Patent Publication Number: US-2007103174-A1

Title: Direct current test apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This patent application incorporates herein by reference the contents of a Japanese Patent Application No. 2004-133955 filed on Apr. 28, 2004, if applicable.  
     BACKGROUND  
      1. Field of the Invention  
      The present invention relates to a direct current (DC) test apparatus for performing a DC test on an electronic device. This patent application incorporates herein by reference the contents of a Japanese Patent Application No. 2004-133955 filed on Apr. 28, 2004, if applicable.  
      2. Related Art  
      Typical test methods used for testing electronic devices such as semiconductor circuits include direct current (DC) tests. Examples of the DC tests are a voltage-application current-measurement test in which a predetermined DC voltage is applied to an electronic device, and a DC voltage supplied to the electronic device as a result of the voltage application is measured, and a current-application voltage-measurement test in which a predetermined DC current is applied to an electronic device, and a DC voltage supplied to the electronic device as a result of the current application is measured.  
       FIG. 1  shows the construction of a typical DC test apparatus  200 . The DC test apparatus  200  performs a voltage-application current-measurement test on an electronic device  300 . The DC test apparatus  200  includes therein a power supply  202 , an amplifier  210 , a plurality of current detecting resistances ( 206 - 1  to  206 - n , n is an integer of 2 or more), an amplifier  212 , and an analog to digital converter (ADC)  204 . The power supply  202  generates a predetermined voltage. The amplifier  210  amplifies the voltage generated by the power supply  202 , and outputs the amplified voltage. The plurality of current detecting resistances  206  respectively provide the same resistance, and are connected in parallel with each other between the amplifier  210  and the electronic device  300 .  
      The voltage applied to the electronic device  300  is fed back into the amplifier  210  so that the amplifier  210  generates a predetermined DC voltage. Here, the amplifier  212  outputs a voltage determined in accordance with a difference in potential between the ends of the current detecting resistances  206 , and the ADC  204  measures a DC current supplied to the electronic device  300  on the basis of the voltage output from the amplifier  212 .  
      Since no patent and other documents related to the present invention have been found, recitation of such documents will be omitted.  
      In the typical DC test apparatus  200 , the amplifiers  210  and  212  are formed on the same semiconductor chip  208 , and the current detecting resistances  206  are formed outside the semiconductor chip  208 . This design results in the DC test apparatus  200  of large size for the following reason. To make the measurement range for the DC current variable, it is required to provide switches to connect/disconnect the plurality of current detecting resistances  206  and to vary the measurement range by switching the respective switches. Therefore, the typical DC test apparatus  200  needs a large circuit separately from the semiconductor chip  208 .  
      In addition, the current detecting resistances  206  need to be fabricated by using the wafer fabrication process in order to be formed on the semiconductor chip  208 . However, the wafer fabrication process has difficulties in forming resistances of small temperature coefficient. Consequently, the resistance value of the current detecting resistances  206  is affected to vary by the change in temperature of the semiconductor chip  208 . This reduces the accuracy in measuring the current.  
     SUMMARY  
      An advantage of some aspects of the present invention is to provide a test apparatus that can solve the above-stated problems. This is achieved by combining the features recited in the independent claims. The dependent claims define further effective specific example of the present invention.  
      A first embodiment of the present invention provides a DC test apparatus for performing a test by applying a DC voltage and a DC current to an electronic device. The DC test apparatus includes a power supply generating section that generates the DC voltage and the DC current, a current detecting resistance provided in series between the power supply generating section and the electronic device, and a current detecting section that detects a level of the DC current based on a difference in potential between ends of the current detecting resistance. Here, the current detecting section includes a reference resistance that has a smaller temperature coefficient than the current detecting resistance, and a temperature compensating section that detects the level of the DC current by multiplying the difference in potential between the ends of the current detecting resistance with a coefficient determined in accordance with a ratio between a resistance value of the current detecting resistance and a resistance value of the reference resistance.  
      The temperature compensating section may have a current detecting amplifier that outputs a voltage determined in accordance with the difference in potential between the ends of the current detecting resistance, an artificial resistance connected in series to an output end of the current detecting amplifier, where the artificial resistance has substantially the same temperature coefficient as the current detecting resistance, and a temperature compensating amplifier that amplifies the voltage output from the current detecting amplifier at an amplification rate determined in accordance with a ratio between a resistance value of the artificial resistance and the resistance value of the reference resistance, and outputs the amplified voltage.  
      A plurality of the current detecting resistances may be provided in parallel with each other between the power supply generating section and the electronic device. It is preferable that the power supply generating section, the current detecting resistance, the current detecting amplifier, the artificial resistance, and the temperature compensating amplifier are formed on the same semiconductor chip, and that the reference resistance is formed outside the semiconductor chip. The current detecting resistance and the artificial resistance may be formed by the same wafer fabrication process.  
      The temperature compensating amplifier may be a differential amplifier, and a positive input terminal of the temperature compensating amplifier may be grounded. The artificial resistance may be provided in series between a negative input terminal of the temperature compensating amplifier and an output terminal of the current detecting amplifier. The reference resistance may be provided in series between an output terminal and the negative input terminal of the temperature compensating amplifier.  
      The DC test apparatus may further include a feedback section that feeds back a voltage applied to the electronic device into the power supply generating section and controls the DC voltage generated by the power supply generating section to be a predetermined voltage, and a measuring section that measures the DC current based on the voltage output from the temperature compensating amplifier. The power supply generating section may control the DC current to be a predetermined current based on the voltage output from the temperature compensating section, and the DC test apparatus may further include a measuring section that measures a voltage applied to the electronic device.  
      Here, all the necessary features of the present invention are not listed in the summary of the invention. The sub-combinations of the features may also become the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows the construction of the typical DC test apparatus  200 .  
       FIG. 2  shows an example of the construction of a DC test apparatus  100  relating to an embodiment of the present invention.  
       FIG. 3  shows another example of the construction of the DC test apparatus  100 . 
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Hereinafter, some embodiments of the present invention will be described. The embodiments do not limit the invention according to the claims, and all the combinations of the features described in the embodiments are not necessarily essential to means provided by aspects of the invention.  
       FIG. 2  shows an example of the construction of a DC test apparatus  100  relating to an embodiment of the present invention. The DC test apparatus  100  performs a test by applying a DC voltage and a DC current to an electronic device  300  which is, for example, a semiconductor device. The DC test apparatus  100  includes therein a power supply  10 , an analog to digital converter (ADC)  12 , a plurality of switches ( 22 ,  24 ,  26  and  28 ), a power supply generating section  30 , a plurality of current detecting resistances ( 32 - 1  to  32 - n , n is an integer of 2 or more), a current detecting section  40 , and a feedback line  48 .  
      The following first briefly describes operations of the test apparatus  100  for performing a voltage-application current-measurement test, where a predetermined DC voltage is applied to the electronic device  300 , and a DC current supplied to the electronic device  300  as a result of the voltage application is measured. When the test apparatus  100  conducts this type of test, the switches  22  and  28  are short-circuited, and the switches  24  and  26  are opened.  
      The power supply  10  generates a predetermined voltage, and the power supply generating section  30  generates a DC voltage determined in accordance with the voltage applied by the power supply  10 . Here, each of the plurality of current detecting resistances  32  is provided in series with the output terminal of the power supply generating section  30  and the input terminal of the electronic device  300  so as to be positioned therebetween. In other words, the current detecting resistances  32  are provided in parallel with each other so as to be positioned between the power supply generating section  30  and the electronic device  300 .  
      The feedback line  48  feeds back the voltage applied to the electronic device  300  into the power supply generating section  30  via the switch  22  so that the power supply generating section  30  generates a predetermined DC voltage. Which is to say, the feedback line  48  and switch  22  together function as a feedback section in the embodiment of the present invention. The power supply generating section  30  is a differential amplifier, for example, and receives the voltage generated by the power supply  10  at its positive input terminal and the voltage fed back by the feedback section at its negative input terminal. Based on such a configuration, the power supply generating section  30  applies a predetermined DC voltage to the electronic device  300 .  
      The current detecting section  40  detects the level of the DC current supplied to the electronic device  300  on the basis of the difference in potential between the ends of the current detecting resistances  32 . To be specific, according to the present embodiment, the current detecting section  40  detects the current flowing one current detecting resistance  32  on the basis of the potential difference. Then, the current detecting section  40  multiplies the detected current with the number of the current detecting resistances  32  connected in parallel, so as to measure the DC current supplied to the electronic device  300 . Here, the test apparatus  100  may additionally include therein switches to vary the number of the current detecting resistances  32  connected in parallel. If such is the case, the test apparatus  100  can alter the measurement range for the DC current by setting the number of the current detecting resistances  32  connected in parallel at different values.  
      The ADC  12  receives, via the switch  28 , a voltage which the current detecting section  40  outputs in accordance with the detected current, and measures the DC current supplied to the electronic device  300  by analog-to-digital converting the voltage. In other words, the ADC  12  functions as a measuring section for measuring the DC current on the basis of the voltage output from a temperature compensating amplifier  38 .  
      The following briefly describes operations of the test apparatus  100  for performing a current-application voltage-measurement test, where a predetermined DC current is applied to the electronic device  300 , and a DC voltage supplied to the electronic device  300  as a result of the current application is measured. When the test apparatus  100  conducts this type of test, the switches  22  and  28  are opened, and the switches  24  and  26  are short-circuited.  
      The power supply  10  generates a predetermined voltage, and the power supply generating section  30  generates a DC current determined in accordance with the voltage applied by the power supply  10 . Here, the power supply generating section  30  is supplied, at its negative input terminal, with a voltage determined in accordance with the current detected by the current detecting section  40 . With such a configuration, the power supply generating section  30  can supply a predetermined DC current to the electronic device  300 . The ADC  12  analog-to-digital converts the voltage that is applied to the electronic device  300  as a result of the application of the predetermined DC current to the electronic device  300 , so as to measure the DC voltage. In other words, the ADC  12  functions as a measuring section for measuring the DC voltage applied to the electronic device  300 .  
      The following explains the construction of the current detecting section  40 . The current detecting section  40  includes therein a temperature compensating section  50  and a reference resistance  14 . The reference resistance  14  has a smaller temperature coefficient than the current detecting resistances  32 . Which is to say, the reference resistance  14  exhibits a smaller change in resistance value when the surrounding temperature changes, when compared to the current detecting resistances  32 .  
      The temperature compensating section  50  detects the level of the DC current supplied to the electronic device  300  by multiplying the difference in potential between the ends of the current detecting resistances  32  with a coefficient determined in accordance with the ratio between the resistance value of the current detecting resistances  32  and the resistance value of the reference resistance  14 . For example, the temperature compensating section  50  multiplies the potential difference between the ends of the current detecting resistances  32  with a coefficient obtained by dividing the resistance value of the reference resistance  14  by the resistance value of the current detecting resistances  32 . In this manner, the temperature compensating section  50  can prevent the degradation in the current detecting accuracy which results from a change in the resistance value of the current detecting resistances  32  caused by a change in the surrounding temperature.  
      According to the present embodiment, the temperature compensating section  50  includes therein a current detecting amplifier  34 , an artificial resistance  36 , and a temperature compensating amplifier  38 . The current detecting amplifier  34  outputs a voltage determined in accordance with the potential difference between the ends of the current detecting resistances  32 . The artificial resistance  36  is connected in series to the output end of the current detecting amplifier  34 . Here, the artificial resistance  36  has substantially the same temperature coefficient as the current detecting resistances  32 .  
      The temperature compensating amplifier  38  amplifies the voltage output from the current detecting amplifier  34  at an amplification rate determined in accordance with the ratio between the resistance value of the artificial resistance  36  and the resistance value of the reference resistance  14 , and outputs the amplified voltage. Here, the temperature compensating amplifier  38  is a differential amplifier, for example, and its positive input terminal is grounded. The artificial resistance  36  is connected in series between the negative input terminal of the temperature compensating amplifier  38  and the output terminal of the current detecting amplifier  34 . The reference resistance  14  is provided in series between the output terminal and the negative input terminal of the temperature compensating amplifier  38 .  
      Here, it is preferable that the power supply generating section  30 , current detecting resistances  32 , current detecting amplifier  34 , artificial resistance  36 , temperature compensating amplifier  38 , switches  22 ,  24 ,  26  and  28 , and feedback line  48  are formed on the same semiconductor chip  20 , and that the reference resistance  14  is formed outside the semiconductor chip  20 . Being provided outside the semiconductor chip  20 , the reference resistance  14  which has a small temperature coefficient can be formed easily. In addition, despite the provision of the plurality of current detecting resistances  32 , the test apparatus  100  can perform temperature compensation with it being possible to achieve small circuit scale. This is because temperature compensation can be made possible by providing one reference resistance  14  outside the semiconductor chip  20 .  
      The current detecting resistances  32  and artificial resistance  36  can be formed by the same wafer fabrication process. Being manufactured by the same wafer fabrication process, the current detecting resistances  32  and artificial resistance  36  can be easily configured to have substantially the same characteristics. Here, the artificial resistance  36  is preferably located in the vicinity of the current detecting resistances  32 .  
      As described above, when the resistance value of the current detecting resistances  32  changes due to the change in temperature, the current detecting section  40  relating to the present embodiment can compensate the change in the resistance value, thereby enabling highly accurate current detection. Because of this advantage, the current detecting section  40  can accurately measure the DC current when performing a voltage-application current-measurement test, and can accurately generate the DC current when performing a current-application voltage-measurement test.  
       FIG. 3  shows another example of the construction of the DC test apparatus  100 . The DC test apparatus  100  relating to this embodiment includes therein resistances  42  and  44 , and an amplifier  46  in addition to the constituents of the DC test apparatus  100  relating to the previous embodiment illustrated with reference to  FIG. 2 . The power supply generating section  30  relating to the present embodiment is an inverting differential amplifier. The negative input terminal of the power supply generating section  30  receives the voltage generated by the power supply  10  via the resistance  42 , and the positive input terminal is grounded.  
      When the DC test apparatus  100  performs a voltage-application current-measurement test, the feedback line  48  feeds back the DC voltage into the negative input terminal of the power supply generating section  30  via the amplifier  46 , switch  22 , and resistance  44 . When the DC test apparatus  100  performs a current-application voltage-measurement test, the current detecting section  40  feeds back the DC current into the negative input terminal of the power supply generating section  30  via the switch  24  and resistance  44 .  
      The DC test apparatus  100  having the above-described construction can also perform temperature compensation with it being possible to achieve a small circuit scale, similarly to the DC test apparatus  100  illustrated with reference to  FIG. 2 .  
      While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alternations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alternations or improvements can be included in the technical scope of the invention.  
      As clearly indicated above, some embodiments of the present invention can provide a DC test apparatus of small circuit scale which can perform temperature compensation for current detection accuracy.