Abstract:
A method and an apparatus for testing transmitter and receiver have been disclosed. One embodiment of the apparatus includes a plurality of multiplexers to select one of a positive transmitter pin and a negative transmitter pin, and a first comparator to compare a voltage of the selected pin with a first reference voltage to determine whether leakage exists at the selected pin. Other embodiments are described and claimed.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to semiconductor devices, and more particularly, to testing input/output of semiconductor devices using on-die design-for-testing circuitry.  
       BACKGROUND  
       [0002]     In a typical computer system, some components are coupled to a device of a chipset via serial buses. The chipset acts as an interface between the components and a processor. As the processor speed increases, the speed of the serial interfaces of the chipset devices has to increase in order to keep up with the processor speed. The speed of a serial interface is typically several times of the speed of the processor.  
         [0003]     With the advent of high-speed serial interface, the design of the interface has become increasingly complicated, and therefore, a more sophisticated and robust testing technique is necessary to test the interface. The conventional method of measuring signals using an external tester is inadequate for fully testing a high-speed serial interface because the speed of legacy testers is limited. Furthermore, the limited number of tester channels in the legacy testers poses another problem in testing the chipset device because there may not be enough tester channels to test every pin of the chipset device as the complexity of the chipset device increases. Because of the limited number of tester channels and the high-speed tests, the transmitter and the receiver of the device are connected on a load board during some high-speed data transfer tests. However, it is still difficult to test for leakage at the pins and/or other parts of the device limited number of tester channels.  
         [0004]     Alternatively, some semiconductor manufacturers replace the legacy testers with high-speed testers in order to provide more tester channels and to speed up the measurement of small signals during testing. However, replacing the legacy testers with the high-speed testers significantly increases the cost of manufacturing chipset devices with high-speed serial interface because the high-speed testers are very expensive.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the appended claims to the specific embodiments shown, but are for explanation and understanding only.  
         [0006]      FIG. 1  shows one embodiment of testing circuitry coupled to a transmitter.  
         [0007]      FIG. 2  shows one embodiment of testing circuitry coupled to a receiver.  
         [0008]      FIG. 3  shows one embodiment of a semiconductor device having an external loop back path.  
         [0009]      FIG. 4  shows an exemplary embodiment of a computer system.  
     
    
     DETAILED DESCRIPTION  
       [0010]     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description.  
         [0011]     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment.  
         [0012]      FIG. 1  shows one embodiment of a transmitter  100  in an input/output interface of a semiconductor device with on-die design-for-testing (DFT) circuitry. The input/output interface may be a serial interface or a parallel interface. The transmitter  100  includes a positive transmitter pin  110 , a negative transmitter pin  112 , two current drivers  120 , two resistors  150  and  152 , and a number of termination resistors  132  and  134 . Each of the positive and negative transmitter pins  110  and  112  is coupled via one of the resistors  150  and  152  to a power supply selected from the group of power supplies  169 . The termination resistors  132  and  134  may be variable resistors. In one embodiment, each of the termination resistors has a resistance of 50 ohms.  
         [0013]     Referring to  FIG. 1 , the DFT circuitry includes a comparator  164 , two multiplexers  160  and  162 , and a number of transistors  170 - 184 . The transistors  182  and  184  couple the variable termination resistors  132  and  134 , respectively, to a power supply so that the termination resistors  132  and  134  may be isolated from the power supply during certain transmitter tests. Furthermore, the transistors  170 - 180  act as switches to allow the selection of two voltage supplies out of a group of voltage supplies  169 . The group of voltage supplies  169  may include Vcc, ground, or a transmitter common mode voltage (TxVcm 1 ). The two selected voltage supplies are coupled to the resistors  150  and  152 .  
         [0014]     The resistors  150  and  152  are further coupled to the positive and negative transmitter pins  110  and  112  respectively. The voltages at the transmitter pins  110  and  112  are input to the multiplexers  160  and  162  respectively. A second transmitter common mode voltage, TxVcm 2  is also input to both multiplexers  160  and  162 . One should appreciate that TxVcm 2  may or may not be the same as TxVcm 1 . In one embodiment, both TxVcm 1  and TxVcm 2  are variable voltage supplies, which may be set at different values. The multiplexers  160  and  162  are configured such that one of the multiplexers  160  and  162  outputs TxVcm 2  while the other multiplexer outputs the voltage of one of the transmitter pins  110  and  112 . The outputs of the multiplexers  160  and  162  are input to the comparator  164 . Therefore, the multiplexers  160  and  162  allow the comparator  164  to compare one of the voltages of the transmitter pins  110  and  112  with TxVcm 2 . The output of the comparator  164  may go to the core logic (not shown) of the semiconductor device. In response to the output of the comparator  164 , the core logic may output a signal to indicate whether there is leakage at the transmitter pins  110  and  112 . In addition to, or as an alternative to, outputting the signal, the core logic may perform other operations in response to the output of the comparator  164 . Details of one embodiment of the transmitter pin leakage test are discussed below.  
         [0015]     In addition to the multiplexers  160  and  162 , the transmitter pins  110  and  112  are each coupled to the corresponding receiver pins via the transistors  190  and  192  respectively. This is also known as an analog loop back path  199  from the transmitter to the receiver. The analog loop back path  199  allows the semiconductor device to perform a self-test on the transmitter and the receiver of the semiconductor device without using an external load board to provide a data loop back path. In one embodiment, the transmitter pins  110  and  112  send certain predetermined data patterns to the receiver pins to test the transmitter and/or the receiver.  
         [0016]     In addition to, or as an alternative to, the self-test, various input/output tests may be performed using the DFT circuitry, such as, for example, a transmitter termination resistor test, a transmitter current driver test, a test on the resistors  150  and  152  of the transmitter, and a transmitter pin leakage test. To illustrate the concept, some embodiments of the transmitter tests are described in details below.  
         [0017]     In one embodiment, to perform the transmitter pin leakage test, deactivating the transistors  182  and  184  cuts off the power supply to the termination resistors  132  and  134 . Activating and/or deactivating the appropriate transistors  170 - 180  may select one of the voltage supplies  169 . For instance, TxVcm 1  can be selected to charge up the positive transmitter pin by activating the transistor  176  and deactivating the transistors  178  and  180 . After charging up the voltage at the positive transmitter pin  110 , the multiplexers  160  and  162  select the voltage of the positive transmitter pin  110  and TxVcm 2  as a reference voltage to input to the comparator  164 . The comparator  164  compares the selected voltages. If the voltage of the transmitter pin  110  drops below TxVcm 2 , there is leakage at the positive transmitter pin  110 . Likewise, the negative transmitter pin  112  can be charged up and compared to TxVcm 2 . If the voltage of the negative transmitter pin  112  rises above TxVcm 2 , then there is leakage at the negative transmitter pin  112 .  
         [0018]     Furthermore, the termination resistors  132  and  134  may be tested with the DFT circuitry as well with external capacitors  345  on the transmitter pins  110  and  112  as shown in  FIG. 3 . The transistors  170 - 180  may be deactivated to cut off the voltage supplies  169 . The transistors  190  and  192  are also deactivated to cut off the analog loop back path  199 . The transistors  182  and  184  are deactivated and then activated to provide a voltage supply on the transmitter pins  110  and  112  via the termination resistors  132  and  134  after a certain period of time. The period of time may be substantially equal to the decay time of an equivalent resistor and capacitor circuitry (also known as the RC decay time). The multiplexers  160  and  162  select the voltage of one of the termination resistors  132  and  134 , and TxVcm 2  as the reference voltage. The comparator compares the selected voltages from the multiplexers  160  and  162 . Then the comparator  164  may output the result to the core logic of the semiconductor device, which may output a signal to indicate the result.  
         [0019]     Likewise, one can activate and/or deactivate the transistors  170 - 184  to select the appropriate voltage supplies and to isolate one or more circuit components, such as the current drivers  120 , or the resistors  150  and  152 , in order to test the one or more isolated circuit components.  
         [0020]     Furthermore, additional DFT circuitry may be coupled between the 10 kΩ resistor  152  and the transistors  170 - 174  for the transmitter pin  112 , as well as between the 10 kΩ resistor  150  and the transistors  176 - 180  for the transmitter pin  110 . For instance, the exclusive-OR (XOR) circuitries for checking the connectivity of the device to a printed circuit board (PCB) may be added as described above. However, one should appreciate that other circuitries may be so added for other tests performed on the device. One advantage of adding DFT circuitry between the resistors  150  and  152  and the transistors  170 - 180  is to avoid disturbing the signal path for regular operations of the device.  
         [0021]      FIG. 2  shows one embodiment of a receiver with DFT circuitry in an input/output interface of a semiconductor device. The receiver  200  includes a positive receiver pin  210 , a negative receiver pin  212 , a squelch detector  266 , a comparator  268 , two capacitors  270  and  272 , and two termination resistors  260  and  262 . In one embodiment, the termination resistors  260  and  262  are each at 50 ohms. The capacitors  270  and  272  may be at 5 pF each. The DFT circuitry of the receiver  200  includes another comparator  220  and a number of transistors  230 - 244  functioning as switches. The positive and negative receiver pins  210  and  212  are coupled to the positive and negative transmitter pins  110  and  112  (referring to  FIG. 1 ), respectively, via the transistors  290  and  292 . As discussed above, coupling the receiver pins  210  and  212  to the transmitter pins  110  and  112  provides an analog loop back path  299  to enable the semiconductor device to perform self-tests on the input/output interface of the semiconductor device.  
         [0022]     Referring to  FIG. 2 , the transistors  238  and  240  couple the termination resistors  260  and  262  to the ground respectively. The transistors  241 - 244  couple the resistors  280  and  282  to one of the common mode voltage supplies, Vcm 1  and Vcm 2 . For example, activating the transistor  242  and deactivating the transistor  241  put Vcm 1  on the resistor  280 . In one embodiment, each of the resistors  280  and  282  has a resistance of 10 kΩ. Transistors  230  and  232  are coupled to each end of the capacitor  270 . Likewise, transistors  234  and  236  are coupled to each end of the other capacitor  272 . The node in between the transistors  230  and  232  and the node in between the transistors  234  and  236  are input to the comparator  220 . The output of the comparator  220  may go to the core logic of the semiconductor device.  
         [0023]     In one embodiment, a receiver leakage test can be performed using the DFT circuitry of the receiver. For example, the positive receiver pin  210  may be tested for leakage by activating the transistor  242  to select Vcm 1  to charge up the positive receiver pin  210 . Then the transistors  236  and  244  are activated to put Vcm 2  onto the other input of the comparator  220 . The transistors  238  and  240  are deactivated to isolate the termination resistors  260  and  262  from the ground. In one embodiment, Vcm1 is substantially equal to Vcc/2 and Vcm2 is substantially within the range of Vcm1 plus 300 mV and Vcm1 minus 300 mV. If the voltage at the positive receiver pin  210  falls below the lower limit of the range of Vcm2, there is leakage at the positive receiver pin  210 . Likewise, the negative receiver pin  212  may be tested for leakage by activating and/or deactivating the appropriate transistors to charge up the negative receiver pin  212  and to select a reference voltage to compare with the voltage at the negative receiver pin  212 .  
         [0024]     One should appreciate that the DFT circuitry in the semiconductor device enables the performance of other tests on the receiver  200 . The transistors  230 - 244  allow various components of the receiver to be isolated and selected voltage supplies to be provided to the particular receiver component during testing. The comparator  220  may compare a voltage at a particular node of the receiver to a selected reference voltage. In addition to the receiver leakage test described above, other examples of receiver tests enabled by the DFT circuitry include a test on the receiver termination resistors  260  and  262 , a test on the capacitors  270  and  272 , and a leakage test on the comparator  266 , etc.  
         [0025]     Furthermore, additional DFT circuitry may be coupled between the transistors  230  and  232 , as well as between the transistors  234  and  236  to implement other tests on the device. For instance, the XOR circuitries for checking the connectivity of the device to a PCB may be added between the transistors  230  and  232  and between the transistors  234  and  236 . However, one should appreciate that other circuitries may also be added for other tests performed on the device. One advantage of adding DFT circuitry between the transistors  230  and  232 , as well as the transistors  234  and  236 , is that the signal path for regular operations of the device is not disturbed by the DFT circuitry added.  
         [0026]     Using internal DFT circuitry to perform various receiver tests frees up tester channels for other usage, which is important for the legacy testers because the number of channels and the test speed of the legacy testers are limited. Furthermore, measuring signals within a semiconductor device with an internal comparator (e.g., the comparator  220  in  FIG. 2 ) is generally faster and more accurate than using an external tester, especially for measuring small signals during the leakage tests.  
         [0027]      FIG. 3  shows one embodiment of a semiconductor device  300  having a receiver  310  and a transmitter  320 . The receiver  310  and the transmitter  320  are coupled to the receiver logic  330  and the transmitter logic  335  within the semiconductor device  300 , respectively. Each of the receiver  310  and transmitter  320  is further coupled to the receiver and transmitter termination resistors  313  and  323  respectively. The transmitter termination resistors  323  are further coupled to a bias voltage supply, V_Bias, while the receiver termination resistors  313  are further coupled to the ground. In addition, the transmitter  320  is coupled to the receiver  310  via two external trace lines  340 . In one embodiment, the trace lines  340  may be coupled to two AC coupling capacitors  345 . The trace lines  340  provide an external data loop back path from the transmitter  320  to the receiver  310  to enable the transmitter  320  and the receiver  310  to perform self-tests, which may include various leakage tests.  
         [0028]     Different values of capacitance may be chosen to perform a leakage test on the semiconductor device by coupling or decoupling the transmitter termination resistors  323 , the current driver of the transmitter (not shown), and/or the receiver termination resistors  313 . For example, each of the AC coupling capacitors  345  may provide a capacitance of 100 nF and each of the trace lines  340  may have a parasitic capacitance of 20 pF. Therefore, decoupling the current driver of the transmitter and coupling the transmitter and receiver termination resistors  323  and  313  may result in an effective capacitance of (20 pF+100 nF). The capability to select different capacitances provides flexibility to test development for the semiconductor device.  
         [0029]     In one embodiment, the leakage from the transmitter  320  and/or the receiver  310  is relatively small. To shorten test time, the internal data loop back path is closed and the receiver termination resistors  313  are decoupled from the receiver  310  such that the signal from the transmitter  320  does not go through the trace lines  340  and the AC coupling capacitors  345 . As a result, the effective capacitance becomes substantially equal to the parasitic capacitance of the trace lines  340 , i.e., 20 pF in the above example.  
         [0030]      FIG. 4  shows an exemplary embodiment of a computer system  400 . The computer system  400  includes a central processing unit (CPU)  410 , a memory controller (MCH)  420 , a number of dual in-line memory modules (DIMMs)  425 , a number of memory devices  427 , an advance graphics port (AGP)  430 , an input/output controller (ICH)  440 , a number of Universal Serial Bus (USB) ports  445 , an audio converter co-decoder (AC Codec)  460 , a switch  450 , and a firmware hub  470 .  
         [0031]     In one embodiment, the CPU  410 , the AGP  430 , the DIMMs  425 , and the ICH  440  are coupled to the MCH  420 . The MCH  420  routes data to and from the memory devices  427  via the DIMMs  425 . The memory devices  427  may include various types of memories, such as, for example, dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate (DDR) SDRAM, or flash memory. In one embodiment, each of the DIMMs  425  is mounted on the same motherboard (not shown) via a DIMM connector (not shown) in order to couple to the MCH  420 . In one embodiment, the USB ports  445 , the AC Codec  460 , and the switch  450  are coupled to the ICH  440 . The switch  450  may be further coupled to a firmware hub  470 , a floppy disk drive  451 , data input devices  453 , such as, a keyboard, a mouse, etc., a number of serial ports  455 , and a number of parallel ports  457 .  
         [0032]     Note that any or all of the components and the associated hardware illustrated in  FIG. 4  may be used in various embodiments of the computer system. However, it should be appreciated that other configuration of the computer system may include one or more additional devices not shown in  FIG. 4 . Furthermore, one should appreciate that the technique disclosed is applicable to different types of system environment, such as a multi-drop environment or a point-to-point environment.  
         [0033]     The transmitter, receiver, and DFT circuitry described above with reference to  FIGS. 1, 2 , and  3  may be incorporated into the input/output interface of various devices in the computer system  400 , such as, for example, the MCH  420 , the ICH  440 , or the switch  450 . Incorporating the DFT circuitry allows the device to perform various tests on the input/output interface of the device without using any tester channel. Furthermore, the tests can be performed in a faster and more accurate manner than using an external tester, particularly those tests involving measurements of relatively small signals (e.g., leakage test). However, one should appreciate that the DFT circuitry illustrated in  FIGS. 1, 2 , and  3  are merely exemplary embodiments for illustrating the technique disclosed. The technique may be implemented with different configurations or combinations of circuitry in other embodiments.  
         [0034]     The foregoing discussion merely describes some exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, the accompanying drawings and the claims that various modifications can be made without departing from the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.