Patent Publication Number: US-2023148109-A1

Title: High Voltage Amplifier Circuit and Analyzer Apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-181024, filed Nov. 5, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high voltage amplifier circuit and an analyzer apparatus. 
     2. Description of the Related Art 
     A high voltage amplifier circuit is known which amplifies an input voltage signal of a few to tens of volts to a high voltage signal of a few kV and outputs it. For example, JP-A-2005-079925 discloses a high output DC amplifier circuit (high voltage amplifier circuit) which has an operational amplifier receiving a voltage signal and a push-pull circuit for amplifying the output signal from the operational amplifier and outputting a high voltage signal and which can output a high voltage signal of a desired voltage value by feeding the high voltage signal from the push-pull circuit back to the operational amplifier via a resistive element. 
     In the high voltage amplifier circuit set forth in JP-A-2005-079925, a push-side field-effect transistor included in the push-pull circuit is driven based on the output current from a push-side photocoupler  13 A. However, the output current from the push-side photocoupler  13 A is feeble and, therefore, it takes time to electrically charge the input capacitance of the push-side field-effect transistor. Therefore, in the high voltage amplifier circuit set forth in JP-A-2005-079925, it is difficult to produce the high voltage signal at a higher response speed when there is a request for a variation of the voltage value of the high voltage signal. 
     SUMMARY OF THE INVENTION 
     In view of the problems described thus far, the present invention has been made. According to some aspects of the present invention, a high voltage amplifier circuit and an analyzer apparatus can be offered which respond at higher speeds. 
     One aspect of the high voltage amplifier circuit associated with the present invention is designed to amplify a first voltage signal applied to an input terminal and to output at an output terminal a second voltage signal of a few kV or higher and comprises a constant current circuit for outputting a constant current signal at the output terminal, an operational amplifier for outputting an amplified control signal based on the first voltage signal, and an amplified voltage output circuit for outputting the second voltage signal based on the constant current signal and on the amplified control signal. The constant current circuit has: a light-emitting device having one end supplied with the constant voltage signal and another end supplied with ground potential; a light responsive electricity generating device for outputting a drive signal in response to light emitted by the light-emitting device; a first transistor having a first terminal, a second terminal, and a third terminal and operating, in response to the drive signal supplied to the first terminal, to generate the constant current signal based on the amplified voltage signal applied to the second terminal and to output the constant current signal at the third terminal; and a current control circuit for detecting the electrical current value of the constant current signal outputted at the third terminal and controlling the supply of the drive signal to the first terminal based on the detection. 
     In this high voltage amplifier circuit, the constant voltage signal continues to be supplied to the light-emitting device and so the light responsive electricity generating device continues to generate the drive signal and outputs it to the first transistor. Consequently, electrical charge is continually stored in the input capacitance of the first transistor which outputs the constant current signal at its output terminal. Thus, if there is a request for a variation of the voltage value of the second voltage signal from the high voltage amplifier circuit and if the voltage value of the first voltage signal applied to the input terminal varies, the time taken to store electrical charge in the input capacitance of the first transistor can be shortened. Also, the responsiveness to a request for a variation of the voltage value of the second voltage signal provided by the high voltage amplifier circuit can be enhanced. 
     Furthermore, in this high voltage amplifier circuit, the constant voltage signal is constantly supplied to the light-emitting device and, therefore, the light responsive electricity generating device continues to generate the drive signal. Consequently, the constant current circuit can be operated without using a high voltage resistance floating power supply. This can suppress the circuit size of the high voltage amplifier circuit. Also, this prevents injection of coupling noise which would occur when a high voltage resistance floating power supply is used. 
     In addition, in this high voltage amplifier circuit, the constant current circuit outputs at the output terminal a constant current signal based on the amplified voltage signal. This reduces the possibility that the responsiveness to a request for a variation of the voltage value of the second voltage signal delivered by the high voltage amplifier circuit will be varied by a load capacitance connected to the high voltage amplifier circuit. Also, this decreases the possibility that the circuit loss will be increased by variations in the load capacitance connected to the high voltage amplifier circuit. 
     One aspect of the analyzer apparatus associated with the present invention includes the high voltage amplifier circuit described in the immediately preceding paragraph. 
     This analyzer apparatus has the high voltage amplifier circuit capable of providing improved responsiveness to a request for a variation of the voltage value of the second voltage signal. Therefore, when an analysis is performed, a wait time for a response can be shortened. 
     As a result, the analysis can be hastened. 
     Furthermore, this analyzer apparatus having the high voltage amplifier circuit is suppressed in circuitry size. If a high voltage resistance floating power supply is used, injection of coupling noise can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing one example of the configuration of a high voltage amplifier circuit  1  of a first embodiment of the present invention. 
         FIG.  2    is a diagram showing one example of the configuration of a high voltage amplifier circuit  1  of a second embodiment. 
         FIG.  3    is a diagram showing one example of the configuration of an electron spectrometer that is one example of an analyzer apparatus. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention are hereinafter described in detail with reference to the drawings, which are only for illustrative convenience. It is to be understood that the embodiments set forth below are not intended to unduly restrict the content of the present invention delineated by the claims and that not all the configurations set forth hereinafter are essential constituent components of the present invention. 
     1. High Voltage Amplifier Circuit 
     1.1 First Embodiment 
       FIG.  1    is a diagram showing one example of the configuration of a high voltage amplifier circuit,  1 , of a first embodiment of the present invention. As shown, the high voltage amplifier circuit  1  comprises an operational amplifier  10 , an amplified voltage output circuit  20 , and a constant current circuit  50 . The high voltage amplifier circuit  1  has a terminal In and another terminal Out. An input voltage Vin is applied to the terminal In and amplified by the high voltage amplifier circuit  1 . An output voltage Vout of a few kV or higher is output at the terminal Out. The high voltage amplifier circuit  1  provides or can provide the output voltage Vout of a few kV or higher. 
     In particular, the constant current circuit  50  equipped in the high voltage amplifier circuit  1  generates a constant current signal based on a voltage signal VH applied to a terminal Hv and outputs the constant current signal at the terminal Out. The operational amplifier  10  of the high voltage amplifier circuit  1  outputs an amplified control signal based on the input voltage Vin applied to the terminal In. The amplified voltage output circuit  20  of the high voltage amplifier circuit  1  generates the output voltage Vout based on the amplified control signal from the operational amplifier  10  and on the constant current signal from the constant current circuit  50  and outputs the output voltage Vout at the terminal Out. That is, the high voltage amplifier circuit  1  has the constant current circuit  50  for outputting the constant current signal at the terminal Out, the operational amplifier  10  for outputting the amplified control signal based on the input voltage Vin, and the amplified voltage output circuit  20  for outputting the output voltage Vout based on the amplified control signal from the operational amplifier  10  and on the constant current signal from the constant current circuit  50 . 
     The configuration of the high voltage amplifier circuit  1  designed as described so far is described in detail with reference to  FIG.  1   . As shown, the constant current circuit  50  has resistors  51 - 57 , transistors  61 - 63 , and a photocoupler  70 . The transistors  61  and  62  of the first embodiment are N-channel MOS transistors, while the transistor  63  is an NPN bipolar transistor. Also shown in  FIG.  1    is an electrical capacitance  59  present between the gate and source terminals of the transistor  62 . 
     The photocoupler  70  includes a light-emitting diode  71  and a photoelectric converter  72 . The light-emitting diode  71  has an anode terminal to which a voltage signal VDH is supplied via the resistor  57 , the voltage signal VDH being a DC voltage signal, for example, of +15 V. The light-emitting diode  71  also has a cathode terminal to which ground potential GND is supplied. 
     The photoelectric converter  72  includes one or more photodiodes. If the photoelectric converter  72  includes a single photodiode, the anode and cathode terminals of the photodiode are electrically connected with an electronic part mounted outside of the photoelectric converter  72 . On the other hand, if the photoelectric converter  72  includes a plurality of photodiodes, these photodiodes are connected in series such that the anode terminal of one of any two successive photodiodes and the cathode terminal of the other are connected together and that the anode terminal of the photodiode located at one end of the series combination of the photodiodes and the cathode terminal of the photodiode located at the other end are electrically connected with the electronic part mounted outside of the photoelectric converter  72 . The anode terminal of the photodiode located at one end either of one photodiode or of the series combination of plural photodiodes is hereinafter referred to as the “anode terminal of the photoconverter  72 ”, and the cathode terminal located at the other end is hereinafter referred to as the “cathode terminal of the photoelectric converter  72 ”. 
     The anode terminal of the photoelectric converter  72  is electrically connected with one end of the resistor  53  and with one end of the resistor  54 . The cathode terminal of the photoelectric converter  72  and the other end of the resistor  54  are electrically connected with the terminal Out. That is, the photoelectric converter  72  and the resistor  54  are connected in parallel. 
     The other end of the resistor  53  is electrically connected with the gate terminal of the transistor  62 . The drain terminal of the transistor  62  is electrically connected with the source terminal of the transistor  61 , while the source terminal of the transistor  62  is electrically connected with one end of the resistor  55 . The electrical capacitance  59  is present between the gate and source terminals of the transistor  62 . The electrical capacitance  59  is equivalent to the input capacitance of the transistor  62 . 
     The drain terminal of the transistor  61  is electrically connected with one end of the resistor  51  and with the terminal Hv. The gate terminal of the transistor  61  is electrically connected with the other end of the resistor  51  and with one end of the resistor  52 . The other end of the resistor  52  is electrically connected with the terminal Out. 
     The other end of the resistor  55  is electrically connected with one end of the resistor  56 , the other end of the resistor  56  being electrically connected with the terminal Out. The other end of the resistor  55  and one end of the resistor  56  are electrically connected with the base terminal of the transistor  63 . The collector terminal of the transistor  63  is electrically connected with the gate terminal of the transistor  62 . The source terminal of the transistor  63  is electrically connected with the terminal Out. 
     The operation of the constant current circuit  50  constructed as described thus far is now described. In the constant current circuit  50 , the voltage signal VDH is supplied to the light-emitting diode  71  of the photocoupler  70 . As a result, the light-emitting diode  71  emits light according to the amount of current produced in response to the voltage signal VDH. The photoelectric converter  72  of the photocoupler  70  receives the light emitted from the light-emitting diode  71  and outputs a current corresponding to the amount of light from the light-emitting diode  71 . The voltage signal VDH is continuously supplied to the light-emitting diode  71  of the present embodiment. Therefore, the photoelectric converter  72  continues to output an electrical current irrespective of the operation of the high voltage amplifier circuit  1 . 
     The output current from the photoelectric converter  72  is supplied to the electrical capacitance  59  via the resistor  53  and thus electrical charge is stored in the electrical capacitance  59 . As a result, a voltage determined by both the amount of current delivered by the photoelectric converter  72  and the resistance value of the resistor  54  is supplied to the gate terminal of the transistor  62 . In consequence, an electrical current induced by the voltage signal VH flows between the drain and source terminals of the transistor  62  and between the drain and source terminals of the transistor  61 . 
     This current induced by the voltage signal VH and flowing between the drain and source terminals of the transistor  61  and between the drain and source terminals of the transistor  62  is supplied to the terminal Out via the resistors  55  and  56 . This induces a voltage across the resistor  56  according to both the current induced by the voltage signal VH and the resistance value of the resistor  56 . If the voltage developed across the resistor  56  exceeds a threshold value for the transistor  63 , then an electrical current is induced between the collector and emitter terminals of the transistor  63 . This controls the voltage value supplied to the gate terminal of the transistor  62  electrically connected with the collector terminal of the transistor  63 . As a result, the value of the current flowing between the drain and source terminals of the transistor  62  is limited. 
     That is, the constant current circuit  50  has: the light-emitting diode  71  whose one end is supplied with the voltage signal VDH and whose other end is supplied with ground potential GND; the photoelectric converter  72  outputting an electrical current according to light emitted by the light-emitting diode; the transistor  62  which is energized according to the output current of the photoelectric converter  72  supplied to the gate terminal of the transistor  62  and which outputs an electrical current at its source terminal, the current being induced by the voltage signal VH applied to the drain terminal; a combination of the resistor  56  and the transistor  63  used for both detection of the electrical current value of the signal induced by the voltage signal VH delivered from the source terminal of the transistor  62  and control of the supply of current and voltage to the gate terminal of the transistor  62  based on the detection. 
     That is, the constant current circuit  50  detects, through the resistor  56 , the value of current flowing between the drain and source terminals of the transistor  62  and controls the operation of the transistor  63  according to the detection performed through the resistor  56 , whereby the amount of current flowing between the drain and source terminals of the transistor  62  is controlled constant. The constant current circuit  50  outputs the current at the terminal Out, the current flowing between the drain and source terminals of the transistor  62  whose amount of current is controlled constant. The electrical current flowing between the drain and source terminals of the transistor  62  whose amount of current is controlled constant is equivalent to a constant current signal. 
     The transistor  61  is mounted to secure a sufficient withstand voltage between the terminals Hv and Out. Therefore, the constant current circuit  50  may have a plurality of transistors  61  or no transistor  61  according to both the voltage value of the voltage signal VH and the withstand voltage of the transistor  62 . In the foregoing description of the present embodiment, the light-emitting diode  71  and the photoelectric converter  72  are contained in the single photocoupler  70 . Alternatively, the light-emitting diode  71  and the photoelectric converter  72  may be separate electronic parts. 
     The configurations and operations of the operational amplifier  10  and of the amplified voltage output circuit  20  are next described. As shown in  FIG.  1   , the operational amplifier  10  has a negative input terminal which is electrically connected with the terminal In via the resistor  11  and with the terminal Out via the resistor  12 . The operational amplifier  10  also has a positive input terminal to which ground potential GND is supplied. The output terminal of the operational amplifier  10  is electrically coupled to the amplified voltage output circuit  20 . 
     The amplified voltage output circuit  20  has resistors  21 - 26 ,  201 - 205 , transistors  31 - 33 ,  211 - 213 , a photocoupler  40 , and a power supply  209 . The transistor  31  of the present embodiment is a PNP bipolar transistor. The transistors  32  and  33  are N-channel MOS transistors. The transistors  211 - 213  are NPN bipolar transistors. Also shown in  FIG.  1    is an electrical capacitance  29  present between the gate and source terminals of the transistor  33 . 
     The output terminal of the operational amplifier  10  is electrically connected with one end of the resistor  21  whose other end is electrically connected with the base terminal of the transistor  31 . Ground potential GND is supplied to the emitter terminal of the transistor  31  via the resistor  22 . The collector terminal of the transistor  31  is electrically connected with the photocoupler  40 . 
     The photocoupler  40  includes a light-emitting diode  41  and a photoelectric converter  42 . The light-emitting diode  41  has an anode terminal electrically connected with the collector terminal of the transistor  31 . The cathode terminal of the light-emitting diode  41  is supplied with a voltage signal VDL via the resistor  23 . The voltage signal VDL is a DC voltage signal of −15 V, for example. 
     The photoelectric converter  42  includes one or more photodiodes. If the photoelectric converter  42  includes a single photodiode, then the anode and cathode terminals of this photodiode are electrically connected with an electronic part mounted outside of the photoelectric converter  42 . On the other hand, if the photoelectric converter  42  includes a plurality of photodiodes, then these photodiodes are connected in series such that the anode terminal of one of any two successive photodiodes and the cathode terminal of the other are connected together and that the anode terminal of the photodiode located at one end of the series combination of the photodiodes and the cathode terminal of the photodiode located at the other end are electrically connected with the electronic part mounted outside of the photoelectric converter  42 . The anode terminal of the photodiode located at one end either of one photodiode or of the series combination of plural photodiodes is hereinafter referred to as the “anode terminal of the photoconverter  42 ”, and the cathode terminal of the photodiode located at the other end is hereinafter referred to as the “cathode terminal of the photoelectric converter  42 ”. 
     The anode terminal of the photoelectric converter  42  is electrically connected with one end of the resistor  201  and with the base terminal of the transistor  211 . The cathode terminal of the photoelectric converter  42  is electrically connected with all of one end of the resistor  202 , one end of the resistor  203 , the collector terminal of the transistor  213 , and the positive terminal of the power supply  209 . The negative terminal of the power supply  209  is electrically connected with a terminal Lv. 
     The other end of the resistor  202  is electrically connected with the collector terminal of the transistor  211 , while the emitter terminal of the transistor  211  is electrically connected with the terminal Lv. The other end of the resistor  202  is also electrically connected with the base terminal of the transistor  212 . 
     The other end of the resistor  203  is electrically connected with the collector terminal of the transistor  212  and with the base terminal of the transistor  213 . The emitter terminal of the transistor  212  is electrically connected with the other end of the resistor  201  and with one end of the resistor  204 . The other end of the resistor  204  is electrically connected with the terminal Lv. 
     The emitter terminal of the transistor  213  is electrically connected with one end of the resistor  205  whose other end is electrically connected with the terminal Lv. The emitter terminal of the transistor  213  is also electrically connected with one end of the resistor  26 . 
     The resistors  201 - 205 , transistors  211 - 213 , and power supply  209  constructed as described thus far operate together to convert the output current from the photocoupler  40  into a voltage. In particular, the conduction states of the transistors  211 - 213  dynamically vary according to the amount of current of the output current from the photocoupler  40 . As a result, a voltage is developed across the resistor  205  based on the value of the output current from the photocoupler  40  and on the value of the output value from the power supply  209 . The voltage developed across the resistor  205  is applied to one end of the resistor  206 . The resistors  201 - 205 , transistors  211 - 213 , and power supply  209  together operate to convert the output current from the photocoupler  40  into a voltage and are herein collectively referred to as a voltage-to-current (I/V) converter circuit  200 . In other words, the I/V converter circuit  200  converts an electrical current based on the output voltage from the operational amplifier  10  into a voltage. 
     The output voltage from the operational amplifier  10  is equivalent to an amplified control signal. The output current delivered from the photoelectric converter  42  included in the photocoupler  40  in response to the output voltage from the operational amplifier  10  is equivalent to an amplified control current signal. The output voltage from the I/V converter circuit  200  which converts the output current from the photoelectric converter  42  included in the photocoupler  40  is equivalent to an amplified control voltage signal. 
     The other end of the resistor  26  is electrically connected with the gate terminal of the transistor  33 . The drain terminal of the transistor  33  is electrically connected with the source terminal of the transistor  32 , while the source terminal of the transistor  33  is electrically connected with the terminal Lv. The electrical capacitance  29  is present between the gate and source terminals of the transistor  33  and equivalent to the input capacitance of the transistor  33 . 
     The drain terminal of the transistor  32  is electrically connected with one end of the resistor  24  and with the terminal Out. The gate terminal of the transistor  32  is electrically connected with the other end of the resistor  24  and with one end of the resistor  25 . The other end of the resistor  25  is electrically connected with the terminal Lv. 
     The operations of the operational amplifier  10  and the amplified voltage output circuit  20  configured as described thus far are now described. The operational amplifier  10  outputs a voltage at its output terminal, the voltage having a value stipulated based on (i) the input voltage Vin applied at the terminal In, (ii) the output voltage Vout appearing at the terminal Out, and (iii) the values of the resistors  11 ,  12 . The output voltage from the operational amplifier  10  is applied to the base terminal of the transistor  31  via the resistor  21 . 
     The transistor  31  is controlled according to the value of the voltage applied to its base terminal such that conduction occurs between the emitter and collector terminals. Consequently, an amount of current corresponding to the value of the voltage supplied to the base terminal flows between the emitter and collector terminals of the transistor  31  and is supplied to the light-emitting diode  41  included in the photocoupler  40 . As a result, the light-emitting diode  41  emits light, and the photoelectric converter  42  of the photocoupler  40  produces an output current corresponding to the amount of light from the light-emitting diode  41 . 
     The output current from the photoelectric converter  42  is applied to the I/V converter circuit  200  and converted into a voltage of a value corresponding to the output current from the photoelectric converter  42 . That is, the I/V converter circuit  200  converts a current based on the value of the voltage delivered from the operational amplifier  10  into a voltage. The output voltage from the I/V converter circuit  200  is supplied to the gate terminal of the transistor  33  via the resistor  26 . 
     The transistor  33  is controlled by the output voltage from the I/V converter circuit  200  which is supplied to the gate terminal of the transistor  33  such that conduction occurs between the drain and source terminals. Furthermore, the transistor  33  is controlled such that conduction occurs between its drain and source terminals. This also controls the transistor  32  such that conduction occurs between its drain and source terminals. In this case, the amount of current flowing between the drain and source of the transistor  33  is stipulated by the value of the voltage which is output from the I/V converter circuit  200  and supplied to the gate terminal of the transistor  33 . That is, the transistor  33  controls the amount of current which flows from the terminal Out toward the terminal Lv out of the current of the constant current signal supplied to the terminal Out by the constant current circuit  50  based on the output voltage from the operational amplifier  10 , i.e., based on the output voltage from the I/V converter circuit  200 . In consequence, the value of the output voltage Vout developed at the terminal Out is controlled. 
     If the value of the output voltage from the I/V converter circuit  200  increased in response to the output voltage from the operational amplifier  10 , the amount of current flowing between the drain and source terminals of the transistor  33  increases. As a result, the voltage value developed at the terminal Out decreases toward the voltage value of the voltage signal VL. On the other hand, if the value of the output voltage from the I/V converter circuit  200  decreases in response to the output voltage from the operational amplifier  10 , the amount of current flowing between the drain and source terminals of the transistor  33  decreases. As a result, the voltage value developed at the terminal Out increases toward the voltage value of the voltage signal VH. 
     That is, the amplified voltage output circuit  20  controls the amount of current flowing toward the terminal Lv out of the output current from the constant current circuit  50  in response to the output voltage from the operational amplifier  10 , thus controlling the voltage value of the output voltage Vout developed at the terminal Out between the voltage value of the voltage signal VH and the voltage value of the voltage signal VL. 
     As described previously, the output voltage Vout produced at the terminal Out is fed back to the operational amplifier  10  via the resistor  12 . The operational amplifier  10  controls the value of the output voltage from the output terminal of the operational amplifier  10  based on (i) the value of the input voltage Vin applied at the terminal In, (ii) the value of the output voltage Vout fed back via the resistor  12 , and (iii) the values of the resistors  11 ,  12 . That is, the operational amplifier  10 , amplified voltage output circuit  20 , and resistors  11 ,  12  together constitute an inverting amplifier circuit. Thus, the high voltage amplifier circuit  1  amplifies the value of the input voltage Vin applied to the terminal In according to both the voltage value of the voltage signal VH and the voltage value of the voltage signal VL, thereby generating the output voltage Vout, and outputs this output voltage at the terminal Out. In particular, the high voltage amplifier circuit  1  generates the output voltage Vout whose value varies between the voltage signal VH on the order of kV applied via the terminal Hv and the voltage signal VL of a few negative kV applied via the terminal Lv in response to the input voltage Vin of ±tens of V and outputs the output voltage Vout at the terminal Out. 
     The terminal In is one example of an input terminal. The terminal Out is one example of an output terminal. The input voltage Vin applied to the high voltage amplifier circuit  1  at the terminal In is one example of a first voltage signal. The output voltage Vout delivered at the terminal Out is one example of a second voltage signal. 
     The light-emitting diode  71  included in the photocoupler  70  of the constant current circuit  50  is one example of a light-emitting device. The voltage signal VDH supplied to the anode terminal of the light-emitting diode  71  is one example of a constant voltage signal. The photoelectric converter  72  included in the photocoupler  70  is one example of a device which generates electricity in response to light. The output current from the photoelectric converter  72  is one example of a drive signal. A voltage developed across the resistor  54  in response to this output current is another example of a drive signal. The transistor  62  is one example of a first transistor. The gate terminal of the transistor  62  is one example of a first terminal. The drain terminal of the transistor  62  is one example of a second terminal. The source terminal of the transistor  62  is one example of a third terminal. The voltage signal VH supplied to the drain terminal of the transistor  62  via the transistor  61  is one example of an amplified voltage signal. 
     A configuration or combination including both the resistor  56  used to detect the amount of current flowing between the drain and source terminals of the transistor  62  and supplied to the terminal Out of the constant current circuit  50  and the transistor  63  controlling the supply of voltage to the gate terminal of the transistor  62  based on the detection performed using the resistor  56  is one example of a current control circuit. The transistor  33  whose drain terminal is electrically connected with the terminal Out via the transistor  32  is one example of a second transistor. 
     1.2 Advantageous Effects 
     In a conventional high voltage amplifier circuit, if an electric current needed to drive a MOS transistor is supplied from a photocoupler, the output current from the photocoupler is quite weak and, therefore, it takes a long time to store electrical charge in the input capacitance of the MOS transistor, making it difficult to achieve quick control of the high voltage amplifier circuit. 
     Faced with this problem, the high voltage amplifier circuit  1  of the present embodiment is so designed that a constant electrical current continues to be supplied to the electrical capacitance  59  via the photocoupler  70 , the capacitance  59  being equivalent to the input capacitance of the transistor  62  of the constant current circuit  50 , so that electrical charge is continually stored in the electrical capacitance  59 . As a result, if the operational state of the high voltage amplifier circuit  1  varies, e.g., if the output voltage Vout from the amplifier circuit  1  is varied in value, it is not necessary to store electrical charge in the electrical capacitance  59  whenever such a variation is made. As a result, it is possible that the value of the output voltage Vout exhibits high responsiveness to the request for the variation. 
     From a viewpoint of enhancing the efficiency at which the input capacitance of a transistor is electrically charged, the use of a power supply circuit capable of producing large output currents may be possible, in which case a high voltage resistance floating power supply is needed and thus there arises a concern that the circuit size of the high voltage amplifier circuit may increase. Furthermore, the coupling capacitance of the floating power supply increases the possibility that noise enters the high voltage amplifier circuit. 
     On the other hand, in the high voltage amplifier circuit  1  of the present embodiment, electrical current is supplied to the constant current circuit  50  using the light-emitting diode  71  and the photoelectric converter  72  operating in response to the light emitted by the diode  71 . Therefore, if the reference potential for operation of the constant current circuit  50  fluctuates, a large power circuit is not needed. As a result, the possibility that the high voltage amplifier circuit  1  increases in circuit size is reduced. Also, introduction of noise into the high voltage amplifier circuit  1  suppressed. 
     Furthermore, in the high voltage amplifier circuit  1  of the first embodiment, the amplified voltage output circuit  20  controls the amount of current flowing through the transistor  33 , whereby the value of the output voltage Vout delivered at the terminal Out can be controlled. This suppresses the output voltage Vout from experiencing crossover distortion. 
     1.3 Second Embodiment 
     A high voltage amplifier circuit  1  of a second embodiment is next described. Those components of this high voltage amplifier circuit  1  of the second embodiment which are similar to their counterparts of the high voltage amplifier circuit  1  of the first embodiment are indicated by the same reference numerals as in the above referenced figures and any repetitive detailed description thereof will hereinafter be simplified or omitted. 
       FIG.  2    shows one example of the configuration of the high voltage amplifier circuit  1  of the second embodiment. In the high voltage amplifier circuit  1  of the first embodiment shown in  FIG.  1   , the I/V converter circuit  200  is configured including the resistors  201 - 205  and the transistors  211 - 213 . On the other hand, in the high voltage amplifier circuit  1  of the second embodiment, the I/V converter circuit  200  is configured from an integrated circuit system  220  including an operational amplifier  221 . In other words, in the high voltage amplifier circuit  1  of the second embodiment, the I/V converter circuit  200  includes the integrated circuit system  220  having the operational amplifier  221 . 
     Because the I/V converter circuit  200  is made of the single integrated circuit system  220 , the converter circuit  200  is immune to noise. The accuracy of the voltage signal delivered to the transistor  33  by the I/V converter circuit  200  is improved. Also, the transistor  33  is driven with improved accuracy. In addition, the loss in the I/V converter circuit  200  is reduced. The capacitance of the power supply  209  can be made smaller than that of the high voltage amplifier circuit  1  of the first embodiment. This allows for miniaturization of the I/V converter circuit  200 . 
     As a result, the high voltage amplifier circuit  1  of the second embodiment yields the same operations and effects as those of the first embodiment. In addition, as the transistor  33  is driven with improved accuracy, the accuracy of the value of the output voltage Vout is improved. Also, the I/V converter circuit  200  and the high voltage amplifier circuit  1  including the converter circuit  200  can be reduced in circuit size. 
     2. Analyzer Apparatus 
     One example of an analyzer apparatus equipped with the above-described high voltage amplifier circuit  1  is next described.  FIG.  3    shows one example of configuration of an electron spectrometer  100  that is one example of the analyzer apparatus equipped with a plurality of high voltage amplifier circuits  1  of the construction described above. Furthermore, the spectrometer  100  has electrostatic lenses  151 ,  152  to which any one or more of output voltages Vout from the high voltage amplifier circuits  1  are supplied. 
     As shown in  FIG.  3   , the electron spectrometer  100  has high voltage amplifier circuits  1   a - 1   e , a controller  120 , a detector  130 , an input lens  150 , an energy analyzer  160 , an entrance slit  170 , an X-ray source  180 , and a power supply unit  181 . The electron spectrometer  100  analyzes a sample  140  in response to a manual control signal entered when a user manipulates a computer  110 . The X-ray source  180  emits X-rays at the sample  140 . As a result, photoelectrons, Auger electrons, and so on are released from the sample  140 . 
     The input lens  150  includes the electrostatic lenses  151  and  152  which focus the electrons (photoelectrons, Auger electrons, etc.) into the entrance slit  170 . The entrance slit  170  is located at the entrance of the energy analyzer  160  and operates to limit electrons incident on the energy analyzer  160 . 
     The energy analyzer  160  is operative to energy analyze the electrons released from the sample  140 . The energy analyzer  160  is an electrostatic hemispherical analyzer, for example, and has an inner hemispherical electrode  161  and an outer hemispherical electrode  162 . A prescribed voltage, for example, is applied between the hemispherical electrodes  161  and  162  to determine an electron pass energy. 
     The detector  130  detects electrons which have been energy analyzed by the energy analyzer  160 , and produces an output signal that is amplified by an amplifier and converted into a digital signal by an A/D converter. The digital signal is then sent to a processing section (not shown) of the controller  120 . Alternatively, the output signal from the detector  130  may be amplified by an amplifier in the controller  120  and converted into a digital signal by an A/D converter. The power supply unit  181  sends a control signal to the X-ray source  180  based on an instruction from the controller  120  to cause the X-ray source  180  to produce X-rays. 
     One high voltage amplifier circuit  1   a  out of the plural high voltage amplifier circuits  1  amplifies an input voltage Vin-a applied from the controller  120  to thereby generate an output voltage Vout-a of a high voltage of −4 kV to +1 kV, for example, and supplies it to the outer hemispherical electrode  162  of the energy analyzer  160 . 
     Another high voltage amplifier circuit  1   b  out of the plural high voltage amplifier circuits  1  amplifies an input voltage Vin-b applied from the controller  120  to thereby generate an output voltage Vout-b of a high voltage of −4 kV to +1 kV, for example, and supplies it to the inner hemispherical electrode  161  of the energy analyzer  160 . 
     A further high voltage amplifier circuit  1   c  out of the plural high voltage amplifier circuits  1  amplifies an input voltage Vin-c applied from the controller  120  to thereby generate an output voltage Vout-c of a high voltage of −4 kV to +1 kV, for example, and supplies it to the entrance slit  170 . 
     A yet high voltage amplifier circuit  1   d  out of the plural high voltage amplifier circuits  1  amplifies an input voltage Vin-d applied from the controller  120  to thereby generate an output voltage Vout-d of a high voltage of −1 kV to +15 kV, for example, and supplies it to the electrostatic lens  152 . 
     A still other high voltage amplifier circuit  1   e  out of the plural high voltage amplifier circuits  1  amplifies an input voltage Vin-e applied from the controller  120  to thereby generate an output voltage Vout-e of a high voltage of −1 kV to +15 kV, for example, and supplies it to the electrostatic lens  151 . 
     Where an analysis is performed over an energy range from 0 to 3,000 eV, for example, using the electron spectrometer  100  constructed as described thus far, if the energy range that passes through the energy analyzer  160  is set to 3,000 eV, the energy resolution in the analysis is restricted by the position sensing resolution of the detector  130 . In particular, if the detector  130  has 10 channels, for example, it follows that each channel detects energies over a wide range of about 300 eV. This creates the possibility that the resolution necessary for analysis may not be obtained. In the electron spectrometer  100 , therefore, an energy range that passes through the energy analyzer  160  is set to on the order of 10 eV, for example. Collection of a spectrum over a wide energy range is accomplished by detecting intensities with the detector  130  while varying the values of voltages supplied to the electrostatic lenses  151 ,  152 , inner hemispherical electrode  161 , outer hemispherical electrode  162 , and entrance slit  170  according to the energy to be analyzed. 
     However, where the values of the output voltages Vout-a to Vout-e from the high voltage amplifier circuits  1   a - 1   e  are varied, the timing at which there occurs a request for variations of the voltage values delivered from the controller  120  deviates from the timing at which the output voltages Vout-a to Vout-e delivered from the high voltage amplifier circuits  1   a - 1   e  to the electrostatic lenses  151 ,  152 , inner hemispherical electrode  161 , outer hemispherical electrode  162 , and entrance slit  170  reach their given voltage values owing to the responsiveness of the high voltage amplifier circuits  1   a - 1   e . That is, time differences occur. Therefore, if energy conditions for analysis are varied, a wait time is set into the electron spectrometer  100  to secure sufficient time for the output voltages Vout-a to Vout-e from the high voltage amplifier circuits  1   a - 1   e  to reach their given voltage values. 
     On the other hand, in the electron spectrometer  100  of the present embodiment, the output voltages Vout-a to Vout-e from the high voltage amplifier circuits  1   a - 1   e  exhibit excellent responsiveness to variations in the values of the input voltages Vin-a to Vin-e. This can shorten the wait time for the values of the output voltages Vout-a to Vout-e from the high voltage amplifier circuits  1   a - 1   e  to reach the given voltage values. Consequently, the electron spectrometer  100  of the present embodiment can perform energy analysis faster than in the prior art. 
     In the present embodiment, the electron spectrometer  100  is exemplified as one example of an analyzer apparatus. Analyzer apparatuses to which the high voltage amplifier circuit or circuits  1  are applicable are not restricted to the electron spectrometer  100  but rather the high voltage amplifier circuits  1  can be applied to various kinds of analyzer apparatuses including mass spectrometers, electron microscopes (such as a scanning electron microscope and a transmission electron microscope), and Auger electron microscopes. 
     While embodiments and modified embodiments of the present invention have been described thus far, the invention is not restricted thereto. Rather, the invention can be practiced in various aspects without departing from the gist of the invention. For example, the foregoing embodiments can be appropriately combined. 
     It is to be understood that the present invention embraces configurations (e.g., configurations identical in function, method, and results or identical in purpose and advantageous effects) which are substantially identical to the configurations described in the above embodiments. Furthermore, the invention embraces configurations which are similar to the configurations described in the above embodiments except that their nonessential portions have been replaced. Additionally, the invention embraces configurations which are identical in advantageous effects to, or which can achieve the same object as, the configurations described in the above embodiments. Further, the invention embraces configurations which are similar to the configurations described in the above embodiments except that a well-known technique is added.