Abstract:
An integrated circuit ( 1 ) comprises a monitor (M 1 , M 3 , M 3 ) operable to produce monitor data in dependence upon a measured parameter of the integrated circuit ( 1 ); and a self test controller ( 28 ) connected to receive monitor data from the monitor (M 1 , M 2 , M 3 ). The self-test controller is also operable to output self test data from the integrated circuit. The monitor includes an output shift register (SR 1 , SR 2 , SR 3 ) and is operable to output monitor data through the shift register (SR 1 , SR 2 , SR 3 ). Such a system enables simplified communication of system self test results on an integrated circuit.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to integrated circuit (IC) architectures, and in particular to signal integrity self-test (SIST) architectures. 
       BACKGROUND OF THE INVENTION 
       [0002]    Advances in manufacturing technology have enabled larger and denser circuits to be placed on single semi-conductor integrated circuits. This is especially the case when the circuits are realised as regular or cellular structures, for example Random Access Memory. A major problem associated with high density device is that of testing. In order to maintain higher reliability, device test procedures need to provide good coverage of possible faults that occur in the integrated circuit. 
         [0003]    One technique for providing testing of an integrated circuit is the so-called SIST architecture (signal integrity self-test architecture). The purpose of SIST architecture is to allow real time monitoring of important parameters which characterise the electrical behaviour of the integrated circuit. For example, monitors can be provided to detect cross talk, supply noise, substrate noise, temperature, switching activity, clock duty cycle etc. An SIST architecture has the advantage that testing can be performed before use during a test and debug process, and also during use (on-line). 
         [0004]      FIG. 1  of the accompanying drawings is a block diagram illustrating an integrated circuit including previously considered Signal Integrity Self Test (SIST) architecture. The integrated circuit  1  comprises a number of functional cores or modules  2 . These modules may perform analogue, digital or memory functions. For simplicity, it has been assumed that all cores are the same size. It will be readily appreciated that such techniques are not limited to an integrated circuit having cores of the same size. In addition, the normal interconnections and buses, which perform communication controls between the different functional cores, have been omitted from the diagram for the sake of clarity. 
         [0005]    The integrated circuit  1  includes a monitor control block  4  which communicates with a number of monitors (not shown in  FIG. 1 ) using a monitor selection bus  6 . A reference and compare circuit  8  outputs a self-test signal from an output  10  in dependence upon received signals from the monitors. The monitors supply monitor output signals via a bus structure  12 . The monitors are intended to be designed as standard cells, so that they can be located anywhere within each standard-cell block. 
         [0006]      FIG. 2  of the accompanying drawings illustrates a functional core  2  from the integrated circuit of  FIG. 1 . The core  2  includes a plurality of monitors  16  connected to a decoder  14  and to the bus structure  12 . In  FIG. 2 , the functional blocks relating to the function of the core have been omitted for the sake of clarity.  FIG. 2  illustrates an exemplary core having four monitors  16 . It will be readily appreciated that the core can be provided with any number of monitors in dependence upon the parameters to be measured. As mentioned above, different sensors are used to monitor different phenomena: cross talk, supply noise, substrate noise, temperature, switching activity, clock duty-cycle, etc. 
         [0007]    The SIST architecture ( FIG. 1 ) allows access to each individual monitor in a core using the monitor selection bus  6 , which is controlled by the monitor control block  4 . The monitor control block  4  includes a memory, which contains specific codes through which a certain monitor in a specific core can be selected. The output of the selected monitor is usually converted to a DC value or into a differential signal, which is then connected to the bus structure  12 . This bus structure  12  may either be connected directly to a bondpad  10  of the integrated circuit, or, as shown, it may be connected to the reference and compare circuit  8 . In one particular example, the reference and compare circuit  8  operates to determine whether the output signal from the monitor is within a certain allowed range. The reference and compare block  8  may contain reference values for each kind of monitor. 
         [0008]    The monitor control block  4  can be placed on the integrated circuit, but can also be an external controller, for example a software program or an analysis tool. In all cases, it is necessary to provide a means to communicate between all monitors  16  and the monitor control block  4 . 
         [0009]    Such previously considered SIST architectures have the disadvantage that interfacing between the SIST monitors and the controller is complex. It is therefore desirable to provide a simplified interfacing technique for SIST architectures. 
       SUMMARY OF THE PRESENT INVENTION 
       [0010]    According to one aspect of the present invention there is provided an integrated circuit comprising: a monitor operable to produce monitor data in dependence upon a measured parameter of the integrated circuit; and a self test controller connected to receive monitor data from the monitor, and operable to output self test data from the integrated circuit, characterised in that the monitor includes an output shift register and is operable to output monitor data through the shift register. 
         [0011]    According to another aspect of the present invention, there is provided a method of operating signal integrity self test on an integrated circuit, the method comprising: monitoring a parameter of the integrated circuit using a first monitoring and producing monitor output data therefrom; supplying the monitor output data to a self test controller; and supplying self test output data in dependence upon the monitor output data, characterised in that supplying the monitor output data comprises: loading a first shift register associated with the first monitor with the monitor output data; clocking such monitor data through the first shift register; and outputting the monitor data from the first shift register. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  is a block diagram illustrating a SIST architecture of an integrated circuit; 
           [0013]      FIG. 2  is a block diagram illustrating a functional core of the architecture of  FIG. 1 ; 
           [0014]      FIG. 3  is a block diagram illustrating one embodiment of an aspect of the present invention; and 
           [0015]      FIG. 4  is a flow chart illustrating a method embodying another aspect of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Embodiments of the present invention are concerned with providing simplified communication with monitors on an integrated circuit, and to allow savings in the area occupied by the monitors on the integrated circuit. 
         [0017]    In embodiments of the present invention the means for providing communication with the monitors is implemented as a shift register, as illustrated in  FIG. 3 . In  FIG. 3 , an integrated circuit  1  is provided with three functional blocks,  22 ,  24  and  26 . Each of these blocks performs a function appropriate to the operation of the integrated circuit. It will be appreciated that the integrated circuit can be provided with any number of functional blocks, of any size, and performing any function for the integrated circuit  1 . 
         [0018]    The integrated circuit  1  is provided with an SIST controller  28  which itself has an interface  30 . The SIST controller  28  operates to control signal integrity self test functions of the integrated circuit  1  and to output SIST results from the integrated circuit using the interface  30 . 
         [0019]    Each of the functional blocks  22 ,  24 ,  26  is provided with at least one monitor M 1 , M 2 , M 3 . It will be readily appreciated that the number of monitors is not limited by the present invention, and that the monitor or monitors can provide any appropriate output measurements. 
         [0020]    Each of the monitors M 1 , M 2 , M 3  is provided with a monitor interface (SR 1 , SR 2 , SR 3 ) for supplying outputs to the SIST controller  28 . In embodiments of the present invention, these monitor interfaces are provided by shift registers SR 1 , SR 2 , SR 3 . The shift registers SR 1 , SR 2 , SR 3  and the SIST controller  28  are connected in series with one another to form a shift register loop  32 . Each shift register SR 1 , SR 2 , SR 3  operates in conventional manner, and can accept data input at either end thereof. That is, data is supplied to one end of the shift register and subsequent clock cycles cause the data to move through the shift register until being output from the shift register concerned. Data can be transferred around the shift register loop  32  in either direction, under the control of the SIST controller  28 . 
         [0021]    Measurements output by the monitors M 1 , M 2 , M 3  are supplied to the respective shift registers SR 1 , SR 2 , SR 3  for transfer, via the shift register loop  32 , to the SIST controller  28 . Using such a loop  32  of shift registers SR 1 , SR 2 , SR 3  enables the number of communication lines to be reduced in contrast with previous techniques. Indeed, the shift register loop used in embodiments of the present invention allows the use of a single communication wire for the monitor outputs. The SIST controller  28  controls transfer of data through the shift registers and ultimately output from the interface  30 . The SIST controller  28  clocks measurement data from one position in the shift register concerned to the next position, or to the next shift register, or to the controller  28 , as appropriate. The clocking of data around the loop  32  can be synchronized to make maximum use of the shift register positions, by avoiding conflicts of data. 
         [0022]    In such a technique, data output from a monitor is transferred around the loop  32 , through one or more of the shift registers, until it reaches the SIST controller  28  for processing. 
         [0023]      FIG. 4  is a flowchart illustrating steps in a method embodying one aspect of the present invention. At step A, the monitor operates to monitor the associated parameter of the integrated circuit to produce monitor data. At step B, the shift register of the monitor concerned is loaded with the monitor data, and at Step C the data is clocked through the first shift register. Step D illustrates that the clock data is then clocked through the further shift registers as required, in order that the data can be transferred to the controller at Step E. It will be readily appreciated that each monitor in the integrated circuit can monitor parameters and load its own shift register at any time when there is a free shift register slot available. In addition, a monitor may produce more than one monitor output, which are clocked in series around the shift register loop  32 . It will also be readily appreciated that for the last shift register in the loop, the data is clocked through that shift register and directly transferred to the controller, and does not need to be clocked through further shift registers. In effect, step D is omitted for the last monitor in the loop. 
         [0024]    The major advantages of this communication technique are that it is flexible (it still allows various forms of implementation and control of the monitors). It is bi-directional and single wire, which results in small area and reduced costs and re-use can be made of existing knowledge in controlling these monitors, since only minor modifications are necessary to use scan test input/output pads of the integrated circuit. 
         [0025]    In exemplary embodiments of the present invention, the monitors  16  output values in one of the following formats: 
         [0026]    The monitor determines the required value in a digital format, e.g. an 8-bit word. and sends it to the monitor control block  4 . Such monitors use an analogue-to-digital conversion to convert a measurement to the required output format. 
         [0027]    The monitor acts as a decision element: it compares the value of the characteristic to a setting provided by the monitor control block. The result of the comparison is output in digital form.