Abstract:
A waveform controller for an IC tester includes selectors and OR circuits for incorporating an edge of a strobe signal into a driver signal system and allows the use of the edge of the strobe signal as a driver signal edge for driver pins.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a waveform controller for generating various waveforms for an IC tester. 
     2. Description of the Related Art 
     Explanation is presented with reference to the figures regarding the prior art. 
     Explanation is first presented regarding an embodiment of a semiconductor IC tester described in Japanese Patent Laid-open No. 110357/95 as an example of a prior-art waveform controller for an IC tester. 
     FIG. 1 is a circuit diagram showing the construction of the prior art, and FIG. 2 is a chart showing the waveform generated by the prior art. 
     The three edge signals T 1 -T 3  are each outputted at times corresponding to a desired timing edge by a timing generator (not shown). A control signal transmitted from waveform memory (not shown) is supplied to another terminal of AND gate  12  not shown in the figure. The various waveforms for an IC tester are produced by the time settings of signals T 1 -T 3  and the content of waveform memory. Here, waveform memory stores waveform data for forming waveforms. 
     Signals T 1 -T 3  pass through skew variable regulators  11   1 - 11   3 , respectively, and are inputted to AND gates  12 S and  12 R. The output from the AND gates  12 S are transmitted to OR gate  14 S through a respective skew regulator  13 S. The output from the AND gates  12 R are similarly transmitted to OR gate  14 R through skew regulators  13 R. A set signal is outputted from OR gate  14 S, and a reset signal is outputted from OR gate  14 R. 
     Signal T 3  is also outputted as signal DREL through skew variable regulator  11   3 , AND gate  12   3 , and skew regulator  13   3 . Signal T 4  is outputted as signal DRET through skew variable regulator  11   4 , AND gate  12   4 , and skew regulator  13   4 . Signals T 5  and T 6  are both used as strobe signals. 
     In a per-pin tester of the prior art, since waveforms are generated to output three edge signals for set signals and three edge signals for reset signals in each cycle as shown in FIG. 2, as for SBC (Surrounded by Complement) waveforms to a driver, three edge signals T 1 -T 3  of FIG. 1 are split into two to obtain each set and reset signals. As a result, two systems of skew regulators must be provided for one edge signal. 
     SUMMARY OF THE INVENTION 
     In view of the problem of the prior art, it is an object of the present invention to provide a waveform controller for an IC tester with the purpose of decreasing the number of skew regulators to half or fewer than the number used in the prior art and thus reducing both circuit scale and power consumption. 
     As a solution to the above-described problem, the present invention provides a waveform controller for an IC tester that includes selectors and OR circuits for inserting strobe-signal edge signals into the driver signal system, and thus allows an edge signal for strobes to be used as a driver signal edge for driver pins. 
     The present invention allows the number of provided skew regulators to be reduced to half the number or fewer than are used in the prior art by using strobe-signal edge signals as driver waveform edges when using for pins dedicated to the driver, and the invention therefore has the effect of reducing both circuit scale and power consumption. 
     The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings which illustrate examples of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing the construction of the prior art; 
     FIG. 2 is a chart showing the waveforms generated by the prior art; 
     FIG. 3 is a circuit diagram showing the construction of an embodiment of the present invention; and 
     FIG. 4 is a chart showing the waveforms generated by the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Explanation is next presented regarding embodiments of the present invention with reference to the accompanying figures. 
     FIG. 3 is a circuit diagram showing the construction of an embodiment of the present invention, and FIG. 4 is a chart showing the waveforms generated by the embodiment. 
     In the prior art, only three edge signals T 1 -T 3  were used as SBC waveform outputs to driver pins. Edge signals for the comparator strobe (Signals T 5  and T 6  in FIG. 1) were therefore not used in the SBC waveform to driver pins. 
     In this embodiment of the present invention, six edge signals T 1 -T 6  are used for driver pins by using selectors  2  and OR gates  4  as shown in FIG. 3 to insert signals T 5  and T 6  into the set and reset system. 
     The six signals T 1 -T 6  are each outputted by a timing generator (not shown) at timings that correspond to the desired edge signals. A control signal transmitted from waveform memory (not shown in the figure) is supplied to another terminal of AND gate  3  not shown in the figure. Each of the waveforms for IC tester use are then produced by the timing settings of signals T 1 -T 6  and the content of waveform memory. 
     Signals T 1 -T 4  are inputted to AND gates  3   1 - 3   4  through skew variable regulator  1   1 - 1   4 , respectively, and signals T 3  and T 5 -T 6  are input to AND gates  3   5  and  3   6  through skew variable regulators  1   3  and  1   5 - 1   6  and selectors  2 S and  2 R. Specifically, selector  2 S switches between and selects either signal T 3  or signal T 5 , and selector  2 R switches between and selects either signal T 3  or signal T 6 , and selector  2 R switches between and selects either signal T 3  or signal T 6  in accordance with signal DRMOD that is set to driver-dedicated pins that do not use a strobe. Selector  2 S then outputs to AND gate  3   5 , and selector  2 R outputs to AND gate  3   6 . 
     OR gate  4 S sets either signal T 1  from AND gate  3   1  or signal T 5  from AND gate  3   5  as the set signal and outputs the selected signal, and OR gate  5 S sets one of signal T 1 , signal T 5 , and signal T 3  from AND gate  3   3  as set signal and outputs the selected signal. OR gate  4 R similarly sets either signal T 2  from AND gate  3   2  or signal T 6  from AND gate  3   6  as a reset signal and outputs the selected signal , and OR gate  5 R sets one of signal T 2 , signal T 6 , and signal T 4  from AND gate  3   4  as reset signal and outputs the selected signal. 
     The output signals of OR gate  5 R and OR gate  5 S are respectively inputted to the reset (R) and set (S) terminals of Set/Reset-flip-flop  6  provided in the following section, and further, are impressed through driver  7  to each driver pin of the IC element under test as the test waveform shown in FIG.  4 . 
     Since each of outputted edge signals T 1 -T 6  can be used fixed as a set signal or reset signal, the skew regulators for one edge signal can be reduced to just one system, and two systems of skew regulators, i.e., one for set signals and the other for reset signals, need not be provided for one edge signal as in the prior art. 
     While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.