Patent Document

BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor integrated circuit device including a charge pump circuit. 
         [0003]    2. Description of Related Art 
         [0004]    Recently, electronic units have been introduced into automobiles to realize security, comfort and low power consumption. As a result, the noise generated by the operation of the electronic units affects the operation of the electronic units per se. Preferably, such noise should be reduced. 
         [0005]    In a first prior art semiconductor integrated circuit device including a semiconductor power switch, a charge pump circuit for generating a sufficiently higher voltage than a power supply voltage is used to completely turn ON the semiconductor power switch (see:  FIG. 2  of Japanese Unexamined Patent Publication (Kokai) No. 8-336277). The charge pump circuit is constructed by a rectangular oscillating circuit for generating a clock signal and a step-up circuit clocked by the clock signal for generating a voltage higher than the power supply voltage. In this case, the step-up circuit includes a capacitor and diodes. This will be explained later in detail. 
         [0006]    In the above-described first prior art semiconductor integrated circuit device, however, the charging and discharging operation of the capacitor at a high frequency caused by the rectangular oscillating circuit flows an operating current including a large ripple component through the charge pump circuit, thus generating a large noise. 
         [0007]    In a second prior art semiconductor integrated circuit device, a constant current source is connected in series to the charge pump circuit of the first prior art semiconductor integrated circuit device, so that the constant current of the constant current source absorbs the large ripple component of the operating current flowing through the charge pump circuit, thus decreasing the noise. Also, a Zener diode is connected in parallel to the charge pump circuit of the first prior art semiconductor integrated circuit device (see:  FIG. 4  of Japanese Unexamined Patent Publication (Kokai) No. 8-336277). This also will be explained later in detail. 
         [0008]    In the above-described second prior art semiconductor integrated circuit device, however, if the power supply voltage is too low, i.e., lower than the Zener voltage such as 6V of the Zener diode, the constant current of the constant current source cannot absorb the ripple component of the operating current of the charge pump circuit, which would not suppress the noise. 
         [0009]    Note that Japanese Unexamined Patent Publication (Kokai) No. P2005-33865A discloses a semiconductor integrated circuit device including a charge pump circuit where an output current is detected by a current detection circuit and an input current twice the output current is supplied by a current limiting circuit to the charge pump circuit. 
       SUMMARY 
       [0010]    The present invention seeks to solve one or more of the above-mentioned problems. 
         [0011]    According to the present invention, in a semiconductor integrated circuit device including a charge pump circuit flowing an operating current therethrough, a current circuit is adapted to receive the operating current and a substantially constant current and generate an inverse current relative to the operating current and the substantially constant current. 
         [0012]    The operating current of the charge pump circuit is compensated for by the inverse current within the current circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments as compared with the prior art, taken in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a circuit diagram illustrating a first prior art semiconductor integrated circuit device; 
           [0015]      FIG. 2  is a circuit diagram illustrating a second prior art semiconductor integrated circuit device; 
           [0016]      FIG. 3  is a timing diagram showing the operating current of the charge pump circuit and the constant current of the constant current source of  FIG. 2 ; 
           [0017]      FIG. 4  is a circuit diagram illustrating a first embodiment of the semiconductor integrated circuit device according to the present invention; and 
           [0018]      FIG. 5  is a circuit diagram illustrating a second embodiment of the semiconductor integrated circuit device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Before describing the preferred embodiments, prior art semiconductor integrated circuit devices will be explained in detail with reference to  FIGS. 1 ,  2  and  3  in order to facilitate the understanding of the present invention. 
         [0020]    In  FIG. 1 , which illustrates a first prior art semiconductor integrated circuit device (see:  FIG. 2  of Japanese Unexamined Patent Publication(Kokai) No. 8-336277), a power source  30  is connected via a power supply line V CC  and a ground line GND to an n-channel power MOS transistor  32  and a load  31  connected in series. The voltage at the ground line GND is a common ground such as a vehicle body. 
         [0021]    In order to completely turn ON the n-channel power MOS transistor  32 , a voltage applied to the gate needs to be higher than V CC  by 5 to 10V. Such a high voltage is generated by a charge pump circuit  40  for generating a voltage of 2·V CC . 
         [0022]    The charge pump circuit  40  is constructed by a rectangular oscillating circuit  41  whose output is buffered by an inverter  42 . The output node  43  of the inverter  42  is connected to a capacitor  44 . The capacitor  44  is connected via a diode  45  to the power supply line V CC , so that the capacitor  44  is charged by the power supply line V CC . The node between the capacitor  44  and the diode  45  is connected via a diode  46  is connected to the gate of the n-channel power MOS transistor  32 . Switches  47  and  48  are provided such that the switch  47  connects a node  49  from the power supply line V CC  and the switch  48  connects the gate of the n-channel power MOS transistor  32  to the ground line GND and disconnects the gate of the n-channel power MOS transistor  32  from the ground line GND. 
         [0023]    The charging and discharging operation of the capacitor  44  at a high frequency caused by the rectangular oscillating circuit  41  generates a large noise. 
         [0024]    In  FIG. 2 , which illustrates a second prior art semiconductor integrated circuit device (see:  FIG. 4  of Japanese Unexamined Patent Publication (Kokai) No. 8-336277), the charge pump circuit  40  of  FIG. 1  is connected via a floating node  51  to a constant current source  53  which is also connected to a ground node  52  which serves as the ground line GND. Further, a Zener diode  54  is connected in parallel to the charge pump circuit  40 . 
         [0025]    As a result, as illustrated in  FIG. 3  (see:  FIG. 8  of Japanese Unexamined Patent Publication (Kokai) No. 8-336277), even when an operating current i op (t) caused by the charging and discharging operation of the capacitor  44  have a large ripple component, a constant current I const  defined by the constant current source  53  absorbs such a large ripple component of the operating current i op (t), so that the constant current I const  flows from the power supply line V CC  to the ground line GND. In other words, an approximate DC current flows from the power supply line V CC  to the ground line GND, so as to suppress the noise. 
         [0026]    In the semiconductor integrated circuit device of  FIG. 2 , however, if the voltage at the power supply line V CC  is too low, i.e., lower than the Zener voltage such as 6V of the Zener diode  54 , a current flowing therethrough is very small, so that 
         [0000]      I cons ≈i op (t) 
         [0000]    As a result, the current I const  is not constant, so that the current I const  cannot absorb the ripple component of the operating current i op (t) of the charge pump circuit  40 , which would not suppress the noise. 
         [0027]    In  FIG. 4 , which illustrates a first embodiment of the semiconductor integrated circuit device according to the present invention, a semiconductor integrated circuit device  10  is constructed by a charge pump circuit  1  connected between the power supply line V CC  and a connection node N 1 , a constant current source  2  connected to the power supply line V CC  for generating a constant current I const , a current circuit  3  connected to the connection node N 1 , the constant current source  2 , the power supply line V CC  and the ground line GND, and an n-channel power MOS transistor  4  controlled by the charge pump circuit  1  is connected between the power supply line V CC  and an output terminal OUT. 
         [0028]    A load  20  and a power source  30  are connected to a semiconductor integrated circuit device  10 . In more detail, the load  20  is connected between the output terminal OUT and the ground line GND. The power source  30  is connected between the power supply line V CC  and the ground line GND. 
         [0029]    The charge pump circuit  1  is formed by a rectangular oscillating circuit  11  for generating a clock signal CLK and a step-up circuit  12  clocked by the clock signal CLK to generate a step-up voltage 2·V CC . In more detail, the clock generating circuit  11  includes CMOS inverters  111 ,  112 ,  113  and  114  connected in series between the power supply line V CC  and the connection node N 1 , a CMOS inverter  115  connected to the output of the CMOS inverter  113  for generating the clock signal CLK, a resistor  116  connected between the output of the CMOS inverter  113  and the input of the CMOS inverter  111 , and a capacitor  117  connected between the output of the CMOS inverter  114  and the input of the CMOS inverter  111 . On the other hand, the step-up circuit  12  includes diodes  121  and  122  connected in series between the power supply line V CC  and the gate of the n-channel power MOS transistor  4 , and a capacitor  123  connected between the output of the CMOS inverter  115  and the connection node between the diodes  121  and  122 . In this case, the anode of the diode  121  is connected to the power supply line V CC , and the cathode of the diode  121  is connected to the anode of the diode  122  whose cathode is connected to the gate of the n-channel power MOS transistor  4 . 
         [0030]    The constant current source  2  is formed by an n-channel depletion type MOS transistor where a source is connected to a gate, for example. 
         [0031]    The current circuit  4  is formed by four n-channel MOS transistors  300 ,  301 ,  302  and  303 . The n-channel MOS transistors  300  and  301  form a current mirror circuit CM 1  with an input current terminal connected to the connection node N 1  and an output current terminal connected to the constant current source  2 . On the other hand, the n-channel MOS transistors  302  and  303  form a current mirror circuit CM 2  with an input current terminal connected to the constant current source  2  and an output current terminal connected to the power supply line V CC . 
         [0032]    Thus, since the n-channel MOS transistor  301  forms the current mirror circuit CM 1  with the n-channel MOS transistor  300 , a current i 1  flowing through the n-channel MOS transistor  301  is represented by 
         [0000]        i   1   =i   op ( t ) 
         [0000]    Also, since the n-channel MOS transistors  301  and  302  have a common drain, a current i 2  flowing through the n-channel MOS transistor  302  is represented by 
         [0000]        i   2   =I   const   −i   op ( t ) 
         [0000]    Further, since the n-channel MOS transistor  303  forms the current mirror circuit CM 2  with the n-channel MOS transistor  302 , a current i 3  flowing through the n-channel MOS transistor  303  is represented by 
         [0000]        i   3   =I   const   −i   op ( t ) 
         [0033]    Thus, in the semiconductor integrated circuit device  10  of  FIG. 4 , the total current that flows from the power supply line V CC  to the ground line GND is 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
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         [0034]    Thus, the operating current i op (t) flowing through the n-channel MOS transistor  300  is compensated for by the currents i 1 , i 2  and i 3  within the current circuit  3 , so that the constant current 2·I const  flows from the power supply line V CC  to the ground line GND. In other words, an approximate DC current flows from the power supply line V CC  to the ground line GND, so as to suppress the noise. In this case, in order for the constant current 2·I const  to absorb the large ripple component of the operating current i op (t) of the charge pump circuit  1 , a large current does not need to be supplied to the semiconductor integrated circuit device. 
         [0035]    On the other hand, even if the voltage at the power supply line V CC  is low, but higher than twice the threshold voltage of the MOS transistors, i.e., about 2V, the constant current 2·I const  can be maintained. As a result, the current 2·I const  is constant, so that the constant current 2·I const  can absorb the ripple component of the operating current i op (t) of the charge pump circuit  1 , which would suppress the noise. 
         [0036]    In  FIG. 5 , which illustrates a second embodiment of the semiconductor integrated circuit device according to the present invention, a voltage clamp circuit  5  is added to the elements of the semiconductor integrated circuit device  10  of  FIG. 4 . The voltage clamp circuit  5  is formed by a depletion-type p-channel MOS transistor  51 , a Zener diode  52  whose Zener voltage is 6V, for example, and a resistor  53 . In this case, the depletion-type p-channel MOS transistor  51  is connected between the connection node N 1  and the n-channel MOS transistor  300 , and is controlled by a voltage between the Zener diode  52  and the resistor  53  connected in series between the power supply line V CC  and the ground line GND. Note that the resistor  53  can be replaced by a drain-to-gate connected MOS transistor serving as a resistance element. 
         [0037]    Also, the Zener diode  52  can limit the voltage applied to the capacitor  123  to a definite voltage such as 6V, the capacitor  123  can have a thin and small insulator, which is advantageous in integration. 
         [0038]    Further, even when the voltage at the power supply line V CC  is lower than the Zener voltage such as 6V of the Zener diode  52  so that the Zener diode  52  is in an OFF state, since a bias voltage is still applied through the resistor  53  to the gate of the depletion-type p-channel MOS transistor  51 , the charge pump circuit  1  can be normally operated. 
         [0039]    In the above-described embodiments, the power supply line V CC  and the ground line GND can be replaced with each other. In this case, the p-channel and n-channel MOS transistors are replaced by n-channel and p-channel MOS transistors, respectively. 
         [0040]    It is apparent that the present invention is not limited to the above-described embodiments, but may be modified and changed without departing from the scope and sprit of the present invention.

Technology Category: 5