Abstract:
A semiconductor integrated circuit device includes a control circuit for coping with time differences in signals propagating along by differences in routes of the circuit device. In a definite data interval when changes of all signals have been completed, the control circuit outputs a received signal. In an indefinite data interval when changes of all signals have not been completed, the control circuit outputs a fixed signal irrespective of signal level of a received signal. The control circuit thus prevents irregular signal changes caused by the time differences before definition of data to subsequent circuits.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor integrated device having a complementary metal oxide semiconductor (CMOS) structure. More particularly, this invention relates to a semiconductor integrated device capable of reducing power dissipation, and a method of designing such a semiconductor integrated device. 
     BACKGROUND OF THE INVENTION 
     Due to advance of frontier techniques, fabrication of fast, highly integrated, large scale integrated circuits (“ICs”) has become possible in recent years. Therefore, construction of a fast, large capacity system has become possible. In such a system, however, an increase in power dissipation poses a problem. It has become very important to reduce the power dissipation of ICs used in devices in the system. By the way, the power dissipation of each IC is determined by charge and discharge currents of transistors that flow in order to activate the IC, through currents of transistors flowing at the time of IC operation, leakage currents of transistors flowing at the time of standstill of the IC, and so on. 
     As a conventional semiconductor integrated device in which a major part of power dissipation is occupied by the above described charge and discharge currents, a semiconductor integrated device having, for example, a CMOS structure (hereafter referred to as CMOS circuit) will now be described. 
     FIG. 17 is a diagram showing the current path of the conventional CMOS circuit. Reference number  101  denotes a PMOS transistor, and reference number  102  denotes a NMOS transistor. Moreover, reference number  104  denotes a power supply, and reference number  105  denotes ground connection (“GND”). Thus, an inverter circuit is formed. Reference number  103  denotes a load capacitor caused by wiring connected to an output of the inverter circuit and a circuit of a subsequent stage. 
     Following currents flow through this inverter circuit. That is, a through current  111 , a charge current  112 , and a discharge current  113 . In switchover of “ON” and “OFF” of the PMOS transistor  101  and the NMOS transistor  102 , the through current  111  flows from the power supply  104  to the GND  20  through the PMOS transistor  101  and the NMOS transistor  102 , when both the PMOS transistor  101  and the NMOS transistor  102  temporarily turn “ON.” When the PMOS transistor  101  is “ON,” the charge current  112  flows from the power supply  104  into the load capacitance  103  through the PMOS transistor  101 . When the NMOS transistor  102  is “ON,” the discharge current  113  flows from the load capacitor  103  into the GND  105  through the NMOS transistor  102 . 
     By the way, power dissipation P caused by the charge current  112  and the discharge current  113  can be represented by equation (1) 
     
       
         P=(½) CV 2   (1)  
       
     
     FIG. 18 is a diagram showing an example of a conventional semiconductor integrated device. FIG. 19 is a time chart showing operation of the conventional semiconductor integrated device. In FIG. 18, reference numeral  100  denotes an IC chip made of a CMOS element. Reference numerals  2 ,  3 ,  4 ,  10  and  11  denote independent internal block circuits in the IC chip  100 . Reference numeral  5  denotes an inverter circuit functioning as a driver of a clock signal clk. Reference numeral  6  denotes a plurality of flip-flop circuits. Reference numeral  7  denotes an internal block circuit included in the internal block circuit  4 . Reference numerals  8  and  13  denote composite gate circuits. Reference numerals  9  and  12  denote driver circuits. Reference symbols a, b, c, d, e, clk,  5   o,    6   a,    6   b,    6   c,    6   d,    6   e,    7   a,    7   b,    7   c,    7   d,    7   e,    8   o  and  9   o  denote signals. 
     First of all, in the IC chip  100 , for example, signals such as an output signal a of the internal block circuit  2 , an input signal b input from the outside, a signal c generated within the internal block circuit  4 , a signal d generated outside the internal block circuit  4 , an output signal e of the internal block circuit  3  are individually output to the flip-flop circuits  6 . The flip-flop circuits  6  latch the received signal at a falling edge of a clock signal  5   o  received via the inverter circuit  5 . 
     The internal block circuit  7  receives the signals  6   a  to  6   e  output from the flip-flop circuits  6 , generates and outputs signals  7   a  to  7   e.    
     Upon receiving output signals  7   a  to  7   e  of the internal block circuit  7 , the composite gate circuit  8  outputs a signal  8   o  assembled therein. The driver circuit  9  outputs a signal  9   o  having predetermined drive capability. Thereafter, the output signal  9   o  is transmitted to a plurality of circuits located inside and outside the internal block circuit  4 . 
     Operation of the IC chip  100  will now be explained in detail with reference to FIG.  19 . Reference symbols A, A 1 , A 2 , A 3 , B, B 1 , B 2 , C 1 , C 2 , D, D 1 , D 2 , D 3 , E, E 1 , E 2  and E 3  denote signal data of “1” or “0”. Reference characters tda, tdb, tdc, tdd and tde denote delay time of data. Reference symbols (i− 1 ), i, and (i+ 1 ) denote periods. Reference symbols  9 (i− 1 ),  9   i,  and  9 (i+ 1 ) denote output values of the driver circuit  9  in the period (i− 1 ), period i, and period (i+ 1 ), respectively. 
     First, data of signals a to e received by the internal block circuit  4  are latched by a falling edge of the clock signal  5   o  in the (i− 1 ) period. Since at this time the signals a to e are latched by the same clock signal  5   o,  the output signals  6   a  to  6   e  simultaneously change to “A 1 ”, “B”, “C 1 ”, “D 1 ” and “E”. 
     Data of the flip-flop circuits  6  are passed through individual paths in the internal block circuit  7  and output. When output from the internal block circuit  7 , therefore, the delay times tda, tdb, tdc, tdd and tde of respective paths are added. In other words, the output signals  7   a  to  7   e  of the internal block circuit  7  changes to data “A 1 ”, “B”, “C 1 ”, “D 1 ” and “E” at respective time points. 
     Subsequently, data output from the internal block circuit  7  are assembled in the composite gate circuit  8  to produce the signal  8   o.  Furthermore, the signal  8   o  is converted in the driver circuit  9  to the signal  9   o  having predetermined drive capability. Thereafter, the signal  9   o  is transmitted to a plurality of circuits provided inside and outside the internal block circuit  4 . 
     When different delay times are added to a plurality of synchronized signals because of difference in path as in the above described conventional semiconductor circuit apparatus, however, there is a possibility that, for example, the output signal  8   o  of the composite gate circuit  8  of a subsequent stage will operate irregularly depending upon changes of the input signals until changes of all input signals are completed. Furthermore, an irregular change of the output signal  8   o  is also propagated/reflected to the output signal  9   o  of the driver circuit  9  following the composite gate circuit  8 , and thereafter the change is propagated to all subsequent circuits. 
     In this way, in the conventional semiconductor integrated device, the above described irregularly changing signal is propagated to all subsequent circuits. Although the signal change is unnecessary in the circuit operation, charge and discharge currents flow as a result of this signal change, resulting in a problem. 
     Furthermore, since the unnecessary signal change is propagated to all subsequent circuits as described above, the charge and discharge currents disadvantageously increase as the semiconductor integrated device as a whole becomes large in scale and high in performance. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a semiconductor integrated device capable of reducing the charge and discharge currents which are unnecessary for circuit operation, and reducing the power dissipation of the apparatus as a whole. 
     The semiconductor integrated device according to this invention comprises a control circuit disposed to cope with time difference caused in changes of a plurality of signals by difference in routes. This control circuit outputs a received signal in a definite data interval when changes of all signals have been completed, and outputs a fixed signal irrespective of a signal level of a received signal in an indefinite data interval when changes of all signals have not been completed. The control circuit thus prevents irregular signal changes caused by the time difference before definition of data from being prevented to subsequent circuits. 
     The method of designing a semiconductor integrated device according to this invention comprises the steps of setting conditions of disposition locations of a control circuit beforehand, searching circuit components and signal operations satisfying the conditions at time of work on CAD, and disposing the control circuit, in response to existence of circuit components and signal operations satisfying the conditions. 
    
    
     Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a configuration of a semiconductor integrated device according to a first embodiment of the present invention; 
     FIG. 2 is a time chart showing operation of the semiconductor integrated device according to the first embodiment; 
     FIG. 3 is a diagram showing a configuration of a semiconductor integrated device according to a second embodiment of the present invention; 
     FIG. 4 is a time chart showing operation of the semiconductor integrated device according to the second embodiment; 
     FIG. 5 is a diagram showing a configuration of a semiconductor integrated device according to a third embodiment of the present invention; 
     FIG. 6 is a time chart showing operation of the semiconductor integrated device according to the third embodiment; 
     FIG. 7 is a diagram showing a configuration of a semiconductor integrated device according to a fourth embodiment of the present invention; 
     FIG. 8 is a diagram showing a configuration of a semiconductor integrated device according to a fifth embodiment of the present invention; 
     FIG. 9 is a diagram showing characteristic features of a semiconductor integrated device according to a sixth embodiment of the present invention; 
     FIG. 10 is another diagram showing characteristic features of a semiconductor integrated device according to a sixth embodiment of the present invention; 
     FIG. 11 is still another diagram showing characteristic features of a semiconductor integrated device according to a sixth embodiment of the present invention; 
     FIG. 12 is still another diagram showing characteristic features of a semiconductor integrated device according to a sixth embodiment of the present invention; 
     FIG. 13 is a diagram showing characteristic features of a semiconductor integrated device according to a seventh embodiment of the present invention; 
     FIG. 14 is a diagram showing characteristic features of a semiconductor integrated device according to an eighth embodiment of the present invention; 
     FIG. 15 is a diagram showing characteristic features of a semiconductor integrated device according to a ninth embodiment of the present invention; 
     FIG. 16 is another diagram showing characteristic features of a semiconductor integrated device according to a ninth embodiment of the present invention; 
     FIG. 17 is a diagram showing a current path of a conventional CMOS circuit; 
     FIG. 18 is a diagram showing an example of a conventional semiconductor integrated device; and 
     FIG. 19 is a time chart showing operation of a conventional semiconductor integrated device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a semiconductor integrated device according to the present invention will be described in detail by referring to the accompanying drawing. By the way, the present invention is not limited by the embodiments. 
     FIG. 1 is a diagram showing a configuration of a semiconductor integrated device according to a first embodiment of the present invention. In FIG. 1, Reference numeral  1  denotes an IC chip made of a CMOS device. Reference numerals  2 ,  3 ,  4 ,  10  and  11  denote independent internal block circuits included in the IC chip  1 . Reference numeral  5  denotes an inverter circuit functioning as a driver of clk. Reference numeral  6  denotes a plurality of flip-flop circuits. Reference numeral  7  denotes an internal block circuit included in the internal block circuit  4 . Reference numerals  8  and  13  denote composite gate circuits (which may be internal block circuits). Reference numerals  9  and  12  denote driver circuits. Reference numeral  14  denotes a control circuit disposed between the composite gate circuit  8  and the driver circuit  9 . Reference symbols a, b, c, d, e, clk,  5   o,    6   a,    6   b,    6   c,    6   d,    6   e,    7   a,    7   b,    7   c,    7   d,    7   e,    8   o,    9   o  and  14   o  denote signals. 
     For example, the power dissipation of the above described IC chip  1  is determined by charge and discharge currents of transistors let flow in order to activate the circuits included in the IC chip, through currents of transistors flowing at the time of operation of the IC, leak currents of transistors flowing at the time of standstill of the IC, and so on. In the first embodiment, therefore, there will be described a semiconductor integrated device corresponding to a fast, highly integrated and large scale IC, and capable of reducing the charge and discharge currents required to activate the IC together with the through currents and the leak currents. 
     First of all, in the IC chip  1 , for example, signals such as the signal a output from the internal block circuit  2 , the signal b input from the outside, the signal c generated within the internal block circuit  4 , the signal d generated outside the internal block circuit  4 , the signal e output from the internal block circuit  3  are individually output to the flip-flop circuits  6 . The flip-flop circuits  6  latch the received signal at a falling edge of a clock signal  5   o  received via the inverter circuit  5 . 
     Upon receiving output signals  6   a  to  6   e  of respective flip-flop circuits  6 , the internal block circuit  7  outputs output signals  7   a  to  7   e  respectively passed through individual paths. Upon receiving output signals  7   a  to  7   e  of the internal block circuit  7 , the composite gate circuit  8  outputs a signal  8   o  assembled therein. 
     Upon receiving the output signal  8   o  of the composite gate circuit  8 , the control circuit  14  removes an indefinite component caused by delay difference values of the signals  7   a  to  7   e  included in the signal  8   o,  according to a control signal generated on the basis of the clock signal  5   o.  Moreover, the control circuit  14  outputs a signal  14   o  with the indefinite component removed. Upon receiving the signal  14   o,  the driver circuit  9  outputs a signal  9   o  having predetermined drive capability. Thereafter, the output signal  9   o  is transmitted to a plurality of circuits located inside and outside the internal block circuit  4 . 
     Operation of the IC chip  1  will be described in detail with reference to FIG.  2 . Reference symbols A, A 1 , A 2 , A 3 , B, B 1 , B 2 , C 1 , C 2 , D, D 1 , D 2 , D 3 , E, E 1 , E 2  and E 3  denote signal data of “1” or “0”. Reference characters tda, tdb, tdc, tdd and tde denote delay time of data. Reference symbols (i− 1 ), i, and (i+ 1 ) denote periods. Reference symbols  9 (i− 1 ),  9   i,  and  9 (i+ 1 ) denote output values of the driver circuit  9  in the period (i− 1 ) , period i, and period (i+ 1 ), respectively. Reference symbols T( 1 - 1 ) and T ( 1 - 2 ) denote control intervals generated by a control signal. 
     First, data of signals a to e received by the internal block circuit  4  are latched by a falling edge of the clock signal  5   o  in the (i− 1 ) period. Since at this time the signals a to e are latched by the same clock signal  5   o,  the output signals  6   a  to  6   e  simultaneously change to “A 1 ”, “B”, “C 1 ”, “D 1 ” and “E”. 
     Data of the flip-flop circuits  6  are passed through individual paths in the internal block circuit  7  and output. When output from the internal block circuit  7 , therefore, the delay times tda, tdb, tdc, tdd and tde of respective paths are added. In other words, the output signals  7   a  to  7   e  of the internal block circuit  7  changes to data “A 1 ”, “B”, “C 1 ”, “D 1 ” and “E” at respective time points. 
     Subsequently, data output from the internal block circuit  7  are assembled in the composite gate circuit  8  to produce the signal  8   o.  At this time, time difference is caused in change timing of the input signals  7   a  to  7   e  of the composite gate circuit  8  by difference in the paths. Until changes of all input signals are completed, the output signal  8   o  of the composite gate circuit  8  changes irregularly according to changes of the input signals. In other words, an indefinite component is included in the output signal  8   o.    
     Upon receiving the output signal  8   o,  the control circuit  14  outputs the signal  8   o  fed from the composite gate circuit  8  as the signal  14   o,  as it is during the interval T( 1 - 1 ) and outputs the fixed signal  14   o  irrespective of the signal level of the signal  8   o  during the interval T( 1 - 2 ), according to the control signal generated on the basis of the clock signal  5   o.  Furthermore, the signal  14   o  is converted in the driver circuit  9  to the signal  9   o  having predetermined drive capability. Thereafter, the signal  9   o  is transmitted to a plurality of circuits provided inside and outside the internal block circuit  4 . As shown in FIG. 2, the interval T( 1 - 2 ) is not necessarily synchronized with the clock signal  5   o.    
     Thus, in the semiconductor integrated device according to the first embodiment, there is provided a control circuit having the following configuration. That is, when time difference is caused in change timing of a plurality of signals by difference in the paths, the control circuit outputs the received signal as it is during an interval having no possibility of a signal change, i.e., a definite data interval, whereas the control circuit outputs the fixed signal irrespective of the signal level of the received signal during an interval having a possibility of a change of at least one signal, i.e., an indefinite data interval. Owing to such a configuration, propagation of unnecessary signal changes occurring in the conventional technique can be prevented. As a result, the charge and discharge currents of the whole apparatus can be reduced remarkably. Furthermore, for the same reason, the power dissipation of the whole apparatus can also be reduced remarkably. 
     Furthermore, in the semiconductor integrated device according to the first embodiment, not only the charge and discharge currents can be reduced, but also operation of transistors caused by unnecessary signal changes is eliminated. In other words, unnecessary switchover operation of a PMOS transistor and an NMOS transistor from “ON” to “OFF” and vice versa is eliminated. As a result, a through current occurring when both transistors are “ON” can also be reduced. 
     FIG. 3 is a diagram showing a configuration of a second embodiment of a semiconductor integrated device according to the present invention. The same components as those of the above described first embodiment are denoted by like characters, and description thereof will be omitted. Reference symbol  14   a  denotes a concrete example of the control circuit  14  described above, and it is a control circuit formed of an AND gate. Precisely, this control circuit  14   a  is formed of a 2-input AND gate circuit. A first input terminal of the AND gate circuit is supplied with the output signal  8   o  of the composite gate circuit  8 . A second input terminal of the AND gate circuit is supplied with the clock signal  5   o.  The output signal  14   o  of the control circuit  14   a  is supplied to the driver circuit  9  at the later stage. 
     Characteristic features of the operation of the IC chip according to the second embodiment will now be described in detail with reference to FIG.  4 . However, only operation which is different from that of the first embodiment described earlier will be described. In should be noted that, reference symbols T( 2 - 1 ) and T( 2 - 2 ) represent control intervals generated by a control signal. 
     The control circuit  14   a  (AND gate) receives the output signal  8   o  of the composite gate circuit  8  and the clock signal  5   o  serving as a control signal. During the interval T( 2 - 1 ) with the clock signal  5   o  being high logical level (“H”), the control circuit  14   a  outputs the input signal  8   o  as it is. During the interval T( 2 - 2 ) with the clock signal  5   o  being low logical level (“L”), the control circuit  14   a  outputs “L” irrespective of the signal level of the input signal  8   o.  As a result, an unnecessary component (indefinite component) in the input signal  8   o  can be removed. 
     Thus, in semiconductor integrated device according to the second embodiment, it is determined according to the state of the clock signal  5   o  serving as the control signal whether the signal input to the control circuit should be output as it is or a fixed signal should be output irrespective of the signal level of the input signal. Propagation of unnecessary signal changes is thus prevented. As a result, effects similar to those of the first embodiment are obtained. In addition, by setting the duty cycle to such a value (for example, 30% in FIG. 4) that an indefinite component of the input signal can be removed, only the signal of the definite interval can be output certainly. 
     FIG. 5 is a diagram showing a configuration of a semiconductor integrated device according to a third embodiment of the present invention. The same components as those of the above described first embodiment are denoted by like characters, and description thereof will be omitted. Reference symbol  14   b  denotes a concrete example of the control circuit  14  described above. Precisely, this control circuit  14   b  is formed of a latch circuit. The control circuit  14   b  is formed of a D latch circuit. A first terminal D of the D latch circuit serving as a data terminal is supplied with the output signal  8   o  of the composite gate circuit  8 . A second terminal T of the D latch circuit serving as a clock terminal is supplied with the clock signal  5   o.  The output signal  14   o  of the control circuit  14   b  is supplied to the following driver circuit  9 . 
     Characteristic features of the operation of the IC chip according to the third embodiment will now be described in detail with reference to FIG.  6 . Only operation which is different from that of the first embodiment described earlier will be described. In FIG. 6, reference symbol T( 3 - 1 ) and T( 3 - 2 ) represent control intervals generated by a control signal. 
     The control circuit  14   b  (D latch circuit) receives the output signal  8   o  (data terminal D) of the composite gate circuit  8  and the clock signal  5   o  (clock terminal T) serving as a control signal. At a rising edge of the clock signal  5   o,  the control circuit  14   b  (D latch circuit) outputs the received input signal  8   o,  and holds the output over the intervals T( 3 - 1 ) and T( 3 - 2 ). As a result, an unnecessary component (indefinite component) in the input signal  8   o  can be removed. 
     Thus, in semiconductor integrated device according to the third embodiment, the input signal is latched at a rising edge of the clock and held until the next rising edge. Propagation of unnecessary signal changes is thus prevented. As a result, effects similar to those of the first embodiment are obtained. In addition, by causing the rising edge of the clock always in a definite data interval, i.e., in such a position that an indefinite component of the input signal can be removed, only the signal of the definite interval can be output certainly. 
     FIG. 7 is a diagram showing a configuration of a semiconductor integrated device according to a fourth embodiment of the present invention. The same components as those of the above described first embodiment are denoted by like characters, and description thereof will be omitted. In FIG. 7, reference symbol  15  denotes a control signal generation circuit for generating a control signal on the basis of a plurality of signals such as the clock signal  5   o,  signals f, g fed from other internal block circuits, and a signal h input from the outside, and  15   o  denotes the generated control signal. 
     Thus, in semiconductor integrated device according to the fourth embodiment, the control signal is generated on the basis of a plurality of signals such as the clock signal, signals fed from other internal block circuits, and an external input signal. The control interval can be freely set according to various conditions irrespective of the clock signal. As compared with the foregoing embodiments, therefore, the propagation signal can be controlled in a finer manner. In FIG. 7, the control signal generation circuit  15  has been applied to the configuration of the first embodiment. However, the control signal generation circuit  15  is not restricted to the configuration of the first embodiment, but it can be applied the configuration of the second embodiment or the configuration of the third embodiment as well. 
     FIG. 8 is a diagram showing a configuration of a semiconductor integrated device according to a fifth embodiment of the present invention. The same components as those of the above described first to fourth embodiments are denoted by like characters, and description thereof will be omitted. In FIG. 8, reference symbols  14 A,  14 B,  14 C and  14 D denote a control circuit described with reference to one of the first to third embodiments, and reference symbols  5   a,    5   b,    5   c  and  5   d  denote control signals for controlling the control circuits  14 A,  14 B,  14 C and  14 D, respectively. 
     In the fifth embodiment, the control circuits are disposed in a stage preceding the large-scale internal block circuit  2 , in a stage preceding the internal block circuits  3  and  4 , in a stage preceding the internal block circuit  10 , and in a stage preceding the internal block circuit  11 . The plurality of control circuits are formed so as to be capable of being controlled individually by independent control signals  5   a  to  5   d.  While the control signals are provided individually here, the same control signal may also be used. Operation of each of the control circuits is similar to that explained with reference to FIG. 2, FIG. 4 or FIG. 6 described earlier, and description thereof will be omitted. 
     Thus, in semiconductor integrated device according to the fifth embodiment, effects similar to those of the first to fourth embodiments described earlier are obtained. In addition, since control circuits are disposed in stages preceding comparatively large scale internal clock circuits, propagation of unnecessary signal changes can be reduced by taking a block as the unit. Furthermore, since the number of control circuits is kept at a required minimum, increase in scale of the chip size can be prevented. 
     FIG. 9 to FIG. 12 are diagrams for explaining the characteristic features of a semiconductor integrated device according to a sixth embodiment. Components of the present embodiment are the same as those of the above described first to fifth embodiments. Therefore, the components of the present embodiment are denoted by like characters, and description thereof will be omitted. 
     In FIG.  9  and FIG. 11, reference symbols tda, tdb, tdc, tdd and tde denote data delay times of signals  7   a  to  7   e  of FIGS. 10 and 12, respectively. Reference symbols Td 1 (min) and Td 2 (min) denote the shortest delay time among the delay times tda to tde, respectively. Reference symbols Td 1 (max) and Td 2 (max) denote the longest delay time among the delay times, respectively. Reference character Td denotes a time serving as a decision criterion (threshold) as to whether a control circuit should be disposed. 
     Characteristic features of the operation of the IC chip according to the sixth embodiment will now be described in detail with reference to FIG. 9 to FIG.  12 . For example, when difference values among delay times of the signals  7   a  to  7   e  input to the composite gate circuit  8  are great as shown in FIG. 9, the composite gate circuit  8  changes according to changes of the input signals. At this time, charge and discharge currents flow through the composite gate circuit  8  according to signal changes. In addition, unnecessary signal changes are propagated to subsequent circuits, and charge and discharge currents flow through the subsequent circuits. 
     On the other hand, when difference values among delay times of the signals  7   a  to  7   e  input to the composite gate circuit  8  are small as shown in FIG. 11, the output signal  8   o  becomes definite in a very short time in the composite gate circuit  8  and charge and discharge currents are not generated by an indefinite component. 
     In the sixth embodiment, therefore, a control circuit is not disposed as shown in FIG. 12 when difference values among delay times of the signals input to the composite gate circuit  8  are small as shown in FIG. 11, whereas a control circuit  14  (which may be  14   a  or  14   b ) is disposed as shown in FIG. 10 when difference values among delay times of the signals input to the composite gate circuit  8  are great as shown in FIG.  9 . In other words, it is determined on the basis of difference values among delay times of the signals input to the composite gate circuit  8  in the sixth embodiment whether the control circuit should be disposed. 
     To be concrete, the time Td serving as the decision criterion as to whether a control circuit should be disposed is set beforehand. The shortest delay time Td(min) and the longest delay time Td(max) among the delay times tda to tde of signals input to the composite gate circuit  8  are measured. A difference between them, i.e., (Td(max)−Td(min)) is compared with the decision criterion time Td. For example, if 
     
       
         Td(max)−Td(min)≧Td,  
       
     
     then a control circuit is disposed on the output side of the composite gate circuit  8 . If 
     
       
         Td(max)−Td(min)&lt;Td,  
       
     
     then a control circuit is not disposed. By the way, the decision criterion time Td is arbitrary. For example, the decision criterion time Td may be set to the operation speed of the composite gate circuit  8 . 
     Thus, in the sixth embodiment, a control circuit is not disposed on the output side of the composite gate circuit when difference values among delay times of the signals input to the composite gate circuit are small, whereas a control circuit is disposed on the output side of the composite gate circuit when difference values among delay times of the signals input to the composite gate circuit are great. As a result, effects similar to those of the above described first to fourth embodiments are obtained. In addition, since the disposition location of the control circuit can be selected, disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     FIG. 13 is a diagram for explaining the characteristic features of a semiconductor integrated device according to a seventh embodiment. Basic components of the present embodiment are the same as those of the above described first to fifth embodiments. Therefore, the components of the present embodiment are denoted by like characters, and description thereof will be omitted. In FIG. 13, reference symbol  13   a  denotes an inverter circuit connected to the driver circuit  9 . Reference numeral  16  denotes load capacitance of the output of the driver circuit  9 . Reference numeral  17  denotes wiring between the driver circuit  9  and the inverter circuit  13 . 
     Characteristic features of the IC chip according to the seventh embodiment will now be described in detail with reference to FIG.  13 . For example, when wiring becomes very long between specific circuits to which the output signal of the composite gate circuit  8  is propagated, a control circuit  14  (which may also be  14   a  or  14   b ) is connected to the output of the composite gate circuit  8 , in the present embodiment. In other words, when wiring  17  for propagating the output signal of the composite gate circuit  8  between the driver circuit  9  and the inverter circuit  13  is very long disposition wiring, a control circuit is provided on the output side of the composite gate circuit  8  as shown in FIG.  13 . 
     Load capacitance C of the output of the driver circuit  9  becomes the sum of output wiring capacitance C 1  of the driver circuit  9  and input gate capacitance Cg of the inverter circuit  13   a  connected to the driver circuit  9 , and it can be represented by the following equation. 
     
       
         C=C1+Cg  (2)  
       
     
     Therefore, power dissipation P at the time of operation of the driver circuit  9  is represented by the following equation. 
     
       
         P=(½) Cv=(½) (C1+Cg) V 2   (3)  
       
     
     As the load capacitance becomes smaller, the charge and discharge currents flowing at the time of operation of the driver circuit  9  becomes smaller and the current consumption also becomes smaller. 
     Furthermore, the output wiring capacitance C 1  is in proportion to wiring length L. The input gate capacitance Cg is in proportion to the fan-out number (hereafter referred to as FO number) of a circuit connected to the output of the wiring. If the wiring length L between the circuits becomes very long, therefore, then the wiring capacitance C 1  increases and the power dissipation of the composite gate circuit itself at the time of operation becomes great even when the FO number is 1 or very small. 
     Thus, when wiring between specific circuits to which the output signal of the composite gate circuit is propagated becomes longer than a predetermined length and there is such disposition wiring that charge and discharge currents and power dissipation become great, a control circuit is disposed on the output side of the composite gate circuit, in the seventh embodiment. As a result, effects similar to those of the first to fourth embodiments described earlier are obtained. In addition, since the disposition location of the control circuit can be selected, disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     FIG. 14 is a diagram for explaining the characteristic features of a semiconductor integrated device according to an eighth embodiment. Basic components of the present embodiment are the same as those of the above described first to fifth and seventh embodiments. Therefore, the components of the present embodiment are denoted by like characters, and description thereof will be omitted. In FIG. 14, reference symbol  13   b  denotes a plurality of inverter circuits connected to the driver circuit  9 . 
     Characteristic features of the IC chip according to the eighth embodiment will now be described in detail with reference to FIG.  14 . For example, when the output signal of the composite gate circuit  8  is propagated to very many circuits, a control circuit  14  (which may also be  14   a  or  14   b ) is connected to the output of the composite gate circuit  8 , in the present embodiment. In other words, when the output signal of the composite gate circuit  8  is propagated to a plurality of inverter circuit  13   b,  a control circuit is provided on the output side of the composite gate circuit  8  as shown in FIG.  14 . 
     As shown in the equation (2), load capacitance C of the output of the driver circuit  9  becomes the sum of output wiring capacitance C 1  of the driver circuit  9  and input gate capacitance Cg of the inverter circuit  13  connected to the driver circuit  9 . Therefore, power dissipation P at the time of operation of the driver circuit  9  is represented by the equation (3) As the load capacitance becomes smaller, the charge and discharge currents flowing at the time of operation of the driver circuit  9  becomes smaller and the current consumption also becomes smaller. 
     Furthermore, the output wiring capacitance C 1  is in proportion to wiring length L. The input gate capacitance Cg is in proportion to the fan-out number (hereafter referred to as FO number) of a circuit connected to the output of the wiring. If the FO number becomes great, therefore, then the wiring capacitance Cg increases and the power dissipation of the composite gate circuit itself at the time of operation becomes great even when the wiring length L is very short. 
     Thus, when the output signal of the composite gate circuit is propagated to more circuits than a prescribed number of circuits, or the output of the composite gate circuit is connected to a circuit having a very large drive capability, a control circuit is disposed on the output side of the composite gate circuit, in the eighth embodiment. As a result, effects similar to those of the first to fourth embodiments described earlier are obtained. In addition, since the disposition location of the control circuit can be selected, disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     FIG.  15  and FIG. 16 are diagrams for explaining the characteristic features of a semiconductor integrated device according to a ninth embodiment. Basic components of the present embodiment are the same as those of the above described first to fifth and eighth embodiments. Therefore, the components of the present embodiment are denoted by like characters, and description thereof will be omitted. In FIG. 15 reference symbols  8 A and  8 B denote composite gate circuits, and  9 A and  9 B denote driver circuits. Reference symbols  13 A and  13 B denote a plurality of inverter circuits connected to the driver circuits  9 A and  9 B, respectively. 
     In FIG. 15, a plurality of signals output from the internal block  7  are output to different composite gate circuits. In addition, an output signal of the first composite gate circuit  8 A is output from the driver circuit  9 A via a control circuit  14  (which may also be  14   a  or  14   b ). An output signal of the second composite gate circuit  8 B is output from the driver circuit  9 B without being passed through a control circuit. 
     Characteristic features of the IC chip according to the ninth embodiment will now be described in detail with reference to FIG.  15  and FIG.  16 . Reference symbols  8   a  and  8   b  denote output signals of the composite gate circuits  8 A and  8 B, respectively. Reference symbols  9   a  and  9   b  denote output signals of the driver circuits  9 A and  9 B, respectively. Reference symbols n( 8   a ) and n( 8   b ) denote the numbers of times of signal changes of the output signals  8   a  and  8   b,  respectively. 
     In the present embodiment, the number of times the signal changes from “H” to “L” or “L” to “H” on each of signal lines in the IC chip is counted. On a signal line having a large number of times of signal changes, a control circuit  14  (which may also be  14   a  or  14   b ) is inserted. To be concrete, even if the composite gate circuits  8 A and  8 B are the same in output wiring length L and FO number as shown in FIG. 15, a control circuit is disposed on the output side of the composite gate circuit  8 A, when the number of times of signal changes n( 8   a ) of the output signal  8   a  of the composite gate circuit  8 A is greater than a predetermined number of times N as shown in FIG.  16 . On the other hand, a control circuit is not disposed when the number of times of signal changes n( 8   b ) is less than a predetermined number of times N as in the output signal  8   b  of the composite gate circuit  8 B. 
     The reason why such a configuration is adopted is as follows. That is, a signal line having a large number of times of signal changes is considered to have a high possibility of containing unnecessary signal changes. Irrespective of the disposed wiring and circuit configuration, an insertion location of the control circuit is selected according to the number of times of signal changes of subject signal lines. By the way, the predetermined number of times N serving as the decision criterion is arbitrary, and it may be different from signal line to signal line. 
     Furthermore, the predetermined number of times N serving as the decision criterion may be determined on the basis of a toggle factor of the signal line. The toggle factor indicates the number of periods over which the subject signal line has changed, in all periods of a certain function pattern. If the subject signal line changes over 20 periods in a function pattern of 100 periods, the toggle factor of the signal line becomes 20%. Therefore, signal changes n (signal) of the subject signal line can be represented by the following equation 
     
       
         n (signal)=(the number of periods)×(toggle factor)  
       
     
     As a matter of fact, however, there is a possibility that there are unnecessary signal changes until the signal level becomes definite in the period because of the signal propagation delay difference and soon. Therefore, a signal change during one period is not limited to once. If n (signal)&gt;(the number of periods)×(toggle factor), therefore, it is meant that there are unnecessary signal changes on the signal line. 
     In the ninth embodiment, therefore, the number N of times of signal changes serving as the decision criterion is determined by the following equation. 
     
       
         N=(the number of periods)×(toggle factor)  
       
     
     or 
     
       
         N=(the number of periods)×(toggle factor)+α 
       
     
     (where α is arbitrary) 
     By using N thus determined, it is determined whether a control circuit should be inserted. As a result, a control circuit can be effectively inserted on a signal line having unnecessary signal changes. 
     Thus, in the ninth embodiment, even if different composite gate circuits are the same in output wiring length L and FO number, a control circuit is disposed on the output side of one of the composite gate circuits, when the number of times of signal changes of the composite gate circuit is greater than a predetermined number of times N. On the other hand, a control circuit is not disposed when the number of times of signal changes is less than a predetermined number of times N. As a result, effects similar to those of the first to fourth embodiments described earlier are obtained. In addition, since the disposition location of the control circuit can be selected in more detail than the eighth embodiment, disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     In the fifth to ninth embodiments, it is also possible to set conditions of disposition locations of a control circuit beforehand, search circuit components and signal operations satisfying the conditions at the time of work on the CAD such as logical synthesis of disposition wiring, automatic disposition wiring, and simulation, and automatically insert a control circuit designed beforehand and described in any of the first to third embodiments when the conditions are satisfied. As a result, the disposition location of the control circuit can be selected in the CAD work stage. Therefore, the time required for insertion location selection can be reduced remarkably. In addition, the disposition forgetting can be prevented. Furthermore, the design time for control circuit insertion can also be shortened. 
     As heretofore described, according to this invention, there is provided a control circuit having a configuration as follow. That is, when time difference is caused in change timing of a plurality of signals by difference in the paths, the control circuit outputs the received signal as it is during an interval having no possibility of a signal change, i.e., a definite data interval, whereas the control circuit outputs the fixed signal irrespective of the signal level of the received signal during an interval having a possibility of a change of at least one signal, i.e., an indefinite data interval. Owing to such a configuration, propagation of unnecessary signal changes occurring in the conventional technique can be prevented. Therefore, there is brought about an effect that the charge and discharge currents of the whole apparatus can be reduced remarkably. Furthermore, for the same reason, there is brought about an effect that the power dissipation of the whole apparatus can also be reduced remarkably. Furthermore, not only the charge and discharge currents can be reduced, but also operation of transistors caused by unnecessary signal changes is eliminated. In other words, unnecessary switchover operation of a PMOS transistor and an NMOS transistor from “ON” to “OFF” and vice versa is eliminated. As a result, there is brought about an effect that a through current occurring when both transistors are “ON” can also be reduced. 
     Furthermore, it is determined according to the state of the clock signal serving as the control signal whether the signal input to the control circuit should be output as it is or a fixed signal should be output irrespective of the signal level of the input signal. Propagation of unnecessary signal changes is thus prevented. In addition, therefore, by setting the duty cycle of the clock signal to such a value that an indefinite component of the input signal can be removed, there is brought about an effect that only the signal of the definite interval can be output certainly. 
     Furthermore, the input signal is latched at a rising edge of the clock and held until the next rising edge. Propagation of unnecessary signal changes is thus prevented. In addition, by causing the rising edge of the clock always in a definite data interval, i.e., in such a position that an indefinite component of the input signal can be removed, there is brought about an effect that only the signal of the definite interval can be output certainly. 
     Furthermore, the control signal is generated on the basis of a plurality of signals such as the clock signal, signals fed from other internal block circuits, and an external input signal. The control interval can be freely set according to various conditions irrespective of the clock signal. Therefore, there is brought about an effect that the propagation signal can be controlled in a finer manner. 
     Furthermore, control circuits are disposed in stages preceding comparatively large scale internal clock circuits. Therefore, there is brought about an effect that propagation of unnecessary signal changes can be reduced by taking a block as the unit. Furthermore, since the number of control circuits is kept at a required minimum, there is brought about an effect that increase in scale of the chip size can be prevented. 
     Furthermore, a control circuit is not disposed on the output side of the composite gate circuit when difference values among delay times of the signals input to the composite gate circuit are small, whereas a control circuit is disposed on the output side of the composite gate circuit when difference values among delay times of the signals input to the composite gate circuit are great. As a result, the disposition location of the control circuit can be selected. Therefore, there is brought about an effect that disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     Furthermore, when wiring between specific circuits to which the output signal of the composite gate circuit is propagated becomes longer than a predetermined length and there is such disposition wiring that charge and discharge currents and power dissipation become great, a control circuit is disposed on the output side of the composite gate circuit. As a result, the disposition location of the control circuit can be selected. Therefore, there is brought about an effect that disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     Furthermore, when the output signal of the composite gate circuit is propagated to more circuits than a prescribed number of circuits, or the output of the composite gate circuit is connected to a circuit having a very large drive capability, a control circuit is disposed on the output side of the composite gate circuit, in the present embodiment. As a result, the disposition location of the control circuit can be selected. Therefore, there is brought about an effect that disposition of useless control circuits can be prevented and the chip size can be remarkably reduced. 
     Furthermore, even if different composite gate circuits are the same in output wiring length L and FO number, a control circuit is disposed on the output side of one of the composite gate circuits, when the number of times of signal changes of the composite gate circuit is greater than a predetermined number of times N. On the other hand, a control circuit is not disposed when the number of times of signal changes is less than a predetermined number of times N. As a result, the disposition location of the control circuit can be selected in more detail. Therefore, there is brought about an effect that disposition of useless control circuits can be prevented more efficiently and the chip size can be remarkably reduced. 
     Furthermore, it is possible to automatically select the disposition location of the control circuit in the CAD work stage and automatically insert a control circuit. Therefore, there is brought about an effect that the time required for insertion location selection can be reduced remarkably and the disposition forgetting can be prevented. Furthermore, there is brought about an effect that the design time for control circuit insertion can also be shortened. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.