Abstract:
A phase difference between clock signals in an integrated circuit is determined after the integrated circuit is packaged. The phase difference can thereby be adjusted so that the effect of the unequal loading on the clock signal timing may be reduced. Determining the phase difference after the integrated circuit is packaged may reduce the cost of fabricating the integrated circuit by reducing the amount of compensation which may need to be performed during the fabrication process. The phase difference may be provided by a selection means which can include at least one fuse that is cut by a laser or an RC circuit controlled by a voltage level applied to at least one pin of the integrated circuit. The phase may be adjusted as described above in input pipelines that receive data, output pipelines that output data from the integrated circuit, and in interface circuits that control operation of the integrated circuit.

Description:
This application is a Divisional of prior application Ser. No. 09/295,177; filed Apr. 20, 1999, now U.S. Pat. No. 6,175,258. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to integrated circuits in general, and more particularly, to clocking in integrated circuits. 
     BACKGROUND OF THE INVENTION 
     As the operational speed of integrated circuits increases there may also be a decrease in margins associated with clock signals that operate the integrated circuits. The integrated circuits may include interface circuits that transmit and receive data to and from the integrated circuit and clock signals that are connected to subsystems in the integrated circuit which provide synchronous operation thereof. Moreover, the interface circuits may operate at speeds that exceed the operational speed of the integrated circuit, thereby further reducing the clock signal margins. For example, in some conventional systems integrated circuit memories are connected to a Central Processing Unit (CPU). Accordingly, the integrated circuit memories may be required to transmit and receive data to/from the CPU at clock signal rates that approach those of the CPU. In addition, unequal loading of the clock signals in the integrated circuit memory may further reduce the clock signal margins. Consequently, it may be difficult to test the interface circuits, particularly if the clock signals that provide for the synchronous operation of the interface circuits are unequally loaded. 
     FIG. 1 is a block diagram that illustrates conventional interface circuits that clock signal data into an integrated circuit. According to FIG. 1, a Receiver Delay Lock Loop (RDLL) generates two synchronous clock signals based on RxClk: RCLK and MCLK. As shown in FIG. 1, RCLK is used to operate an interface circuit  2  and an input pipeline  5  while MCLK is used to operate the input pipeline  5  into which data is input. Furthermore, MCLK is connected to fewer loads than RCLK which may cause the phase of RCLK to lag the phase of MCLK as shown in FIG.  2 . 
     FIG. 2 is a timing diagram that illustrates data setup and hold times for the input pipeline  5  of FIG.  1 . According to FIG. 2, the timing of RCLK is delayed with respect to RxClk and MCLK so that the setup and hold times (tS and tH) for the input data are delayed by Δtsh. Accordingly, the margin for clocking data into the input pipeline  5  may be reduced. In particular, the additional loads on RCLK may cause a delay in RCLK with respect to MCLK such that a falling edge of RCLK normally used to clock signal data into the input pipeline  5  is delayed almost a full cycle as shown in FIG.  2 . Accordingly, the falling edge of RCLK used to clock signal data into the input pipeline  5  may correspond to a falling edge of MCLK in the next clock signal cycle. 
     FIG. 3 is a block diagram that illustrates conventional interface circuits that clock signal data out of an integrated circuit. According to FIG. 3, a Transmit Delay Lock Loop (TDLL)  4  generates two synchronous clock signals based on TxClk: TCLK and MTCLK. As shown in FIG. 3, TCLK is used to operate the output pipeline  6  while MTCLK is fed back to the TDLL  4  to maintain lock in the TDLL  4 . Furthermore, MTCLK is connected to fewer loads than TCLK which may cause TCLK to lag MTCLK as shown in FIG.  4 . 
     FIG. 4 is a timing diagram that illustrates data valid times for the output pipeline  6  of FIG.  3 . In particular, the timing of TCLK is delayed with respect to TxClk and MTCLK so that the valid times: tQ_max and tQ_min for data output from the output pipeline  6  is delayed by ΔtQ. Accordingly, the margin for clocking data from the output pipeline  6  may be reduced. 
     In some conventional integrated circuits, a reduction in the clock signal margin described above may be controlled by monitoring the manufacturing process of the integrated circuit and compensating for the reduced clock signal margin during the fabrication of the integrated circuit wafer. For example, the clock signal margin may change due to the structure of the integrated circuit, the integrated circuit package, and internal control signals. Therefore, the clock signal margin in the integrated circuit may be measured and compensated for during the wafer fabrication process, thereby possibly increasing the cost of the integrated circuit fabrication process. Consequently, there continues to exist a need to compensate for clock signal margins due to differential loads between clock signals in integrated circuits. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to allow a reduction in the cost of fabricating integrated circuits. 
     It is another object of the present invention to allow improvements in clock signal margins of clock signals having unequal loading in integrated circuits. 
     These and other objects of the present invention are provided by determining a phase difference between clock signals in an integrated circuit after the integrated circuit is packaged. The phase difference may thereby be reduced so that the effect of the unequal loading on the clock signal timing may be reduced. Determining the phase difference after the integrated circuit is packaged may reduce the cost of fabricating the integrated circuit by reducing the amount of compensation which may need to be performed during the fabrication process. 
     In another aspect of the present invention, the phase adjustment comprises a delay that is applied to a clock signal. The amount of the delay is provided an RC circuit or a chain of inverters. The phase adjustment may thereby be controlled to reduce the phase difference between the clock signals. The phase difference may be adjusted as described above in input pipelines that receive data, output pipelines that output data from the integrated circuit, and in interface circuits that control operations of the integrated circuit. 
     In a first embodiment, the delay is applied to a first clock signal generated by a lock loop circuit to align an edge of the first clock signal with an edge of a second generated clock signal. In a second embodiment, the delay is applied to a clock signal that is input to the lock loop circuit to thereby control the margin associated with each of the clock signals generated by the lock loop circuit equally. In a third embodiment, the delay is determined by the phase adjuster. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram that illustrates conventional interface circuits that clock signal data into an integrated circuit; 
     FIG. 2 is a timing diagram that illustrates data setup and hold times for the input pipeline  5  of FIG. 1 
     FIG. 3 is a block diagram that illustrates conventional interface circuits that clock signal data out of an integrated circuit; 
     FIG. 4 is a timing diagram that illustrates operations of the output pipeline  6  of FIG. 3; 
     FIG. 5A is a block diagram of a first embodiment of a compensation circuit  11  according to the present invention; 
     FIG. 5B is a block diagram of the phase adjuster  19  of FIG. 5A; 
     FIG. 5C is a circuit diagram of a first embodiment of the phase adjuster of FIG. 5A; 
     FIG. 5D is a circuit diagram of a second embodiment of the phase adjuster of FIG. 5A; 
     FIG. 6 is a timing diagram that illustrates operations of the compensation circuit  11  of FIG. 5A; 
     FIG. 7 is a block diagram of a second embodiment of a compensation circuit  21  according to the present invention; 
     FIG. 8 is a timing diagram that illustrates operations of the compensation circuit  21 ; 
     FIG. 9 is a block diagram of a third embodiment of a compensation circuit  31  that reduces a phase difference between clock signals according to the present invention; 
     FIG. 10 is a timing diagram that illustrates operations of the compensation circuit  31  of FIG. 9; 
     FIG. 11 is a block diagram of a fourth embodiment of a compensation circuit  41  according to the present invention; 
     FIG. 12 is a timing diagram that illustrates operations of the compensation circuit  41  of FIG. 11; 
     FIG. 13 is a block diagram of a fifth embodiment of a compensation circuit  51  according to the present invention; 
     FIG. 14 is a block diagram of the phase adjuster  59  of FIG. 13; 
     FIG. 15 is a schematic diagram of an embodiment of the phase detector  65  of FIG. 14; 
     FIG. 16 is a schematic diagram of an embodiment of the phase controller  67  of FIG. 14; and 
     FIG. 17 is a timing diagram that illustrates operations of a compensation circuit  51  of FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. The delay lock loop circuits described herein may comprise a phase lock loop circuit that generates clock signals in synchronization with each other with respect to an input clock signal. 
     FIG. 5A is a block diagram of a first embodiment of a compensation circuit  11  according to the present invention. In particular, RxClk is input to a Receiver Delay Lock Loop (RDLL)  17  which generates two synchronous clock signals: RCLK and MCLK 1 . RCLK is provided to an interface circuit  13  to control the input of data to the integrated circuit and to an input pipeline  15 . MCLK 1  is provided to a phase adjuster  19  that delays MCLK 1  to provide MCLK 2  which is fed back to the RDLL  17  and provided to the input pipeline  15 . As shown in FIG. 5A, MCLK 2  is connected to fewer loads than RCLK. While the phase of RxClk and MCLK may be almost the same as that of DLL, the phase of RCLK and MCLK 1  may be different due to a loading difference. If so, the phase adjuster  19  aligns the phase of RCLK with that of MCLK 1 . 
     FIG. 5B is a block diagram of a phase adjuster  19  of FIG.  5 A. According to FIG. 5B, MCLK 1  is provided to a delay circuit  12  which delays MLCK 1  by a determined time to provide MCLK 2 . The determined time provided by the delay circuit  12  is provided by an RC circuit or a chain of inverters. 
     FIG.  5 C and FIG. 5D are circuit diagrams of the delay circuit of FIG.  5 A. According to FIG. 5C, the determined time provided by RC circuits is controlled by selecting which connections (formed at selected steps of the fabrication of the integrated circuit) remain intact in the manufacture process. For example, in FIG. 5C a first delay is selected by cutting options  2  and  3  with a laser thereby leaving option  1  intact. Accordingly, the delay is provided by the RC combination applied to MCLK 1 . According to FIG. 5D, the determined time provided by the chain of inverters is controlled by options in a fashion similar to that described above. The options may comprise metal layers. 
     FIG. 6 is a timing diagram that illustrates compensation for unequal loading of clock signals in an integrated circuit according to the present invention. In particular, RxCLK is provided to the RDLL  17  which generates RCLK and MCLK 2  via the phase adjuster  19 . As shown in FIG. 6, RCLK is delayed so that a falling edge of MCLK 2  is aligned with a falling edge of RCLK. Accordingly, the setup and hold times tS and tH, compensate for Δtsh described above. 
     FIG. 7 is a block diagram of a second embodiment of a compensation circuit  21  according to the present invention. As shown in FIG. 7, TxClk is provided to the compensation circuit  21  that generates two clock signals: MTCLK 1  and TCLK. As shown in FIG. 7, MTCLK 2  has fewer loads than TCLK. A phase adjuster  27  compensates for the different loads between MTCLK 2  and TCLK by adjusting TCLK to reduce the phase difference between MTCLK 2  and TCLK. 
     FIG. 8 is a timing diagram that illustrates compensation for unequal loading of clock signals in an integrated circuit according to the present invention. In particular, TCLK is adjusted to align a falling edge of MTCLK 2  which compensates for ΔtQ_max by adjusting the timing of tQ_max/tQ_min. 
     FIG. 9 is a block diagram of a third embodiment of a compensation circuit  31  that reduces a phase difference between clock signals according to the present invention. According to FIG. 9, RxClk is input to a phase adjuster  37  that produces RxClk_i by delaying RxClk. RxClk_i is input to a lock loop circuit RDLL  39  which generates two clock signals: RCLK and MCLK. RCLK is provided to the interface circuit  33  and an input pipeline  35  while MCLK is provided to the input pipeline  35  and fed back to the RDLL  39  as a lock signal. In particular, MCLK has fewer loads than RCLK. According to FIG. 9, the delay provided by the phase adjuster  37  is adjusted to control the phases of RCLK and MCLK. 
     FIG. 10 is a timing diagram that illustrates operations of the compensation circuit  31  of FIG.  9 . According to FIG. 10, the hatched portions of the edges of RxClk_i, RCLK and MCLK may be controlled to align the desired falling edge with a corresponding falling edge of RxClk thereby controlling Δtsh. 
     FIG. 11 is a block diagram of a fourth embodiment of a compensation circuit  41  according to the present invention. According to FIG. 11, TxClk is provided to a phase adjuster  47  which delays TxClk to produce TxClk_i. TxClk_i is provided to a lock loop circuit TDLL  45  which produces two clock signals: TCLK and MTCLK. TCLK is provided to an output pipeline  43  while MTCLK is fed back to the TDLL  45  as a lock signal. According to FIG. 11, the timing of falling edges of TCLK may be adjusted by controlling the delay provided by the phase adjuster  47 , thereby adjusting the timing of which the output pipeline  43  outputs data. 
     FIG. 12 is a timing diagram that illustrates operations of the compensation circuit  41  of FIG.  11 . According to FIG. 12, the hatched portions of TxClk_i, TCLK and MTCLK can be controlled using the phase adjuster  47  to control the timing of the output data and thereby controlling ΔtQ. 
     FIG. 13 is a block diagram of a fifth embodiment of a compensation circuit  51  according to the present invention. According to FIG. 13, RxClk is provided to a lock loop circuit RDLL  57  that generates two clock signals: RCLK and MCLK. RCLK is provided to interface circuit  53  and an input pipeline  55 , while MCLK is provided to the input pipeline  55  and fed back to the RDLL  57  as a lock signal. A phase adjuster  59  in the compensation circuit  51  determines the phase difference between MCLK and RCLK and adjusts the phase of RCLK to reduce the phase difference therebetween. 
     FIG. 14 is a block diagram of the phase adjuster  59  of FIG.  13 . According to FIG. 14, RCLK is provided via line  61  to a phase detector  65  along with MCLK via line  63 . The phase detector  65  detects the phase difference between MCLK and RCLK and provides detecting signals DET and DET_B which provide a voltage levels that indicate the phase difference between MCLK and RCLK. A phase controller  67  controls the phase of RCLK based on the detection signals DET, DET_B and MCLK. 
     FIG. 15 is a schematic diagram of an embodiment of the phase detector  65  of FIG.  14 . According to FIG. 15, a phase difference receiver  71  generates sensing signals SEN and SEN_B based on the phase difference between RCLK and MCLK. A phase difference  73  amplifies the sensing signals SEN and SEN_B to provide detector signals DET and DET_B which indicates the phase difference between RCLK and MCLK. 
     FIG. 16 is a schematic diagram of an embodiment of the phase controller  67  of FIG.  14 . According to FIG. 16, a voltage level generator  91  generates a phase adjustment signal XDRI based on the detecting signals DET and DET_B. A phase adjuster driver  93  adjusts the phase of RCLK according to the phase adjustment signal XDRI and MCLK. 
     FIG. 17 is a timing diagram that illustrates operations of the phase detector  65  and phase controller  67  of FIG.  14 . According to FIG. 17, if the phase of the initial RCLK applied to line  61  is after the phase of MCLK, the voltage levels of MCLK at the gates of NMOS transistors  77 ,  79  exceed the voltage levels of RCLK at the gates of NMOS transistors  75 ,  81 . Consequently, the voltage level of the first sensing signal SEN is driven towards VCC and the voltage level of the second sensing signal SEN_B is driven towards VSS. In particular, the NMOS transistors  75  and  77  are about the same size, thus when the voltage level at the gate of the NMOS transistor  77  is higher than the voltage level applied to the gate of the NMOS transistor  75 , more current flows through the NMOS transistor  77  than through the NMOS transistor  75 . 
     Similarly, the NMOS transistors  79 ,  81  are about the same size, thus when the voltage level at the gate of the NMOS transistor  79  is higher than the voltage level at the gate of the NMOS transistor  81 , more current flows through the NMOS transistor  79 . Accordingly, the voltage level of the first sensing signal SEN is higher than the voltage level of the second sensing signal SEN_B. The phase difference amplifier  73  then amplifies the first sending signal SEN to provide the first detection signal DET and amplifies the second sensing signal SEN_B to provide the second detection signal DET_B. 
     The first detection signal DET is applied to the gate of the NMOS transistor  97  and the second detection signal DET_B is applied to the gate of the NMOS transistor  95 . The higher voltage level of the first detection signal DET causes more current to flow through the NMOS transistor  97  which causes the voltage level at the node N 98  to be driven towards VSS, thereby generating the XDRI signal. 
     The XDRI signal is provided to the phase adjuster driver circuit  93  that reduces the phase difference between RCLK and MCLK based on the voltage level of the XDRI signal. Moreover, the reduced phase difference is fed back to the input of the phase detector via line  61 , thereby indicating that the phase difference between MCLK and RCLK has been reduced from the initial tS and initial tH to the final tH and final tS to provide the final RCLK as shown in FIG.  17 . 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.