Patent Abstract:
A scan test generation method includes dividing a single clock domain into a plurality of regions; incorporating a test pattern generation control circuit in each of the regions; selecting one of a skewed-load mode and a broadside mode as a test pattern generation mode by the test pattern generation control circuit for each region; generating a test pattern determined based on selected one of the test pattern generation mode for each region; and generating a test pattern such that the skewed-load mode and the broadside mode are mixed in a single clock domain.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Continuation application of U.S. patent application Ser. No. 13/842,370, filed on Mar. 15, 2013, which is based on Japanese Patent Application Nos. 2012-065077 filed on Mar. 22, 2012, and 2012-223947 filed on Oct. 9, 2012, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a scan test circuit which can be suitably used as a scan test circuit that executes a delay fault test, for example. 
         [0003]    In recent years, there is a tendency toward a reduction in the area and cost of semiconductor integrated circuits. To reduce the test time and percent defective which affect the cost, almost all types of semiconductor integrated circuits have been subjected a scan test for a delay fault. Modes for generating a test pattern for use in a scan test for a delay fault (hereinafter referred to as “delay fault test pattern”) include a broadside mode and a skewed-load mode. The delay fault test pattern is generally generated using the broadside mode in terms of ease of design. However, the broadside mode has a problem that the number of test patterns is relatively increased as compared with the skewed-load mode, and it is difficult to increase a delay fault coverage. For this reason, there is an increasing demand for reducing the number of delay fault test patterns and improving the test quality to reduce the test cost, by generating a delay fault test pattern using the skewed-load mode, though there are many restrictions in design in the skewed-load mode. 
         [0004]    Japanese Unexamined Patent Application Publication No. 2008-096440 discloses a configuration in which one or more normal scan FFs are replaced with extended scan FFs in a scan chain including a plurality of normal scan FFs. Japanese Unexamined Patent Application Publication No. 2008-096440 also discloses a technique in which extended scan FFs are controlled in the skewed-load mode and normal scan FFs are controlled in the broadside mode. Assume herein that a component area occupied by the extended scan FFs is larger than a component area occupied by the normal scan FFs. 
       SUMMARY 
       [0005]    In the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440, it is necessary to increase the number of normal scan FFs to be replaced with extended scan FFs so as to fully obtain the effects of improving the delay fault coverage and reducing the number of delay fault test patterns. Accordingly, the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 has a problem that if the effects of reducing the number of delay fault test patterns and improving the delay fault coverage are fully obtained, an area overhead (hereinafter, referred to as “area OH”) is increased. Other problems and new features become evident from the description of the specification and the accompanying drawings. 
         [0006]    According to an aspect of the present invention, a delay fault test pattern generation control circuit includes: a test pattern generation mode control unit that is supplied with a clock identical with the clock supplied to a clock domain (logic circuit) to be controlled, and selects one of a skewed-load mode and a broadside mode as a test pattern generation mode; and a scan enable signal output unit that outputs a scan enable signal, which is determined based on the test pattern generation mode, to the clock domain (logic circuit). 
         [0007]    According to the above-mentioned aspect of the present invention, it is possible to improve the delay fault coverage without increasing the area overhead. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other aspects, advantages and features will be more apparent from the following description of certain embodiments taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1A  is a block diagram of a logic circuit according to a first embodiment; 
           [0010]      FIG. 1B  is a block diagram of a multiplexer-type scan flip-flop according to the first embodiment; 
           [0011]      FIG. 1C  is a block diagram of a delay fault test pattern generation control circuit according to the first embodiment; 
           [0012]      FIG. 2  is a timing diagram for generating a skewed-load mode test pattern according to the first embodiment; 
           [0013]      FIG. 3  is a timing diagram for generating a broadside mode test pattern according to the first embodiment; 
           [0014]      FIG. 4  is a block diagram of a delay fault test pattern generation control circuit according to a second embodiment; 
           [0015]      FIG. 5A  is a block diagram of a delay fault test pattern generation control circuit according to a third embodiment; 
           [0016]      FIG. 5B  is a block diagram of a logic circuit according to the third embodiment; 
           [0017]      FIG. 6  is a block diagram of a delay fault test pattern generation control circuit according to a fourth embodiment; 
           [0018]      FIG. 7  is a timing diagram for generating a test pattern according to the fourth embodiment; 
           [0019]      FIG. 8  is a timing diagram for generating a test pattern according to the fourth embodiment; 
           [0020]      FIG. 9  is a timing diagram for generating a test pattern according to the fourth embodiment; 
           [0021]      FIG. 10A  is a block diagram of a delay fault test pattern generation control circuit according to a fifth embodiment; 
           [0022]      FIG. 10B  is a circuit block diagram of a clock gating cell (CGC  65 ) according to the fifth embodiment; 
           [0023]      FIG. 10C  is a block diagram of the delay fault test pattern generation control circuit according to the fifth embodiment; 
           [0024]      FIG. 11  is a timing diagram for generating a test pattern according to the fifth embodiment; 
           [0025]      FIG. 12  is a block diagram of a delay fault test pattern generation control circuit according to a sixth embodiment; 
           [0026]      FIG. 13  is a block diagram of a delay fault test pattern generation control circuit according to a seventh embodiment; 
           [0027]      FIG. 14  is a timing diagram for generating a test pattern according to the seventh embodiment; 
           [0028]      FIG. 15  is a block diagram of a delay fault test pattern generation control circuit according to an eighth embodiment; 
           [0029]      FIG. 16  is a block diagram of a delay fault test pattern generation control circuit according to a ninth embodiment; and 
           [0030]      FIG. 17  is a block diagram of a delay fault test pattern generation control circuit according to a tenth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       [0031]    Embodiments of the present invention will be described below with reference to the drawings. Referring to  FIGS. 1A ,  1 B, and  1 C, a configuration example of a scan test circuit including a delay fault test pattern generation control circuit  200  and a logic circuit  201  will be described. The logic circuit  201  is controlled using the delay fault test pattern generation control circuit  200 . 
         [0032]    The logic circuit  201  includes scan FFs (SF  3 , SF  4 , SF  5 , SF  6 , SF  7 , and SF  8 ) forming a scan chain (C 1 ); an AND gate (AND)  11 , an AND  12 , and an inverter (INV)  21 , each of which is a combinational circuit for connecting the SFs; and a transition delay fault (TDF) that is defined at a data input terminal A of the AND  12 . 
         [0033]    A scan-in terminal (SI) and a data output terminal (Q) of each SF of the logic circuit  201  are connected as follows in the order of the configuration of the scan chain (C 1 ). That is, for example, the scan-in terminal (SI) of the SF  3 —the data output terminal (Q) of the SF  3 —the scan-in terminal (SI) of the SF  4 —the data output terminal (Q) of the SF  4 —the scan-in terminal (SI) of the SF  5 —the data output terminal (Q) of the SF  5 —the scan-in terminal (SI) of the SF  6 —the data output terminal (Q) of the SF  6 —the scan-in terminal (SI) of the SF  7 —the data output terminal (Q) of the SF  7 —the scan-in terminal (SI) of the SF  8 —the data output terminal (Q) of the SF  8 —a scan-out signal (SOT) for scan chain. 
         [0034]    A clock terminal (CLK) of each SF of the logic circuit  201  is connected to a signal line for an external clock signal (CLK). A scan enable terminal (SMC) of each SF of the logic circuit  201  is connected to a local scan enable terminal (LSMC) of the delay fault test pattern generation control circuit  200 . 
         [0035]    A data input terminal (A) of the AND  11  is connected to the data output terminal (Q) of the SF  8 . A data input terminal (B) of the AND  11  is connected to the data output terminal (Q) of the SF  7 . A data output terminal (Z) of the AND  11  is connected to a data input terminal (D) of the SF  3 . 
         [0036]    The data input terminal (A) of the AND  12  is connected to the data output terminal (Q) of the SF  3 . The data input terminal (B) of the AND  12  is connected to the data output terminal (Q) of the SF  4 . The data output terminal (Z) of the AND  12  is connected to the data input terminal (D) of the SF  5 . 
         [0037]    The data input terminal (A) of the INV  21  is connected to the data output terminal (Q) of the SF  6 . The data output terminal (Z) of the INV  21  is connected to the data input terminal (D) of the SF  4 . 
         [0038]    Each SF may be a multiplexer-type scan FF, for example. A configuration example of the multiplexer-type scan FF will now be described with reference to  FIG. 1B . A multiplexer-type SF  202  includes a multiplexer (MUX)  220  and a D-FF (DFF)  221 . A “0” input terminal of the MUX  220  is connected to the data input terminal (D) of the multiplexer-type SF  202 . A “1” input terminal of the MUX  220  is connected to the scan-in terminal (SI) of the multiplexer-type SF  202 . A select terminal of the MUX  220  is connected to the scan enable terminal (SMC) of the multiplexer-type SF  202 . An output terminal of the MUX  220  is connected to the data input terminal of the DFF  221 . A clock terminal of the DFF  221  is connected to the clock terminal (CLK) of the multiplexer-type SF  202 . The data output terminal of the DFF  221  is connected to the data output terminal (Q) of the multiplexer-type SF  202 . 
         [0039]    Next, the configuration of the delay fault test pattern generation control circuit  200  will be described with reference to  FIG. 1C . The delay fault test pattern generation control circuit  200  includes an SF  1 , an SF  2 , and an OR gate (OR)  31 . The SF  1  determines the local scan enable signal (LSMC) which is output to the six SFs of the logic circuit  201 . In the case of generating a test pattern by use of ATPG, when “1” is set to the SF  1  as an initial value, a test pattern for a skewed-load mode is generated, and when “0” is set to the SF  1  as an initial value, a test pattern for a broadside mode is generated. The SF  1  corresponds to a test pattern generation mode control unit that selects one of the skewed-load mode and the broadside mode as a test pattern generation mode of a delay fault test. 
         [0040]    The SF  2  is a scan FF that prevents an adverse effect of the control value of the SF  1  on the toggle signal value of the SF  3 , which is connected to the head of the scan chain within the logic circuit unit, in the case of generating a skewed-load mode pattern. The toggle signal value of the SF  3  is a signal value for allowing the signal value output from the SF  3  to transit. When the test pattern generation mode is the skewed-load mode, the SF  2  corresponds to a toggle value control unit that performs a scan shift operation on the toggle value, which is set to allow the value held in the SF  3  to transit, and outputs the toggle value. 
         [0041]    The functions of the SF  2  will be described in more detail. For example, a description is given of the case where a test pattern is generated using the skewed-load mode to check the transition from “1” to “0” in the TDF. In this case, it is necessary to set the initial value of the SF  1  to “1” so as to generate a test pattern using the skewed-load mode. It is also necessary to set the initial value of the SF  3  to “1” so as to allow the value to transit from “1” to “0” in the TDF. Next, it is necessary for the SF  3  to capture “0” at the next clock timing (launch clock application time) so as to allow the value to transit from “1” to “0” in the TDF. In this case, when the SF  2  is not present, the output value of the SF  1  is captured into the SF  3 . That is, since “1” is set as the initial value to the SF  1  so as to generate the test pattern using the skewed-load mode, “1” is output at the next clock timing. In this case, the SF  3  captures “1”, which makes it difficult for the SF  3  to check the transition from “1” to “0”. For this reason, the SF  2  is provided and the initial value of the SF  2  is set to “0”, thereby enabling the SF  3  to capture “0” at the next clock timing. Thus, the provision of the SF  2  prevents the value of the SF  1  from being directly output to the SF  3 , which is the head of the scan chain within the logic circuit  201 , when “1” is set to the SF  1  so as to generate the test pattern using the skewed-load mode. 
         [0042]    The OR  31  is a gate for allowing a global scan enable signal (GSMC) or a signal output from the SF  1  to propagate as the local scan enable signal (LSMC) to be output to the six SFs during the scan shift operation. The OR  31  corresponds to a scan enable signal output unit that outputs the signal output from the SF  1 , which is determined based on the test pattern generation mode, to the SF  3  to SF  8 . 
         [0043]    The delay fault test pattern generation control circuit  200  receives the global scan enable signal (GSMC), a scan-in signal (SIN) of the scan chain, and a scan test mode signal (TE). The global scan enable signal (GSMC) indicates the signal value “1” during the scan shift operation, and indicates the signal value “0” in the cases other than the scan shift operation. The scan test mode signal (TE) indicates the signal value “1” during a scan test, and indicates the signal value “0” in the cases other than the scan test. Further, the delay fault test pattern generation control circuit  200  outputs the local scan enable signal (LSMC) to the logic circuit ( 201 ). 
         [0044]    The data input terminal (D) and the scan enable terminal (SMC) of the SF  1  of the delay fault test pattern generation control circuit  200  are connected to the signal line of the global scan enable signal (GSMC). The scan-in terminal (SI) of the SF  1  is connected to the scan chain through which the scan-in signal (SIN) propagates. The clock terminal (CLK) of the SF  1  is connected to the signal line of the external clock signal (CLK). The data output terminal (Q) of the SF  1  is connected to the data input terminal (B) of the OR  31  and the data input terminal (D) and the scan-in terminal (SI) of the SF  2 . A reset-bar terminal (RESETB) of the SF  1  is connected to the signal line of the external scan test mode signal (TE). The reset-bar terminal (RESETB) of the scan FF (SF  1 ) is connected to the signal line of the external scan test mode signal (TE) so that a user logic is prevented from being destroyed by resetting the SF  1  during a user mode. In other words, when the logic circuit  201  is used not for a scan test but for a normal operation, the reset-bar terminal (RESETB) is used to prevent the value set to the SF  1  from propagating to the logic circuit  201 . 
         [0045]    The scan enable terminal (SMC) of the SF  2  of the delay fault test pattern generation control circuit  200  is connected to the signal line of the global scan enable signal (GSMC). The clock terminal (CLK) of the SF  2  is connected to the signal line of the external clock signal (CLK). The data output terminal (Q) of the SF  2  is connected to the scan-in terminal (SI) of the SF  3  of the logic circuit  201 . 
         [0046]    Assume herein that the external clock signals (CLK) that are connected to the SF  1  and SF  2  of the delay fault test pattern generation control circuit  200  and to the SF  3  to SF  8  of the logic circuit  201  are the same. That is, the SF  1  to the SF  8  belong to the same clock domain. In other words, the delay fault test pattern generation control circuit  200  may control the transition of signals in the scan FFs belonging to the same clock domain. As a result, the SF  1  to the SF  8  are controlled using the same external clock signal (CLK), thereby facilitating control of the transition of signals such as the local scan enable signal (LSMC), for example. Since the SF  1  to the SF  8  belong to the same clock domain, the transition of the local scan enable signal (LSMC) between a launch clock and a capture clock of each of the SF  1  to the SF  8  can be easily controlled, for example. Such a signal transition control may also be referred to as “at-speed control”. 
         [0047]    The data input terminal (A) of the OR  31  of the delay fault test pattern generation control circuit  200  is connected to the signal line of the global scan enable signal (GSMC). The data input terminal (B) of the OR  31  is connected to the data output terminal (Q) of the SF  1 . The data output terminal (Z) of the OR  31  is connected to the signal line of the local scan enable signal (LSMC). 
         [0048]    Referring next to  FIG. 2 , a description is given of a timing diagram illustrating that a test pattern is generated by setting the SF  1  of the delay fault test pattern generation control circuit  200  to the signal value “1” immediately before a launch clock application time (LCE), i.e., a skewed-load mode test pattern is generated. Setting of the SF  1  to the signal value “1” immediately before the LCE indicates that the SF  1  outputs the signal value “1” immediately before the LCE. 
         [0049]    As for a fault to be detected, assume herein that the transition delay fault (TDF) shown in  FIG. 1A  is an STF (Slow To Fall) fault (hereinafter, “target fault F 1 ”). Note that each signal that does not directly affect the detection of the target fault F 1  is represented by oblique lines in  FIG. 2 , and is herein represented as an X value. The X value is an indefinite value that can take “0” or “1”. The signal value of the data input terminal (D) of the SF  1  is the same as the signal value of the global scan enable signal (GSMC), so the description thereof is omitted. 
         [0050]    To detect the target fault F 1 , it is necessary to set the signal value of the data output terminal (Q) of the SF  2  to “0”, set the signal value of the data output terminal (Q) of the SF  3  to “1”, and set the signal value of the data output terminal (Q) of the SF  4  to “1”, immediately before the launch clock application time (LCE). It is also necessary to set the signal value of the data output terminal (Q) of the SF  3  to “0” and set the signal value of the data output terminal (Q) of the SF  4  to “1”, immediately before a capture clock application time (CCE). That is, it is necessary to set the above-mentioned signal values so as to allow the value of the data output terminal (Q) of the SF  3  to transit from “1” to “0” before and after the application of the launch clock. Hereinafter, the circuit operation for detecting the target fault F 1  will be described in chronological order. 
         [0051]    A period from time (T 0 ) to time (T 2 ) and a period from time (T 5 ) to time (T 7 ) corresponds to a scan shift cycle in which the global scan enable signal (GSMC) is set to “1”. That is, during the period from time (T 0 ) to time (T 2 ), the value of the test pattern generated using the ATPG is set to each of the SF  1  to the SF  7  by use of the scan chain. A period from time (T 2 ) to time (T 3 ) corresponds to an external input signal supply cycle in which the GSMC is set to “0”. A period from time (T 3 ) to time (T 4 ) corresponds to a launch clock cycle in which the launch clock is applied. A period from time (T 4 ) to time (T 5 ) corresponds to a capture clock cycle in which the capture clock is applied. 
         [0052]    At time (T 0 ), the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  are set as follows. 
         [0053]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(0, 1, 1, X, X, X, X, X, X, X) 
         [0054]    At time (CE 1 ), the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  at time (T 1 ) after the application of the scan shift clock signal (CLK) are set as follows. 
         [0055]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(1, 0, 1, 1, X, X, X, X, X, X) 
         [0056]    At time (T 2 ), the global scan enable signal (GSMC) transits from the signal value “1” to the signal value “0”. At time (T 2 ) and time (T 3 ) after the application of the scan shift clock signal (CLK) at time (CE 2 ), the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  are set as follow. 
         [0057]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(X, 1, 0, 1, 1, X, X, X, X, 1) 
         [0058]    At time (LCE), the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  at time (T 4 ) after the application of the launch clock are set as follows. 
         [0059]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(X, 0, 1, 0, 1, 1, X, X, X, 0) 
         [0060]    At time (CCE), the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  at time (T 5 ) after the application of the capture clock are set as follows. 
         [0061]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(X, 0, 0, X, X, 0, X, X, X, X) 
         [0062]      FIG. 2  shows a time chart during the normal operation in which the delay fault (STF) of the target fault F 1  does not occur. When the delay fault (STF) of the target fault F 1  is present, the signal captured into the SF  5  at the time of application of the capture clock at time (CCE) indicates the signal value “1” of the AND  12  prior to the transition of the SF  3 . In this case, the scan-in signal (SIN), the status values of the SFs, and the signal value of the AND  12  are set as follows. 
         [0063]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  12 (Z))=(X, 0, 0, X, X, 1, X, X, X, X) 
         [0064]    In the scan shift operation after time (T 5 ), the signal value of the SF  5 , which is captured at the capture cycle, is observed using the scan-out terminal (SOT) of the scan chain (C 1 ). In this case, when the output value of the SF  5  is “1”, it can be determined that the delay fault (STF) has occurred. 
         [0065]    Referring next to  FIG. 3 , a description is given of a timing diagram illustrating that a test pattern is generated by setting the SF  1  of the delay fault test pattern generation control circuit  200  to the signal value “0” immediately before the launch clock application time (LCE), i.e., a broadside mode test pattern is generated. 
         [0066]    As for a fault to be detected, assume herein that the transition delay fault (TDF) shown in  FIG. 1A  is an STF (Slow To Fall) fault (hereinafter, “target fault F 2 ”). Note that each signal that does not directly affect the detection of the target fault F 2  is represented by oblique lines in  FIG. 3 , and is herein represented as an X value. The signal value of the data input terminal (D) of the SF  1  is the same as the signal value of the global scan enable signal (GSMC), so the description thereof is omitted. 
         [0067]    To detect the target fault F 2 , it is necessary to set the signal value of the data output terminal (Q) of the SF  6  to “0”, set the signal value of the data output terminal (Q) of the SF  7  or the data output terminal (Q) of the SF  8  to “0”, set the signal value of the data output terminal (Q) of the SF  3  to “1”, and set the signal value of the data output terminal (Q) of the SF  4  to “1”, immediately before the launch clock application time (LCE). It is also necessary to set the signal value of the data output terminal (Q) of the SF  3  to “0” and set the signal value of the data output terminal (Q) of the SF  4  to “1”, immediately before the capture clock application time (CCE). That is, it is necessary to set the above-mentioned signal values so as to allow the value of the data output terminal (Q) of the SF  3  to transit from “1” to “0” before and after the application of the launch clock. Hereinafter, the circuit operation for detecting the target fault F 2  will be described in chronological order. 
         [0068]    For convenience of explanation, assume herein that the signal value of the data output signal (Q) of the SF  8  is “0” and the signal value of the data output terminal (Q) of the SF  7  is “X” immediately before the launch clock application time (LCE). 
         [0069]    The description of each cycle from time (T 0 ) to time (T 7 ) is the same as that in the case of generating the skewed-load mode test pattern, so the description thereof is omitted. 
         [0070]    At time (T 0 ), the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , and INV  21  are set as follows. 
         [0071]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(X, 1, 1, X, 0, X, 0, X, X, X, X, X) 
         [0072]    At time (CE 1 ), the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , and INV  21  at time (T 1 ) after the application of the scan shift clock signal (CLK) are set as follows. 
         [0073]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(0, X, 1, 1, X, 0, X, 0, X, X, X, X) 
         [0074]    At time (T 2 ), the global scan enable signal (GSMC) transits from the signal value “1” to the signal value “0”. At time (CE 2 ), the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , and INV  21  at time (T 2 ) and time (T 3 ) after the application of the scan shift clock signal (CLK) are set as follows. 
         [0075]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(X, 0, X, 1, 1, X, 0, X, 0, 0, 1, 1) 
         [0076]    At time (LCE), the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , and INV  21  at time (T 4 ) after the application of the launch clock are set as follows. 
         [0077]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(X, 0, 0, 0, 1, 1, X, X, X, X, X, 0) 
         [0078]    At time (CCE), the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , INV  21  at time (T 5 ) after the application of the capture clock are set as follows. 
         [0079]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(X, 0, 0, X, X, 0, X, X, X, X, X, X) 
         [0080]      FIG. 3  shows a time chart during the normal operation in which the delay fault (STF) of the target fault F 2  does not occur. When the delay fault (STF) of the target fault F 2  is present, the signal captured into the SF  5  at the time of application of the capture clock at time (CCE) indicates the signal value “1” of the AND  12  prior to the transition of the SF  3 . In this case, the scan-in signal (SIN), the status values of the SFs, and the signal values of the AND  11 , AND  12 , and INV  21  are set as follows. 
         [0081]    (SIN, SF  1 (Q), SF  2 (Q), SF  3 (Q), SF  4 (Q), SF  5 (Q), SF  6 (Q), SF  7 (Q), SF  8 (Q), AND  11 (Z), INV  21 (Z), AND  12 (Z))=(X, 0, 0, X, X, 1, X, X, X, X, X, X) 
         [0082]    In the scan shift operation after time (T 5 ), the signal value of the SF  5 , which is captured at the capture cycle, is observed using the scan-out terminal (SOT) of the scan chain (C 1 ). In this case, when the output value of the SF  5  is “1”, it can be determined that the delay fault (STF) has occurred in the transition delay fault (TDF). 
         [0083]    As described above, the use of the SF  1  in the delay fault test pattern generation control circuit  200  according to the first embodiment enables execution of a test for the logic circuit  201  using the test patterns of the skewed-load mode and the broadside mode. 
         [0084]    In the first embodiment, the delay fault test pattern generation control circuit  200  including one RESETB-equipped scan FF, one scan FF, and one OR gate is incorporated for each clock domain in the entire circuit. Accordingly, only the delay fault test pattern generation control circuits  200  corresponding to the number of clock domains occupy the area OH. In many cases, the number of clock domains is less than 100. 
         [0085]    In the case of a circuit including one million FFs, the area OH of the first embodiment is (one RESETB-equipped scan FF+one scan FF+OR gate)×100, at maximum. The area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is (normal FF+OR gate)×20000 (the number of FFs corresponding to 2% of the entire FFs). For comparison, consideration is given to the case where the area OH of the configuration according to the first embodiment and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 are converted into the number of transistors. Assuming that the reset-bar terminal RESETB-equipped scan FF corresponds to 40 Tr; the scan FF corresponds to 38 Tr; the normal FF corresponds to 28 Tr; and the OR gate corresponds to 6 Tr, the area OH of the first embodiment is represented by (40+38+6)×100=8400 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. Thus, the area OH of the first embodiment is about 1/80 of that of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the configuration of the first embodiment provides an advantageous effect of drastically reducing the area OH as compared with the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. 
         [0086]    In the first embodiment, the ATPG tool can continuously try to generate test patterns using the skewed-load mode and the broadside mode in a calculation process for one target fault. In other words, the execution of a test involving the skewed-load mode or the execution of a test involving the broadside mode can be selected depending on the initial value set to the SF  1  of the delay fault test pattern generation control circuit  200  and on the initial values set to other SFs so as to set a transition value which is necessary for testing the target fault. Accordingly, the initial value set to each SF is changed upon generation of the test pattern using the ATPG tool, thereby making it possible to generate test patterns including a test mode involving the skewed-load mode and a test mode involving the broadside mode. 
         [0087]    In the case of generating a test pattern for a delay fault test in an arbitrary section, for example, if a test pattern in the skewed-load mode cannot be generated, a test pattern in the broadside mode can be generated by changing the value of each SF. As a result, the probability of generating a test pattern capable of detecting a target fault is increased, leading to an improvement in the delay fault coverage. 
         [0088]    The case where the test pattern in the skewed-load mode cannot be generated will now be described. As for a fault to be detected, assuming that the transition delay fault (TDF) is an STR (Slow To Rize) fault in  FIG. 1A , consideration is given to the operation when the STR fault is a detection target (hereinafter referred to as “target fault F 3 ”). 
         [0089]    It is necessary to propagate the STR fault to the data output terminal (Z) of the AND  12  so as to detect the target fault F 3 . Accordingly, it is necessary to set, as the signal value of the data output terminal (Q) of the SF  3 , a value that causes transition from the signal value “0” to the signal value “1” before and after the application of the launch clock. It is also necessary to set the signal value of the SF  4 (Q) to “1” after the application of the launch clock. 
         [0090]    When the ATPG tool sets the signal value of the data output signal (Q) of the SF  1  to “1” and generates a test pattern using the skewed-load mode, the signal to be captured into each SF upon application of the launch clock is captured from the scan-in terminal (SI). Thus, the signal value captured into the SF  4  that drives the data output terminal (B) of the AND  12  corresponds to the signal value of the data output signal (Q) of the SF  3  connected with the scan-in terminal (SI) of the SF  4 . Since the signal value of the data output signal (Q) of the SF  3  before the application of the launch clock is “0”, the signal value of the data output signal (Q) of the SF  4  after the application of the launch clock is “0”. When the signal value of the data output signal (Q) of the scan FF (SF  4 ) after the application of the launch clock is “0”, the data input terminal (B) of the AND  12  indicates the value “0”, which makes it difficult to allow the STR fault of the target fault F 3  to propagate to the data output terminal (Z) side of the AND  12 . Accordingly, the ATPG tool determines that the STR fault of the target fault F 3  cannot be detected based on the test pattern in the skewed-load mode. 
         [0091]    Then, the ATPG tool sets the signal value of the data output terminal (Q) of the SF  1  to “0”, and tries to generate the test pattern in the broadside mode. In this case, the signal to be captured into each SF upon application of the launch clock is captured from the data input terminal (D). The signal values to be captured into the data input terminals (D) of the SF  3  and the SF  4  can be determined using the SF  7 , the SF  8 , and the SF  6 . The ATPG tool can set the signal values of (SF  3 , SF  6 , SF  7 , and SF  8 ) respectively to (0, 0, 1, 1) before the application of the launch clock. Accordingly, the signal values of the data output terminals (Q) of the scan FFs (SF  3  and SF  4 ), which are respectively (0 and X) before the application of the launch clock, can be respectively set to (1 and 1) after the application of the launch clock. This allows the STR fault of the target fault F 3  to propagate to the data output terminal (Z) of the AND  12 . This enables the data input terminal (D) of the SF  5  to capture the STR fault of the target fault F 3  and to detect the delay fault, which cannot be detected using the skewed-load mode, by using the broadside mode. In particular, a larger number of delay faults can be detected at the initial stage of the ATPG, which enables obtainment of a high delay fault coverage with a small number of test patterns. 
       Second Embodiment 
       [0092]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  204  according to a second embodiment will be described with reference to  FIG. 4 . 
         [0093]    The delay fault test pattern generation control circuit  204  has a configuration in which one of the scan FFs, i.e., the SF  2 , of the delay fault test pattern generation control circuit  200  is replaced with a normal FF (NF  41 ). 
         [0094]    The data input terminal (D) of the NF  41  is connected to the data output terminal Q of the SF  1 . The clock terminal (CLK) of the NF  41  is connected to the signal line of the external clock signal (CLK). The data output terminal (Q) of the NF  41  is connected to the scan chain (C 1 ) of the logic circuit  201 . 
         [0095]    The other circuit configuration of the delay fault test pattern generation control circuit  204  is similar to that of the delay fault test pattern generation control circuit  200  shown in  FIG. 1 , so the description thereof is omitted. The circuit configuration of the logic circuit  201  and the circuit configuration of the multiplexer-type scan FF  202  are the same as those shown in  FIG. 1 , so the description thereof is omitted. 
         [0096]    The delay fault test pattern generation control circuit  204  operates in the same manner as in the timing diagram shown in  FIGS. 2 and 3 , so the detailed description of the operation is omitted. 
         [0097]    In the second embodiment, the delay fault test pattern generation control circuit  204  including one RESETB-equipped scan FF, one normal FF, and one OR gate is incorporated for each clock domain in the entire circuit. Accordingly, only the delay fault test pattern generation control circuits  204  corresponding to the number of clock domains occupy the area OH. 
         [0098]    Also in the second embodiment, the delay fault test pattern generation control circuit  204  is converted into the number of transistors under the same conditions as those of the first embodiment. When 100 delay fault test pattern generation control circuits  204  are incorporated, the area OH is represented by (reset-bar terminal RESETS-equipped scan FF+normal FF+OR gate)×100=(40+28+6)×100=7400 Tr. The area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. The area OH of the second embodiment is about 1/90 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the second embodiment provides an advantageous effect of reducing the area OH. The second embodiment also provides an advantageous effect of further reducing the area OH as compared with the first embodiment. 
       Third Embodiment 
       [0099]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  205  according to a third embodiment, and a configuration example of a logic circuit  203 , which is controlled by the delay fault test pattern generation control circuit  205 , will be described with reference to  FIGS. 5A  and  5 B. 
         [0100]    The delay fault test pattern generation control circuit  205  has a configuration in which the SF  2  of the delay fault test pattern generation control circuit  200  is omitted. The data output terminal (Q) of the SF  1  of the delay fault test pattern generation control circuit  205  is connected to the scan-in terminal (SI) of an SF  2 B of the logic circuit  203 . The other circuit configuration of the delay fault test pattern generation control circuit  205  is similar to that of the delay fault test pattern generation control circuit  200  shown in  FIG. 1 , so the description thereof is omitted. 
         [0101]    The logic circuit  203  is different from the logic circuit  201  in that the scan FF (SF  2 B) is added as a part of a user circuit unit at the fan-in side of the SF  3  on the scan chain (C 1 ). The data output terminal (Q) of the SF  2 B is connected to the scan-in terminal (SI) of the SF  3 . The scan enable terminal (SMC) of the SF  2 B is connected to the signal line of the local scan enable signal (LSMC) which is output by the delay fault test pattern generation control circuit  205 . The clock terminal (CLK) of the SF  2 B is connected to the signal line of the external clock terminal (CLK). The circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1 , so the description thereof is omitted. 
         [0102]    The delay fault test pattern generation control circuit  205  operates in the same manner as in the timing diagram shown in  FIGS. 2 and 3 . Accordingly, the detailed description of the circuit operation shown in  FIG. 5  is omitted. Note that SF  2 (Q) in the timing diagram shown in  FIGS. 2 and 3  is replaced with SF  2 B(Q). 
         [0103]    In the third embodiment, the delay fault test pattern generation control circuit  205  including one RESETB-equipped scan FF and one OR gate is incorporated for each clock domain in the entire circuit. Accordingly, only the delay fault test pattern generation control circuits  205  corresponding to the number of clock domains occupy the area OH. 
         [0104]    Also in the third embodiment, the delay fault test pattern generation control circuit  205  is converted into the number of transistors under the same conditions as those of the first embodiment. When 100 delay fault test pattern generation control circuits  205  are incorporated, the area OH is represented by (reset-bar terminal RESETB-equipped scan FF+OR gate)×100=(40+6)×100=4600 Tr. The area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)*20000=680000 Tr. Accordingly, the area OH of the third embodiment is about 1/150 of the area OH of the configuration disclosed in the Japanese Unexamined Patent Application Publication No. 2008-096440. Thus, the third embodiment provides an advantageous effect of reducing the area OH. The third embodiment also provides an advantageous effect of further reducing the area OH as compared with the first and second embodiments. 
         [0105]    In the delay fault test pattern generation control circuit  205 , the SF  2  and NF 2  for setting a toggle value upon generation of the test pattern in the skewed-load mode are not present. Thus, the delay fault coverage of the skewed-load mode may be lowered as compared with the first and second embodiments. However, in the case of generating the test pattern using the ATPG, an interpolation function for generating a test pattern using the broadside mode according to the signal value set to the SF  1  is activated. This also provides an advantageous effect of improving the final delay fault coverage. 
         [0106]    While the configuration in which the SF  2 B is provided in the logic circuit  203  is described in the third embodiment, similar effects can be obtained also in the configuration in which the SF  2 B is omitted. 
       Fourth Embodiment 
       [0107]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  206  according to a fourth embodiment, and a configuration example of the logic circuit  203 , which is controlled by the delay fault test pattern generation control circuit  206 , will be described with reference to  FIG. 6 . 
         [0108]    The delay fault test pattern generation control circuit  206  has a configuration in which the SF  1  and the SF  2  of the delay fault test pattern generation control circuit  200  are omitted. Further, in the configuration of the delay fault test pattern generation control circuit  206 , a normal FF (NF  51 ) and a scan FF (SF  1 B) are added. The NF  51  generates a transition operation for the local scan enable signal (LSMC) at the time when the launch clock operates during the skewed-load operation. The SF  1 B generates a transition operation for the local scan enable signal (LSMC) at the time when the capture clock operates. The SF  1 B corresponds to a capture-clock-time scan enable control unit that causes the local scan enable signal (LSMC) to transit during the capture clock time. 
         [0109]    The data output terminal (Q) of the SF  1 B of the delay fault test pattern generation control circuit  206  is connected to the data input terminal (D) of the NF  51 . The data output terminal (Q) of the NF  51  is connected to each of the data input terminal (B) of the OR  31  and the scan-in terminal (SI) of the SF  2 B of the logic circuit  203 . The global scan enable signal (GSMC), which is input to the delay fault test pattern generation control circuit  206 , is connected to each of the data terminal (D) and the scan enable terminal (SMC) of the SF  1 B and the data input terminal (A) of the OR  31 . The scan-in signal (SIN) of the scan chain is connected to the scan-in terminal (SI) of the SF  1 B. The scan test mode signal (TE) is connected to the reset-bar terminal (RESETB) of the NF  51 . The clock signal (CLK), which is input to the delay fault test pattern generation control circuit  206 , is connected to each of the clock terminal (CLK) of the SF  1 B and the clock terminal (CLK) of the NF  51 . The data output terminal (Z) of the OR  31  outputs the local scan enable signal (LSMC) and is connected to the logic circuit  203 . 
         [0110]    The circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1 , so the description thereof is omitted. Similarly, the circuit configuration of the logic circuit  203  is similar to that shown in  FIG. 5 , so the description thereof is omitted. 
         [0111]      FIG. 7  is a waveform chart when the LSMC signal of the delay fault test pattern generation control circuit  206  outputs the same waveform as that shown in  FIG. 3 . In the delay fault test pattern generation control circuit  206 , the signal value of the data output signal (Q) of the SF  1 B at time (T 1 ) and time (T 2 ) is “0”. In this case, at time (T 3 ) and time (T 4 ) before the application of the launch clock and the capture clock at time (LCE) and time (CCE), respectively, the signal value of the data output signal (Q) of the NF  51  is “0”. Accordingly, the signal value of the local scan enable terminal (LSMC) is “0” during the capture cycle period from time (T 2 ) to time (T 5 ). The description of the operation of scan FFs subsequent to the SF  2 B is omitted. 
         [0112]      FIG. 8  is a waveform chart when the LSMC signal of the delay fault test pattern generation control circuit  206  outputs the same waveform as that shown in  FIG. 2 . A description is given of the case where the signal value of the data output signal (Q) of the SF  1 B at time (T 1 ) is “1” and the signal value of the data output signal (Q) of the SF  1 B at time (T 2 ) is “0”. In this case, at time (T 3 ) before the application of the launch clock at time (LCE), the signal value of the data output signal (Q) of the NF  51  is “1”. Further, at time (T 4 ) before the application of the capture clock at time (CCE), the signal value of the data output signal (Q) of the NF  51  is “0”. Accordingly, the signal value of the local scan enable terminal (LSMC) in the period from time (LCE) to time (T 5 ) is “0”. The description of the operation of scan FFs subsequent to the SF  2 B is omitted. 
         [0113]      FIG. 9  illustrates the case where the signal value of the data output signal (Q) of the SF  1 B at time (T 1 ) and time (T 2 ) is “1”. In this case, at time (T 3 ) and time (T 4 ) before the application of the launch clock and the capture clock at time (LCE) and time (CCE), respectively, the signal value of the data output signal (Q) of the NF  51  is “1”. Accordingly, at time (T 4 ), the signal value of the local scan enable terminal (LSMC) is “1”, and the signal value of the local scan enable terminal (LSMC) is “0” only in the period from time (CCE) to time (T 5 ). Further, at time (T 5 ), the global scan enable signal (GSMC) returns to “1” and the local scan enable signal (LSMC) also returns to “1”. Accordingly, at all clock application times (CE 1 , CE 2 , LCD, CCE, CE 3 , and CE 4 ), the scan enable signals of all the SFs indicate “1”. Thus, in the period from time (T 0 ) to time (T 7 ), all the SFs of SF  1 B to SF  8  perform a shift register operation. 
         [0114]    In the first to third embodiments, the SF  1  plays the role of determining one of the skewed-load mode and the broadside mode, and the role of generating the transition signal of the local scan enable signal (LSMC) in each of the skewed-load mode and the broadside mode. On the other hand, in the fourth embodiment, the NF  51  plays the role of generating the transition signal of the local scan enable signal (LSMC) during the launch clock time in the skewed-load mode. 
         [0115]    Furthermore, the fourth embodiment is different from the first to third embodiments in that the SF  1 B generates the transition signal of the local scan enable signal (LSMC) during the capture clock time. 
         [0116]    Also in the fourth embodiment, the delay fault test pattern generation control circuit  206  is converted into the number of transistors under the same conditions as those of the first embodiment. Assuming that the number of transistors of the reset-bar terminal RESETB-equipped normal FF is 30 Tr and the other conditions are the same as those of the embodiment 1, the area OH of the fourth embodiment is represented by (38+30+6)×100=7400 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. The area OH of the fourth embodiment is 1/90 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the fourth embodiment provides an advantageous effect of reducing the area OH. 
         [0117]    In the delay fault test pattern generation control circuit  206 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby allowing each scan FF to capture the signal value from the scan chain during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. The capturing of the signal value from the scan chain during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  206  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
       Fifth Embodiment 
       [0118]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  207  according to a fifth embodiment will be described with reference to  FIG. 10A . 
         [0119]    The delay fault test pattern generation control circuit  207  has a configuration in which a scan FF (SF  61 ), an inverter (INV  62 ), an OR gate (OR  63 ), a NAND gate (NAND  64 ), and a clock gating cell (CGC  65 ) are added to the delay fault test pattern generation control circuit  206 . The SF  1 B corresponds to the capture-clock-time scan enable control unit that causes the local scan enable signal (LSMC) to transit during the capture clock time. The SF  1 B corresponds to a capture clock output control unit that outputs a gated clock signal (GCLK) during the capture clock time. The SF  61  corresponds to a launch clock output control unit that outputs the gated clock signal (GCLK) during the launch clock time. When the local scan enable signal (LSMC) is “0” during the capture clock time, i.e., when the scan FFs (SF  1  to SF  8  and SF  2 B) capture signals from the D terminal of each scan FF during the capture clock time, the INV  62  generates a control signal necessary for forcibly outputting the gated clock signal (GCLK). The OR  63  corresponds to a control unit that causes the gated clock signal (GCLK) to be output during the shift cycle time. The NAND  64  corresponds to a capture clock stop control unit that forcibly stops supply of the gated clock signal (GCLK) when the SF  1 B and the NF  51  have status values of “0” and “1”, respectively, during the capture clock time, i.e., when the scan FFs (SF  1  to SF  8  and SF  2 B) capture signals from the SI terminal of each scan FF during the capture clock time. 
         [0120]    The data output terminal (Q) of the SF  1 B of the delay fault test pattern generation control circuit  207  is connected to each of the input terminal (D) of the NF  51  and the input terminal of the INV  62 . The data output terminal (Q) of the NF  51  is connected to each of the data input terminal (B) of the OR  31 , the data input terminal (A) of the NAND  64 , and a scan input terminal (SI) of the SF  61 . The data output terminal (Q) of the SF  61  is connected to the data input terminal (B) of the OR  63 . The output signal of the SF  61  is output as the scan-output signal (SOT) of the delay fault test pattern generation control circuit  207  and is supplied to the logic circuit  203 . The output terminal (Z) of the OR  63  is connected to the scan enable terminal (SMC) of the CGC  65 . The data output terminal (Z) of the NAND  64  is connected to the clock enable terminal (CEN) of the CGC  65 . The output terminal of the INV  62  is connected to each of the data input terminal (D) of the SF  61  and the data input terminal (B) of the NAND  64 . The scan-in signal (SIN) of the scan chain is connected to the scan-in terminal (SI) of the SF  1 B. The scan test mode signal (TE) is connected to each of the reset-bar terminal (RESETB) of the NF  51  and the reset-bar terminal (RESETB) of the SF  61 . The clock signal (CLK), which is input to the delay fault test pattern generation control circuit  207 , is connected to each of the clock terminal (CLK) of the SF  1 B, the clock terminal (CLK) of the NF  51 , the clock terminal (CLK) of the SF  61 , and the clock terminal (CLK) of the CGC  65 . The global scan enable signal (GSMC), which is input to the delay fault test pattern generation control circuit  207 , is connected to each of the data input terminal (D) and the scan enable terminal (SMC) of the SF  1 B, the scan enable terminal (SMC) of the SF  61 , the data input terminal (A) of the OR  31 , and the data input terminal (A) of the OR  63 . The output signal from the data output terminal (Z) of the OR  31  is output as the local scan enable signal (LSMC) and is supplied to the logic circuit  203 . The output signal from the gated clock terminal (GCLK) of the CGC  65  is output as the gated clock signal (GCLK) and is supplied to the logic circuit  203 . 
         [0121]    Subsequently, the circuit configuration of the clock gating cell (CGC  65 ) will be described with reference to  FIG. 10B . The clock gating cell (CGC  65 ) includes an OR gate (OR  66 ), a latch (LAT  67 ), and an AND gate (AND  68 ). The scan enable terminal (SMC) of the CGC  65  is connected to the input terminal (A) of the OR  66 . The clock enable terminal (CEN) of the CGC  65  is connected to the data input terminal (B) of the OR  66 . The data output terminal (Z) of the OR  66  is connected to the data input terminal (D) of the LAT  67 . The data output terminal (Q) of the LAT  67  is connected to the data input terminal (A) of the AND  68 . The data output terminal (Z) of the AND  68  is connected to the gated clock terminal. (GCLK) of the CGC  65 . The clock terminal (CLK) of the CGC  65  is connected to each of the gate bar terminal (GB) of the LAT.  67  and the data input terminal (B) of the AND  68 . 
         [0122]    Subsequently, the block diagram of the delay fault test pattern generation control circuit  207  according to the fifth embodiment will be described with reference to  FIG. 10C . The global scan enable signal (GSMC) is supplied to each of a capture-clock-time scan enable control unit  301 , a scan enable signal output unit  303 , and a capture-clock-time gated clock control unit  304 . The scan test mode signal (TE) is supplied to each of a test pattern generation mode control unit  302  and the capture-clock-time gated clock control unit  304 . The external clock signal (CLK) is supplied to each of the capture-clock-time scan enable control unit  301 , the test pattern generation mode control unit  302 , and the capture-clock-time gated clock control unit  304 . The output signal of the capture-clock-time scan enable control unit  301  is supplied to each of the test pattern generation mode control unit  302  and the capture-clock-time gated clock control unit  304 . The output signal of the test pattern generation mode control unit  302  is supplied to each of the scan enable signal output unit  303  and the capture-clock-time gated clock control unit  304 . The output signal of the scan enable signal output unit  303  is output as the local scan enable signal (LSMC). The output signal of the capture-clock-time gated clock control unit  304  is output as the gated clock signal (GCLK). The capture-clock-time scan enable control unit  301  is composed of the SF  1 B. The test pattern generation mode control unit  302  is composed of the NF  51 . The scan enable signal output unit  303  is composed of the OR  31 . The capture-clock-time gated clock control unit  304  is composed of the INV  62 , the NF  61 , the OR  63 , the NAND  64 , and the CGC  65 . The delay fault test pattern generation control circuit  207  also has a scan chain configuration in which the SIN terminal and the SOT terminal are set as a start point and an end point, respectively, but the description of the scan chain configuration is herein omitted. 
         [0123]    The circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1C , so the description thereof is omitted. Similarly, the circuit configuration of the logic circuit  203  is similar to that shown in  FIG. 5B , so the description thereof is omitted. 
         [0124]      FIG. 11  is a waveform chart when the LSMC signal of the delay fault test pattern generation control circuit  207  outputs the same waveform as that shown in  FIG. 9 .  FIG. 11  differs from  FIG. 9  in that the waveform of the gated clock signal (GCLK) which is the output signal of the delay fault test pattern generation control circuit  207  is added. The waveforms of signals (signals ranging from CLK to NF  51 ) other than the gated clock signal (GCLK) of the delay fault test pattern generation control circuit  207  are the same as those shown in  FIG. 9 , so the description thereof is omitted. When the status values of the SF  1 B and the NF  51  are “1” and “1”, respectively, at time (T 3 ), the status values of the SF  1 B and the NF  51  are “0” and “1”, respectively, and the status value of the SF  61  is “0” at time (T 4 ). Accordingly, when the scan test mode signal (TE) indicates “1”, the data output terminals of the OR  63  and the NAND  64  indicate “0” and “0”, respectively, at time (T 4 ). Thus, at time (CCE), the CGC  65  cannot output the clock signal (CLK) of the delay fault test pattern generation control circuit  207 . This makes it impossible to supply the capture clock signal to the logic circuit  203  from the gated clock terminal (GCLK) of the delay fault test pattern generation control circuit  207  as shown in an area  110 . At time (LCE), the SF  61  captures the signal value “0” which is obtained such that the signal value “1” at time (T 3 ) of the SF  1 B is inverted by the INV  62 . Also at time (CCE), the SF  61  operates in a similar manner and captures the signal value “1”. At time (CE 3 ), the SF  61  captures the signal value “0” of the NF  51  at time (T 5 ). At time (CE 3 ), the SF  2 B of the logic circuit  203  captures the signal value “1” of the SF  61  at time (T 5 ). After time (T 5 ), the scan shift operation is carried out, so the description of the scan shift operation of the SF  61  to the SF  7  is omitted. 
         [0125]    In the fourth embodiment, the SF  1 B and the NF  51  play the role of generating the transition signal of the local scan enable signal (LSMC) during the launch clock time and the capture clock time. On the other hand, in the fifth embodiment, when the transition of the local scan enable signal (LSMC) occurs, for example, when capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  occurs during the capture clock time, the CGC  65  performs control to prevent the capture clock signal from being supplied to the logic circuit  203 . 
         [0126]    Also in the fifth embodiment, the delay fault test pattern generation control circuit  207  is converted into the number of transistors under the same conditions as those of the first embodiment. Assuming that the number of transistors of the inverter is 2 Tr; the number of transistors of the 2-input NAND gate is 4 Tr; the number of transistors of the clock gating cell is 20 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the fifth embodiment is represented by (38+30+40+2+6+6+4+20)×100=14600 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. The area OH of the fifth embodiment is about 1/46 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the fifth embodiment provides an advantageous effect of reducing the area OH. 
         [0127]    As in the fourth embodiment, in the delay fault test pattern generation control circuit  207 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby allowing each scan FF to stop the capture operation from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  207  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0128]    Furthermore, in the fifth embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the fifth embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
       Sixth Embodiment 
       [0129]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  208 , which is used to control the logic circuit  203 , a configuration example of a logic circuit  73  including a clock gating cell (CGC  72 ) and a scan FF (SF  71 ), and a configuration example of an AND  70  according to a sixth embodiment will be described with reference to  FIG. 12 . 
         [0130]    The delay fault test pattern generation control circuit  208  has a configuration in which the clock gating cell (CGC  65 ) is omitted from the delay fault test pattern generation control circuit  207  and the data input terminal of the SF  61  is connected to the GSMC. The configurations other than the connection designation of the data input terminal of each of the clock gating cell (CGC  65 ) and the SF  61  are the same as those of the delay fault test pattern generation control circuit  207 , so the description of the configuration of the delay fault test pattern generation control circuit  208  is omitted. 
         [0131]    The data output terminal (Z) of the OR  31  of the delay fault test pattern generation control circuit  208  is connected to the scan enable terminal (SMC) of the SF  1  to SF  8  and SF  2 B of the logic circuit  203 . The data output terminal (Z) of the OR  63  of the delay fault test pattern generation control circuit  208  is connected to the scan enable terminal (SMC) of the CGC  72 . The data output terminal (Z) of the NAND  64  of the delay fault test pattern generation control circuit  208  is connected to the data input terminal (A) of the AND  70 . The data output terminal (Z) of the AND  70  is connected to the clock enable terminal (CEN) of the CGC  72 . The data output terminal of the SF  71  of the logic circuit  73  is connected to each of the data input terminal (B) of the AND  70  and the scan input terminals of other scan FFs of the logic circuit  73 . The data input terminal (D) and the scan input terminal (SI) of the SF  71  are connected to other logic gates of the logic circuit  73 , but the description thereof is omitted. The scan enable terminal (SMC) of the SF  71  of the logic circuit  73  is supplied with the GSMC signal which is supplied to the delay fault test pattern generation control circuit  208 . The clock terminals (CLK) of the SF  71  and the CGC  72  of the logic circuit  73  are supplied with the same clock signal CLK as that supplied to the delay fault test pattern generation control circuit  208 . The gated clock terminal (GCLK) of the CGC  72  of the logic circuit  73  is connected to the clock terminals (CLK) of the SF  1  to SF  8  and SF  2 B of the logic circuit  203 . 
         [0132]    The delay fault test pattern generation control circuit  208  implements the same functions as those of the delay fault test pattern generation control circuit  207  by combining the clock gating cell CGC  72 , which is preliminarily included in the logic circuit  73 , and the AND  70 , which is newly added, in place of the clock gating cell CGC  65  held in the delay fault test pattern generation control circuit  207 . 
         [0133]    The circuit configuration of the clock gating cell CGC  72  is similar to that of the clock gating cell CGC  65 , so the description thereof is omitted. The SF may be a multiplexer-type SF, for example, and the circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1B , so the description thereof is omitted. Similarly, the circuit configuration of the logic circuit  203  is similar to that shown in  FIG. 5B , so the description thereof is omitted. 
         [0134]    The operation of the delay fault test pattern generation control circuit  208 , which includes the operations of the AND  70  and the CGC  72 , is similar to the operation of the delay fault test pattern generation control circuit  207  illustrated in  FIG. 11 , so the description thereof is omitted. 
         [0135]    Also in the sixth embodiment, the delay fault test pattern generation control circuit  208  is converted into the number of transistors under the same conditions as those of the first embodiment. Assume in the sixth embodiment that the delay fault test pattern generation control circuit  208  and the AND  70  are configured in combination. Assuming that the number of transistors of the inverter is 2 Tr; the number of transistors of the 2-input NAND gate is 4 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the sixth embodiment is represented by (38+30+40+2+6+6+4+6)×100=13200 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. Thus, the area OH of the sixth embodiment is about 1/51 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the sixth embodiment provides an advantageous effect of reducing the area OH. 
         [0136]    As in the fifth embodiment, in the delay fault test pattern generation control circuit  208 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby allowing each scan FF to stop the capture operation for capturing data from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  208  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0137]    Further, in the sixth embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the sixth embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
         [0138]    Furthermore, in the sixth embodiment, the delay fault test pattern generation control circuit  208  is not disposed on a clock line of an existing circuit. Therefore, the sixth embodiment also provides an advantageous effect of suppressing an increase in skew on the clock line. 
       Seventh Embodiment 
       [0139]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  209 , which is used to control the logic circuit  203 , a configuration example of the logic circuit  73 , which is controlled by the delay fault test pattern generation control circuit  209 , and a configuration example of the AND gate (AND  70 ) according to a seventh embodiment will be described with reference to  FIG. 13 . 
         [0140]    The delay fault test pattern generation control circuit  209  has a configuration in which an AND gate (AND  81 ) and an NOR gate (NOR  82 ) are added to the delay fault test pattern generation control circuit  208 ; the scan FF (SF  61 ) is replaced with a normal FF (NF  80 ); and the 2-input OR gate (OR  63 ) is replaced with a 3-input OR gate (OR  83 ). The SF  1 B corresponds to each of the capture-clock-time scan enable control unit that causes the local scan enable signal (LSMC) to transit during the capture clock time, and the capture clock output control unit that causes the gated clock signal (GCLK) to be output during the capture clock time. The NF  80  corresponds to the launch clock output control unit that causes the gated clock signal (GCLK) to be output during the launch clock time. When the local scan enable signal (LSMC) indicates “0” during the capture clock time, i.e., when the scan FFs (SF  1  to SF  8  and SF  2 B) capture signals from the D terminal of each scan FF during the capture clock time, the INV  62  generates a control signal necessary for forcibly outputting the gated clock signal (GCLK). The OR  83  corresponds to the control unit that causes the gated clock signal (GCLK) to be output during the shift cycle time. The NAND  64  corresponds to the capture clock stop control unit that forcibly stops supply of the gated clock signal (GCLK) when the SF  1 B and the NF  51  have status values of “0” and “1”, respectively, during the capture clock time, i.e., when the scan FFs (SF  1  to SF  8  and SF  2 B) capture signals from the SI terminal of each scan FF during the capture clock time. 
         [0141]    The data output terminal (Q) of the SF  1 B of the delay fault test pattern generation control circuit  209  is connected to each of the data input terminal (D) of the NF  51 , the data input terminal (A) of the NOR  82 , and the input terminal of the INV  62 . The data output terminal (Q) of the NF  51  is connected to each of the data input terminal (B) of the OR  31  and the data input terminal (A) of the NAND  64 , and the output signal of the data output terminal (Q) of the NF  51  is output as the scan-output signal (SOT) of the delay fault test pattern generation control circuit  209  and is supplied to the logic circuit  203 . The data output terminal (Z) of the OR  83  is connected to the scan enable terminal (SMC) of the CGC  72 . The data output terminal (Z) of the NAND  64  is connected to the data input terminal (A) of the AND  70 . The data output terminal (Z) of the AND  70  is connected to the clock enable terminal (CEN) of the CGC  72 . The output terminal of the INV  62  is connected to the data input terminal (B) of the NAND  64 . The scan-in signal (SIN) of the scan chain is connected to the scan-in terminal (SI) of the SF  1 B. The scan test mode signal (TE) is connected to each of the reset-bar terminal (RESETB) of the NF  51  and the data input terminal (B) of the AND  81 . A delay fault test mode signal (TDFMODE) of the delay fault test pattern generation control circuit  209  indicates “0” at the time of generating a stuck-at fault test pattern, and indicates “1” in the other modes including a mode for generating a delay fault test pattern. The delay fault test mode signal (TDFMODE) is connected to each of the data input terminal (A) of the AND  81  and the data input terminal (B) of the NOR  82 . The data output terminal (Z) of the AND  81  is connected to the reset-bar terminal (RESETB) of the NF  80 . The data output terminal (Z) of the NOR  82  is connected to the data input terminal (B) of the OR  83 . The clock signal (CLK), which is input to the delay fault test pattern generation control circuit  209 , is connected to each of the clock terminal (CLK) of the SF  1 B, the clock terminal (CLK) of the NF  51 , and the clock terminal (CLK) of the NF  80 . The global scan enable signal (GSMC), which is input to the delay fault test pattern generation control circuit  209 , is connected to each of the data input terminal (D) and the scan enable terminal (SMC) of the SF  1 B, the data input terminal (D) of the NF  80 , the data input terminal (A) of the OR  31 , and the data input terminal (A) of the OR  83 . The output signal of the data output terminal (Z) of the OR  31  is output as the local scan enable signal (LSMC) and is supplied to the logic circuit  203 . The data output terminal (Q) of the NF  80  is connected to a data input terminal (C) of the OR  83 . The clock terminals of the SF  71  and the CGC  72  of the logic circuit  73  are supplied with the same clock signal as that input to the delay fault test pattern generation control circuit  209 . The output signal from the gated clock terminal (GCLK) of the CGC  71  is output as the gated clock signal (GCLK) and is supplied to the logic circuit  203 . 
         [0142]    The circuit configuration of the clock gating cell CGC  72  is similar to that of the clock gating cell CGC  65 , so the description thereof is omitted. The circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1B , so the description thereof is omitted. Similarly, the circuit configuration of the logic circuit  203  is similar to that shown in  FIG. 5B , so the description thereof is omitted. 
         [0143]      FIG. 14  is a waveform chart when the LSMC signal of the delay fault test pattern generation control circuit  209  outputs the same waveform as that shown in  FIG. 9 .  FIG. 14  differs from  FIG. 9  in that the waveform of the gated clock signal (GCLK) which is the output signal of the CGC  72  controlled by the delay fault test pattern generation control circuit  209  is added. The waveforms of signals (signals ranging from CLK to NF  51 ) other than the gated clock signal (GCLK) of the CGC  72  controlled by the delay fault test pattern generation control circuit  209  are the same as those shown in  FIG. 9 , so the description thereof is omitted. When the status values of the SF  1 B and the NF  51  are “1” and “1”, respectively, at time (T 3 ), the status values of the SF  1 B and the NF  51  are “0” and “1”, respectively, and the status value of the NF  80  is “0” at time (T 4 ). Accordingly, when both the scan test mode signal (TE) and the delay fault test mode signal (TDFMODE) indicate “1”, the data output terminals of the OR  83  and the NAND  64  indicate “0” and “0”, respectively. Thus, at time (CCE), the CGC  72  cannot output the clock signal (CLK) supplied to the delay fault test pattern generation control circuit  209 . This makes it impossible to supply the capture cock signal to the logic circuit  203  from the gated clock terminal (GCLK) of the CGC  72 , which is controlled by the delay fault test pattern generation control circuit  209 , as shown in the area  110 . Until time (T 3 ), the NF  80  indicates the logical value “1” of the GSMC signal, which is captured until time (CE 2 ), and captures the signal value “0” of the GSM at each of time (LCE) and time (CCE). At time (CE 3 ), the NF  80  captures the signal value “1” of the GSMC. At time (CE 3 ), the SF  2 B of the logic circuit  203  captures the signal value “0” of the NF  51  at time (T 5 ). After time (T 5 ), the scan shift operation is carried out, so the description of the scan shift operation of the SF  2 B to the SF  7  is omitted. 
         [0144]    In the fourth embodiment, the SF  1 B and the NF  51  play the role of generating the transition signal of the local scan enable signal (LSMC) during the launch clock time and the capture clock time. On the other hand, in the seventh embodiment, when the transition of the local scan enable signal (LSMC) occurs, for example, when capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  occurs during the capture clock time, the CGC  72  performs control to prevent the capture clock signal from being supplied to the logic circuit  203 . In the sixth embodiment, when the logical values of the SF  1 B and the NF  51  are “1” and “1”, respectively, the SF  61  controls whether or not to supply the launch clock to the logic circuit  203  from the CGC  72  during the launch clock time. On the other hand, in the seventh embodiment, since the signal value of the NF  80  is “1” during the launch clock time, the launch clock is supplied to the logic circuit  203  without fail. 
         [0145]    Also in the seventh embodiment, the delay fault test pattern generation control circuit  209  is converted into the number of transistors under the same conditions as those of the first embodiment. Assume in the seventh embodiment that the delay fault test pattern generation control circuit  209  and the AND  70  are configured in combination. Assuming that the number of transistors of the inverter is 2 Tr; the number of transistors of each of the 2-input NAND gate and the 2-input NOR gate is 4 Tr; the number of transistors of the 3-input OR gate is 8 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the seventh embodiment is represented by (38+30+30+2+4+4+6+6+8+6)×100=13400 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. Thus, the area OH of the seventh embodiment is about 1/50 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the seventh embodiment provides an advantageous effect of reducing the area OH. 
         [0146]    As in the fourth embodiment, in the delay fault test pattern generation control circuit  209 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby allowing each scan FF to stop the capture operation from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  209  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0147]    Further, in the seventh embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the seventh embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
         [0148]    Further, in the seventh embodiment, the delay fault test pattern generation control circuit  209  is not disposed on a clock line of an existing circuit. Therefore, the seventh embodiment also provides an advantageous effect of suppressing an increase in skew on the clock line. 
       Eighth Embodiment 
       [0149]    Subsequently, configuration example of a delay fault test pattern generation control circuit  210  and the logic circuit  203  according to an eighth embodiment will be described with reference to  FIG. 15 . 
         [0150]    The delay fault test pattern generation control circuit  210  has a configuration in which the clock gating cell CGC  65  is added to the delay fault test pattern generation control circuit  209 . The data output terminal (Z) of the OR  83  is connected to the scan enable terminal (SMC) of the CGC  65 . The data output terminal (Z) of the NAND  64  is connected to the clock enable terminal (CEN) of the CGC  65 . The gated clock terminal (GCLK) of the CGC  65  is connected to the gated clock output terminal (GCLK) of the delay fault test pattern generation control circuit  210 . The clock terminal of the CGC  65  is connected to the clock terminal (CLK) of the delay fault test pattern generation control circuit  210 . The clock signal output from the gated clock output terminal (GCLK) of the delay fault test pattern generation control circuit  210  is supplied to the logic circuit  203 . The other configuration of the delay fault test pattern generation control circuit  210  is similar to that of the delay fault test pattern generation control circuit  209 , so the description thereof is omitted. 
         [0151]    The circuit configuration of the clock gating cell CGC  65  is similar to that shown in  FIG. 10B , so the description thereof is omitted. The circuit configuration of the multiplexer-type SF  202  is similar to that shown in  FIG. 1B , so the description thereof is omitted. Similarly, the circuit configuration of the logic circuit  203  is similar to that shown in  FIG. 5B , so the description thereof is omitted. 
         [0152]    The operation of the delay fault test pattern generation control circuit  210  is similar to that shown in  FIG. 14 , so the description thereof is omitted. 
         [0153]    Also in the eighth embodiment, the delay fault test pattern generation control circuit  210  is converted into the number of transistors under the same conditions as those of the first embodiment. Assuming that the number of transistors of the inverter is 2 Tr; the number of transistors of each of the 2-input NAND gate and the 2-input NOR gate is 4 Tr; the number of transistors of the 3-input OR gate is 8 Tr; the number of transistors of the clock gating cell is 20 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the eighth embodiment is represented by (38+30+30+2+4+4+6+6+8+20)×100=15000 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. The area OH of the eighth embodiment is about 1/45 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the eighth embodiment provides an advantageous effect of reducing the area OH. 
         [0154]    As in the fourth embodiment, in the delay fault test pattern generation control circuit  210 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby allowing each scan FF to stop the capture operation from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  210  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0155]    Further, in the eighth embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the eighth embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
       Ninth Embodiment 
       [0156]    Subsequently, a configuration example of a control circuit obtained by combining the delay fault test pattern generation control circuit  206  and a delay fault test pattern generation control circuit  211  according to a ninth embodiment will be described with reference to  FIG. 16 . 
         [0157]    The delay fault test pattern generation control circuit  211  has a configuration in which the components of the delay fault test pattern generation control circuit  206  are omitted from the delay fault test pattern generation control circuit  210 , thereby making the clock control system independent. 
         [0158]    The scan input terminal of an SF  1 C is connected to the same signal line SIN connected to the scan input terminal of the SF  1 B of the delay fault test pattern generation control circuit  206 . The GSMC is connected to each of the data input terminal (D) and the scan enable terminal (SMC) of the SF  1 C, the data input terminal (A) of the OR  83 , and the data input terminal (B) of the OR  84 . The clock signal CLK is connected to each of the clock terminal (CLK) of the SF  1 C, the clock terminal (CLK) of the NF  80 , and the clock terminal (CLK) of the CGC  65 . The scan test mode signal TE is connected to each of the data input terminal (B) of the AND  81  and the data input terminal of an inverter INV  100 . The delay fault test pattern generation mode signal (TDFMODE) is connected to each of the data input terminal (A) of the AND  81  and the data input terminal (B) of the NOR  82 . The data output terminal (Q) of the SF  1 C is connected to each of the data input terminal (A) of the NOR  82  and the data input terminal of the INV  62 . The data output terminal of the INV  62  is connected to the data input terminal (A) of the OR  84 . The data output terminal (Z) of the NOR  82  is connected to the data input terminal (B) of the OR  83 . The data output terminal (Z) of the OR  84  is connected to the data input terminal (D) of the NF  80 . The data output terminal (Z) of the AND  81  is connected to the reset-bar terminal (RESETB) of the NF  80 . The data output terminal (Z) of the NF  80  is connected to the data input terminal (C) of the OR  83 . The data output terminal (Z) of the OR  83  is connected to the scan enable terminal (SMC) of the CGC  65 . The data output terminal of the INV  100  is connected to the CEN terminal of the CGC  65 . The gated clock terminal (GCLK) of the CGC  65  is connected to the gated clock terminal (GCLK) of the delay fault test pattern generation control circuit  211 . The gated clock terminal (GCLK) of the delay fault test pattern generation control circuit  211  is connected to the clock terminal of the logic circuit  203 . 
         [0159]    The operation of the ninth embodiment is similar to that of the eighth embodiment, and the operation shown in  FIG. 14  is carried out. When the signal value of the SF  1 B of the delay fault test pattern generation control circuit  206  is “1” at time (T 3 ), the delay fault test pattern generation control circuit  211  cannot output the clock from the gated clock (GCLK) at time (CCE). 
         [0160]    Also in the ninth embodiment, the delay fault test pattern generation control circuit  211  is converted into the number of transistors under the same conditions as those of the first embodiment. Assuming that the number of transistors of the inverter is 2 Tr; the number of transistors of each of the 2-input NAND gate and the 2-input NOR gate is 4 Tr; the number of transistors of the 3-input OR gate is 8 Tr; the number of transistors of the clock gating cell is 20 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the ninth embodiment is represented by (38+38+30+30+2+2+4+6+6+6+8+20)×100=19000 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. Thus, the area OH of the ninth embodiment is about 1/35 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the ninth embodiment provides an advantageous effect of reducing the area OH. 
         [0161]    As in the fourth embodiment, in the delay fault test pattern generation control circuits  211  and  206 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby enabling each scan FF to stop the capture operation from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the combination of the delay fault test pattern generation control circuits  211  and  206  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0162]    Further, in the ninth embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the ninth embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
       Tenth Embodiment 
       [0163]    Subsequently, a configuration example of a delay fault test pattern generation control circuit  212  according to a tenth embodiment will be described with reference to  FIG. 17 . 
         [0164]    The delay fault test pattern generation control circuit  212  has a configuration in which the AND  70  is incorporated at the fan-in side of the clock enable terminal (CEN) of the CGC  65 . The data input terminal (A) of the AND  70  is connected to the data output terminal (Z) of the NAND  64 , and the data input terminal (B) of the AND  70  is connected to the clock enable terminal (CEN) of the delay fault test pattern generation control circuit  212 . The data output terminal (Z) of the AND  70  is connected to the clock enable terminal (CEN) of the CGC  65 . 
         [0165]    In the delay fault test pattern generation control circuit  212 , the clock gating cell present in the existing circuit can be replaced with the delay fault test pattern generation control circuit  212 . 
         [0166]    The operation of the delay fault test pattern generation control circuit  212  is similar to the operation of the delay fault test pattern generation control circuit  210  shown in  FIG. 14 , so the description thereof is omitted. 
         [0167]    Also in the tenth embodiment, the delay fault test pattern generation control circuit  212  is converted into the number of transistors under the same conditions as those of the first embodiment. Assuming that the number of transistor of the inverter is 2 Tr; the number of transistors of each of the 2-input NAND gate and the 2-input NOR gate is 4 Tr; the number of transistors of the 3-input OR gate is 8 Tr; the number of transistors of the clock gating cell is 20 Tr; and the other conditions are the same as those of the first embodiment, the area OH of the tenth embodiment is represented by (38+30+30+2+4+4+6+6+8+20+6)×100=15600 Tr, and the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440 is represented by (28+6)×20000=680000 Tr. Thus, the area OH of the tenth embodiment is about 1/43 of the area OH of the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2008-096440. Accordingly, the tenth embodiment provides an advantageous effect of reducing the area OH. 
         [0168]    As in the fourth embodiment, in the delay fault test pattern generation control circuit  212 , the signal value of the local scan enable terminal (LSMC) is set to “1” during capturing, thereby enabling each scan FF to stop the capturing operation from the data input terminal during capturing. In a circuit including a scan compression circuit, when a scan FF irrelevant to a target fault captures a user logic, i.e., an X value from a combinational circuit such as the AND  11 , the X value may be propagated to the compression circuit, which may lower the fault coverage. Suppression of the capture operation during capturing prevents each scan FF from capturing the X value and also prevents the X value from being propagated to the scan compression circuit. As a result, the delay fault test pattern generation control circuit  212  also provides an advantageous effect of improving the final delay fault coverage as compared with the delay fault test pattern generation control circuit  200 . 
         [0169]    Further, in the tenth embodiment, capturing of signals from the SI terminals of the scan FFs (SF  1  to SF  8  and SF  2 B) in the logic circuit  203  does not occur during the capture clock time. Therefore, there is no need to take into consideration the at-speed transfer on the scan chain during timing-driven layout. Accordingly, the tenth embodiment also provides an advantageous effect of shortening the period of designing the timing-driven layout. 
         [0170]    Further, in the tenth embodiment, the clock gating cell of the existing circuit can be incorporated in such a mode that the clock gating cell is replaced with the delay fault test pattern generation control circuit  212 . Therefore, the tenth embodiment also provides an advantageous effect of suppressing an increase in skew on the clock line. 
         [0171]    While the present invention has been described in detail above with reference to embodiments of the invention, the SF  1  is not necessarily provided with a reset-bar terminal. Further, as easily understood by those skilled in the art, the user logic can be prevented from being destroyed also in the configuration in which an AND gate is provided at the output side of the data output terminal (Q) of the SF  1  to thereby enable control of the AND gate by using the scan test mode signal (TE). The same holds true for the SF  61 , NF  51 , and NF  80 . 
         [0172]    The invention made by the present inventors has been described above with reference to embodiments of the present invention. However, the present invention is not limited to the embodiments described above, but may be modified in various manners without departing from the gist of the present invention. 
         [0173]    While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention can be practiced with various modifications within the spirit and scope of the appended claims and the invention is not limited to the examples described above. 
         [0174]    Further, the scope of the claims is not limited by the embodiments described above. 
         [0175]    Furthermore, it is noted that, Applicant&#39;s intent is to encompass equivalents of all claim elements, even if amended later during prosecution. 
         [0176]    The first to tenth embodiments can be combined as desirable by one of ordinary skill in the art. cm What is claimed is:

Technology Classification (CPC): 6