Abstract:
A digital synchronous circuit includes a clock generator for generating a reference clock signal, a plurality of delays for delaying the reference clock signal by predetermined different times, a transition varying buffer for controlling input transitions of the clock signals received from the plurality of the delays, a transition controller for controlling operation of the transition varying buffer, and a plurality of registers driven by the clock signals from the plurality of delays.

Description:
[0001]    The present application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0137603 (filed on Dec. 30, 2008), which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    In a digital device, when a clock signal is defective or unstable, a system may malfunction. A bad connection of a portable terminal and distortion of data transmitted from a facsimile are mostly attributed to instability of a clock signal. The clock signal may be used as an operation source of a digital circuit serves as the core of the circuit. Therefore, frequency accuracy and stability are requirements of the clock signal. Their importance is increasing along with an increased demand for high-speed computation and fast processing. Moreover, the role of the clock signal is so significant to fields requiring reliability, such as communication equipment, that double or multiple clock signals are used for a normal operation in case one clock generation source has errors. 
       SUMMARY 
       [0003]    Embodiments relate to a data reception apparatus such as a digital synchronous circuit that prevents Electro-Magnetic Interference (EMI) and IR drop. 
         [0004]    In accordance with embodiments, a digital synchronous circuit can include art least one of the following: a clock generator for generating a reference clock signal, a plurality of delays for delaying the reference clock signal by predetermined different time, a transition variable buffer for controlling input transitions of the clock signals received from the plurality of the delays, a transition controller for controlling operation of the transition variable buffer, and a plurality of registers driven by the clock signals from the plurality of delays. 
         [0005]    In accordance with embodiments, a digital synchronous circuit can include art least one of the following: a clock generator configured to generate a reference clock signal; a plurality of delays configured to delay the reference clock signal by a predetermined different time; a transition varying buffer configured to control input transitions of the clock signals received from the plurality of the delays; a transition controller configured to control operation of the transition varying buffer; and a plurality of registers driven by the clock signals from the plurality of delays. 
         [0006]    In accordance with embodiments, a digital synchronous circuit can include art least one of the following: a clock generator configured to generate a reference clock signal; a first delay, a second delay and a third delay each configured to delay the reference clock signal by a predetermined different time; a transition varying buffer configured to control input transitions of the clock signals received from the first delay, the second delay and the third delay; a transition controller configured to control operation of the transition varying buffer; and a plurality of registers driven by the clock signals from the plurality of delays. 
         [0007]    In accordance with embodiments, a digital synchronous circuit can include art least one of the following: a clock generator configured to generate a reference clock signal; a first delay, a second delay and a third delay each configured to delay the reference clock signal by a predetermined different time; a transition varying buffer configured to control input transitions of the clock signals received from the first delay, the second delay and the third delay; a transition controller configured to control operation of the transition varying buffer; and a first register connected to and driven by the clock signal from the first delay; a second register connected to and driven by the clock signal from the second delay; and a third register connected to and driven by the clock signal from the third delay. 
     
    
     
       DRAWINGS 
         [0008]    Example  FIG. 1  illustrates a digital synchronous circuit, in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0009]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
         [0010]    Example  FIG. 1  is a block diagram of a digital synchronous circuit in accordance with embodiments. 
         [0011]    As illustrated in example  FIG. 1 , a digital synchronous circuit is applied to a large circuit board along with other multiple chips. For example, the digital synchronous circuit is used in a circuit such as a microprocessor and a synchronous Random Access Memory (RAM). The digital synchronous circuit in accordance with embodiments includes three-stage circuits and registers  400 ,  500  and  600  that are connected to one another. While three registers  400 ,  500  and  600  are illustrated in accordance with embodiments, more registers may be connected as required. The registers  400 ,  500  and  600  are driven by clock generator CLK. While a synchronous system has a plurality of synchronous circuit ends, it uses only one clock generator CLK. 
         [0012]    A crystal oscillator or a phase locked loop (PLL) clock generator may be used as the clock generator CLK. The crystal oscillator generates electronic pulses at every predetermined interval by accurate and regular vibrations as clock pulses or a timing signal, so as to synchronize all operations of each component in a system. The PLL clock generator includes a PLL, a first divider, and a plurality of output buffers and maintains a reference clock signal and a feedback clock signal at the same frequency and phase. 
         [0013]    A clock signal from the clock generator CLK applies delays to the registers  400 ,  500  and  600 . Meaning, delays  100 ,  200  and  300  apply time delays to the registers  400 ,  500  and  600 , respectively. Each register  400 ,  500  and  600  may include one or more flip-flops. The time delays that delays  100 ,  200  and  300  apply to registers  400 ,  500  and  600  are (δa, δb, and δc, respectively. 
         [0014]    The following equation describes a reference clock signal in the digital synchronous circuit illustrated in example FIG.  1 . 
         [0000]      δi−δj&lt;T−D max[i,j]   
         [0000]      δi−δj&gt;−D min[i,j]   
         [0000]      δ i δ j &gt;T−D max[i,j]   
         [0000]      δ i δ j &gt;T−D min[i,j]   
         [0000]    where i and j are paths of output register i and input register j, δi and δj are input delays, T is a clock cycle time, D max[i,j]  is a longest delay from output register i to input register j, and D min [i,j]  is a shortest delay from output register i to input register j. 
         [0015]    Registers  400 ,  500  and  600  are circuits that synchronize and control a plurality of clock signals by eliminating time phase differences, i.e., skews between the clock signals. Although a clock signal is generated from the single clock generator CLK, it is branched into a plurality of clock signals as it passes through delays  100 ,  200  and  300 . In the course of being applied to respective circuit ends, some of the clock signals differ in phase due to phase delay, signal loss, etc. As a consequence, the overall synchronization of the system is not normal. For instance, in case of voice data, the voice is distorted. If control data are exchanged, a deadly error occurs to the system. That&#39;s why a circuit for eliminating the skew, i.e., phase difference between clock signals is introduced to prevent the foregoing phenomenon. 
         [0016]    Transition varying buffer  800  controls an overall relationship between registers  400 ,  500  and  600  by controlling the phase and delay of each clock signal while interworking with register  500 . Meaning, each register  400 ,  500  and  600  determines the slope of an edge at which the clock signal changes from low to high. The time delay of the clock signal depends on the slope. Transition varying buffer  800  can be controlled by connecting transition controller  900  to register  500 . 
         [0017]    As is apparent from the above description, in accordance with embodiments, since the transition varying buffer and the transition controller are added to control the clock input transition of flip-flops, EMI and IR drop of the digital synchronous circuit caused by a change in the clock input transition of the flip-flops can be further mitigated as far as the operation of the digital synchronous circuit allows. 
         [0018]    Although embodiments have been described herein, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.