Patent Abstract:
A low power dynamic logic circuit. By shifting a discharge NMOS transistor of a conventional dynamic logic circuit between an output terminal and a logic block, plus an additional charge and discharge control, the operation speed and power consumption of a dynamic circuit can be effectively improved. Using the charge redistribution to speed up the circuit operation and to reduce the body effect that affects the operation speed, the speed of the novel dynamic logic circuit is enhanced. By transferring the lump capacitor of the charge/discharge, the dynamic power can be effectively reduced. The lower power dynamic logic circuit can be used independently or combined with a conventionally dynamic logic circuit.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a dynamic logic circuit, and more particularly, to a low power dynamic logic circuit. 
     2. Description of the Related Art 
     CMOS dynamic circuits originated in the 1980s. Since the CMOS circuit employing repetitive transistor networks (NMOS transistor network and PMOS network) to implement the circuit required excessive hardware, a single-side transistor network (only NMOS transistor network or PMOS network) replaced the CMOS circuit. However, the single-side transistor network is not supposed to lose the advantage of no static power consumption of the CMOS circuit. With this in mind, the CMOS dynamic circuit is developed and fabricated. 
     FIG. 1 shows a conventional dynamic logic circuit. In FIG. 1, the dynamic logic circuit comprises a PMOS transistor  102 , a logic block  104  and an NMOS transistor  106 . The PMOS transistor  102  and the NMOS transistor  106  are controlled by the same clock signal φ, which is illustrated in FIG.  1 B. The logic block  104  is used to implement a Boolean function. The dynamic logic circuit as shown in FIG. 1 controlled by the clock signal φ works in two phases, that is, a precharge phase and an evaluation phase. When the circuit works in the precharge phase, φ=0, the PMOS transistor  102  is turned on, and the NMOS transistor  106  is turned off. Consequently, the output terminal O is charged to a high voltage (logic 1) via the PMOS transistor  102 . When the circuit works in the evaluation phase, φ=1, the PMOS transistor  102  is turned off, and the NMOS transistor  106  is turned on. Meanwhile, the logic block  104  is connected to the NMOS transistor  106  in series, so that the logic of the output terminal O is determined by the input terminal i to complete the Boolean function of the circuit. 
     FIG. 2A shows the way to use a domino circuit to construct the dynamic logic circuit. In FIG. 2A, two stages of domino circuit logic gates  202  and  204  are coupled to each other. The logic gates  202  and  204  are similar to each other with different complete logic. For example, the logic gate  202  comprises a logic unit  206  coupled to a driver unit  208 , and the logic unit  206  comprises a PMOS transistor  210 , a logic block  212  and an NMOS transistor  214  coupled together. The logic block  212  comprises an NMOS transistor  226  coupled to an NMOS transistor  228 . The logic gate  204  comprises a logic unit  216  coupled to a driver unit  218 . The logic unit  216  comprises a PMOS transistor  220 , a logic block  222  and an NMOS transistor  224  coupled together. The logic block  222  comprises an NMOS transistor  230 . The PMOS transistor  210 , the PMOS transistor  220 , the NMOS transistor  214  and the NMOS transistor  224  are controlled by the same clock signal φ. The driver units  208  and  218  are made of inverters. The relative waveforms of the operation of the circuit are shown as FIG.  2 B. The domino circuit is working in two phases, the precharge phase (φ=0) and the evaluation phase (φ=1). When φ=0, the outputs Q and R of the logic units  206  and  216  are charged up to a high voltage. Through the inverter, the outputs P and Z of the logic gates  202  and  204  are 0. After φ=1, initially, as the outputs P and Z are both low voltage, so that the NMOS transistor  230  to implement the Boolean function is shut off. However, when A and B are both logic 1, the output of the logic unit  206  is 0 after a time delay. Through the inverter, the output P is raised to logic 1. Similarly, when P is logic 1, Z is raised to logic 1 after a time delay. Accordingly, the data evaluation operation is performed sequentially without causing the problem of data race. 
     FIG. 3A shows a way of using a clock delay circuit to construct a dynamic logic circuit. In FIG. 3A, two stages of clock delay circuit logic gates  302  and  304  are coupled to each other. The logic gate  302  comprises a logic unit  306  that further comprises a PMOS transistor  308 , a logic block  310  and an NMOS transistor  312  coupled together. The PMOS transistor  308  and the NMOS transistor  312  are controlled by the clock signal φ. The logic gate  304  comprises a logic unit  314  that further comprises a PMOS transistor  316 , a logic block  318  and an NMOS transistor  320 . The PMOS transistor  316  and the NMOS transistor  320  are controlled by the clock signal φ d . The relative waveforms of the operation of the circuit are shown in FIG.  3 B. In FIG. 3B, the clock delay circuit is operated under two phases, that is, a precharge phase (φ=0, φ d =0) and an evaluation phase (φ=1 and φ d =1). When φ=0, φ d =0, the circuit is in the precharge phase. The outputs P and Z of the logic gates  302  and  304  are logic 1. When φ=1, the logic gate  302  starts the evaluation. Meanwhile, φ d  is still 0. The output P is varied to logic 0 only when the input signals A and B are both logic 1. Consequently, φ d  is changed to 1. Meanwhile, the input of the logic gate  304  is stabilized, the output Z is not damaged by data race, and a correct evaluation can be performed. 
     Both the domino circuit and clock delay circuit are operated by applying the technique of an inverter gate or a clock delay to the logic unit. That is, the major part is still the logic unit. Therefore, if the performance of the logic unit is enhanced, for example, the operation speed is increased and the power consumption is reduced, the overall assembly of circuit can be enhanced. 
     FIG. 4 illustrates a conventional logic unit of a dynamic logic circuit with a NOR function. In FIG. 4, the logic unit of the logic circuit comprises a PMOS transistor  402 , a logic block  404  and an NMOS transistor  406  coupled together. The PMOS transistor  402  and the NMOS transistor  406  are controlled by a clock signal φ. The logic block  404  comprises k NMOS transistors connected in parallel. That is, the logic unit implements the NOR function with k inputs. When the logic block  404  connects k NMOS transistors in parallel, the parasitic capacitance of the drain and source regions are significant. The lump capacitor of the drain regions (including the parasitic capacitor and the wiring capacitor) is denoted by C 1    408 , while the lump capacitor of the source regions (including the parasitic capacitor and the wiring capacitor) is denoted by C 2    410 . When φ=0 the PMOS transistor  402  charges the capacitors C 1    408  and C 2    410  up to V DD  and V DD −V TN , wherein V DD  is the operation voltage, and V TN  is the threshold voltage of the NMOS transistor. When φ=0, most of the input combinations (with a probability of (2 k −1)/2 k ) enables the charges stored in C 1    408  and C 2    410  to leak. As the speed of the logic unit is determined according to the transition from 1 to 0 of the output terminals, the discharging time will seriously affect the operation speed. In addition, this dynamic power consumption is significant with a high probability and is a major factor that affects the power consumption of the circuit. 
     According to the above, the conventional dynamic logic circuit still has a lot drawbacks such as: 
     1. Significant power consumption. 
     2. Long operation time. 
     SUMMARY OF THE INVENTION 
     The invention provides a novel CMOS basic dynamic logic circuit to improve the problems of large power consumption and long operation time for the conventional dynamic logic circuit. 
     The novel dynamic logic circuit provided by the invention comprises a charge unit, coupled to a first clock signal, and a discharge unit, coupled to a second clock signal and the charge unit. The first and the second clock signal are in inverted phase to each other. 
     The charge unit comprises a PMOS transistor, an NMOS transistor, a feedback PMOS transistor and a logic gate. The PMOS transistor has a gate coupled to the first clock signal and a source region coupled to a voltage source. The NMOS transistor has a gate coupled to the first clock signal, a drain region coupled to a drain region of the PMOS transistor, and a source region coupled to the discharge unit. The feedback PMOS transistor has a drain region coupled to the drain region of the NMOS transistor, and a source region coupled to the voltage source. The logic gate has a first terminal coupled to the drain region of the PMOS transistor and a second terminal coupled to a gate of the feedback PMOS transistor. 
     The discharge unit comprises a logic block and an NMOS transistor. The logic block has a first terminal coupled to the charge unit and a second terminal coupled to a ground voltage. The NMOS transistor has a gate coupled to the second clock signal, a drain region coupled to the first terminal of the logic block, and a source region coupled to the ground voltage. The logic block includes an NMOS transistor network. When the first clock signal is logic 0 and the second clock is logic 1, the low power dynamic logic circuit is in a precharge phase. When the first clock signal is logic 1 and the second clock signal is logic 0, the low power dynamic logic circuit is in an evaluation phase. 
     When the circuit is performing the precharge operation, the output terminal is charged to logic 1, where the output terminal is coupled to the drain region of the PMOS transistor of the charge unit. Meanwhile, the charge unit and the discharge unit are isolated by the NMOS transistor of the charge unit. No matter which circuit the logic gate is, and no matter what the output voltage of the logic gate is, the voltage of the output terminal is not affected. The NMOS transistor of the discharge unit is on at this time, and the internal node is precharged to logic 0 (that is, discharging). The internal node is coupled to the drain region of the NMOS transistor of the discharge unit. 
     When the circuit is performing the evaluation operation, the PMOS transistor of the charge unit is off, while the NMOS transistor thereof is on. The charge unit and the discharge unit conduct with each other. The logic value of the output terminal is determined by the logic block. If the logic block is to obtain a value of 0, the output terminal is discharged to 0. If the logic block is to obtain a value of 1, the charge redistribution occurs since the output terminal is precharged to logic 1, while the internal node is precharged to logic 0. Only to make the logic value of the output of the logic gate opposite to that of the output terminal, the feedback PMOS transistor will helps the output terminal and the internal node to recharge to logic 1. The output of the current circuit can be connected to next stage via the logic gate. Or alternatively, an inverter can be added to bring the output to the next stage. 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A shows a conventional dynamic logic circuit; 
     FIG. 1B shows a clock signal of the conventional dynamic logic circuit; 
     FIG. 2A shows a circuit diagram of a conventional dynamic logic circuit connected with a cascaded 2-stage domino circuit; 
     FIG. 2B shows the relative waveforms of the conventional dynamic logic circuit with a cascaded 2-stage domino circuit; 
     FIG. 3A shows a conventional dynamic logic circuit with a cascaded 2-stage clock delay circuit; 
     FIG. 3B shows the relative waveforms of the conventional dynamic logic circuit with a cascaded 2-stage clock delay circuit; 
     FIG. 4 shows a logic unit of a conventional dynamic logic circuit; 
     FIG. 5A shows a novel dynamic logic circuit according to the invention; 
     FIG. 5B shows the relative control sequence diagram of the novel dynamic logic circuit; 
     FIG. 6A shows a possible assembly of the novel dynamic logic circuit; 
     FIG. 6B shows another possible assembly of the novel dynamic logic circuit; 
     FIG. 6C shows another possible assembly of the novel dynamic logic circuit; 
     FIG. 6D shows another possible assembly of the novel dynamic logic circuit; 
     FIG. 6E shows another possible assembly of the novel dynamic logic circuit; 
     FIG. 7 shows a schematic drawing of a logic unit of the novel dynamic logic circuit; 
     FIG. 8 shows a modification of the novel dynamic logic circuit; 
     FIG. 9 shows an application of the novel dynamic logic circuit; and 
     FIG. 10 shows another application of the novel dynamic logic circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 5A shows a basic logic unit of the invention. The logic unit comprises two major parts: a charge unit (CU)  502  coupled to a first clock signal and a discharge unit (DU)  504  coupled to a second clock signal to reduce power consumption and reduce the operation time. The first clock signal has a phase opposite to the phase of the second clock signal. 
     The charge unit comprises a PMOS transistor  506 , an NMOS transistor  508 , a feedback PMOS transistor  510  and a logic gate  512 . The PMOS transistor  506  has a gate coupled to the first clock signal and a source region coupled to a voltage source. The NMOS transistor  508  has a gate coupled to the first clock signal, a drain region coupled to a drain region of the PMOS transistor  506  and a source region coupled to the discharge unit  504  to isolate the connection with the discharge unit. The feedback PMOS transistor  510  has a drain region coupled to the drain region of the PMOS transistor  506 , a source region coupled to the voltage source to provide a voltage to the charge unit  502  for recharging operation, and a gate coupled to a logic gate  512 . The logic gate  512  has a first terminal coupled to the drain region of the PMOS transistor  506 , and a second terminal coupled to the gate of the feedback PMOS transistor  510 . A signal inverse to the drain region of the PMOS transistor  506  is provided from the second terminal of the logic gate to the feedback PMOS transistor  510 . 
     The discharge unit  504  comprises a logic block  514  to implement a Boolean function and an NMOS transistor  516 . The logic block has a first terminal coupled to the charge unit  502  and a second terminal coupled to a ground voltage. The NMOS transistor  516  has a gate coupled to the second clock signal, a drain region coupled to the first terminal of the logic block  514 , and a source region coupled to the ground voltage to discharge the discharge unit  504 . FIG. 5B shows the relative waveforms of the clock control sequence. The circuit is operated in the precharge phase and the evaluation phase. 
     When the first clock signal φ=0 and the second clock signal {overscore (φ)}=1, the circuit is performing a precharge operation. The PMOS transistor  506  in the charge unit  502  is on and the NMOS transistor  508  in the charge unit  502  is off. The output terminal X is charged to logic 1. Meanwhile, the charge unit  502  and the discharge unit  504  are isolated by the NMOS transistor  508 . No matter what circuit the logic gate  512  is, and no matter what the voltage O 1  is, the voltage of the output terminal X is not affected. At the moment, {overscore (φ)}=1, so that the NMOS transistor  516  of the discharge unit  504  is on, and the internal node Y is precharged to logic 0 (discharging). 
     When φ=1, {overscore (φ)}=0, the circuit performs an evaluation operation. Meanwhile, the PMOS transistor  506  and the NMOS transistor  516  are off, and the NMOS transistor  508  is on. The charge unit  502  and the discharge unit  504  conduct with each other. The logic value of the output terminal X is determined by the logic block  514 . If the logic block  514  is to obtain a value of 0, the output terminal X is discharged to 0. If the logic block  514  is to obtain a value of 1, a charge redistribution occurs since the node X is precharged to logic 1 and the node Y is precharged to logic 0. The PMOS transistor  510  will help recharge X and Y up to logic 1 only to let the logic value of O 1  be inverse to the logic value of X. The inputs of the logic unit circuit have to be stabilized before the evaluation operation, or only one transition from 0 to 1 is allowed in the evaluation operation. The output of the current circuit can be connected to a next stage via the output O 1  of the logic gate  512 . Or alternatively, the output O 2  can be brought to connect to the next stage by adding an inverter  518 . 
     FIGS. 6A to  6 E illustrate a few possible assemblies of the dynamic logic circuit as the examples to implement the logic gate. One can easily prove that these assemblies meet the requirements of the above circuit operation. In these circuits, the gate B is optional. These circuits can be applied in different circumstances. 
     FIG. 6A shows a dynamic logic circuit of which the logic gate includes an inverter. 
     FIG. 6B shows a dynamic logic circuit of which the logic gate includes a NAND gate with two inputs. One of the inputs is coupled to logic 1, while the other input is coupled to the drain region of the feedback PMOS transistor. 
     FIG. 6C shows a dynamic logic circuit of which the logic gate includes a NOR gate with two inputs. One of the inputs is coupled to logic 0, while the other input is coupled to the drain region of the feedback PMOS transistor. 
     FIG. 6D shows a dynamic logic circuit of which the logic gate includes a NAND gate with two inputs. One of the inputs is coupled to the first clock signal, while the other input is coupled to the drain region of the feedback PMOS transistor. 
     FIG. 6E shows a dynamic logic circuit of which the logic gate includes a NOR gate with two inputs. One of the inputs is coupled to the second clock signal, while the other input is coupled to the drain region of the feedback PMOS transistor. 
     Second Embodiment 
     FIG. 7 shows a logic unit of a dynamic logic circuit. The dynamic logic circuit comprises a charge unit  702  and a discharge unit  704  coupled to the charge unit  702 . The charge unit  702  comprises a PMOS transistor  706 , an NMOS transistor  708 , a feedback PMOS transistor  710  and a logic gate  712 . The PMOS transistor  706  has a gate coupled to the first clock signal and a source region coupled to a voltage source. The NMOS transistor  708  has a drain region coupled to a drain region of the PMOS transistor  706  and a source region coupled to the discharge unit  704  to isolate the connection with the discharge unit  704 . The feedback PMOS transistor  710  has a drain region coupled to the drain region of the PMOS transistor  706 , and a source region coupled to the voltage source to provide a voltage to the charge unit  702  for recharging operation. The logic gate  712  has an input terminal coupled to the drain region of the PMOS transistor  706 , and an output terminal coupled to the gate of the feedback PMOS transistor  710 . A signal inverse to the drain region of the PMOS transistor  706  is provided to the feedback PMOS transistor  710 . The logic gate comprises an inverter. The PMOS transistor  706  and the NMOS transistor  708  are controlled by the first clock signal φ. The discharge unit  704  comprises a logic block  714  to implement Boolean function and an NMOS transistor  716 . The NMOS transistor  716  has a drain region coupled to the source region of the NMOS transistor  708  of the charge unit  702  to discharge the discharge unit  704 . The NMOS transistor  716  is controlled by the second clock signal {overscore (φ)}. The first and second clock signals are inverted with respect to each other. The output of the circuit is connected to the next stage by bringing the output O 2  from an inverter  718 . C 0    722  is the lump capacitor of the node X, while C 1    720  is the lump capacitor of the node Y. 
     The circuit is operated in the precharge phase and the evaluation phase. When the φ=0 and {overscore (φ)}=1, the circuit is performing a precharge operation. The PMOS transistor  706  is on and the NMOS transistor  708  is off. The output terminal X is charged to logic 1. Meanwhile, the charge unit  702  and the discharge unit  704  are isolated by the NMOS transistor  708 . No matter what the voltage O 1  is, the voltage of the output terminal X is not affected. At the moment, {overscore (φ)}=1, so that the NMOS transistor  716  of the discharge unit  704  is on, and the internal node Y is precharged to logic 0 (discharging). 
     When φ=1, {overscore (φ)}=0, the circuit performs an evaluation operation. Meanwhile, the PMOS transistor  706  and the NMOS transistor  716  are off, and the NMOS transistor  708  is on. The charge unit  702  and the discharge unit  704  are conducted with each other. The logic value of the output terminal X is determined by the logic block  714 . If the logic block  714  is to obtain a value of 0, the output terminal X is discharged as 0. If the logic block  714  is to obtain a value of 1, a charge redistribution occurs since the node X is precharged to logic 1 and the node Y is precharged to logic 0. Only to let the logic value of O 1  inverse to the logic value of X, the PMOS transistor  710  will helps recharge X and Y up to logic 1. 
     FIG. 8 shows an application of the dynamic logic circuit. The application is modified from FIG.  6 D. In addition to the existent advantages, the load of clock signal can be reduced, and the possibility of glitch caused by the output of the NAND gate  802  can be reduced. 
     FIG. 9 shows an application of the invented dynamic logic circuit, wherein the invented dynamic logic circuit is applied to a domino circuit. 
     FIG. 10 shows an application of the invented dynamic logic circuit. In FIG. 10, the dynamic logic circuit is applied to a clock delay circuit. 
     According to the above, the invention includes at least the following advantages: 
     (1) The operation speed is increased. 
     Referring to FIG. 7, comparing the conventional dynamic logic circuit shown in FIG. 4, the NMOS transistor  708  of the charge unit  702  is shifted between the output terminal X and the logic block  714 , and a charge/discharge control is added. Since the lump capacitor C 1    720  is completely discharged by the NMOS transistor  716  in the precharging phase, a charge redistribution occurs to C 0    722  and C 1    720  of the dynamic logic circuit when the evaluation operation starts whatever the input combination is. If the output terminal X is to be discharged to logic 0, the effect will enhance the circuit operation speed. On the other hand, the drain region Y of the NMOS transistor  716  is precharged to logic 0 to moderate the body effect, so that the circuit operation speed is enhanced. The invention uses the charge redistribution to speed up the circuit operation and to reduce the influence of body effect to the operation speed, so that the operation speed of the dynamic logic circuit can be effectively enhanced. 
     (2) The power consumption is reduced. 
     As the CMOS dynamic circuit does not have static power consumption, so that the major power consumption comes from the dynamic power consumption, and can be expressed as        P   =       ∑     i   =   1     n                     α                   C   i          V   DD   2          f   .                                
     In the equation, C i  is the lump capacitance of node i, V DD  and ƒ is the operation voltage and frequency, respectively. If V DD  and ƒ are fixed, only α and C i  are to be considered. αC is defined as the power factor (PF) here. 
     Referring to FIG. 7, the power consumption of the dynamic logic circuit is effectively reduced because the NMOS transistor  708  is shifted between the output terminal X and the logic block  714 . Since the NMOS transistor  708  is shifted upwardly, the circuit has to charge the lump capacitor C 0    722  with a smaller capacitance only. If the probability of leaking the stored charges is large, the power consumption is attributed from the smaller αC 0 . Compared to the αC 1 +α′C 2  of the conventional dynamic logic circuit as shown in FIG. 4, the effect is much smaller. When the circuit complexity is greater, the effect is even more significant. 
     If all the inputs are 0, while entering the evaluation phase, the charges of C 0    722  and C 1    720  are redistributed. The PMOS transistor  710  will help pull up the output terminals X and Y to a high voltage V DD  and V DD −V TN , respectively. The charges stored in node Y are leaked by the NMOS transistor  716  in the next precharge phase. Nevertheless, in this example, the power consumption is still small with a probability of ½ k . 
     (3) The novel dynamic logic circuit can be combined with the conventional one. 
     Different CMOS dynamic logic circuits cannot be cascaded arbitrarily, otherwise, an electrical problem and a data race problem would occur. From certain analysis, referring to FIGS. 9 and 10, the novel dynamic logic circuit can be mixed with the conventional one for use without causing the above problems. Of course, the novel dynamic logic circuit can be used independently. 
     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Technology Classification (CPC): 7