Abstract:
A single-chip common-drain JFET device comprises a drain, two gates and two source arranged such that two common-drain JFETs are formed therewith. Due to the two JFETs merged within a single chip, no wire bonding connection is needed therebetween, thereby without parasitic inductance and resistance caused by bonding wire, and therefore improving the performance and reducing the package cost. The single-chip common-drain JFET device may be applied in buck converter, boost converter, inverting converter, switch, and two-step DC-to-DC converter to improve their performance and efficiency. Alternative single-chip common-drain JFET devices are also provided for current sense or proportional current generation.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is related generally to a novel electronic device and more particularly to a single-chip common-drain JFET device and its applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     As shown in  FIG. 1 , in a conventional DC-to-DC converter  10  to convert an input voltage VIN to an output voltage VOUT, two Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)  12  and  14  are employed for the high-side and low-side power switches in a power stage to be alternatively switched by control signals UG and LG provided by a controller  16  to regulate a current I flowing through an inductor L to charge a capacitor C to produce the output voltage VOUT. When integrated circuit scaled down, MOSFET will have too large conductive resistance to satisfy the designers&#39; requirements and therefore, it is intended for other element having lower conductive resistance for the power switches for less power loss within the switches. Junction Field-Effect Transistor (JFET) is potential candidate as semiconductor switch with lower conductive resistance and lower cost. In U.S. Pat. Nos. 6,580,252 and 6,356,059 to Yu, normally-off enhancement mode JFET is used for the power switches of boost converter and buck converter to reduce the voltage drop loss at ON-state and the state transition time. However, these arts are still not perfect enough. On the other hand, the MOSFETs  12  and  14  of the converter  10  are required to be individually formed in two chips for the heat dissipation issue and therefore, bonding wire of package is needed for the electrically connection between the MOSFETs  12  and  14 , thereby causing parasitic inductance and resistance to degrade the switching performance and efficiency.  
         [0003]     Therefore, it is desired an electronic device with lower conductive resistance than that of MOSFET and without bonding wire of package between switches.  
       SUMMARY OF THE INVENTION  
       [0004]     One object of the present invention is directed to a single-chip common-drain JFET device and its applications. The single-chip common-drain JFET device has lower conductive resistance than that of MOSFET to reduce power loss within switches, and needs no bonding wire for electrical connection between the JFETs in the device, thereby improving the circuit performance and efficiency.  
         [0005]     According to the present invention, a single-chip common-drain JFET device comprises a drain, two gates and two source arranged such that two common-drain JFETs are formed therewith. The current carriers in a JFET are majority carriers which result in lower conductive resistance than a MOSFET, and therefore using JFET as switch will result in less power loss than MOSFET switch. In other words, the heat generated by the current flowing through a JFET is less, and more JFETs can be integrated in a same chip to reduce the package cost. JFET structure is easy to combine multiple JFETs within one chip without side effect even under high current applications. Furthermore, integration of common-drain JFETs in a same chip will have no bonding wire for electrical connection between the JFETs in the same chip, thereby reducing package cost. The switching performance of the JFETs with common-drain within a single chip is also improved since the parasitic inductance and resistance caused by bonding wire of package are avoided. The single-chip common-drain JFET device according to the present invention may be applied in power circuits, such as buck converter, boost converter, inverting converter, switch, and two-step DC-to-DC converter, to improve their circuit performance and efficiency.  
         [0006]     Alternatively, a single-chip common-drain JFET device according to the present invention further comprises a third source in conjunction with the first gate and drain to form a third JFET, such that the source currents at the first and third sources will be proportional to each other and current sense may be achieved therewith.  
         [0007]     Alternatively, a single-chip common-drain JFET device according to the present invention further comprises a third source in conjunction with the first gate and drain to form a third JFET and a fourth source in conjunction with the second gate and drain to form a fourth JFET, such that the source currents at the first and third sources will be proportional to each other and the source currents at the second and fourth sources will be proportional to each other, and current sense may be achieved therewith.  
         [0008]     Alternatively, a single-chip common-drain JFET device according to the present invention comprises a drain, a gate, and two sources arranged such that two JFETs are formed therewith. The source currents at the two sources will be proportional to each other, and therefore the single-chip common-drain JFET device may be used for current sense.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]     These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:  
         [0010]      FIG. 1  shows a conventional DC-to-DC converter;  
         [0011]      FIG. 2  shows a first embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0012]      FIG. 3  shows an embodiment of a structure of the single-chip common-drain JFET device shown in  FIG. 2 ;  
         [0013]      FIG. 4  shows a buck converter implemented with a single-chip common-drain JFET device according to the present invention;  
         [0014]      FIG. 5  shows a boost converter implemented with a single-chip common-drain JFET device according to the present invention;  
         [0015]      FIG. 6  shows a inverting converter implemented with a single-chip common-drain JFET device according to the present invention;  
         [0016]      FIG. 7  shows a switch implemented with a single-chip common-drain JFET device according to the present invention;  
         [0017]      FIG. 8  shows a two-step DC-to-DC converter implemented with single-chip common-drain JFET devices according to the present invention;  
         [0018]      FIG. 9  shows a second embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0019]      FIG. 10  shows an equivalent circuit of the single-chip common-drain JFET device shown in  FIG. 9 ;  
         [0020]      FIG. 11  shows a third embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0021]      FIG. 12  shows a fourth embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0022]      FIG. 13  shows an equivalent circuit of the single-chip common-drain JFET device shown in  FIG. 12 ;  
         [0023]      FIG. 14  shows a fifth embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0024]      FIG. 15  shows a sixth embodiment of a single-chip common-drain JFET device according to the present invention;  
         [0025]      FIG. 16  shows an equivalent circuit of the single-chip common-drain JFET device shown in  FIG. 15 ; and  
         [0026]      FIG. 17  shows a seventh embodiment of a single-chip common-drain JFET device according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     For a first embodiment according to the present invention,  FIG. 2  shows a single-chip common-drain JFET device  20  that comprises a drain D, two separated gates G 1  and G 2 , and two separated sources S 1  and S 2  arranged such that the source S 1 , gate G 1  and drain D form a JFET  22 , and the source S 2 , gate G 2  and drain D form a JFET  24 . Since the common-drain JFETs  22  and  24  are merged in a same chip, it does not need wire bonding connection between the JFETs  22  and  24  as that for the MOSFETs  12  and  14  of  FIG. 1 , and there are no parasitic inductance and resistance caused by the bonding wire between the drains of the JFETs  22  and  24 . As a result, the switching performance of the JFETs  22  and  24  is improved, and the package cost for the JFETs  22  and  24  is reduced. In this embodiment, both the JFETs  22  and  24  are depletion mode JFETs, in another embodiment, however, the JFETs  22  and  24  may be both enhancement mode JFETs, or one depletion mode JFET and one enhancement mode JFET.  
         [0028]      FIG. 3  shows an embodiment of a structure of the single-chip common-drain JFET device  20  implemented with N-channels for illustration, in which an N-type epitaxial layer  28  is formed on one side of a N+ substrate  26  to provide vertical channels, a conductor layer  25  is formed on the opposite side of the substrate  26  to serve as the drain D, P-type conductor layers  222  and  242  in the epitaxial layer  28  are electrically connected, respectively, to the conductor layers  224  and  244  serving the gates G 1  and G 2  above the epitaxial layer  28 , conductor layers  226  and  246  serving the sources S 1  and S 2  above the epitaxial layer  28  are electrically connected to conductor layers  228  and  248 , respectively, and an oxide layer  29  is formed for insulations between the conductor layers  224 ,  226 ,  246 , and  244 .  
         [0029]      FIG. 4  shows a buck converter  30  implemented with the single-chip common-drain JFET device  20 , in which the source S 1  is coupled with an input voltage VIN, the source S 2  is grounded, the drain D is coupled to an output VOUT through an inductor L, and the gates G 1  and G 2  are coupled with control signals UG and LG provided by a controller  32  for alternatively switching the common-drain JFETs  22  and  24  to regulate a current I flowing through the inductor L to charge a capacitor C to produce an output voltage VOUT. Furthermore, for the inductor current sustained when both the JFETs  22  and  24  turn off, a diode  34  is coupled between the drain D and source S 2 . In another embodiment, a parasitic diode within the chip of the device  20  may be used for the diode  34 .  
         [0030]      FIG. 5  shows a boost converter  40  implemented with the single-chip common-drain JFET device  20 , in which the source S 1  is grounded, the source S 2  is coupled to an output VOUT, the drain D is coupled to an input voltage VIN through an inductor L, and the gates G 1  and G 2  are coupled to a controller  42  for alternatively switching the common-drain JFETs  22  and  24  to regulate a current I to charge a capacitor C to produce an output voltage VOUT. Furthermore, for the inductor current sustained when both the JFETs  22  and  24  turn off, a diode  34  is coupled between the drain D and source S 2 . In another embodiment, a parasitic diode within the chip of the device  20  may be used for the diode  34 .  
         [0031]      FIG. 6  shows an inverting converter  50  implemented with the single-chip common-drain JFET device  20 , in which the source S 1  is coupled to an output VOUT, the source S 2  is coupled with an input voltage VIN, the drain D is grounded through an inductor L, and the gates G 1  and G 2  are coupled to a controller  52 . When the JFET  22  turns off and the JFET  24  turns on, the inductor L is storing energy from the input voltage VIN, until the JFET  22  turns on and the JFET  24  turns off, the inductor L releases the stored energy to produce a current I to charge a capacitor C to produce an output voltage VOUT whose waveform is inversely to that of the input voltage VIN. Furthermore, for the inductor current sustained when both the JFETs  22  and  24  turn off, a diode  34  is coupled between the drain D and source S 1 . In another embodiment, a parasitic diode within the chip of the device  20  may be used for the diode  34 .  
         [0032]      FIG. 7  shows a switch  60  implemented with the single-chip common-drain JFET device  20 , in which the source S 1  is coupled with a supply voltage of 5V, the source S 2  is coupled with a supply voltage of 12V, the drain D is coupled to an output VOUT, and the gates G 1  and G 2  are coupled to a controller  62  for switching the common-drain JFETs  22  and  24  to switch the output voltage VOUT between 5V and 12V.  
         [0033]      FIG. 8  shows a two-step DC-to-DC converter  64  implemented with the single-chip common-drain JFET device  20 , in which a first converting stage  66  includes MOSFETs  662  and  664  alternatively switched by control signals UG 1  and LG 1  to convert an input voltage VIN to a regulated voltage VIN 2  for a second converting stage  68 , and the second converting stage  68  includes several switching apparatus each comprising a single-chip common-drain JFET device  20  coupled between the voltage VIN 2  and ground GND, and switched by control signals UG 2  and LG 2 , UG 3  and LG 3 , and UG 4  and LG 4 , to regulate currents I 1 , I 2  and I 3  flowing through inductors L 2 , L 3  and L 4  to charge capacitors C 2 , C 3  and C 4  to produce an output voltage VOUT. For the inductor currents sustained when both the common-drain JFETs  22  and  24  of each respective device  20  turn off, diodes D 1 , D 2  and D 3  are coupled between the drain D and source S 2  of the respective device  20 . In another embodiment, a parasitic diode within the chip of the respective device  20  may be used for the diode D 1 , D 2  or D 3 . In this embodiment  64 , by using the single-chip common-drain JFET devices  20  for the switching apparatus in the second converting stage  68 , there are no parasitic inductance and resistance caused by the bonding wire between the common-drain JFETs  22  and  24  of the respective device  20 . For the first converting stage  66  could completely turn off the current supplied to the devices  20 , each of the device  20  may employ two normally-on JFETs for the common-drain JFETs  22  and  24  to further reduce the conductive resistance thereof, and therefore the two-step DC-to-DC converter  64  will have better conversion efficiency due to less power loss.  
         [0034]      FIG. 9  shows a single-chip common-drain JFET device  70  according to the present invention, which comprises a drain D, a gate G, and two separated sources S 1  and S 2  arranged such that two common-drain and common-gate JFETs  72  and  74  are formed therewith, as shown in  FIG. 10 . Due to the common-drain and common-gate of the JFETs  72  and  74 , the source currents at S 1  and S 2  will have a ratio the same as the size ratio of the JFETs  72  and  74 , and therefore the device  70  may be used for a current sensor. The JFETs  72  and  74  are easy to match to each other since they are formed within a single chip, and precise sense may be achieved accordingly. For other applications, as shown in  FIG. 11 , a diode  76  is coupled between the drain D and source S 1  for a current sustained at the drain D when both the JFETs  72  and  74  turn off. A parasitic diode within the chip of the device  70  may be used for the diode  76 . In the device  70 , both the JFETs  72  and  74  are depletion mode JFETs, in another embodiment, however, the JFETs  72  and  74  may be enhancement mode JFETs.  
         [0035]      FIG. 12  shows a single-chip common-drain JFET device  80  according to the present invention, which comprises a drain D, two separated gates G 1  and G 2 , and four separated sources S 1 -S 4  arranged such that four common-drain JFETs  82 - 88  are formed therewith, as shown in  FIG. 13 . Due to the common-drain and common-gate of the JFETs  82  and  84 , the source currents at S 1  and S 2  will have a ratio the same as the size ratio of the JFETs  82  and  84 . Likewise, due to the common-drain and common-gate of the JFETs  86  and  86 , the source currents at S 3  and S 4  will have a ratio the same as the size ratio of the JFETs  86  and  88 . With the device  80 , switching apparatus and proportional current generation may be obtained. For other applications, as shown in  FIG. 14 , a diode  89  is coupled between the drain D and source  53  for a current sustained at the drain D when all the JFETs  82 - 88  turn off. A parasitic diode within the chip of the device  80  may be used for the diode  89 . In the device  80 , all the JFETs  82 - 88  are depletion mode JFETs, in another embodiment, however, the JFETs  82 - 88  may be all enhancement mode JFETs, or a pair of depletion mode JFETs and a pair of enhancement mode JFETs.  
         [0036]      FIG. 15  shows a single-chip common-drain JFET device  90  according to the present invention, which comprises a drain D, two separated gates G 1  and G 2 , and three separated sources  51 -S 3  arranged such that three common-drain JFETs  92 - 96  are formed therewith, as shown in  FIG. 16 . Due to the common-drain and common-gate of the JFETs  94  and  96 , the source currents at S 2  and S 3  will have a ratio the same as the size ratio of the JFETs  94  and  96 . With the device  90 , switching apparatus and precise current sense may be obtained. For other applications, as shown in  FIG. 17 , a diode  98  is coupled between the drain D and source S 2  for a current sustained at the drain D when all the JFETs  92 - 96  turn off. A parasitic diode within the chip of the device  90  may be used for the diode  98 . In the device  90 , all the JFETs  92 - 96  are depletion mode JFETs, in another embodiment, however, the JFETs  92 - 96  may be all enhancement mode JFETs, or the JFET  92  is a depletion mode JFET and the JFETs  94  and  96  are enhancement mode JFETs, or the JFET  92  is an enhancement mode JFETs and the JFETs  94  and  96  are depletion mode JFETs.  
         [0037]     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.