calibrated irrespective of the electrical differences in the solid-state characteristics of the electronic components.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a calibration apparatus used for a multi-element sensor. More specifically, the present invention is directed to such a calibration apparatus capable of calibrating a high-resolution multi-element sensor used to sense an optical image of a facsimile, or an earth-monitoring multi-element sensor installed on a satellite. 
     2. Description of the Related Art 
     Conventionally, a multi-element sensor installed in a facsimile, or a satellite may sense an image signal, and further is electrically calibrated so as to periodically confirm operation conditions of electronic circuitry employed in an entire system. 
     One typical multi-element sensor introduces the following electric calibration method. That is, while using two levels of signals, namely, a zero level signal and an electric calibration signal as a reference, the sensor signal is electrically calibrated. 
     FIG. 7 is a timing chart for the various signals related to the typical multi-element sensor with respect to the time sequential operation. 
     As shown in FIG.  7 ( a ), an image signal is outputted from the multi-element sensor during a time period of “t1”, either a zero level signal or an offset signal is outputted during a time period of “t2”, and an electric calibration signal is outputted during a time period of “t3”. The time period of “t2” succeeds the first-mentioned time period of “t1”, and the time period of “t3” succeeds this time period of “t2”. 
     Conventionally, the image signal outputted during the time period of “t1” is calibrated based upon both the zero level signal outputted during the time period of “t2” and the electric calibration signal outputted during the time period of “t3”. 
     FIG.  7 ( b ) is a timing chart for indicating an image signal which has been calibrated by employing the zero level signal and the electric calibration signal with respect to the time sequential operation. 
     This conventional calibration method is described in, for example, Japanese Patent Laid-open Publication Nos. Hei5-183143 and Hei9-37022. 
     On the other hand, in a multi-element sensor, a minus-offset may be set to a zero level signal in order to widen a dynamic range of this multi-element sensor. Also, a zero level of this multi-element sensor may be set and this set level exceeds a preselected sensitivity, since this sensor may detect a light amount higher than a preselected light level. 
     In this conventional sensor calibration technique, since the image signal is calibrated based upon the two levels of the zero level signal and the electric calibration signal, both the offset and the gain of this sensor can be hardly corrected. 
     Also, the conventional multi-element sensor calibration apparatus presents the following problem. That is, within the image signals outputted from the multi-element sensor whose elements are arranged in a linear manner, the image signal outputted from the even-numbered multi-element sensor and also the image signal outputted from the odd-numbered multi-element sensor pass through the different registers and the different amplifiers. Since the offset amounts of the respective registers and also the gains of the respective amplifiers are different from each other, there is a slight difference between the electrical characteristics of the image signal derived from the even-numbered multi-element sensor, and the electrical characteristics of the image signal derived from the odd-numbered multi-element sensor. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-described problems, and therefore, has an object to provide a multi-element sensor calibration apparatus capable of continuously calibrating the multi-element sensor irrespective of solid-state characteristic differences produced in registers and also amplifiers, through which image signals of this multi-element sensor pass. 
     To achieve the above-described object, a calibration apparatus used for a multi-element sensor, according to an aspect of the present invention, is featured by comprising: 
     a light reception unit for receiving incident light to convert the received incident light into an electric signal; 
     calibration signal output means for outputting a calibration signal used to calibrate the electric signal; 
     transfer means for transferring the electric signal and the calibration signal; 
     gate means for executing a gating operation of the electric signal in such a manner that when the gate means is set to an ON state, the electric signal derived from the light reception unit is outputted to the transfer means whereas when the gate means is set to an OFF state, outputting of the electric signal to the transfer means is interrupted; and 
     calibration signal output control means for performing an output control of the calibration signal in such a way that when the gate means is set to an ON state, the calibration signal is not outputted to the transfer means, whereas when the gate means is set to an OFF state, the calibration signal is outputted to the transfer means. 
     Also, according to another aspect of the present invention, adjustment means for adjusting a level of the calibration signal is provided between the transfer means and the calibration signal output control means. 
     Also, according to another aspect of the present invention, amplification means for amplifying the electric signal and the calibration signal, which are transferred by the transfer means, is provided at a post stage of the transfer means. 
     Also, according to another aspect of the present invention, the light reception unit includes a plurality of optical sensors; 
     the multi-element sensor calibration apparatus includes at least two sets of each of the calibration signal output means, the transfer means, the gate means, and the calibration signal output control means; and 
     the two sets of gate means are arranged in correspondence with a respective portion of the plurality of optical sensors. 
     Further, according to another aspect of the present invention, the multi-element sensor calibration apparatus is featured by further comprising: 
     at least two sets of adjustment means for adjusting a level of the calibration signal and positioned between the respective calibration signal output control means and the respective transfer means. 
     Further, according to another aspect of the present invention, the multi-element sensor calibration apparatus is featured by further comprising: 
     at least two sets of amplification means for amplifying the electric signals and the calibration signals, which are transferred by the at least two sets of transfer means, positioned at post stages of the respective transfer means, respectively. 
     Also, according to another aspect of the present invention, the calibration signal derived from the calibration signal output means has at least two uniform levels. 
     Also, according to another aspect of the present invention, the gate means and the calibration signal output control means are controlled to substantially simultaneously output the electric signal and the calibration signal. 
     Also, according to another aspect of the present invention, the electric signal contains at least an image signal and a zero level signal. 
     Also, according to another aspect of the present invention, the electric signal contains at least an image signal and an offset signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic diagram for representing a circuit arrangement of a multi-element sensor calibration apparatus  100  according to an embodiment of the present invention; 
     FIG. 2 is a timing chart for showing time sequential variations in operations of transfer gates  12   a / 12   b , input drains  16   a / 16   b , and input gates  18   a / 18   b  of the multi-element sensor indicated in FIG. 1; 
     FIG. 3 is a timing chart for representing time-sequential output states of an image signal, a zero level signal, and an electric calibration signal, which are outputted from the multiplexing circuit  32  of the calibration apparatus  100  under a stable temperature condition; 
     FIG. 4 is a timing chart for representing time-sequential output states of an image signal, a zero level signal, and an electric calibration signal, which are outputted from the multiplexing circuit  32  of the calibration apparatus  100  under a variable temperature condition; 
     FIG. 5 schematically shows an image signal calibrated by the calibration apparatus  100  during temperature variations; 
     FIG. 6 graphically indicates a relationship between an input level of an electric calibration signal used in the calibration apparatus  100  and an output level thereof; and 
     FIG. 7 is a timing chart for representing the time sequential variations in the signals of the conventional multi-element sensor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, a calibration apparatus capable of calibrating a multi-element sensor, according to an embodiment of the present invention, will be described in detail. 
     FIG. 1 is a schematic block diagram for indicating a circuit arrangement of a multi-element sensor calibration apparatus  100  according to an embodiment of the present invention. 
     In FIG. 1, reference numeral  1  shows a multi-element sensor. This multi-element sensor  1  includes the structure described below. 
     First, the structure of this multi-element sensor  1  will now be explained. Reference numeral  10  shows a light receiving unit for converting incident light into an electric (image) signal. As indicated in FIG. 1, this light receiving unit  10  is constituted by “n” pieces of optical sensors “i” to “n”. 
     Reference numerals  12   a  and  12   b  show transfer gates. These transfer gates  12   a  and  12   b  are arranged along the light receiving unit  10  in such a way that this light receiving unit  10  is sandwiched by the transfer gate  12   a  and the transfer gate  12   b . These transfer gates  12   a  and  12   b  are employed so as to supply only a signal outputted from a specific light receiving unit among the signals derived from the light receiving unit  10  to registers  14   a  and  14   b  (which will be discussed later). The transfer gates  12   a  and  12   b  may specify the optical sensors “i” to “n” of the light receiving unit  10  in different time sequential manner. 
     Also, reference numerals  14   a  and  14   b  indicate registers. These registers  14   a  and  14   b  are arranged in such a manner that both the light receiving unit  10  and the transfer gates  12   a / 12   b  are sandwiched by these registers  14   a  and  14   b . The registers  14   a  and  14   b  are provided so as to transfer the signals outputted from the transfer gates  12   a  and  12   b  to output edge portions  15   a  and  15   b  of these registers  14   a  and  14   b , and then output these transferred signals from these output edge portions  15   a  and  15   b . Also, the registers  14   a  and  14   b  transfer calibration signals derived from input drains  16   a  and  16   b  to the output edge portions  15   a  and  15   b , and then output these calibration signals from these output edge portions  15   a  and  15   b , respectively. 
     Reference numerals  16   a  and  16   b  indicate input drains provided at edge portions of the registers  14   a  and  14   b , which are different from the above-explained output edge portions  15   a  and  15   b  thereof. When the input drains  16   a  and  16   b  are set at ON states, the input drains  16   a / 16   b  enter the electric calibration signals unto the registers  14   a  and  14   b , respectively. 
     Reference numeral  18   a  shows an input gate provided between the input drain  16   a  and the register  14   a , and reference numeral  18   b  indicates another input gate provided between the input drain  16   b  and the register  14   b . These input gates  18   a  and  18   b  are employed so as to adjust the input levels of the electric calibration signals derived from the input drains  16   a  and  16   b.    
     The above-explained structural elements constitute the internal arrangement of the multi-element sensor  1 . 
     Next, an internal circuit arrangement of the calibration apparatus  100  capable of calibrating the above-described multi-element sensor  1  will now be described. 
     Referring back to FIG. 1, reference numeral  20  shows a pulse generating circuit for generating a timing pulse used to define the timing of the calibration apparatus  100 . This pulse generating circuit  20  is connected to a CCD driving circuit  22 , a multiplexing circuit  32 , and an A/D converting circuit  34  (which will be explained later). 
     The CCD (charge-coupled device) driving circuit  22  is connected to the above-explained transfer gates  12   a ,  12   b  and the above-described input gates  18   a ,  18   b  of the multi-element sensor  1 . This CCD driving circuit  22  produces a CCD drive pulse so as to drive the transfer gates  12   a ,  12   b  and the registers  14   a ,  14   b.    
     Also, the CCD driving circuit  22  is connected to an electric calibration signal generating circuit  24 . This electric calibration signal generating circuit  24  generates an electric calibration signal in synchronism with the CCD drive pulse outputted from the CCD driving circuit  22 . This electric calibration signal generating circuit  24  is connected to the above-described input drains  16   a  and  16   b , and then outputs the electric calibration signal via these input drains  16   a  and  16   b  to the registers  14   a  and  14   b.    
     Also, the output edge portions  15   a  and  15   b  of the above-described registers  14   a  and  14   b  are connected to amplifying circuits  30   a  and  30   b . These amplifying circuits  30   a  and  30   b  amplify the signals outputted from the output edge portions  15   a  and  15   b . Output terminals of the amplifying circuits  30   a  and  30   b  are connected to the multiplexing circuit  32 . 
     The multiplexing circuit  32  synthesizes the signal outputted from one amplifying circuit  30   a  with the signal outputted from the other amplifying circuit  30   b  in synchronism with the timing pulse outputted from the pulse generating circuit  20 . 
     Since the signals outputted from the amplifying circuits  30   a  and  30   b  are equal to such signals produced by amplifying the signals transferred through the registers  14   a  and  14   b , these output signals contain an image signal, a zero level signal, and an electric calibration signal. 
     Reference numeral  34  indicates an A/D (analog-to-digital) converting circuit for converting an analog signal derived from the multiplexing circuit  32  into a digital signal in synchronism with the timing pulse outputted from the pulse generating circuit  20 . 
     Furthermore, reference numeral  36  indicates a memory circuit for storing thereinto the digital signal outputted from the A/D converting circuit  34 . The digital signal stored in the memory circuit  36  is employed in order to correct a sensitivity of the multi-element sensor  1  and offset thereof. Next, a description will now be made of the operation of the calibration apparatus  100  for calibrating the multi-element sensor  1 , using of the above-described circuit arrangement, according to an embodiment of the present invention. 
     First, in FIG. 1, the pulse generating circuit  20  generates the timing pulse used to define the operation timing of the calibration apparatus  100  for calibrating the multi-element sensor  1 . This timing pulse is outputted to the CCD driving circuit  22 , the multiplexing circuit  32 , and the A/D converting circuit  34 . 
     Next, when light is irradiated onto the light receiving unit of the multi-element sensor  1 , the irradiated light is photoelectrically converted into an electric signal. Then, this electric signal converted by the light receiving unit  10  is transferred to either the register  14   a  or the register  14   b  when either the transfer gate  12   a  or the transfer gate  12   b  is brought into the ON state. After either the transfer gate  12   a  or the transfer gate  12   b  is brought into the OFF state, this photoelectrically-converted signal is successively transferred to either the output edge portion  15   a  or the output edge portion  15   b  in synchronism with the transfer clock signal outputted from the CCD driving circuit  22 . Then, this transferred signal is outputted to the amplifying circuit  30   a ,  30   b.    
     FIG. 2 is a timing chart for representing time-sequential operation states of the transfer gates  12   a ,  12   b ; the input drains  16   a ,  16   b ; and the input gates  18   a ,  18   b.    
     It should be noted that a signal waveform indicated by symbol “W 1 ” represents time-sequential operation changes of the transfer gates  12   a  and  12   b ; another signal waveform indicated by symbol “W 2 ” represents time-sequential operation changes of the input drains  16   a  and  16   b ; and another signal waveform indicated by symbol “W 3 ” indicates time-sequential operation changes of the input gates  18   a  and  18   b.    
     When the transfer gates  12   a  and  12   b  are set to the ON states (namely, time period indicated by symbol “t10”), both the input drains  16   a  and  16   b  are set to the OFF states. After the transfer gates  12   a  and  12   b  are brought into OFF states, the clock signal is transferred through several stages. Thereafter, the input drains  16   a  and  16   b  are ON/OFF-controlled to enter the electric calibration signal to the registers  14   a  and  14   b  (namely, time period indicated by symbol “t20”). The input gates  18   a  and  18   b  may change the input level of the electric calibration signal by changing the voltage levels. 
     In other words, in accordance with this embodiment, when the image signal is entered into either the register  14   a  or the register  14   b , both the input drain  16   a  and the input drain  16   b  are brought into the OFF states so that the electric calibration signal is not entered from the input drain  16   a , or  16   b  into the register  14   a , or  14   b.    
     On the other hand, in the case that the electric calibration signal is entered into the registers  14   a  and  14   b , as indicated in FIG. 2, the input drains  16   a  and  16   b  are repeatedly ON/OFF-controlled, and when the input drains  16   a  and  16   b  are set to the ON states, the electric calibration signal is entered into the registers  14   a  and  14   b . At this time, the transfer gates  12   a  and  12   b  are set to the OFF states so that the image signal passes through the transfer gates  12   a  and  12   b  and thereafter are not entered into the registers  14   a  and  14   b.    
     It should be understood that when the voltages of the input gates  18   a  and  18   b  are changed, the input level of the electric calibration signal may be changed. As a consequence, the sensitivity of the image signal and the offset of this image signal can be calibrated while using more than two levels of the calibration signal and of the zero level signal as the references. 
     The electric calibration signal is inputted from the input drains  16   a  and  16   b , and then is successively transferred in accordance with the transfer clock signal to be supplied to the amplifying circuits  30   a  and  30   b  by performing the control method discussed below. That is, this control is carried out in such a manner that when the electric signal outputted from the light receiving unit is transferred through several stages of either the register  14   a  or the register  14   b , while the above-explained transfer operation is carried out, the ON/OFF states of either the input drain  16   a  or the input drain  16   b  are periodically switched. 
     When the electric calibration signal is entered into the registers  14   a  and  14   b , the input level of the electric calibration signal may be adjusted by the input gates  18   a  and  18   b.    
     The image signals having very low levels transferred by the registers  14   a  and  14   b  are amplified by the amplifying circuits  30   a  and  30   b . The image signal amplified by the amplifying circuit  30   a  is synthesized with the image signal amplified by the amplifying circuit  30   b  in the multiplexing circuit  32 . The image signal synthesized by the multiplexing circuit  32  is supplied to the A/D converting circuit  34  so as to be converted into a digital image signal. It should also be noted that the image signals transferred by the registers  14   a  and  14   b  contain the zero level signal and the electric calibration signal. 
     This digital image signal is stored into the memory circuit  36 , and then the stored digital image signal is used to correct the sensitivity of the image signal and the offset of this image signal. 
     FIG. 3 is a timing chart for representing time-sequential output states of an image signal, a zero level signal, and an electric calibration signal, which are outputted from the multiplexing circuit  32  of the calibration apparatus  100  under a stable temperature condition. 
     As shown in FIG. 3, the image signal is outputted from the multi-element sensor  1  during a time period of “t1”, either the zero level signal or the offset signal is outputted during a time period of “t2”, and the electric calibration signal is outputted during a time period of “t3”. The time period of “t2” succeeds the first-mentioned time period of “t1”, and the time period of “t3” succeeds this time period of “t2”. 
     In this drawing, the ordinate represents an output voltage, and the abscissa denotes time. 
     As indicated in this drawing, the image signals having the various levels are outputted, depending upon the imaging objects, whereas the electric calibration signals have more uniform levels, with the even-numbered electric calibration signals being different from the odd-numbered electric calibration signals, depending on the solid-state characteristic differences of the registers and the amplifying circuits. 
     Next, a description will now be made of signals outputted from the multiplexing circuit  32  in the case that the level of the image signal is varied due to temperature variations. FIG. 4 is a timing chart for representing time-sequential output states of an image signal, a zero level signal, and an electric calibration signal, which are outputted from the multiplexing circuit  32  of the calibration apparatus  100  an unstable temperature condition. Similar to FIG. 3, in FIG. 4, the image signal is outputted from the multi-element sensor  1  during a time period of “t1”, either the zero level signal or the offset signal is outputted during a time period of “t2”, and the electric calibration signal is outputted during a time period of “t3”. The time period of “t2” succeeds the first-mentioned time period of “t1”, and the time period of “t3” succeeds this time period of “t2”. 
     In this drawing, the ordinate represents an output voltage, and an abscissa denotes time. 
     As indicated in FIG. 4, even when the image signal is varied due to the temperature variations occurred in the CCD circuit unit, both the zero level (or offset level) of the image signal and the gain of this image signal can be corrected while using the zero level signal and the electric calibration signals having more than two levels as the reference values. 
     Also, as to shifts in the offset and the gain, and also the minus offset component, as indicated in FIG. 5, the image signal for one line may be simply corrected. These shifts are caused by the solid-state differences, since the different registers  14   a / 14   b  and the different amplifying circuits  30   a / 30   b  are employed. FIG. 5 indicates the calibrated image signals in a case in which the temperature is varied. 
     FIG. 6 graphically shows a relationship between an input level of an electric calibration signal and an output level thereof. In this graphical representation, the straight line indicated by symbol “A 1 ” corresponds to a relationship between an input level of an electric calibration signal and an output level thereof under a stable temperature condition. Also, another straight line indicated by symbol “A 2 ” corresponds to a relationship between an input level of an electric calibration signal and an output level thereof under an unstable temperature condition. 
     In other words, when the signal level of the image signal is varied in response to the temperature changes, since the signal level of the electric calibration signal is also varied, the electric calibration can be carried out. 
     As previously described, in accordance with this embodiment, as indicated in FIG. 3, as the output signal derived from the register for one time period, after the image signal having the various signal levels is outputted in accordance with the imaging objects, the zero level (otherwise offset) signal is outputted from this register. Immediately after this zero level signal, one set of the electric calibration signal having a plurality of uniform levels is outputted from the register. In FIG. 3, this electric calibration signal has two uniform levels. 
     As a consequence, even when these images such as the image signal, the zero level signal, and the electric calibration signal pass through the registers  14   a  and  14   b  having the different solid-state characteristics, and further the amplifying circuits  30   a  and  30   b  having different solid-state characteristics, the calibration can be easily carried out. 
     The multi-element sensor calibration apparatus according to this embodiment can achieve the following effects. 
     As the first effect, even when the below-mentioned electrical characteristics of the electronic components are varied, the image signals derived from the multi-element sensor can be continuously corrected, or calibrated. For instance, the signal levels of the image signals change due to temperature changes. Also, the levels and the gains of the zero level signals (otherwise, offset signals) are different from each other depending upon the odd-numbered pixels and the even-numbered pixels, because of the solid-state electrical characteristic differences in two sets of registers and amplifying circuits. 
     The reason why the image signals can be continuously corrected is given as follows: while the transfer gate is turned ON, the image signal of the multi-element sensor is entered into the register, whereas while the transfer gate is turned OFF, the electric calibration signal is entered from the input drain via the input gate to the register. As a result, the image signal, the electric calibration signal, and the zero level (offset) signal can be outputted for one time period. 
     As a second effect, even when the zero level (offset) signal is offset to the minus level, the image signal of the multi-element sensor can be corrected. 
     This is because when more than 3 levels of the image signals are corrected, the minus offset component can be detected. 
     While the multi-element sensor calibration apparatus of the present invention has been described in detail, when the gate means is set to the ON state, the image signal is entered into the transfer means of the multi-element sensor, whereas when the gate means is set to the OFF state, the calibration signal is outputted from the calibration signal output control means to the transfer means. Since the electric signals containing the image signal and the zero level (offset) signal, and further the calibration signal are outputted at the same time, even when there is a temperature variation, the image signal outputted from the light receiving unit of the multi-element sensor can be corrected. 
     It is thus apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention. 
     Finally, the present application claims the priority of Japanese Patent Application No. Hei9-308871 filed Nov. 11, 1997, which is herein incorporated by reference.