Semiconductor integrated circuit which can be tested by an LSI tester having a reduced number of pins

Abstract: An LSI (10) to be tested includes a high speed interface (50), a FIFO buffer (16) for temporarily storing the data supplied from the high speed interface (50) to an internal circuit (11) of the LSI (10), a selector (24) outputting a selected one of an output of the internal circuit (11) and an output of the FIFO buffer (16) to the high speed interface (50), and a sequencer (17) responding to the a test signal (TEST) to control the selector (24) so that the data supplied from the high speed interface (50) to an internal circuit (11) is looped back through the FIFO buffer (16) and the selector (24) to the high speed interface (50). Thus, the LSI (10) including a high speed interface (50) can be tested by use of a high speed LSI tester having a reduced number of pins smaller than the number of all the function terminals of the LSI to be tested.

Description: The present invention relates to a semiconductor integrated circuit and a method for testing the same, and more specifically to a semiconductor configured to be tested for operation and characteristics of internal circuits in response to test data given from an external. Description of related art From US-A-5 331 571, a high speed integrated circuit for testing and emulating is known. This circuit is intended for emulation of an embedded microcontroller or microprocessor. It is not suitable if the circuit operates at ultra-high speeds such as more than a few GHz. In the process for developing and manufacturing semiconductor integrated circuits (called an "LSI" hereinafter), defective LSIs are distinguished from non-defective LSIs, and causes of defective in the defective LSIs are investigated and analyzed in order to elevate quality and productivity. One that has been performed in discovering and analyzing the defective LSIs is an LSI test. This LSI test includes various kinds of content, which can roughly divided into a function test and a parametric test. The function test is a test paying the attention to the function of the LSI. For example, this test is performed by setting various parameters such as a supply voltage, an operation temperature, an input signal timing, etc. for determining a test condition, to typical values expected at the time of development and manufacturing of the LSI, in order to know whether or not an expected function of the LSI is completely realized. On the other hand, the parametric test is a test paying the attention to the operation condition range of the LSI. In this test, each of the parameters which determines the same test condition as that for the function test is changed to know whether or not the LSI exerts a predetermined function and a predetermined characteristics in an operation condition range defined by the prescribed specification of the LSI. Mainly, the parametric test includes a DC parametric test for testing a DC characteristics and an AC parametric test for testing, for example, a signal propagation delay between an input terminal and an output terminal, a characteristics of a timing edge. A method for executing the above mentioned LSI tests, fundamentally includes giving a test data from an external to input terminals of an LSI to be tested, so that the result of an operation of an internal circuit of the LSI to be tested in response to the given test data is outputted to the external from output terminals of the LSI to be tested, and then, observing the result of an operation obtained from the output terminals of the LSI to be tested. In this method, the internal circuit of the LSI to be tested is tested. Referring to Figure 1, there is shown a block diagram illustrating a conventional LSI to be tested. The shown LSI is generally designated by Reference Numeral 20, and includes an internal circuit 21 constituted of sequential circuits and combinational circuits suitably combined to achieve desired functions. A test data is applied through input terminals 211 to 21X and input buffers 23I to 23X to the internal circuit 21, and data outputted from the internal circuit 21 is outputted through output buffers 241 to 24X and output terminals 221 to 22X to an external of the LSI 20. Figure 2 illustrates a conventional manner in which the LSI shown in Figure 1 is tested by an LSI tester. In Figure 2, elements corresponding to those shown in Figure 1 are given the same Reference Numerals. In Figure 2, the LSI tester is generally designated by Reference Numeral 3, and various pins of the LSI test 3 are connected to the input terminals 211 to 21X and the output terminals 221 to 22X of the LSI 20 to be tested. The LSI tester 3 generates a test data corresponding to each item of test, and supplies the generated test data to the input terminals 211 to 21X of the LSI 20. Thus, the test data is actually applied to the internal circuit 21 of the LSI 20. The internal circuit 21 performs an operation corresponding to each applied test data, and outputs the result of operation as a test result data, which is received through the output terminals 221 to 22X of the LSI 20 by the LSI tester 3, so that the non-defect/defect of the operation and characteristics is discriminated. A series of operations such as the above mentioned operation are sequentially performed by the LSI tester 3 in accordance with a predetermined program, for the purpose of executing predetermined items of test. In the above mentioned LSI test method as mentioned above, however, it is required to apply the test data to all of the input terminals of the LSI, and fetch all the test result data of the LSI through all the output terminals of the LSI. Therefore, it is necessary to use an LSI tester having pins of the number corresponding to all function pins of an LSI to be tested, namely, a device under test (often abbreviated to "DUT"). In addition, the LSI tester is required to have a speed and precision sufficient to comply a timing test of the LSI to be tested. Recently, the operation frequency of LSI has been increased with advanced semiconductor technology, and therefore, a high speed LSI tester is required in order to test the high speed LSI. In other words, there is now required a high speed LSI tester having pins of the number corresponding to all function pins of an LSI to be tested and having a test rate corresponding to the operation frequency of the high speed LSI. In general, the high speed LSI tester is more expensive than a low speed LSI tester. In the high speed LSI tester, in particular, a cost for one pin is also more expensive than that in the low speed LSI tester. Accordingly, the high speed, multi-pin LSI tester becomes very expensive. Because of recent elevated function and increased complication of the LSI, the number of pins in the LSI is apt to increase, and therefore, the expense for the LSI tester correspondingly becomes large. On the other hand, all the function pins of the high speed LSI are not at a high speed. For example, in a high-speed serial communication LSI, only a few terminals for the high-speed serial communication operate at an ultra high speed of a few 100 GHz to a few GHz, and most of the remaining terminals only operates on the order of a few 10 MHz. Therefore, from a viewpoint of both development cost and manufacturing cost, it is not convenient to prepare a high-speed multi-pin LSI tester having a number of pins, all of which have a speed and precision capable of complying with the highest speed one of the terminals of the LSI to be tested. Japanese Patent Application Laid-open Publication No. JP-4-220576 has proposed a testing method which can reduce the number of pins of the LSI tester required for the test. Referring to Figure 3, there is illustrated the method proposed by JP-4-220576. As shown in Figure 3, a test data is supplied in the form of a serial data to an LSI 40 to be tested, in which the serial test data is converted by a serial-to-parallel conversion circuit 43 into a plurality of parallel test data, which are supplied to a plurality of circuits 41l to 41n to be tested constituting the integrated circuit. With this arrangement, it is possible to reduce the number of test terminals of the LSI tester/ However, this proposed method can perform the function test of the internal circuit of the LSI, but cannot perform a test for knowing whether or not the timing of an external interface of the LSI to be tested can meet with the specification of the LSI. Because, since the test data is supplied to the circuits to be tested in the LSI through the serial-to-parallel conversion circuit 43, the data actually applied to the circuits to be tested is different from the specification of the LSI. Summary of the Invention Accordingly, it is an object of the present invention to provide a semiconductor integrated circuit which has overcome the above mentioned defect of the conventional one. Another object of the present invention is to provide a semiconductor integrated circuit capable of testing a high speed interface of the semiconductor integrated circuit itself by use a high speed LSI tester having only pins of a necessary minimum number which is smaller than the total number of all functional terminals of the semiconductor integrated circuit to be tested. The above and other objects of the present invention are achieved in accordance with the present invention by a semiconductor integrated circuit comprising: a timing input means for receiving a timing signal from an external; a data input means for receiving an input data from the external; a data output means for outputting an output to the external; a latch means for latching the data supplied through the data input means on the basis of the timing signal; a gate means for controlling a supplying of data to the data output means on the basis of the timing signal; a loopback means for looping back the data latched in the latch means to the gate means; and a loopback activating means for activating the loopback means. Preferably, the loopback means includes a memory for storing the loopback data. In addition, the loopback means also includes a means for controlling the loopback data stored in the memory. Furthermore, the loopback activating means controls a loopback mode in response to a predetermined signal from the external. The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is a block diagram illustrating a conventional LSI to be tested; Figure 2 illustrates a conventional manner in which the LSI shown in Figure 1 is tested by a conventional LSI tester; Figure 3 illustrates a conventional testing method which can reduce the number of pins of the LSI tester; Figure 4 is a block diagram of one embodiment of the semiconductor integrated circuit in accordance with the present invention; Figure 5 is a timing chart illustrating the operation timing in the loopback operation of the first embodiment; Figure 6 illustrates a principle of loopback operation in the semiconductor integrated circuit in accordance with the present invention; and Figure 7 is a block diagram of a system for testing a high-speed interface of the semiconductor integrated circuit in accordance with the present invention. Description of the Preferred embodiments Referring to Figure 4, there is shown a block diagram of one embodiment of the semiconductor integrated circuit in accordance with the present invention. In Figure 4, an LSI is generally designated by Reference Numeral 10, and includes an internal circuit 11 operating at a slow clock, input/output buffers 12 and 13, an input buffer 14, an output buffer 15, a FIFO (first-in first out) buffer 16, a sequencer 17 for controlling a loopback operation explained hereafter, a serial-to-parallel converter 18, a parallel-to-serial converter 19, an input latch 25, an output latch 26, an input buffer 22, an output buffer 23 and a selector 24, which are connected as shown. A portion surrounded by a dotted line 50 is a high speed interface portion which operates with a fast clock. In addition, Reference Numerals 101 to 108 designate an external terminal, and Reference Numeral 121 indicates a slow clock. Reference Numeral 122 shows a test control signal for starting a loopback test. Reference Numeral 123 is a write signal for the FIFO buffer 16, and Reference Numeral 124 is a read signal for the FIFO buffer 16. Reference Numeral 125 designates a switchover control signal for switching a data path in a loopback test mode. Reference Numeral 126 shows a data bus for transferring the parallel input obtained from the serial-to-parallel converter 18, into the internal circuit 11. Reference Numeral 127 is a data bus for transferring an output data of the internal circuit 11 to the selector 24. Reference Numeral 128 indicates an output data bus of the FIFO buffer 16 coupled to the selector 24. Reference Numeral 129 is a fast clock signal, and Reference Numeral 130 designates a fast data input/output bus. Now, operation of the shown LSI in accordance with the present invention will be described. Here, assume that data is transferred between a low speed interface which is shown in a left hand of Figure 4 and which operates with the slow clock SCLK, and a high speed interface which is shown in a right hand of Figure 4 and operating with the fast clock FCLK. Data supplied through the terminals 102, 103 and 104 to the LSI 10 is applied to the internal circuit 11 of he LSI 10 through the buffers 12, 13 and 14. The input data is processed in the internal circuit 11, and thereafter, the result of processing is supplied through the data bus 127 and the selector 24 to the parallel-to-serial converter 19, which is converted into a serial fast data. The serial fast data is outputted through the output latch 26 driven by the fast clock FCLK, and through and the output buffer 23, and also through the fast data input/output bus 130 to the terminal 107 as a fast data. On the other hand, a data transfer from the high speed interface to the low speed interface is made as follows: The fast data FDATA supplied through the terminal 107 is fed through the fast data input/output bus 130 and the input buffer 22 and latched in the latch 25 in synchronism with the fast clock FCLK supplied through the terminal 108. The data latched in the input latch 25 is converted by the serial-to-parallel converter 18 into a low speed parallel data, which is supplied through the data bus 126 to the internal circuit 11. After the data is processed in the internal circuit 11, the result of processing is outputted through the buffer 12, 13 and 15 to the low speed interface terminals 102, 103 and 105. Next, a loopback operation in the LSI of this embodiment will be described. The loopback operation is started in response to the test control signal TEST supplied through the terminal 106. When the loopback operation is started, the sequencer 17 activates the switchover control signal 125 for switching to the data path at the time of the loopback test. In response to the switchover control signal 125, the selector 24 selects the output of the FIFO buffer 16, so that the output data bus 128 of the FIFO buffer 16 is coupled to the input of the parallel-to-serial converter 19. In this case, the data applied to the terminal 107 is supplied through the input buffer 22 and the input latch 25 as mentioned above to the serial-to-parallel converter 18, and is converted by the serial-to-parallel converter 18 to a slow data, which is outputted to the data bus 126. In this course, the sequencer 17 activates the FIFO buffer write signal 123 so that the data on the data bus 126 is written into the FIFO buffer 16. This writing of the data into the FIFO buffer 17 is performed by the number of times set in the sequencer 17, so that a loopback data is prepared. Thereafter, the sequencer 17 activates the FIFO buffer read signal 124, so that the loopback data prepared in the FIFO buffer 16 is read out to the output data bus 128 and supplied through the selector 24 to the parallel-to-serial converter 19. The read-out data is converted by the parallel-to-serial converter 19 into a fast data, which is outputted through the output latch 26 and the output buffer 23 to the terminal 107. Figure 5 is a timing chart illustrating the operation timing in the loopback operation of the above mentioned LSI in accordance with the present invention. In Figure 5, "TEST" indicates the test control signal 122. SCLK shows the slow clock signal 121, and FCLK indicates the fast clock signal 129. FDATA shows the fast data 130. "BUS 126" indicates data on the data bus 126 for transferring the data from the serial-to-parallel converter 18 to the internal circuit 11, and "BUS 128" shows data on the output data bus 128 of the FIFO buffer 16. In addition, "WRITE SIGNAL 123 indicates the FIFO buffer write signal 123, and "READ SIGNAL 124" shows the FIFO buffer read signal 124. "SWITCHOVER CONTROL SIGNAL 125" designates the switchover control signal 125 supplied from the sequencer 17 to the selector 24. Referring to Figure 5, the writing to the FIFO buffer 16 is performed at a rising edge of the write signal 123, and the reading from the FIFO buffer 16 is performed at a rising edge of the read signal 124. Also referring to Figure 5, in response to the active test control signal TEST supplied through the terminal 106, the sequencer 17 starts to control the loopback operation. First, the sequencer 17 activates the switchover control signal 125 into a logical high level, so that the selector 24 selects the output data bus 128 of the FIFO buffer 16. Thus, the fast serial data FDATA supplied through the terminal 107 is converted by the serial-to-parallel converter 18 to a parallel data on the data bus 126, and the data on the data bus 126 is written into the FIFO buffer 16 in order in accordance with the FIFO buffer write signal 123 from the sequencer 17. The data written into the FIFO buffer 16 is read out in accordance with the FIFO buffer read signal 124 from the sequencer 17, and outputted to the output data bus 128, so that it is converted by the parallel-to-serial converter 19 to the fast data which is outputted through the terminal 107. In the example shown in Figure 5, the writing of a second data D2 into the FIFO buffer 16 from the data bus 126 overlaps in time with the reading-out of a first data D1 written in the FIFO buffer 16 to the output data bus 128. However, the embodiment is not limited to this fashion. For example, it is needless to say that after a predetermined number of data have been written into the FIFO buffer 16, the data written in the FIFO buffer 16 can be read out. Referring to Figure 6, there is illustrated a principle of the loopback testing in the above mentioned embodiment of the LSI in accordance with the present invention. As seen from Figure 6, a test pattern given as an input data 67 from an external is observed as an output data 68 in the external. Thus, this test makes is possible to test a high speed interface of an LSI 60 including a high speed input circuit 62 and a high speed output circuit 63. A loopback circuit 64 responds to a loopback instruction signal 66 for setting the LSI 60 into a loopback operation mode, and turns back the signals supplied from the high speed input circuit 62 into the high speed output circuit 63. Incidentally, in the embodiment shown in Figure 4, the fast data (FDATA) is inputted and outputted through the input/output terminal 107, but the input data terminal and the output data terminal can be provided independently of each other as shown in Figure 6. Referring to Figure 7, there is shown a block diagram of a system for testing the high-speed interface of the first embodiment of the LSI in accordance with the present invention. In Figure 7, Reference Numeral 70 designates a high speed LSI tester, which includes a plurality of output drivers 71 to 73, an input buffer 74, a comparator 74, a timing generator 76, a test pattern memory 77 and an expected value pattern memory 78, which are coupled as shown. In addition, Reference Numeral 700 designates an LSI in accordance with the present invention, which corresponds to the first embodiment shown in Figure 4. Reference Numeral 701 shows logic circuits and input/output circuits other than a high speed interface. The high speed interface includes a loopback circuit 702 and a high speed input/output circuit 703. Furthermore, Reference Numeral 710 designates an input terminal for receiving an LSI test instruction signal, and Reference Numeral 711 shows a fast clock input terminal. Reference Numeral 712 indicates a fast data input/output terminal. Reference Numeral 713 designates an internal bus for transferring the input data to the logic circuits and input/output circuits 701, and Reference Numeral 714 shows a loopback data outputted from the loopback circuit 702. In the high speed LSI tester 70, on the other hand, Reference Numerals 715 to 717 designate a timing signal generated by the timing generator 76 for designating a timing of outputting a test pattern supplied from the test pattern memory, to the LSI 700 to be tested. Reference Numeral 718 shows a strobe signal to be supplied to the comparator 75, for indicating a timing where an output of the LSI 700 under test is compared with the expected pattern from the expected pattern memory 78. Reference Numeral 719 indicates an output of the comparator 75 indicating the result of comparison. Now, operation of the high speed LSI tester 70 will be described with reference to Figure 7. The test pattern memory 77 stores a number of test patterns to be supplied to the terminals of the LSI 700. Therefore, the test patterns stored in the test pattern memory 77 are sequentially read out to be supplied from the high speed LSI tester 70 through the output drivers 71 to 73 to the LSI 700. The signals outputted from the high speed LSI tester 70 is controlled by the timing signals 715 to 717 generated in the timing generator 76. The LSI 700 performs an operation in accordance with the given test pattern, and the result of operation is outputted from the input/output terminal 712. The high speed LSI tester 70 fetches the result of operation of the LSI 700 through the input buffer 74, and the result of operation is compared in the comparator 75 with an operation expected value pattern stored in the expected value pattern memory 78 at a timing designated by the timing signal 718 generated by the timing generator 76. The comparison result signal 719 is outputted from the comparator 75. In the following, an example of the AC parametric test in the LSI testing system shown in Figure 7, will be described in connection with an input setting time (setup time), an input hold time (hold time) and an output delay time of an input/output data 712 (data inputted or outputted through the terminal 712) of the LSI 700 with reference to a clock 711 (applied to the terminal 711). First, explanation will be made on the case of testing the delay time of the output data of the LSI 700 to be tested. The patterns stored in the test pattern memory 77 are read out, and the signal is given through the terminal 710 to the LSI 700. With this, as mentioned in connection with the first embodiment, the LSI 700 is put in the loopback test mode. Then, in accordance with the patterns read out from the test pattern memory 71, the clock signal is applied to the clock terminal 711 and the input data is supplied to the input/output terminal 712. At this time, the timing signals 716 and 717 generated in the timing generator 76 are controlled to ensure that the input data is supplied through the high speed input/output circuit 703 into the internal circuit of the LSI 700 at a timing giving the input data a sufficient margin in comparison with the clock signal. By the high speed input/output circuit 703, the input data is looped back by the loopback circuit 702 through the high speed input/output circuit 703 after a predetermined time, with the result that the looped-back data is outputted through the input/output terminal 712. The high speed LSI tester 70 receives this outputted looped-back data through the input buffer 74, and the comparator 75 compares the received looped-back data with the expected value pattern stored in the expected value pattern memory 78 at a timing designated by the timing signal 718 generated by the timing generator 76. Thus, the comparison result signal 719 is outputted from the comparator 75. Here, by setting the timing signal 718 to the maximum value of the output delay time of the input/output data, it is possible to test whether or not the output data outputted from the input/output terminal 712 meets with the standard of the output delay time. Next, explanation will be made on the setting time and the holding time of the input data of the LSI to be tested. In this case, it is sufficient if the output timing of the data is controlled to the effect that the timing of the input data given to the input/output terminal 712 becomes the minimum value of the input setup time or the minimum value of the hold time. If the LSI having the setup time and hold time in accordance with the standard, the input data is properly inputted to the high speed input/output circuit 703 in accordance with the loopback procedure of the data as mentioned above, and the same data as the input data can be observed as the looped-back output data. Therefore, when the received pattern is compared with the expected value pattern, a coincidence can be obtained. If the LSI does not have the setup time and hold time in accordance with the standard, the result of comparison indicates inconsistency. Namely, a defective LSI can be detected. Incidentally, by setting the timing of the input/output signal in accordance with the standard value and by performing the function testing of the LSI to be tested, it is possible to perform a test for knowing whether or not the AC parameter values meet with the standard values. This non-defective/defective test is ordinarily called a "GO/NOGO TEST", and is performed in a mass production test. As seen from the above, by separately and sequentially performing the test of the high speed input/output circuit 703 of the LSI 700 by use of the loopback circuit 702 in the embodiment mentioned above, it is possible to perform a test using a high speed LSI tester 70 having a reduced number of pins in comparison with the total number of all the terminals of the LSI 700. Therefore, if the LSI to be tested includes a plurality of high speed input/output circuits 703, it is sufficient if the high speed LSI tester 70 has a timing precision required by the high speed input/output circuits and a required number of (high speed) pins corresponding to the number of pins of the high speed input/output circuits. Accordingly, in connection with the high speed interface of the LSI, the high speed LSI tester having only a small number of high speed pins can quickly and precisely perform not only the function test, but also the parametric test such as whether or not the AC parameter meets with the standard value. On the other hand, in connection with the low speed interface of the LSI, for example, a multi-pin low speed LSI tester can be used. Accordingly, the test expense can be reduced. In addition, the test method in accordance with the present invention can reduce the number of high speed test probes of the high speed LSI tester required for testing the LSI having a high speed interface. In this point, the test expense can be also reduced. On the other hand, the LSI in accordance with the present invention includes the loopback testing circuit operating in response to a test control signal and consisting of a control circuit for realizing the loopback control, a storing circuit for storing the output data from the high speed input circuit, and a selector for selecting either the output of the internal circuit and the output of the storing circuit. Therefore, the loopback circuit is very compact, and the expense of the LSI including the testing circuit can be suppressed. The invention has thus been shown and described with reference to the specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the illustrated structures but changes and modifications may be made within the scope of the appended claims.

Claims: A semiconductor integrated circuit comprising a timing input means (108,711) for receiving a timing signal from the external; a data input means (67,107) for receiving an input data from the external; a data output means (68,107) for outputting an output to the external; a latch means (25,26) for latching the data supplied through said data input means on the basis of said timing signal; a gate (62,63,703) means for controlling a supplying of data to said data output means on the basis of said timing signal; a loopback means (64,702) for looping back the data latched in said latch means to said gate means; and a loopback activating means (66) for activating said loopback means. A semiconductor integrated circuit claimed in Claim 1 wherein said loopback means includes a memory (16) for storing the loopback data. A semiconductor integrated circuit claimed in Claim 2 wherein said loopback means (64,702) also includes a means for controlling the loopback data stored in said memory. A semiconductor integrated circuit claimed in Claim 3 wherein said loopback activating means (66) controls a loopback mode in response to a predetermined signal from the external.

Inventors: ARAI TOMOHISA, ARAI, TOMOHISA
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: G06F11
IPC codes: G01R31, H01L21, H01L27, G06F11