Built-in self test circuit

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a built-in self test (BIST) circuit, and more particularly, to a BIST circuit which is capable of generating a test pattern including series of test input signals and test result signals.

[0003] (b) Description of the Related Art

[0004] A BIST circuit is incorporated in an LSI for testing the function of the LSI. The LSI is evaluated by the BIST circuit as to non-defectiveness in the function thereof after the completion of the product. FIG. 10 shows a conventional BIST circuit incorporated in a system LSI (logic circuit), described in Patent Publication JP-A-8-15382.

[0005] A plurality of scan paths <b>62</b> are formed each grouping the flip-flops disposed in the internal circuit of the LSI <b>61</b>, when a test mode is selected for the LSI. Each scan path <b>62</b> connects the group of flip-flops in a cascade (serial) connection, and is associated with a corresponding scan-in pin <b>65</b> which receives a series of input scan-in signals, i.e., scan-in signal pattern. The received scan-in signal pattern is shifted forward along the scan path <b>62</b> through the flip-flops, which operate with a clock signal, to be output from the scan path <b>62</b>.

[0006] Each scan-in signal passed by the scan path <b>62</b> is delivered to a corresponding logic gate <b>66</b>, and compared by using a logic operation in the logic gate <b>66</b> against the scan-in signal which is directly input to the logic gate <b>66</b>. The comparison results are delivered to the data compression unit <b>64</b> from the logic gates <b>66</b>. In the logic operation for the comparison, an external pin <b>67</b> is used for receiving a specified signal, which masks some signals liable to assuming unstable states of logic after passing the scan path. The data output from the data compression unit <b>64</b> is delivered to an external LSI tester through the scan-out pins (not shown). By examining the data from the data compression unit <b>64</b>, presence or absence of a defect in the internal circuit of the LSI can be judged. The circuit test using the above scan paths costs a large amount of time due to the configuration wherein the serially connected flip-flops consecutively shift the scan-in signal responding to the clock signal.

[0007] The BIST circuit is also used for examining the non-defectiveness of memory cells in a semiconductor memory device such as a DRAM. In the evaluation of memory cells, a variety of test patterns including a marching pattern and a checkered pattern are generally used. The BIST circuit includes a test pattern generator block for generating test patterns including a series of data patterns and a variety of address patterns, the latter specifying the memory cells from the first address to the final address. The BIST circuit writes and reads data “1” or “0” specified by the data pattern into/from memory cells of the addresses specified by the address pattern, and compares the read data against the preceding write data to examine the non-defectiveness of the memory cells and corresponding interconnects. The BIST circuit incorporated in the DRAM generally includes a test pattern generator block having a larger circuit scale due to the large number of test patterns being needed for examining the function of the DRAM.

[0008] Patent Publication JP-A-2000-76894 describes a BIST circuit having a test pattern generator, which generates another test pattern while using a counter, after a test using a previous test pattern is finished. This BIST circuit can generate a large number of test patterns by using a single pattern generator while suppressing the increase of the circuit scale.

[0009] As understood from the above description, the BIST circuits are designed for testing the presence or absence of defects in the LSIs after the fabrication processes thereof, the LSIs including a logic circuit and/or memory device. It is to be noted that the BIST circuit should also be designed correctly for achieving the function thereof because the BIST circuit itself is also one of the electric circuits in the LSI. The functions of the LSI including the BIST circuit are verified or examined based on the operations and the test results by the BIST circuit generating the test pattern during the test operation.

[0010] It is effective to verify the correctness of the circuits in the LSI by examining the interconnects therein during the design stage thereof for achieving reduction of costs and turn around time of the LSI by preventing defects from occurring in the next stages. In such a case, the verification must be achieved in both the internal circuit and the BIST circuit of the LSI. It is noted, for the design verification of the interconnects in the circuit, the test patterns generated by the test pattern generator in the BIST circuit may be effectively used.

[0011] However, since the ordinary test patterns generated by the test pattern generator are dedicated to finding the physical defects in the LSI, the number of test patterns is large. Thus, if the ordinary test patterns are used for verifying the LSI in the design stage thereof, the verification necessitates a larger amount of test time. In addition, if the verification test patterns for use in the design verification are manually created separately from the ordinary test patterns to be generated by the BIST circuit, this costs huge man-hours to thereby raise the fabrication costs of the LSI.

[0012] In view of the above, it is an object of the present invention to provide a BIST circuit capable of facilitating the design verification of an LSI including the BIST circuit which generates test patterns for testing the internal circuit of the LSI.

[0013] It is another object of the present invention to provide a method for verifying the design of an LSI including a BIST circuit by using the test patterns to be generated by the BIST circuit itself.

[0014] The present invention provides a built-in self test (BIST) circuit for testing an internal circuit of an LSI, including a verification test pattern generator for generating a verification test pattern, wherein the verification test pattern is dedicated to verification of electric connections in the LSI.

[0015] The present invention also provides a method for testing the LSI by using the BIST circuit according to the present invention.

[0016] In accordance with the BIST circuit and the method of the present invention, since the test patterns to be generated by the verification test pattern generator in the BIST circuit are used for verification of design connections in the LSI during the design stage thereof, man-hours for creating the verification test patterns can be reduced. In addition, since the number of test patterns to be generated by the verification test pattern generator can be much smaller than the number of test patterns to be generated by the conventional test pattern generator due to the limited usage thereof, the time length needed to verify the design connections in the LSI can be reasonably short.

[0017] The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram of an LSI including a BIST circuit according to a first embodiment of the present invention.

[0019]FIG. 2 is a block diagram of the BIST circuit shown in FIG. 1.

[0020]FIGS. 3A to <b>3</b>C are schematic diagrams of data stored in th4e memory cells during a marching pattern test.

[0021]FIGS. 4A and 4B are schematic diagrams of data stored in the memory cells during a checkered pattern test.

[0022]FIGS. 5A to <b>5</b>C are block diagrams of the verification test pattern generator, marching pattern generator and checkered pattern generator, respectively, shown in FIG. 2.

[0023]FIGS. 6A and 6B are schematic diagrams of address transition in the verification test pattern generator and marching pattern generator, respectively.

[0024]FIG. 7 is a block diagram of another example of the test pattern generator.

[0025]FIG. 8 is a block diagram of a system LSI including BIST circuits according to a second embodiment of the present invention.

[0026]FIG. 9 is a block diagram of one of the BIST circuits shown in FIG. 8.

[0027]FIG. 10 is a block diagram of an LSI including a conventional BIST circuit.

PREFERRED EMBODIMENTS OF THE INVENTION

[0028] The BIST circuit according to the present invention is preferably incorporated in an LSI including a logic circuit and/or memory device, such as system LSI, logic LSI and DRAM.

[0029] If the BIST circuit according to the present invention is incorporated in a logic LSI or logic core block, for example, another BIST circuit is preferably incorporated therein including a test pattern generator which generates a scan-in test pattern and a scan-out data expected pattern for conducting a scan path test. The scan path test is generally used for examining the presence or absence of a physical defect in the LSI during a product test. The physical defect may arise due to an incomplete fabrication step such as in a diffusion step or etching step in the fabrication process of the LSI. For detecting the physical defect, the verification test pattern may be used in the product test while assisting the scan path test.

[0030] The design verification test pattern is preferably described in a behavior level language for allowing a defect to be found in the early stage of the design of the LSI.

[0031] Now, the present invention is more specifically described with reference to accompanying drawings, wherein similar constituent elements are designated by similar reference numerals.

[0032] Referring to FIG. 1, an LSI including a BIST circuit according to a first embodiment of the present invention is implemented as a dynamic random access memory (DRAM) device <b>10</b>. The DRAM device <b>10</b> includes a RAM block <b>11</b>, the BIST circuit <b>12</b> for testing the RAM block <b>11</b>, an address selector <b>13</b> for switching the address inputs of the RAM block <b>15</b> depending on a normal mode or a test mode, and a data selector <b>14</b> for switching the data inputs of the RAM block <b>15</b> depending on the normal mode or the test mode. These circuit elements are formed on a single semiconductor chip.

[0033] The RAM block <b>11</b> includes a memory cell array <b>15</b> including a plurality of memory cells arranged in an array, an address buffer <b>16</b> for receiving an input address signal to deliver the same to the memory cell array <b>15</b>, row and column decoders <b>17</b> and <b>18</b> for decoding the input address signal delivered through the address buffer <b>16</b>, and a data buffer <b>19</b> for transferring data between the memory cell array <b>15</b> and an external circuit.

[0034] The row decoder <b>17</b> decodes the row address of the address signal, whereas the column address decoder <b>18</b> decodes the column address of the address signal and transfers data between the data buffer <b>19</b> and the column of the memory cell array <b>15</b> specified by the column address.

[0035] The address selector <b>13</b> has address input terminals connected to the normal-mode address pins <b>21</b> and address output terminals of the BIST circuit <b>12</b>, and address output terminals connected to the address buffer <b>16</b>. The address selector <b>13</b> has a control terminal connected to a test-mode signal input pin <b>27</b> for receiving a test mode signal from outside the chip, selecting the input address signal received from outside the chip in the normal mode and the address signal delivered from the BIST circuit <b>12</b> in the test mode. The data selector <b>14</b> has a control terminal connected to the test mode input pin <b>27</b>, connecting normal-mode data input/output pins <b>38</b> to the data buffer <b>19</b> in the normal mode whereas connecting data output terminals of the BIST circuit <b>12</b> to the data buffer <b>19</b> in the test mode.

[0036] The BIST circuit <b>12</b> has terminals connected to the test-mode signal input pin <b>27</b>, test result output pins <b>28</b>, a clock input pin <b>29</b>, and the input terminals of the address selector <b>13</b> and the data selector <b>14</b>. The BIST circuit <b>12</b> is activated by the active level of the test mode signal for selecting the test mode of the DRAM device, generating therein verification test pattern including address patterns, command pattern specifying read or write operation, and write data and expected data for the test mode without an additional input signal.

[0037] The BIST circuit <b>12</b> compares the read data read from the memory cell array <b>15</b> against the expected data generated in the BIST circuit <b>12</b> during the test mode, delivering therefrom the comparison results to outside the DRAM device <b>10</b> through the test result output pin <b>28</b>. The BIST circuit <b>12</b> is inactivated by the inactive level of the test mode signal for selecting the normal mode, whereby the RAM block <b>11</b> performs normal write and read operations between the same and the external circuit through the data input/output pins <b>25</b>.

[0038] Referring to FIG. 2, the BIST circuit <b>12</b> includes a test pattern generator block <b>30</b> which includes a verification test pattern generator <b>31</b>, a marching pattern generator <b>32</b> and a checkered pattern generator <b>33</b>, an address signal generator <b>34</b>, a test-input data generator <b>35</b>, an expected data generator <b>36</b> and a comparator <b>37</b>.

[0039] Each pattern generator <b>31</b>, <b>32</b> or <b>33</b> in the test pattern generator block <b>30</b> generates a corresponding specified pattern, and delivers an address pattern <b>301</b> in the specified pattern to the address signal generator <b>34</b> as a serial-data signal. The address signal generator <b>34</b> delivers an address signal <b>302</b> including row and column addresses to the RAM block <b>11</b> through the address selector <b>13</b> and the address inputs of the RAM block <b>11</b>. The write data signal <b>303</b> in the specified pattern generated by each pattern generator <b>31</b>, <b>32</b> or <b>33</b> is fed to the test-input data generator <b>35</b>. The test-input data generator <b>35</b> generates test write data <b>304</b> based on the input write data signal <b>303</b>, delivering the test write data <b>304</b> to the RAM block <b>11</b> through the data selector <b>14</b> and the data inputs of the RAM block <b>11</b>.

[0040] The test-input data generator <b>35</b> is implemented as a timing controller, for example, which controls the timing of the input of data to the RAM block <b>11</b> in synchrony with the input of the address signal to the RAM block <b>11</b>. The read data signal <b>305</b> generated by each pattern generator <b>31</b>, <b>32</b> or <b>33</b> is delivered to the expected data generator <b>36</b>, which generates expected data for each memory cell and delivers the same to the comparator <b>37</b>. The expected data generator <b>36</b> is implemented as a timing controller, similarly to the input data generator. The comparator <b>37</b> compares the read data <b>307</b> read from each memory cell against the expected data <b>306</b>, delivering the comparison results as a test result signal <b>308</b> to outside the DRAM device <b>10</b> through the test result output pin <b>28</b>.

[0041] Each of the RAM block <b>11</b> and constituent elements <b>31</b> to <b>37</b> of the BIST circuit <b>12</b> is subjected to separate design verification at a circuit level thereof in the design stage of CAD. The verification test pattern generator <b>31</b> is provided herein for verifying the correctness of interconnections between the BIST circuit <b>12</b> and the RAM block <b>11</b>. In operation of the product test mode, a “START” signal first assumes an active level to activate the BIST circuit <b>12</b> after the test mode signal is activated.

[0042] In the pattern generator block <b>30</b>, the verification test pattern generator <b>31</b> first starts for the test of the connections responding to the active level of the START signal. After the test is finished based on the verification test pattern generated by the verification test pattern generator <b>31</b>, the marching pattern generator <b>32</b> and then the checkered pattern generator <b>33</b> start for the operational test of the RAM block <b>11</b>. If the verification is to be conducted based only on the verification test pattern during the design stage of the RAM device, then provision of the clock signal to the BIST circuit <b>12</b> is stopped after the completion of the design verification test based on the verification test pattern generated by the pattern generator <b>31</b>.

[0043] Referring to FIGS. 3A to <b>3</b>C, there are consecutively shown lists of data stored in the memory cells during the marching pattern test of the product test which is conducted based on the pattern generated by the marching pattern generator <b>32</b>. First, all the N memory cells of first to N-th addresses (or address zero to address N−1) in the memory cell array are initialized to store therein data “0” by consecutively writing data “O” in the ascending order of the addresses. This situation is shown in FIG. 3A.

[0044] Subsequently, data “0” is read from the memory cell of 1st address (referred to as simply “1st address” hereinafter) in the first row and the first column, and then compared against the expected data, followed by writing data “1” into the 1st address, reading the data “1” from the 1st address, and comparing the read data against the expected data, thereby ending the test for the 1st address.

[0045] Thereafter, the test is performed for the next, 2nd address (address “1”) in the second row and the first column, wherein a similar procedure is conducted for the 2nd address. The test is consecutively performed for the addresses in the subsequent rows in the ascending order of the addresses along the first column. FIG. 3B shows the stored data after the test for the 3rd address is completed, wherein 1st to 3rd addresses store therein data “1” whereas the remaining addresses store therein data “0”. After the test is finished for the first column, the test is performed for the next column similarly to the first column in the ascending order of the addresses, and continued up to the N-th address in the last row and the last column, whereby the first stage of the marching pattern test is finished. The data stored in the memory cells at the end of the first stage is shown in FIG. 3C.

[0046] Thereafter, the second stage of the marching pattern test is performed beginning with the N-th address toward the first address in the descending order. The test in the second stage of the marching pattern test is performed by reading the stored data “1” from the selected address, comparing the read data against the expected data, then storing data “0” in the selected address, reading the data “0” from the selected address and comparing the read data against the expected data. The data stored in all the memory cells shift from the state shown in FIG. 3C through the state shown in FIG. 3B to the final state shown in FIG. 3A.

[0047] The marching pattern test is conducted for detecting a degeneration defect wherein the data in a memory cell is fixed either at “1” or at “0”, a coupling defect wherein data is defectively written in a memory cell upon writing the data in an adjacent memory cell, and a defect in the address decoder.

[0048] Referring to FIGS. 4A and 4B, there are shown lists of data during the procedure in the checkered pattern test. First, initialization is performed to store data “0” and “1” in all the memory cells so that data “0” and “1” thus stored appear alternately as viewed from the first address to the N-th address. This situation is shown in FIG. 4A. Subsequently, the data “0” and “1” are read consecutively from the first address to the N-th address, and compared against the expected data.

[0049] Thereafter, data “1” and “0” are stored in all the memory cells so that data “1” and “0” thus stored appear alternately as viewed from the first address to the N-th address. This situation is shown in FIG. 4B. The stored data are then read consecutively from the first address to the N-th address, and the read data is compared against the expected data. In the checkered pattern test, both the read and write operations are conducted in the ascending order of the addresses. The checkered pattern test is conducted for detecting a degeneration defect and a pattern sensitive defect.

[0050] The verification test pattern generator <b>31</b> generates a verification test pattern, wherein the data used for writing and reading operations are similar to the data used in the marching pattern test. However, the number of selected addresses in the verification test pattern generator <b>31</b> is different from that of the marching pattern test.

[0051] More specifically, the addresses selected for writing and reading operations in the design verification test correspond to 2ⁿ-th addresses wherein n is an integer, while skipping the other addresses. This is because it is sufficient that the design verification pattern test be used for detecting a connection defect of the interconnects in the RAM device. The connection defect can be detected by specifying the row address lines and the column address lines only once for every row address line and every column address line.

[0052] Thus, the design verification pattern test is conducted by specifying one of the 2ⁿ-th addresses, reading data “0” from the specified address, comparing the read data against the expected data, writing data “1” in the specified address, reading the data “1” from the each specified address and comparing the read data against the expected data. After the test for the specified address is finished, another 2ⁿ-th address is specified in the ascending order and is subjected to similar read and write operations. The 2ⁿ-th addresses are selected in both the ascending order and the descending order of the addresses.

[0053] The procedure for skipping selection of the addresses will be described hereinafter. For selecting the addresses in the ascending order, the second address, i.e., address “1” is first selected as the starting address, then the next address is obtained by multiplying the number “1” of the starting address by two, and the subsequent addresses are obtained by consecutively multiplying the numbers of the addresses previously specified by two until the multiplied number exceeds N−1. That is, the selected address are 1, 2, 4, 8, • • • .

[0054] For selecting the addresses in the descending order, assuming that the first value for parameter A equals “1”, the starting address is specified by the number (i.e., N−1) of the last address minus A. Subsequently, while replacing the previous value for A by the next value for A which is obtained by A=A×2, the next address is obtained by the number (N−1) of the last address minus A. This procedure is iterated until the value for parameter A exceeds the number of the last address. The practical circuit which achieves calculation of these addresses may be implemented by a counter for counting the number of clock pulses in a clock signal and an associated logic circuit for performing calculation based on the count in the counter. In an alternative, the circuit may be implemented by using a shift register.

[0055]FIGS. 5A to <b>5</b>C show examples of the pattern generators <b>31</b>, <b>32</b> and <b>33</b>, respectively. The verification test pattern generator <b>301</b> shown in FIG. 5A includes a shift register <b>41</b> for generating an address pattern <b>301</b> and a verification data generator <b>42</b> for generating a write data pattern <b>303</b> and an expected data pattern <b>305</b>. The shift register <b>41</b> receives an input test-mode clock signal CLK to thereby generate the address pattern <b>301</b>, and delivers the address pattern <b>301</b> to the address generator <b>34</b> shown in FIG. 2.

[0056] In the initialization, write data “0” is iteratively output as the write data pattern <b>303</b> from the verification data generator <b>42</b> each time the outputs <b>301</b> of the shift register <b>41</b> are changed. After the initialization, verification test pattern generator <b>31</b> shifts in a marching test mode, whereby the outputs of the shift register <b>41</b> are once reset to “0”, as shown at the top figure in FIG. 6A, which shows an example of a 4-bit configuration of the shift register <b>41</b>. Then, the addresses are specified in the ascending order, wherein the least significant bit of the outputs is first set at “1”, and the data “1” is shifted toward the most significant bit at each clock pulse, as shown at the remaining figures in FIG. 6A.

[0057] The verification data generator <b>42</b> delivers the expected data for each address delivered from the shift register <b>41</b> as the expected data pattern <b>305</b>. The verification data generator <b>42</b> delivers “0” for the first expected data, then delivers “1” for the next expected data, and then alternates expected data “0” and “1” each time the shift register <b>41</b> changes its outputs <b>301</b>. For specifying the addresses in the descending order, all the outputs of the shift register <b>41</b> are set at “1” for the initialization, then data “0” is set at the most significant bit and shifted toward the least significant bit.

[0058] The marching pattern generator <b>32</b>, as shown in FIG. 5B, includes an up/down counter <b>43</b> for counting the test-mode clock pulses to generate an address pattern, and a marching data generator <b>44</b> for generating write data and expected data similar to those generated by the verification test pattern generator <b>31</b>. FIG. 6B shows an example of the shift of the outputs of the up/down counter <b>43</b> in the case of a 4-bit address configuration.

[0059] The checkered pattern generator <b>33</b>, as shown in FIG. 5C, includes a counter <b>45</b> for counting the test-mode clock pulses, and a checkered data generator <b>46</b> for delivering “0” and “1” alternately each time the counter <b>45</b> changes its output until the count in the counter <b>45</b> exceeds the number (N−1) of the last address. The counter <b>45</b> counts up at the count of N−1, and iterates delivering all the addresses twice.

[0060] Referring to FIG. 7, another example of the test pattern generator block <b>30</b> includes a register <b>47</b> for storing address patterns for all of the different test modes and a single pattern generator <b>48</b>. The single pattern generator <b>48</b> receives one of a verification pattern mode signal <b>401</b>, a marching pattern mode signal <b>402</b> and a checkered pattern mode signal <b>403</b> to operate in a corresponding test mode. The single pattern generator <b>48</b> operates with the input test-mode clock signal CLK to generate write data and expected data for each test mode.

[0061] Referring to FIG. 8, a system LSI generally designated by numeral <b>20</b> includes a logic core block <b>21</b>, a user logic block <b>23</b>, a first BIST circuit <b>25</b> for testing the logic core block <b>21</b>, a plurality of RAM blocks <b>22</b>, a plurality of second BIST circuits <b>26</b> each disposed corresponding to one of the RAM blocks <b>22</b>, and a test controller <b>24</b> for controlling the BIST circuits <b>25</b> and <b>26</b>.

[0062] The logic core block <b>21</b> operates for processing of desired tasks, the user logic block <b>23</b> converts the data delivered from the logic core block <b>21</b> into a data format which the user interface can recognize, the plurality of RAM blocks <b>22</b> temporarily store therein data for the logic core block <b>21</b>, and the test controller <b>24</b> controls the system LSI <b>20</b> to operate in a test mode. The BIST circuits <b>25</b> and <b>26</b> are used for testing the system LSI <b>20</b> in the physical configuration during the product test of the LSI <b>20</b> as well as in the design verification test during the design stage of the system LSI <b>20</b>.

[0063] The test controller <b>24</b> assumes an active level upon input of the test command signal, thereby delivering the test-mode clock signal and a test start signal to the BIST circuits <b>25</b> and <b>26</b>. Each of the BIST circuits <b>25</b> and <b>26</b> is activated by these signals to operate for testing the system LSI <b>20</b>. After the BIST circuits <b>25</b> and <b>26</b> deliver the test result signals to the test controller <b>24</b>, the test results are output from the test controller <b>24</b>. Each of the BIST circuits <b>26</b> associated with the RAM blocks <b>22</b> has a configuration similar to that described in the first embodiment, and thus the detailed description thereof is omitted herein.

[0064] Referring to FIG. 9, the BIST circuit <b>25</b> associated with the logic core block <b>21</b> includes a verification test pattern generator <b>51</b>, a scan test pattern generator <b>52</b>, an input data generator <b>53</b>, an output data compression unit <b>54</b>, a scan-in data generator <b>55</b>, and a scan-out data compression unit <b>56</b>, which operate in combination for testing the logic core block <b>21</b>.

[0065] The verification test pattern generator <b>51</b> is activated upon receiving the test start signal <b>201</b> and the test-mode clock signal <b>202</b> from the test controller <b>24</b>, thereby generating a verification test pattern <b>203</b>, which may include serial data, to deliver the same to the input data generator <b>53</b> and the output data compression unit <b>54</b>. The input data generator <b>53</b> generates an input signal pattern <b>204</b>, which may include parallel data, based on the verification test pattern <b>203</b>, to thereby deliver the same to the logic core block <b>21</b> at the input pins thereof.

[0066] The output data compression unit <b>54</b> generates an expected data pattern of the output pins of the logic core block <b>21</b> based on the verification test pattern <b>203</b> delivered from the verification test pattern generator <b>51</b>, comparing the outputs <b>205</b> from the logic core block <b>21</b> against the expected pattern to deliver the comparison results as the test result signal <b>206</b> to the test controller <b>24</b> after compression thereof.

[0067] The scan test pattern generator <b>52</b> is activated after a specified time length elapsed from generation of the test start signal <b>201</b> and thus the design verification test is completed, thereby generating a scan test pattern <b>207</b> for testing the logic core block <b>21</b> suing the scan paths. In addition, the scan test pattern generator <b>52</b> delivers a scan-mode test signal to the logic core block <b>21</b> through the scan-mode pin thereof, thereby allowing the flip-flops in the internal circuit of the logic core block <b>21</b> to be connected into a plurality of scan paths.

[0068] The scan-in data generator <b>55</b> receives the scan test pattern, which may include serial data, from the scan test pattern generator <b>52</b>, thereby generating a scan test data <b>209</b> based on the scan test pattern to deliver the same to the logic core block <b>21</b> through the scan-in pins. The scan-out data compression unit <b>56</b> generates scan-out expected data based on the scan test pattern <b>207</b>, comparing the outputs of the logic core block <b>21</b> through the scan-out pins against the scan-out expected data to deliver the comparison results as a test result signal <b>206</b> to the test controller <b>24</b> after compression thereof.

[0069] After the product system LSI is fabricated, a product test is conducted by inputting a test command signal. The test command signal triggers a design connection test by using the verification test pattern, wherein connections in the logic core block <b>21</b> are examined. After the design connection test is finished, a scan path test is started while using the scan test pattern generated by the scan test pattern generator <b>52</b>. The results of both the tests are delivered to the test controller <b>24</b>, which outputs the test results to outside the system LSI.

[0070] The BIST circuits <b>12</b>, <b>25</b> and <b>26</b> are also used in the design verification test during the design stage of the LSI, as described hereinafter. When the circuit design for determining the circuit connections in the LSI is completed in the design stage of the LSI, the BIST circuits are used for design verification. In this stage of the verification, a simulation is conducted for verification of the circuit connections by a CAD system using the test patterns to be generated by the pattern generators <b>31</b> and <b>51</b>. In the design verification, the design connection test of the logic core block <b>21</b> performed using the verification test pattern generated by the pattern generator <b>51</b> reduces the time length for the verification test compared to the time length of the scan path test, whereas the test of the DRAM blocks performed using the less number of test patterns reduces the time length of the test compared to the product test for the DRAMs. The design verification of the internal circuit including the BIST circuits during the design stage allows a possible defect to be found in the early stage of the production, preventing later occurrence of redesign of the LSI.

[0071] The test bench based on which the verification test pattern is created for verification of the gate-level design may be such as generally used by designers in the register transfer level (RTL) at the initial design stage of the LSI. Such a simulation generally costs a longer time length compared to the actual product test; however, this time length may be reduced by limiting the number of the test patterns to the extent needed to detect only the accuracy of the circuit connections. In the design stage, after the verification test using the verification test pattern generated by the pattern generator <b>51</b> is finished, the simulation is ended without conducting the scan path test using the pattern generated by the scan test pattern generator <b>52</b>.

[0072] Although a singe test command signal is used in the above embodiment for both the verification and scan path tests testing the connections and the functions of the LSI, the connection test and the functional test may be started by separate test command signals.

[0073] Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alterations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention.