Patent Publication Number: US-7716544-B2

Title: Path data transmission unit

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the benefit of Korean Patent Application No. 10-2005-0076970, filed on Aug. 22, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present disclosure relates to a path data transmission unit, and more particularly, to a path data transmission unit that transmits normal data and test data in a normal mode and a test mode, respectively, through two separate output terminals wherein one of the two data types concurrently transmitted from the two output terminals has a predetermined voltage level. 
   2. Discussion of the Related Art 
   Circuits that are designed to externally monitor data processed internally in function blocks or data transferred between function blocks have an advantage in that checking the operational status of the function blocks and detecting the function blocks having an error can be easily performed later on, without disassembling a wafer or a package. 
   In most digital systems, a plurality of shift registers connected in series is used to transfer and store data, and output data from a plurality of the shift registers connected in series is transmitted to predetermined function blocks. When the system does not operate normally, the place at which the problem occurs should be detected. For such detection, test data is transmitted to a first shift register of the shift registers connected in series and then shifted. Then the test data is transmitted to the function blocks. The operational status of the function blocks can be checked by testing data subsequently transmitted from the function blocks in response to the transmitted input test data. This detection method is called a scan method. 
     FIG. 1  illustrates a part of a conventional system to which the scan method is applied. 
   Referring to  FIG. 1 , the conventional system  100  includes function blocks  140  that perform predetermined functions, and a plurality of shift registers  110 , 120  and  130 . 
   The first shift register  110  receives normal data ND through a first input terminal D, receives test data TD through a second input terminal TI, stores the test data TD, and transmits the test data TD through an output terminal Q in response to a clock signal CLK. It is determined, based on a test enable signal TE, whether it is a normal mode or a test mode. The first shift register  110  stores and transmits the normal data ND in the normal mode, and stores and transmits the test data TD in the test mode. A second shift register  120  operates in response to an output Q from the first shift register  110 . The second shift register  120  operates normally only when the test enable signal TE indicates the test mode, and the other operational characteristics thereof are the same as those of the first shift register  110 . A third shift register  130  operates in response to an output signal of a function block  140 . The third shift register  130  operates only when the test enable signal TE indicates the normal operation mode, and the other operational characteristics thereof are the same as those of the first shift register  110 . 
   When the test enable signal TE indicates the test mode, the test data TD which is transmitted through the output terminal Q of the first shift register  110  is transmitted to the second input terminal TI of the second shift register  120 . When the test enable signal TE indicates the normal mode, the normal data ND which is transmitted through the output terminal Q of the first shift register  110  is transmitted to the function block  140 . After being processed by predetermined arithmetic operations, the normal data is transmitted to the third shift register  130 . 
   Hereinafter, the data path formed when the data is transmitted from the output terminal Q of the first shift register  110  to the second input terminal TI of the second shift resister  120  is referred to as a first path Path 1 , and the data path formed when the data is transmitted from the output terminal Q of the first shift register  110  to the first input terminal D of the third shift resister  130  is referred to as a second path Path 2 . In addition, the function block to be tested in a test mode is assumed to operate in response to the test data TD transmitted from the output terminal Q of the second shift resister  120 , although the connection is not shown in the figure. 
   It is preferable that, in the test mode, only the first path Path 1  is enabled, so that the test data TD is stored in the second shift register  120  and that, in the normal mode, only the second path Path 2  is enabled, so that the normal data ND is processed by the function block  140  and stored in the third shift register  130 . Referring to  FIG. 1 , although the third shift resister  130  does not operate in response to the test enable signal TE in the test mode, however, the second path Path 2  is activated, so that the function block  140  operates. Therefore, power consumption increases. 
     FIG. 2  is an internal circuit diagram of the shift resisters  110 , 120 , and  130  illustrated in  FIG. 1   
   Referring to  FIG. 2 , the normal data ND or the test data TD is selected according to the test enable signal, and the selection operation is performed inside the dotted rectangle. The shift resisters shown in  FIG. 2  are constructed with commonly used master-slave type flip-flops, and a description of the method of operation of the shift registers is omitted. 
   As illustrated in  FIG. 1 , even though two separate data paths Path 1  and Path 2  are not used simultaneously, it is not possible to enable only one path due to the structure using the output of the first shift register  110  as a common input of the second and third shift registers. 
   SUMMARY OF THE INVENTION 
   Exemplary embodiments of the present invention provide a path data transmission unit in which, if one of a normal path for handling normal data or a test path for handling test data is selected, the other path is disabled to reduce electric power consumption. 
   According to an exemplary embodiment of the present invention, there is provided a path data transmission unit that operates in response to a test enable signal and a clock signal, comprising: a first input terminal that receives normal data; a second input terminal that receives test data; a first output terminal that maintains a voltage level of the normal data while the test enable signal indicates a test mode, outputs a first voltage level at the moment when the test enable signal indicates a change from the test mode to a normal operation mode, and then outputs the normal data while the normal operation mode continues and a second output terminal that outputs the test data when the test enable signal indicates the test mode and maintains a voltage level of test data outputted in the test mode. 
   According to an exemplary embodiment of the present invention, there is provided a path data transmission comprising: an edge detector that transmits an edge detection signal for a test enable signal that indicates a normal mode or a test mode; a first path data transmission block that transmits a first path data in response to the test enable signal, the edge detection signal, a clock signal, normal data, and a second path data; and a second path data transmission block that transmits the second path data in response to the test enable signal, the clock signal, and test data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention can be understood in more detail from the following descriptions taken in conjunction with the attached drawings in which: 
       FIG. 1  is a circuit diagram showing a part of a conventional system to which a scan method is applied; 
       FIG. 2  is an internal circuit diagram of one of the shift registers shown in  FIG. 1 ; 
       FIG. 3  is a circuit diagram showing a part of a system using a path data transmission unit according to an exemplary embodiment of the present invention; 
       FIG. 4  is a block diagram showing a path data transmission unit according to an exemplary embodiment of the present invention; 
       FIG. 5  is an internal circuit diagram showing an example of an edge detector used in the circuit shown in  FIG. 4 ; 
       FIG. 6  is a circuit diagram showing an example of a first selector used in the circuit of  FIG. 4 ; 
       FIG. 7  is a circuit diagram showing an example of a second selector used in the circuit of  FIG. 4 ; 
       FIG. 8  is a circuit diagram showing an example of a logic multiplier used in the circuit of  FIG. 4 ; and 
       FIG. 9  is a wave form diagram showing an internal signal of the edge detector shown in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 3  is a circuit diagram showing a part of a system using a path data transmission unit according to an exemplary embodiment of the present invention. 
   Referring to  FIG. 3 , the system  300  includes a first path data transmission unit  310 , a second path data transmission unit  320 , a third path data transmission unit  330 , and a function block  340 . Internal circuits of the three path data transmission units  310 ,  320 , and  330  will be described in detail with reference to  FIG. 4 . 
   The first path data transmission unit  310  transmits normal data ND to the second path Path 2 , which is a normal path, via a first input terminal D and a first output terminal Q, when the test enable signal TE indicates a normal mode. The first path data transmission unit  310  transmits test data TD to the first path Path 1  via a second input terminal TI and a second output terminal TQ, when the test enable signal TE indicates the test mode. 
   In the middle of the second path Path 2 , there is a function block  340 , which includes a plurality of logic gates and flip-flops used to perform predetermined operations. In other words, the normal data ND transmitted from the first output terminal Q of the first path data transmission unit  310  is processed by the function block  340  and transmitted to the second path data transmission unit  320 . The output of the function block  340  is directly transmitted to other predetermined function blocks (not shown) and used to perform additional operations of the overall device. In addition, the output of the second path data transmission unit  320  that receives the output data of the function block  340  may be transmitted to other internal function blocks to be used for subsequent operations. 
   The second path data transmission unit  320 , however, is used as a tool for checking whether the function block  340  operates normally in the test mode. In other words, the test data is transmitted to the function block  340  and, in response to the test data, the output signal is transmitted to the second path data transmission unit  320 . Therefore, if the output of the second path data transmission unit  320  is checked from the outside of the system, it can be determined whether the function block  340  operates normally or not. 
   In  FIG. 3 , only one function block  340  is illustrated, but in a real system, although not shown, a plurality of the function blocks exist, and normal data or test data is transmitted to the function blocks from the path data transmission unit (not shown). 
   In order to verify the electrical characteristics of the function blocks, every function block may be tested, but in general, the electrical characteristics of only a few selected function blocks need be tested. Accordingly, not only the normal data but also the test data need not be transmitted to the unselected function blocks. In a case when a function block (not shown) other than the function block  340  is to be tested, while the first path data transmission unit  310  and the third path data transmission unit  330 , which are connected in series, transmit the test data normally, no data should be transmitted to the function block  340 . Thus, the data that is transmitted from the first output terminal Q of the first path data transmission unit  310  is designed to have a predetermined DC value. The predetermined DC value will be described in detail below with reference to  FIG. 4 . 
   Accordingly, if a system is configured to have the path data transmission units  310 ,  320 , and  330  according to an exemplary embodiment of the present invention, the predetermined DC voltage is applied to the unselected function blocks while the test data is transmitted to the selected function block, so that the unselected function blocks cannot operate. 
     FIG. 4  is a block diagram showing a path data transmission unit according to an exemplary embodiment of the present invention. 
   Referring to  FIG. 4 , the path data transmission unit includes an edge detector  410 , a first path data transmission block  420 , and a second path data transmission block  460 . 
   The edge detector  410  detects an edge when the test enable signal TE changes from a voltage level indicating the test mode to a voltage level indicating the normal mode and transmits an edge detection signal ED. The edge detection signal is used to prevent the transmission of an unwanted error signal to function blocks when the test enable signal TE is transiting from the test mode to the normal mode. 
   In the explanation below, the voltage of the test enable signal TE in the test mode is assumed to be higher than the voltage level of the test enable signal TE in the normal mode. The edge detector  410  and the operations thereof will be described in detail with reference to  FIGS. 5 and 9 . 
     FIG. 5  is an internal circuit diagram showing an example of the edge detector  410  shown in  FIG. 4 . 
     FIG. 9  is a wave form diagram showing an internal signal of an edge detector shown in  FIG. 5 . 
   Referring to  FIG. 5 , the edge detector  410  includes a buffer  411 , an exclusive OR gate  412 , an inverter  413 , and an AND gate  414 . 
   The buffer  411  transmits a test enable signal TE delayed for a predetermined time BD. Referring to  FIG. 9 , the delay times BD of the rising and falling edges in signal a are assumed to be the same for the convenience of description. 
   The exclusive OR gate  412  transmits signal b that is determined based on the logic status of the test enable signal TE and the signal a. The signal b changes to a logic high state after a predetermined delay time D 1  from the rising edge of the test enable signal TE. Similarly, the signal b changes to a logic low state after a predetermined delay time from the falling edge of the test enable signal TE. Although the delay time of the falling edge is not illustrated, the delay times of the rising and falling edges are assumed to be equal to each other. The signal b goes high not only at the rising edge but also at the falling edge of the test enable signal TE. 
   The inverter  413  transmits a signal c that is a phase inverted signal of the test enable signal TE. The signal c changes to a logic low state after a predetermined delay time D 2  from the rising edge of the test enable signal TE. The signal c changes to a logic high state after a predetermined delay time from the falling edge of the test enable signal TE. Here, the delay times of the rising and falling edges are assumed to be equal to each other, and the delay time of the falling edge is not illustrated. 
   In general, the delay time D 2  of the inverter  413  is shorter than the delay time D 1  of the exclusive OR gate  412 . In other words, the delay time D 1  is longer than the delay time D 2 . 
   The AND gate  414  transmits an edge detection signal ED that is a logic multiplication of signals b and signal c. There is no response of the edge detection signal ED for the signal b occurring at the rising edge of the test enable signal TE and the corresponding signal c. As described above, the delay time D 1  is longer than the delay time D 2 , so that the logic multiplication results in a logic low state for the AND gate  414 . On the other hand, there is a response of the edge detection signal ED in the form of a pulse for the signal b occurring at the falling edge of the test enable signal TE and the corresponding signal c. 
   The first path data transmission block  420  outputs a first path data Q in response to the test enable signal TE, the edge detection signal ED, the clock signal CLK, the normal data ND, and the second path data TQ. The first path data transmission block  420  includes a first selector  430 , a second selector  440 , and a first flip-flop  450 . 
     FIG. 6  is a circuit diagram showing an example of the first selector  430  used in the circuit of  FIG. 4 . 
   Referring to  FIG. 6 , the first selector  430  selects one of the normal data ND and the second path data TO and outputs the selected data as a first selection signal S_D in response to the edge detection signal ED. The first selector  430  may be implemented by a multiplexer. The first selector  430  selects the normal data ND when the edge detection signal ED is in a logic low state, that is, “0”, and selects the second path data TQ when the edge detection signal ED is in a logic high state, that is, “1”. 
     FIG. 7  is a circuit diagram showing an example of the second selector  440  used in the circuit of  FIG. 4 . 
   Referring to  FIG. 7 , the second selector  440  transmits a first clock signal CLK 1  using the clock signal CLK, the test enable signal TE and the predetermined DC voltage corresponding to a logic high state “1” in response to the edge detection signal ED. The second selector  440  includes an inverter  441 , an AND gate  442 , a buffer  443 , and a multiplexer  444 . The inverter  441  inverts the phase of the test enable signal TE. The AND gate  442  logic multiplies the clock signal CLK and the output signal of the inverter  441 . The buffer  443  transmits a signal obtained by delaying the edge detection signal ED for a predetermined time. The multiplexer  444  selects either the output signal of the AND gate  442  or the predetermined DC voltage “1” and outputs the selected one in response to the edge detection signal ED delayed for a predetermined time by the buffer  443 . Here, “1” means a DC voltage corresponding to a logic high state. The multiplexer  444  selects the output of the AND gate  442  when the edge detection signal ED is in a logic low state “0” and selects the predetermined DC voltage “1” when the edge detection signal is in a logic high state “1”. The multiplexer  444  outputs the selected one as a first clock signal CLK 1 . 
   The first flip-flop  450  shown in  FIG. 4  stores the first selection signal S_D and transmits the first path data Q in response to the first clock signal CLK 1  and transmits the first path data Q. 
   A second path data transmission block  460  transmits the second path data TQ in response to the test enable signal TE, the clock signal CLK and the test data TD. The second path transmission block  460  includes a logic multiplier  470  and a second flip-flop  480 . 
     FIG. 8  is a circuit diagram showing an example of logic multiplier  470  used in the circuit of  FIG. 4 . 
   Referring to  FIG. 8 , the logic multiplier  470  transmits the second clock signal CLK 2  which is a logic multiplication of the test enable signal TE and the clock signal CLK. 
   The second flip-flop  480  shown in  FIG. 4  stores the test data TD and transmits the second path data TQ in response to the second clock signal CLK 2 . 
   The first flip-flop  450  and the second flip-flop  480  may be implemented by using any kind of flip-flop. Since the flip-flops are not directly related to the present invention, description of the flip-flips is omitted. 
   Now, the operations of the path data transmission unit according to exemplary embodiments of the present invention shown in  FIGS. 4 to 8  will be described. 
   First, the moment when the test enable signal TE is transiting from a logic high state to a logic low state will be described. 
   Referring  FIG. 9 , the edge detection signal ED forms a pulse in response to the moment when the test enable signal TE transits from a logic high state to a logic low state. The moment when the test enable signal TE is transiting from a logic high state to a logic low state means a moment when the mode changes from the test mode to the normal mode. At this time, the pulse of the edge detection signal ED is used to prevent transmission of unexpected data to the function block  340  that operates in response to receiving the first path data Q. 
   If the edge detection signal ED changes to a logic high state, the second path data TQ is selected as the first selection signal S_D and the logic high state is selected as the first clock signal CLK 1  which is transmitted from the multiplexer  444  of the second selector  440 . 
   If the edge detection signal ED changes to a logic low state, the normal data ND is selected as the first selection signal S_D. Since the test enable signal TE that is transmitted to the inverter  441  of the second selector  440  is in a logic low state, the clock signal CLK is transmitted from the AND gate  442 . Accordingly, the clock signal CLK that is transmitted from the AND gate  442  is selected as the first clock signal CLK 1  that is transmitted from the multiplexer  444  of the second selector 
   The first clock signal CLK 1 , which is used in the first flip-flop  450 , is in a logic high state and operates in the same way as the clock signal CLK after a predetermined time in response to the edge detection signal ED that occurred as a pulse at the moment when the test enable signal TE changes from a logic high state to a logic low state. Accordingly, the first flip-flop  450  transmits the second path data TQ, which is received through the input terminal D when the first clock signal CLK 1  is in a logic high state, as the first path data Q at the moment when the first clock signal CLK 1  changes to a logic low state for the first time. Then, the first flip-flop  450  transmits the normal data ND in response to the continuing first clock signal CLK 1 . 
   Now, the steady state in which the test enable signal TE indicates the normal operation mode and the steady state in which the test enable signal TE indicates the test mode will be described. The steady state means a part of a signal that is not located on the edge of the signal. 
   When the test enable signal TE maintains a logic high state that is the steady state indicating the test mode, the edge detection signal ED is in a logic low state. Accordingly, the first selector  430  selects the normal data ND as the first selection signal S_D. When the test enable signal TE is in the logic high state, the output of the AND gate  442  is fixed to a logic low state. Since the first clock signal CLK 1  that is transmitted from the multiplexer  444  of the second selector  440  is fixed to a logic low state, the first flip-flop  450  that operates in response to the first clock signal CLK 1  does not operate. On the other hand, since the clock signal CLK is transmitted from the AND gate  470  of the second selector  460 , the second path data TQ of the second flip-flop  480  that operates in response to the second clock signal CLK 2  transmits the test data TD. 
   When the test enable signal TE maintains a logic low state that is the steady state indicating the normal operation mode, the edge detection signal ED is in a logic low state. Accordingly, the first selector  430  selects the normal data ND as the first selection signal S_D. When the test enable signal TE is a logic low state, the output of the AND gate  442  is the clock signal CLK. Since the first clock signal CLK 1  which is transmitted from the multiplexer  444  of the second selector  440  is the clock signal CLK, the first flip-flop  450  that operates in response to the first clock signal CLK 1  transmits the normal data ND as the first path data Q. On the other hand, since the output of the AND gate  470  of the second selector  460  is fixed to a logic low state, the second flip-flop  480  that operates in response to the second clock signal CLK 2  does not operate. 
   To sum up, when the test enable signal TE indicates the test mode, the first path data transmission block  420  maintains a voltage level of the normal data ND while the test enable signal TE indicates the test mode. Also, the first path data transmission block  420  outputs a first voltage level at the moment when the test enable signal TE indicates a change from the test mode to a normal operation mode and outputs the first path data Q equal to the normal data ND while the normal operation mode continues. 
   When the test enable signal TE indicates the test mode, the second path data transmission block  460  outputs the second path data TQ equal to the test data TD and maintains a voltage level of test data TD outputted in the test mode. In this example, the first voltage level is the voltage level of the second path data TQ right before the test enable signal TE changes from the test mode to the normal mode. 
   As described above, a path data transmission unit according to exemplary embodiments of the present invention prevents unnecessary power consumption in a test mode and there is provided an advantage in that the path data transmission unit prevents the function block from malfunctioning even in a transient state during which the system changes from the test mode to the normal mode. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention, as defined by the appended claims.