Abstract:
There is provided an amplitude varying driver circuit operable to output an output signal, which is an amplified input signal being supplied. The amplitude varying driver circuit includes: a plurality of differential amplifiers provided in parallel with one another, wherein a signal corresponding to the input signal is input into each base terminal thereof; a resistor section, which is provided in series with the plurality of differential amplifiers, operable to establish potential of the output signal according to total current flowing to the plurality of differential amplifiers; and an amplitude control transistor, which is provided in series with the plurality of differential amplifiers, operable to define total current flowing to the plurality of differential amplifiers.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a test apparatus including an amplitude varying driver circuit which outputs an output signal according to an input signal, and an amplitude varying driver circuit. More particularly, the present invention relates to an amplitude varying driver circuit which outputs an output signal, which is an amplitude-changed input signal.  
         [0003]     2. Description of Related Art  
         [0004]     Conventionally, a circuit using a differential amplifier as a circuit for changing amplitude of an input signal and outputting the signal is known. Such a circuit controls a current flowing to the differential amplifier, and generates and outputs a potential of the output signal according to the current using a resistor connected to the differential amplifier in series.  
         [0005]     In such a circuit, when increasing amplitude varying range, change of the current flowing to the differential amplifier increases, and it is difficult to maintain quality of an output wave between a high amplitude output and a low amplitude output.  
         [0006]     Since a transition frequency of a transistor is dependent on a current flowing to the transistor, transition frequencies differ between a high amplitude output and a low amplitude output. Generally, a transistor, which is suitable for the transition frequency optimal for the high amplitude output, is selected. However, in such a case, the transition frequency for the low amplitude output will decrease, and sufficient switching characteristic will not be attained, and a waveform of the high frequency wave will deteriorate.  
         [0007]     On the other hand, when the transistor, which is suitable for the transition frequency optimal for the low amplitude output, is selected, the high amplitude output may exceed the limit of the collector current of the transistor.  
         [0008]     Therefore, it is an object of the present invention to provide an amplitude varying driver circuit and a test apparatus which can solve the problem of the conventional technology described above. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.  
       SUMMARY OF INVENTION  
       [0009]     To solve the above-mentioned problem, according to a first aspect of the present invention, there is provided an amplitude varying driver circuit operable to output an output signal, which is an amplified input signal being supplied. The amplitude varying driver circuit includes: a plurality of differential amplifiers provided in parallel with one another, wherein a signal corresponding to the input signal is input into each base terminal thereof; a resistor section, which is provided in series with the plurality of differential amplifiers, operable to establish potential of the output signal according to total current flowing to the plurality of differential amplifiers; and an amplitude control transistor, which is provided in series with the plurality of differential amplifiers, operable to define total current flowing to the plurality of differential amplifiers.  
         [0010]     The amplitude varying driver circuit may further include an amplitude control section operable to control the total current defined by the amplitude control transistor according to amplitude of the output signal to be output. Moreover, it may further include a drive control unit operable to control a current flowing to each of the differential amplifiers based on an amplitude of the output signal to be output, respectively.  
         [0011]     The amplitude varying driver circuit may further include a plurality of individual current control transistors, which are provided corresponding to and the differential amplifiers, wherein the plurality of individual current control transistors are provided in series with the corresponding differential amplifiers, wherein the drive control unit may control current flowing to the differential amplifier corresponding to the individual current control transistor by controlling the voltage applied to a base terminal of each of the individual current control transistors.  
         [0012]     The drive control unit may make the differential amplifiers of quantity according to amplitude of the output signal to be output operate. Moreover, the drive control unit may control current flowing to the operating differential amplifiers to be substantially the same as one another.  
         [0013]     The amplitude varying driver circuit may further include a pre-driver circuit operable to control amplitude of a signal input into each base terminal of the plurality of differential amplifiers according to amplitude of the output signal to be output. Moreover, it may further include a potential fixed transistor, which is provided between the resistor section and the plurality of differential amplifier, operable to apply voltage to a base terminal thereof.  
         [0014]     According to a second aspect of the present invention, there is provided a test apparatus operable to test an electronic device. The test apparatus includes: a pattern generating section operable to generate a test pattern for testing the electronic device; a waveform shaping section operable to generate an input signal to be input into the electronic device based on the test pattern; an amplitude varying driver circuit operable to input an output signal, which is the amplified input signal, into the electronic device; and a decision section operable to compare a signal output from the electronic device with a supplied expected value signal, and to decide acceptability of the electronic device, wherein the amplitude varying driver circuit includes: a plurality of differential amplifiers provided in parallel with one another, wherein a signal corresponding to the input signal is input into each base terminal thereof; a resistor section, which is provided in series with the plurality of differential amplifiers, operable to establish potential of the output signal according to total current flowing to the plurality of differential amplifiers; and an amplitude control transistor, which is provided in series with the plurality of differential amplifiers, operable to define total current flowing to the plurality of differential amplifiers.  
         [0015]     The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a drawing exemplary showing a configuration of a test apparatus  200  according to an embodiment of the present invention.  
         [0017]      FIG. 2  is a drawing exemplary showing a configuration of an amplitude varying driver circuit  100 .  
         [0018]      FIG. 3  is a drawing exemplary showing operation of the amplitude varying driver circuit  100  explained in  FIG. 2 .  
         [0019]      FIG. 4  is a drawing showing another example of a configuration of the amplitude varying driver circuit  100 .  
         [0020]      FIGS. 5A and 5B  are drawings exemplary showing operation of the amplitude varying driver circuit  100  explained in  FIG. 4 , in which  FIG. 5A  is a drawing exemplary showing operation of a pre-driver circuit  118 , and  FIG. 5B  is a drawing exemplary showing operation of each differential amplifier  106 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The invention will now be described based on preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiments are not necessarily essential to the invention.  
         [0022]      FIG. 1  is a drawing exemplary showing a configuration of a test apparatus  200  according to an embodiment of the present invention. The test apparatus  200  is an apparatus for testing an electronic devices  300 , such as a semiconductor circuit, and includes a pattern generating section  210 , a waveform shaping section  220 , a timing generating section  230 , an amplitude varying driver circuit  100 , and a decision section  240 . The pattern generating section  210  generates a test pattern for testing the electronic device  300 . The test pattern is a digital signal which is expressed by 1/0 patterns.  
         [0023]     The waveform shaping section  220  generates an input signal which is to be input into the electronic device  300  based on the test pattern. For example, the input signal having a voltage according to the test pattern is generated for each given timing.  
         [0024]     The timing generating section  230  generates a timing clock having desired frequency, and supplies it to the waveform shaping section  220 . The waveform shaping section  220  generates a voltage according to the test pattern according to a pulse of the timing clock.  
         [0025]     The amplitude varying driver circuit  100  inputs an output signal according to the input signal to the electronic device  300 . For example, the amplitude varying driver circuit  100  generates an output signal by changing the amplitude of the input signal according to the specification of the electronic device  300 .  
         [0026]     The decision section  240  compares the signal output from the electronic device  300  with the given expected value signal, and decides the acceptability of the electronic device  300 . The pattern generating section  210  may generate an expected value signal based on the test pattern.  
         [0027]      FIG. 2  is a drawing exemplary showing a configuration of the amplitude varying driver circuit  100 . The amplitude varying driver circuit  100  is a circuit which generates an output signal according to an input signal. The amplitude varying driver circuit  100  includes resistor sections ( 102 - 1 ˜ 102 - 2 , to be collectively referred to as  102  hereinafter), potential fixed transistors ( 103 - 1 ˜ 103 - 2 , to be collectively referred to as  103  hereinafter), a plurality of differential amplifier ( 106 - 1 ,  106 - 2 , . . . , to be collectively referred to as  106  hereinafter) provided in parallel, a pre-driver circuit  118 , a drive control unit  120 , an amplitude control section  122 , individual current control transistors ( 112 - 1 ˜ 112 - 2 , to be collectively referred to as  112  hereinafter), a amplitude control transistor  114 , and a resistor  116 .  
         [0028]     Each of the differential amplifiers  106  includes transistors  108  and  110  provided in parallel, and a signal according to the input signal is input into a base terminal of each transistor.  
         [0029]     The resistor sections  102  are provided in series with a plurality of differential amplifiers  106 . That is, these are provided in series to the differential amplifiers  106 , respectively. The resistor section  102 - 1  connects with the collector terminal of the transistor  108  of each of the differential amplifiers  106 , and the resistor section  102 - 2  connects with the collector terminal of the transistor  110  of each differential amplifier  106 . The resistor sections  102  generate potential of output signals (Vout 1 , Vout 2 ) according to the total current flowing to the plurality of differential amplifiers  106 .  
         [0030]     The amplitude control transistor  114  and each of the plurality of differential amplifiers  106  are provided in series, and specifies the total current flowing to the plurality of differential amplifiers  106 . That is, the amplitude of the output signal is settled according to the voltage applied to the base terminal of the amplitude control transistor  114 . In this example, the amplitude control transistor  114  connects with an emitter terminal of each of the differential amplifiers  106 , and the amplitude control transistor  114  is grounded via the resistor  116 .  
         [0031]     By such configuration, even if it is the case where a high amplitude output signal is to be output, required current can be distributed and the current flowing to one of the differential amplifiers  106  can be made low. Therefore, the waveform quality difference between the high amplitude signal and the low amplitude signal may be reduced.  
         [0032]     Moreover, the amplitude control section  122  controls the total current defined by the amplitude control transistor  114  according to the amplitude of the output signal to be output. That is, the voltage applied to the base terminal of the amplitude control transistor  114  is changed according to the amplitude of the output signal. By such control, the output signal having desired amplitude is generated.  
         [0033]     Moreover, the drive control unit  120  controls the current flowing to each differential amplifier  106  based on the amplitude of the output signal to be output, respectively. In this example, each of the individual current control transistors  112  is provided corresponding to each of the differential amplifiers, and is connected to the corresponding emitter terminal of the differential amplifier  106  in series. Then, the drive control unit  120  controls the current flowing to the differential amplifiers  106  corresponding to the individual current control transistors  112  by controlling the voltage applied to the base terminals of the individual current control transistors  112 , respectively.  
         [0034]     For example, the drive control unit  120  settles the quantity of the operating differential amplifiers  106  and controls each of the current control transistors  112  corresponding to the operating differential amplifiers  106  to ON state so that the current flowing to each of the differential amplifiers  106  becomes within a predetermined limit. The range of the current flowing to a differential amplifier  106  is predetermined within the range in which the differential amplifier  106  can operate properly.  
         [0035]     By such control, the current flowing to each of the differential amplifiers  106  can be controlled within the predetermined proper range, and the differential amplifiers  106  can be used in the proper current range. Therefore, the variation of the waveform quality between the high amplitude output and the low amplitude output can be reduced, and an output signal, of which the amplitude varies a lot, can be generated with sufficient accuracy.  
         [0036]     Moreover, the pre-driver circuit  118  controls the amplitude of the signals input into base terminals of the plurality of differential amplifiers  106  according to the amplitude of the output signal to be output. The pre-driver circuit  118  receives the input signals, changes the amplitudes of the input signals according to the amplitudes of the output signals to be output, and inputs them to the base terminals of the differential amplifiers  106 , respectively. For example, for the current flowing to each of the differential amplifier  106 , the pre-driver circuit  118  changes the amplitudes of the input signals, respectively, and inputs them so that the differential amplifiers  106  may operate properly. In this example, the pre-driver circuit  118  generates signals which are to be supplied to the base terminals of the differential amplifiers  106 .  
         [0037]     Moreover, the potential fixed transistors  103  are provided between the resistor sections  102  and the plurality of differential amplifiers  106 , and fixed voltage is applied to each base terminal. Thereby, the potential of the collector terminal of each of the differential amplifiers  106  can be maintained at substantially constant, and charge/discharge to/from the capacitance component by switching operation of the differential amplifiers  106  can be prevented. Therefore, the differential amplifiers  106  can be operated speedy with sufficient accuracy.  
         [0038]     In this example, when the current flowing to the amplitude control transistor  114  is within the predetermined proper current limit for a differential amplifier  106 , the drive control unit  120  makes only one differential amplifier  106  (the differential amplifier  106 - 1  in this example) to be operated. That is, the individual current control transistor  112 - 1  is controlled to be in ON state, and other individual current control transistors  112  are controlled to be in OFF state.  
         [0039]      FIG. 3  is a drawing exemplary showing operation of the amplitude varying driver circuit  100  explained with reference to  FIG. 2 . In  FIG. 3 , an axis of abscissa shows set values of the amplitude of the output signals, and an axis of ordinate shows the current flowing to each individual current control transistor  112 .  
         [0040]     When the total current of the drive control unit  120  flowing to the amplitude control transistor  114  is greater than larger than the proper current range of a differential amplifier  106 , the total current is divided by the upper limit of the proper current range, the differential amplifiers  106  of the quantity of the quotient of the division are made to operate at the upper limit of the proper current range (straight line of the current waveform in  FIG. 3 ), and the current, of which the value is equal to the remainder of the differential, flows to another differential amplifier  106  (curved section of the current waveform in  FIG. 3 ). That is, each of the individual current control transistors  112  are controlled so that tail current may flow to a pair of each of the differential amplifiers  106  in order as the set amplitude of the output signal increases.  
         [0041]     At this time, the pre-driver circuit  118  supplies signals according to the input signals to the base terminals of the operating differential amplifiers  106 .  
         [0042]     By such control, when the total current flowing to the amplitude control transistor  114  is high, current can be dispersedly flows to the plurality of differential amplifiers  106 . Therefore, each of the differential amplifiers  106  can be made to operate in the proper current range.  
         [0043]      FIG. 4  is a drawing showing another example of a configuration of the amplitude varying driver circuit  100 . The amplitude varying driver circuit  100  in this example includes the same configuration as the amplitude varying driver circuit  100  explained with reference to  FIG. 2  except for the pre-driver circuit  118 .  
         [0044]     Although the pre-driver circuit  118  in  FIG. 2  generates signals to the base terminals of the differential amplifiers  106 , respectively, the pre-driver circuit  118  in this example generates a common signal to the differential amplifiers  106  and supplies it. Like the case explained with reference to  FIG. 2 , the pre-driver circuit  118  changes the amplitudes of the input signals, respectively, and inputs them so that each of the differential amplifiers  106  may operate properly. For example, the amplitudes of the input signals are made to vary in proportion to the set amplitudes of the output signals.  
         [0045]     Moreover, according to this example, the drive control unit  120  controls the individual current control transistors  112  so that tail current may flow to a pair of each of the differential amplifiers  106  in order as the set amplitude of the output signal increases as is explained in  FIG. 3 . Thereby, each of the differential amplifiers  106  can be made to operate in the proper current range by simple control.  
         [0046]     Moreover, according to the configuration shown in  FIG. 4 , the drive control unit  120  may control each of the individual current control transistors  112  so that the current flowing to the operating differential amplifiers  106  may be substantially the same as one another. Next, operation of the amplitude varying driver circuit  100  in the case of substantially the same current flows to each of the differential amplifiers  106  will be explained.  
         [0047]      FIGS. 5A and 5B  are drawings exemplary showing operation of the amplitude varying driver circuit  100  explained with reference to  FIG. 4 .  FIG. 5A  is a drawing exemplary showing operation of the pre-driver circuit  118 , and  FIG. 5B  is a drawing exemplary showing operation of the individual current control transistors  112 . Moreover, in  FIG. 5A , an axis of abscissa indicates set-up values of the amplitude of the output signals, and an axis of ordinate indicates set-up values of the amplitudes of the signals output from the pre-driver circuit  118 . Moreover, in  FIG. 5B , an axis of abscissa indicates set-up values of the amplitudes of the output signals, and an axis of ordinate indicates the current flowing to the individual current control transistors  112 .  
         [0048]     The drive control unit  120  makes only one differential amplifier  106  operate when the current flowing to the amplitude control transistor  114  is within the predetermined proper current for a differential amplifier  106  (the differential amplifier  106 - 1  in this example). That is, the individual current control transistor  112 - 1  is controlled to be in ON state, and other individual current control transistors  112  are controlled to be in an OFF state.  
         [0049]     Then, the pre-driver circuit  118  amplifies the input signal according to the set amplitude of the output signal and supplies it to the base terminal of each of the differential amplifiers  106 . At this time, the current flowing to the differential amplifier  106 - 1  is equal to the current I which flows to the amplitude control transistor  114 .  
         [0050]     Moreover, when the total current flowing to the amplitude control transistor  114  is greater than the proper current range of a differential amplifier  106 , the drive control unit  120  divides the total current by the upper limit of the proper current range, and the differential amplifiers  106  of the quantity of the raised quotient of the division are made to operate. That is, the individual current control transistors  112  corresponding to the differential amplifiers  106  are controlled in the ON state. Then, it is controlled so that the current flowing to the operating differential amplifiers  106  becomes substantially the same as one another. Since the range of fluctuation of current flowing to each of the differential amplifier  106  becomes small according to such control, the output signal having large varying amplitude range is generable with sufficient accuracy.  
         [0051]     Moreover, as shown in  FIG. 5A , when the quantity of the operating differential amplifier  106  changes, the pre-driver circuit controls the amplitudes of the signals supplied to the base terminals of the operating differential amplifiers  106  so that the continuity of the total current flowing to the operating differential amplifiers  106  may be maintained.  
         [0052]     Although the present invention has been described by way of an exemplary embodiment, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention. It is obvious from the definition of the appended claims that embodiments with such modifications also belong to the scope of the present invention.  
         [0053]     As is apparent from the above-mentioned explanation, according to the present invention, variation in waveform quality between a high amplitude output and a low amplitude output can be reduced, and an output signal having wide varying amplitude range can be generated with sufficient accuracy.