Abstract:
An object of the present invention is to obtain a frequency division circuit including a flip-flop circuit capable of low-voltage and high-frequency operation. The frequency division circuit has bipolar transistors and MOS transistors. Thus, the circuit includes transistors that are connected to the transistor to which the clock input is input, that execute the differential operation after being input with data input signals, and that output signals of resistors, and also transistors that are similarly connected to the transistor to which Ck is input and that hold signals of resistors, transistors that are connected to the transistor to which Ck is input and that output signals of resistors, and transistors that are connected to the transistor to which NCk is input and that hold signals of resistors.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a frequency division circuit using a flip-flop circuit combining therein bipolar transistors and MOS transistors and a buffer circuit.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 2  shows a conventional frequency division circuit comprising a flip-flop circuit  21  using bipolar transistors and a buffer circuit  22 . The reference numerals  211 - 228  stand for bipolar transistors,  231 —a power source voltage terminal,  201 - 204 —load resistors,  205 - 208 —resistors determining the current of a constant current source. Pairs of transistor  211  and transistor  214 , transistor  212  and transistor  213 , transistor  215  and transistor  218 , transistor  216  and transistor  217 , transistor  221  and transistor  222 , and transistor  223  and transistor  224  form respective differential pairs. A data signal D is inputted to the base of the bipolar transistor  211 , and a data signal ND is inputted to the base of the bipolar transistor  214 . As for the clock signals Ck and NCk, the clock signal Ck is inputted to the bipolar transistors  222 ,  223 , and the clock signal NCk is inputted to the bipolar transistor  221 ,  224 .  
         [0005]     The operation principle will be described below. When a HIGH signal is inputted as a clock signal to a clock input terminal  234  (clock signal LOW is inputted to the clock input terminal  235 ), the bipolar transistors  221 ,  224  are switched ON and the differential pair formed by the bipolar transistors  211 ,  214  and the differential pair formed by the bipolar transistors  216 ,  217  become operative. Owing to the operation of the differential pair formed by the bipolar transistors  211 ,  214 , the output of the load resistors  201 ,  202  is outputted in response to signals of data signals D, ND inputted to the data input terminals  232 ,  233 . The output data of the load resistors  201 ,  202  are inputted to the differential pair formed by the bipolar transistors  215 ,  218 . The operation of the bipolar transistors  215 ,  218  is OFF, the operation of the bipolar transistors  216 ,  217  is ON, and the output signal of the load resistors  203 ,  204  holds the data preceding the input of the clock signals to the clock input terminals  234 ,  235 .  
         [0006]     When a HIGH signal is inputted as a clock signal to a clock signal input terminal  235  (clock signal LOW is inputted to the clock input terminal  234 ), the bipolar transistors  222 ,  223  are switched ON and the differential pair formed by the bipolar transistors  212 ,  213  and the differential pair formed by the bipolar transistors  215 ,  218  become operative. Owing to the operation of the differential pair formed by the bipolar transistors  212 ,  213 , the output of the load resistors  201 ,  202  holds the previous output state. The output signals of the load resistors  201 ,  202  are inputted to the differential pair formed by the bipolar transistors  215 ,  218 . The operation of the bipolar transistors  215 ,  218  is ON, the operation of the bipolar transistors  216 ,  217  is OFF, and the output signal of the load resistors  203 ,  204  is outputted in response to the clock signals inputted from the clock input terminals  234 ,  235  and data signals outputted from the load resistors  201 ,  202 .  
         [0007]     Furthermore, when the output terminal of the frequency division circuit does not shift the level of the output signal voltage, output terminals  241 ,  242  are used. When the output voltage of the flip-flop circuit  21  is level shifted and outputted, the output voltage is shifted and outputted by using the buffer circuit  22 . This buffer circuit  22  comprises bipolar transistors  219 ,  220 ,  227 ,  228  with a short delay time.  
         [0008]     In the case of a bipolar transistor three-stage structure shown in  FIG. 2 , the base-emitter voltage Vbe of each transistor is 0.7 V, the base-collector voltage Vbc is 0.1 V, and when the voltage applied to the load resistor of the flip-flop circuit is taken as 0.3 V, the minimum necessary power source voltage becomes 0.7×3+0.1×3+0.3=2.7 V. As a result, the flip-flop circuit  21  with the bipolar transistor three-stage structure is inadequate for low-voltage operation.  
         [0009]      FIG. 3  shows a conventional frequency division circuit comprising a flip-flop circuit  31  using MOS transistors and a buffer circuit  32 . The reference numerals  311 - 328  stand for MOS transistors and the reference numerals  301 - 304  stand for load resistors. Pairs of MOS transistor  311  and MOS transistor  314 , MOS transistor  312  and MOS transistor  313 , MOS transistor  315  and MOS transistor  318 , MOS transistor  316  and MOS transistor  317 , MOS transistor  321  and MOS transistor  322 , and MOS transistor  323  and MOS transistor  324  form respective differential pairs. A data signal D is inputted to the base of the MOS transistor  311 , and a data signal ND is inputted to the base of the MOS transistor  314 . As for the clock signals Ck and NCk, the clock signal Ck is inputted to the MOS transistors  322 ,  323 , and the clock signal NCk is inputted to the bipolar transistor  321 ,  324 .  
         [0010]     The operation principle will be described below. When a HIGH signal is inputted as a clock signal to a clock input terminal  334  (clock signal LOW is inputted to the clock input terminal  335 ), the MOS transistors  321 ,  324  are switched ON and the differential pair formed by the MOS transistors  311 ,  314  and the differential pair formed by the MOS transistors  316 ,  317  become operative. Owing to the operation of the differential pair formed by the MOS transistors  311 ,  314 , the output of the load resistors  301 ,  302  is outputted in response to signals of data signals D, ND inputted to the data input terminals  332 ,  333 . The output data of the load resistors  301 ,  302  are inputted to the differential pair formed by the MOS transistors  315 ,  318 . The operation of the MOS transistors  315 ,  318  is OFF, the operation of the MOS transistors  316 ,  317  is ON, and the output signal of the load resistors  303 ,  304  holds the data preceding the input of the clock signals to the clock input terminals  334 ,  335 .  
         [0011]     When a HIGH signal is inputted as a clock signal to a clock signal input terminal  335  (clock signal LOW is inputted to the clock input terminal  334 ), the MOS transistors  322 ,  323  are switched ON and the differential pair formed by the MOS transistors  312 ,  313  and the differential pair formed by the MOS transistors  315 ,  318  become operative. Owing to the operation of the differential pair formed by the MOS transistors  312 ,  313 , the output of the load resistors  301 ,  302  holds the previous output state. The output signals of the load resistors  301 ,  302  are inputted to the differential pair formed by the MOS transistors  315 ,  318 . The operation of the MOS transistors  315 ,  318  is ON, the operation of the MOS transistors  316 ,  317  is OFF, and the output signal of the load resistors  303 ,  304  is outputted in response to the clock signals inputted from the clock input terminals  334 ,  335  and data signals outputted from the load resistors  301 ,  302 .  
         [0012]     Furthermore, when the output terminal of the frequency division circuit does not shift the level of the output signal voltage, output terminals  341 ,  342  are used. When the output voltage of the flip-flop circuit  31  is level shifted and outputted, the output voltage is shifted and outputted by using the buffer circuit  32 . This buffer circuit comprises MOS transistors  319 ,  320 ,  327 ,  328 .  
         [0013]     In the case of a MOS transistor three-stage structure shown in  FIG. 3 , the minimum required source voltage becomes lower than that of the configuration using bipolar transistors. In particular, the minimum required source voltage of a MOS with a low threshold voltage decreases and the flip-flop circuit  31  is suitable for low-voltage operation. However, because MOS transistors have a frequency characteristic worse that that of the bipolar transistors, the operation frequency decreases.  
         [0014]     Further, because MOS transistors are provided in the buffer circuit  32 , the delay time of input and output signals of the buffer circuit  32  becomes much longer than that of the buffer circuit  22  comprising bipolar transistors.  
         [0015]     A flip-flop circuit of another embodiment disclosed in Japanese Patent Application Laid-open No. H9-69759A (shown in  FIG. 4 ) was suggested as a frequency division circuit comprising a flip-flop circuit using bipolar transistors and capable of operating at a low voltage.  
         [0016]     The conventional circuit shown in  FIG. 4  constitutes a latch circuit comprising a first transistor differential pair Q 1 -Q 3 , a second transistor differential pair Q 4 -Q 6 , first and second load resistors R 11 , R 12 , and constant current sources Q 13 , R 19 , Q 14 , R 20 . Similarly, another latch circuits is composed of a third transistor differential pair Q 7 -Q 9 , fourth transistor differential pair Q 10 -Q 12 , third and fourth load resistors R 13 , R 14 , and constant current sources Q 15 , R 22 , Q 16 , and R 21 . This conventional flip-flop circuit reads the data of data input D, D bar when a clock input T is HIGH and outputs the read-out data to Q and Q bar when the clock input T is LOW.  
         [0017]     In this conventional circuits, the transistors Q 1 , Q 4 , Q 7 , and Q 10  into which the clock signals are inputted and the emitters of transistors Q 2 , Q 3 , Q 5 , Q 6 , Q 8 , Q 11 , and Q 12  into which the data input signals are inputted are connected via emitter return resistors R 15 -R 18  to conduct switching. As a result, the number of stacking stages of transistors Q 1 -Q 12  and Q 13 -Q 16  connected between the power source and GND is reduced by one. Reducing by one the number of transistor stages between the power source and GND enables the low-voltage operation.  
         [0018]     In the conventional flip-flop circuit  21  using bipolar transistors shown in  FIG. 2 , the minimum necessary power source voltage is high, making the circuit inadequate for low-voltage operation. Furthermore, the conventional flip-flop circuit  31  using MOS transistors shown in  FIG. 3  is adequate for low-voltage operation, but the operation frequency in the frequency characteristic decreases with respect to that of the flip-flop circuit using bipolar transistors. Furthermore, in the conventional example shown in  FIG. 4 , in order to produce a low-voltage flip-flop circuit comprising only bipolar transistors, the clock signal input uses the output of the differential circuit and the flip-flop circuit itself has a folded-type structure. Therefore, the electric current apparently increases over that of a three-stage longitudinally stacked structure of transistors.  
       SUMMARY OF THE INVENTION  
       [0019]     The present invention was achieved to resolve the above-described problems and it is an object thereof to obtain a flip-flop circuit suitable for low-voltage operation and having a high operation frequency and a frequency division circuit using such flip-flop circuit.  
         [0020]     In order to attain the above-described object the flip-flop circuit in accordance with the present invention has a three-stage configuration of transistors connected between the power source voltage and GND, this configuration being identical to the conventional configuration. In this configuration, using bipolar transistors for the upper-stage transistors of the three-stage structure enables the circuit to operate in a frequency range up to a high frequency, and using MOS transistors with a low threshold for the transistors of the medium and lower stages of the three-stage structure of the flip-flop circuit ensures low-voltage operation.  
         [0021]     The flip-flop circuit of the first invention comprises a MOS transistor ( 121 ) to which a clock input NCk shown in  FIG. 1  is input, bipolar transistors ( 111 ,  114 ) having emitters thereof commonly connected to the MOS transistor, executing a differential operation after being input with data input signals (D, ND), and outputting signals of load resistors ( 101 ,  102 ), a MOS transistor ( 122 ) to which a clock input (Ck) is input, bipolar transistors ( 112 ,  113 ) having emitters thereof commonly connected to this MOS transistor, executing a differential operation after being input with output signals of load resistors ( 101 ,  102 ), and holding the signals of load resistors ( 101 ,  102 ), a MOS transistor ( 123 ) to which a clock input (Ck) is input, bipolar transistors ( 115 ,  118 ) having emitters thereof commonly connected to this MOS transistor, executing a differential operation after being input with output signals of load resistors ( 101 ,  102 ), and outputting signals of load resistors ( 103 ,  104 ), a MOS transistor ( 124 ) to which a clock input (NCk) is input, and bipolar transistors ( 116 ,  117 ) having emitters thereof commonly connected to this MOS transistor, executing a differential operation after being input with output signals of load resistors ( 103 ,  104 ), and holding the signals of load resistors ( 103 ,  104 ).  
         [0022]     In the flip-flop circuit of the second invention, the layout of transistors of each pair in four sets of bipolar transistors ( 111 ,  112 ), ( 113 ,  114 ), ( 115 ,  116 ), ( 117 ,  118 ) forming differential pairs is such that they have common collector electrodes.  
         [0023]     A MOS transistor with a low threshold is comprised as the MOS transistor comprised in the flip-flop circuit of the third invention.  
         [0024]     The frequency division circuit of the fourth invention comprises the flip-flop circuit of the first to third inventions and a buffer circuit comprising bipolar transistors ( 119 ,  120 ) and has MOS transistors ( 127 ,  128 ) in the current sources.  
         [0025]     The frequency division circuit comprising the flip-flop circuit in accordance with the present invention and the buffer circuit enables low-voltage and high-frequency operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a circuit diagram of a flip-flop circuit and a frequency division circuit of one embodiment of the present invention;  
         [0027]      FIG. 2  is a circuit diagram of a conventional flip-flop circuit using bipolar transistors;  
         [0028]      FIG. 3  is a circuit diagram of the conventional flip-flop circuit using MOS transistors; and  
         [0029]      FIG. 4  is a circuit diagram of another conventional flip-flop circuit using bipolar transistors. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     The preferred embodiments of the present invention will be described below with reference to  FIG. 1 .  
         [0031]      FIG. 1  is a structural drawing illustrating a frequency division circuit of the embodiment of the present invention, this circuit comprising a flip-flop circuit  11  and a buffer circuit  12 . Referring to  FIG. 1 , the reference numerals  101 - 104  stand for load resistors,  111 - 120 —bipolar transistors,  121 - 128 —MOS transistors. The MOS transistors  121 - 128  comprise low-threshold MOS transistors.  
         [0032]     The flip-flop circuit  11  is produced by connecting the load resistors  101 - 104 , bipolar transistors  111 - 118 , and MOS transistors  121 - 126  as shown in  FIG. 1 . The buffer circuit  12  is provided by connecting the bipolar transistors  119 ,  120  and MOS transistors  127 ,  128  as shown in  FIG. 1 .  
         [0033]     The bipolar transistor  111  and bipolar transistor  114 , bipolar transistor  112  and bipolar transistor  113 , bipolar transistor  115  and bipolar transistor  118 , bipolar transistor  116  and bipolar transistor  117 , MOS transistor  121  and MOS transistor  122 , and MOS transistor  123  and MOS transistor  124  represent differential pairs.  
         [0034]     The bipolar transistor  111  and bipolar transistor  112 , bipolar transistor  113  and bipolar transistor  114 , bipolar transistor  115  and bipolar transistor  116 , and bipolar transistor  117  and bipolar transistor  118  have common collectors, and load resistors  101 - 104  are connected between a power source voltage terminal  131  and respective common collectors.  
         [0035]     Further, a data input terminal  132  is connected to the base of the bipolar transistor  111 , and the data input terminal  133  is connected to the base of the bipolar transistor  114 . Furthermore, the emitter of the bipolar transistor  111  and the emitter of the bipolar transistor  114  are connected, and the emitter of the bipolar transistor  112  and the emitter of the bipolar transistor  113  are connected. The base of the bipolar transistor  112  is connected to the collector of the bipolar transistor  113  ( 114 ) and the base of the bipolar transistor  118 . The base of the bipolar transistor  113  is connected to the collector of the bipolar transistor  111  ( 112 ) and the base of the bipolar transistor  115 .  
         [0036]     Further, the emitter of the bipolar transistor  115  and the emitter of the bipolar transistor  118  are connected, and the emitter of the bipolar transistor  116  and the emitter of the bipolar transistor  117  are connected. Furthermore, the base of the bipolar transistor  116  is connected to the base of the collector of the bipolar transistor  117  ( 118 ), and the base of the bipolar transistor  117  is connected to the base of the collector of the bipolar transistor  115  ( 116 ). Further, the collector of the bipolar transistor  115  ( 116 ) is connected to an output terminal  141 , and the collector of the bipolar transistor  117  ( 118 ) is connected to the output terminal  142 .  
         [0037]     The drain of the MOS transistor  121  is connected to the emitter of the bipolar transistor  111  ( 114 ), the gate of the MOS transistor  121  is connected to the clock input terminal  134 , the drain of the MOS transistor  122  is connected to the emitter of the bipolar transistor  112  ( 113 ), the gate of the MOS transistor  122  is connected to the clock input terminal  135 , and the MOS transistor  121  and MOS transistor  122  have common sources.  
         [0038]     Furthermore, the drain of the MOS transistor is connected to the emitter of the bipolar transistor  115  ( 118 ), the gate of the MOS transistor  123  is connected to the clock input terminal  135 , the drain of the MOS transistor  124  is connected to the emitter of the bipolar transistor  116  ( 117 ), the gate of the MOS transistor  124  is connected to the clock input terminal  134 , and the MOS transistor  123  and MOS transistor  124  have common sources.  
         [0039]     Gates of the MOS transistor  125  and MOS transistor  126  are connected to a bias terminal  136  of a low-current source, the drain of the MOS transistor  125  is connected to the source of the MOS transistor  121  ( 122 ), the drain of MOS transistor  126  is connected to the source of the MOS transistor  123  ( 124 ), and the sources of the MOS transistor  125  and MOS transistor  126  are connected to a GND terminal  137 .  
         [0040]     In the buffer circuit  12 , the collectors of the bipolar transistor  119  and bipolar transistor  120  are connected to the power source voltage terminal  131 , the collector of the bipolar transistor  115  ( 116 ) is connected to the base of the bipolar transistor  120 , the collector of the bipolar transistor  117  ( 118 ) is connected to the base of the bipolar transistor  119 , the emitter of the bipolar transistor  119  is connected to the output terminal  138  and the drain of the MOS transistor  127 , and the emitter of the bipolar transistor  120  is connected to the output terminal  139  and the drain of the MOS transistor  128 .  
         [0041]     Further, the bias terminal  136  of the low-current source is connected to the gate of the MOS transistor  127 ,  128 , and the sources of MOS transistor  127  and MOS transistor  128  are connected to the GND  137 .  
         [0042]     Thus, in the present embodiment the differential pair of the bipolar transistors  111 ,  114 , the differential pair of the bipolar transistors  112 ,  113 , the differential pair of bipolar transistors  115 ,  118 , and the differential pair of bipolar transistors  116 ,  117  comprise bipolar transistors of a differential model with a common collector electrode, thereby reducing the parasitic capacitance of the collector. The MOS transistors  125 - 128  are the current sources.  
         [0043]     The operation principle is described below. When a HIGH signal is inputted as a clock signal to a clock signal input terminal  134  (clock signal LOW is inputted to the clock input terminal  135 ), the bipolar transistors  121 ,  124  are switched ON and the differential pair formed by the bipolar transistors  111 ,  114  and the differential pair formed by the bipolar transistors  116 ,  117  become operative. Owing to the operation of the differential pair formed by the bipolar transistors  111 ,  114 , the output of the load resistors  101 ,  102  is outputted in response to signals of data signals D, ND inputted to the data input terminals  132 ,  133 . The output data of the load resistors  101 ,  102  are inputted to the differential pair formed by the bipolar transistors  115 ,  118 . The operation of the bipolar transistors  115 ,  118  is OFF, the operation of the bipolar transistors  116 ,  117  is ON, and the output signal of the load resistors  103 ,  104  holds the data preceding the input of the clock signals to the clock input terminals  134 ,  135 .  
         [0044]     When a HIGH signal is inputted as a clock signal to a clock signal input terminal  135  (clock signal LOW is inputted to the clock input terminal  134 ), the bipolar transistors  122 ,  123  are switched ON and the differential pair formed by the bipolar transistors  112 ,  113  and the differential pair formed by the bipolar transistors  115 ,  118  become operative. Owing to the operation of the differential pair formed by the bipolar transistors  112 ,  113 , the output of the load resistors  101 ,  102  holds the previous output state. The output signals of the load resistors  101 ,  102  are inputted to the differential pair formed by the bipolar transistors  115 ,  118 . The operation of the bipolar transistors  115 ,  118  is ON, the operation of the bipolar transistors  116 ,  117  is OFF, and the output signal of the load resistors  103 ,  104  is outputted in response to the clock signals inputted from the clock input terminals  134 ,  135  and data signals outputted from the load resistors  101 ,  102 .  
         [0045]     Furthermore, when the output terminal of the frequency division circuit does not shift the level of the output signal voltage, output terminals  141 ,  142  are used. When the output voltage of the flip-flop circuit  11  is level shifted and outputted, the output voltage is shifted and outputted by using the buffer circuit  12 . This buffer circuit  12  comprises bipolar transistors  119 ,  120  with a short delay time. However, the transistors of the current source comprise the MOS transistors  127 ,  128  for unification with the transistors of the current source of the flip-flop circuit.  
         [0046]     The flip-flop circuit operating in the above-described manner comprises a differential pair of the bipolar transistors  111 ,  114 , a differential pair of the bipolar transistors  112 ,  113 , a differential pair of the bipolar transistors  115 ,  118 , and a differential pair of the bipolar transistors  116 ,  117 . Thus, it comprises bipolar transistors of a differential model with common collector electrode that have excellent high-frequency characteristics. As a result the parasitic capacitance of the collector is reduced. The reduction of the collector capacitance enables the operation with the output signal of the load resistance  101 - 104  having a higher frequency.  
         [0047]     Furthermore, the MOS transistors  121 - 124  are provided as the inputs of the clock signals  134 ,  135 , and MOS transistors  125 - 128  are provided as current sources. Thus, low-threshold MOS transistors are provided. As a result, the operation is possible at a minimum necessary power source voltage which is lower that that of the structure using only bipolar transistors, as in the conventional example shown in  FIG. 2 .  
         [0048]     Thus, employing bipolar transistors of a differential model and low-threshold MOS transistors and using a structure in which the transistors are stacked in three stages makes it possible to realize a frequency division circuit comprising the flip-flop circuit  11  capable of operating at a low power voltage and providing for a high frequency characteristic and a buffer circuit  12 .  
         [0049]     As explained hereinabove, the present invention provides a frequency division circuit comprising a flip-flop circuit and suitable for low-voltage and high-frequency operation.