Abstract:
A charge-pump circuit without reverse current is disclosed. The charge-pump circuit includes: several diode equivalent networks connecting in series, between any two of adjacent diode equivalent networks having a node with a corresponding voltage-boost level, wherein the low voltage end in the diode equivalent network with lowest voltage-boost level is the input of the charge-pump circuit, and the input receives an input voltage signal; a voltage-boost capacitor network having an end to electronically couple to one of the node and the other end to electronically couple to a pulse signal, wherein the pulse signal has a high-voltage level and a low-voltage level to raise a voltage level at the node with voltage-boost as high-voltage level and low-voltage level switches; and a reverse current cut-off circuit electronically coupled to the diode equivalent networks to enable and disable the diode equivalent networks, wherein the reverse current cut-off circuit has two conductive paths.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a charge pump circuit, and more especially, to a charge-pump circuit using a reverse current cut-off circuit to improve the electronic efficiency and reliability. 
         [0003]    2. Background of the Related Art 
         [0004]    In recent years, such a charge pump circuit has been used frequently as a power supply circuit capable of outputting a voltage higher than an input voltage without using an inductor, and supplying a power supply voltage to a load requiring a relatively small consumption current.  FIG. 1  shows a circuit diagram of conventional dual phase charge pump circuit. The charge pump circuit includes a diode-connected NMOS transistor and number of capacitors. The diode-connected NMOS transistor has a threshold voltage and connects to a node where two NMOS transistors couples with. The circuit&#39;s operation is that the circuit has two inverse impulse signals φ 1  and φ 2  to charge capacitors for the purpose of raising voltage. According to the conductive path the circuit&#39;s clock cycle has a setup period and a pumping period. In the setup period, the pulse signal φ 1  is low level, and the dual phase charge pump circuit  100  turns on the first charging path  110 , then the NMOS transistor is turned on for raising the voltage of first node  120  to Vin−Vt, and the voltage of capacitor C 1  is charged to Vin−Vt. In the pumping period, the pulse signal φ 1  is high level to Vφ, and the voltage of capacitor C 1  is at same level Vφ to raise the voltage of first node  120  to Vin+(Vφ−Vt). When the first node&#39;s  120  voltage is higher than the threshold voltage Vt in the NMOS transistor, the second charging path  130  is closed to raise the voltage of the second node  130  to Vin+(Vφ−Vt)−Vt. Reasonably, at next period the voltage of the second node  130  is going to Vin+2(Vφ−Vt). 
         [0005]    To summarize, a dual phase charge pump circuit with n nodes has the output voltage shown in equation (1-1) 
         [0000]        V out= V in+ N *( Vφ−Vt )− Vt    (1-1) 
         [0006]    From equation 1-1, because the effect of the MOS&#39;s characteristic of threshold voltage, the charging efficiency in the dual phase charge pump circuit  100  is decreased, thus causing inefficiency for the system. Especially in low power supply condition, the threshold voltage has great effect on the operation of the dual phase charge pump circuit. In some applications, the inefficiency of the dual phase charge pump circuit will consume more power when charging the circuit, and is their shortcomings. 
         [0007]    Many varieties of charge pump circuit were released to overcome the problem, for example the  FIG. 2  shows an improved charge pump circuit  200  disclosed in U.S. Pat. No. 6,670,844. The charge pump circuit  200  includes depletion-type N-channel MOS transistors each having its gate and drain interconnected via a diode connection and individually having their respective sources and drains interconnected thereby defining multiple stages interconnected in cascade, and capacitor elements individually connected to the respective sources of the MOS transistors. The charge pump circuit  200  operates as follows. A given input voltage is applied to the drain and gate of the initial stage MOS transistor 1 . Then a clock signal and an inverted clock signal are alternately supplied to the MOS transistors via the respective capacitor elements so that a boosted voltage is obtained from the final stage MOS transistor. But at the switching of clock cycle, the characteristic of depletion-type MOS transistors cannot make the charge pump circuit  200  turned off as the voltage of node A is raised. Then a reverse current leakage Iq, which is equal to the effect of charging inefficiency caused by the threshold voltage of enhancement-type NMOS transistor in  FIG. 1 , decreases the system&#39;s efficiency. Furthermore, the overflow from reverse current leakage Iq sometimes damages the system and lowers the reliability; so the system need extra protect circuit to keep the reliability. In contrast, this causes the product&#39;s cost and disadvantages. 
         [0008]    For reducing the reverse current leakage Iq, the improved charge pump circuit  200  changes the W/L ratio of the depletion-type NMOS transistors. But this way just minimizes the reverse current leakage Iq, and cannot stop it all. Besides the difficulties of manufacturing will increase the cost and the electronic interference, and make the reliability decreased. 
         [0009]    For this reason, a charge pump circuit with the stable reliability and without reverse current in needed. 
       SUMMARY OF THE INVENTION 
       [0010]    In order to solve the problems mentioned above, the present invention provides a charge-pump circuit using series connected equivalent diodes composed of depletion-type MOS transistor to avoid the threshold voltage loss to increase the efficiency of raising voltage thereon. 
         [0011]    In one aspect of the invention, a charge-pump circuit is implemented. The charge-pump circuit includes a reverse current cut-off circuit to cut off the reverse current for enhancing the performance of raising voltage. 
         [0012]    In another aspect of the invention, a charge-pump circuit with a reverse current cut-off circuit is implemented. The fabrication of the charge-pump circuit is straight and easy, and save the cost of production. 
         [0013]    In another aspect of the invention, a charge-pump circuit with a reverse current cut-off circuit is implemented. The reverse current cut-off circuit can cut off the reverse current to reduce the electronic interference. 
         [0014]    In another aspect of the invention, a charge-pump circuit is implemented. The charge-pump circuit includes a voltage stabilizing circuit to output stable voltage. 
         [0015]    In one embodiment, the charge-pump circuit includes: a plurality of diode equivalent networks connecting in series, between any two of the adjacent diode equivalent networks having a node with a corresponding voltage-boost level, wherein the low voltage end in the diode equivalent network with lowest voltage-boost level is the input of the charge-pump circuit, and the input receives an input voltage signal; at least a voltage-boost capacitor network having an end to electronically couple to one of the node and the other end to electronically couple to a pulse signal, wherein the pulse signal has a high-voltage level and a low-voltage level to raise a voltage level at the node with voltage-boost as the high-voltage level and the low-voltage level switch; and at least a reverse current cut-off circuit electronically coupled to the diode equivalent networks to enable and disable the diode equivalent networks, wherein the reverse current cut-off circuit has at least two conductive paths. 
         [0016]    Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The foregoing aspects and many of the accompanying advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0018]      FIG. 1  is a circuit diagram of a conventional dual phase charge pump circuit; 
           [0019]      FIG. 2  is a circuit diagram of a conventional charge pump circuit; 
           [0020]      FIG. 3  is a circuit diagram of a 4-order charge-pump circuit in accordance with one embodiment of the present invention; 
           [0021]      FIG. 4  is a circuit diagram of a 4-order charge-pump circuit in first input state according to one embodiment of the present invention; 
           [0022]      FIG. 5  is a circuit diagram of a charge-pump circuit in second input state according to one embodiment of the present invention; 
           [0023]      FIG. 6  is a circuit diagram of a 4-order charge-pump circuit in first input state in accordance with one embodiment of the present invention; and 
           [0024]      FIG. 7  is a circuit diagram of a 4-order charge-pump circuit in second input state in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIG. 3  is a 4-order charge-pump circuit in accordance with one embodiment of the present invention. The 4-order charge-pump circuit  300  includes a first reverse current cut-off circuit  310   a , a second reverse current cut-off circuit  310   b , a third reverse current cut-off circuit  310   c , a fourth reverse current cut-off circuit  310   d , a first equivalent diode  320   a , a second equivalent diode  320   b , a third equivalent diode  320   c , a fourth equivalent diode  320   d , a first voltage-boost capacitor  330   a , a second voltage-boost capacitor  330   b , a third voltage-boost capacitor  330   c , and a fourth voltage-boost capacitor  330   d , wherein every reverse current cut-off circuit  310  is made of a pair of switches. In this embodiment, the reverse current cut-off circuit  310  is made of, but not limited to, an enhancement-type NMOS transistor and an enhancement-type PMOS transistor. In other embodiments, the pair of switches can be any of switches having same characteristic of mutually opposite conductivity, like electromagnetic switches or semiconductor switches. 
         [0026]    In every reverse current cut-off circuit  310  the enhancement-type NMOS transistor is electronically coupled to the enhancement-type PMOS transistor through source-to-source or drain-to-drain connection. Transistors in every reverse current cut-off circuit  310  have their gates connected to a common node. In addition, every equivalent diode  320  includes a depletion-type NMOS transistor and an enhancement-type PMOS transistor resided in the reverse current cut-off circuit  310 . The voltage in the gate of enhancement-type PMOS transistor controls it&#39;s conduction, when the enhancement-type PMOS transistor is conductive and the enhancement-type NMOS transistor is cut-off, the gate and drain terminals can be considered an equivalent diode in connection. In this embodiment, the switch pair in the reverse current cut-off circuit  310  control the equivalent diode  320 , which is composed of depletion-type NMOS transistor and the enhancement-type PMOS transistor resided in reverse current cut-off circuit  310 , to enable or disable. In this embodiment the circuit formed by the gate and drain terminals of the depletion transistor can be replaced by an equivalent switch element. For example, a PMOS transistor or an enhancement-type PMOS transistor also can implement this switching function. 
         [0027]    Accordingly, the equivalent diode  320  is a kind of diode equivalent network, and the voltage-boost capacitor can be seen as a voltage-boost capacitor network. 
         [0028]    Furthermore, a terminal of the reverse current cut-off circuit  310  is electronically connected to the ground (GND) for the loop of reverse current cut-off circuit with the diode equivalent network to enable and disable. It is worth noted for the present invention that the ground can be any lower voltage level and not limited to zero. 
         [0029]    Accordingly, the four-order charge-pump circuit  300  is described below: The first equivalent diode  320   a  connects to the second equivalent diode  320   b  in serial, and a first node Node 1  is their connection point. The second equivalent diode  320   b  connects to the third equivalent diode  320   c  in serial, and a second node Node 2  is their connection point. The third equivalent diode  320   c  connects to the fourth equivalent diode  320   d  in serial, and a first node Node 3  is the connection point. The source terminal of fourth equivalent diode  320   d  is the fourth order&#39;s voltage output Vout. 
         [0030]    In every reverse current cut-off circuit  310 , the switch pair have their enhanced MOS transistor&#39;s gate electronically coupled together, thus a fourth node Node 4 , a fifth node Node 5 , a sixth node Node 6 , and a seventh node Node 7  are formed. 
         [0031]    In every reverse current cut-off circuit  310 , both enhanced MOS transistors&#39; gate or drain electronically are coupled together, thus an eighth node Node 8 , a ninth node Node 9 , a tenth node Node 10 , and an eleventh node Node 11  are formed. 
         [0032]    A first voltage-boost capacitor  330   a  is electronically coupled to Node 1 , a second voltage-boost capacitor  330   b  is electronically coupled to Node 2 , a third voltage-boost capacitor  330   c  is electronically coupled to Node 3 , and a fourth voltage-boost capacitor  330   d  is electronically coupled to the fourth order&#39;s voltage output Vout. The voltage-boost capacitor  330  is a depletion NMOS transistor having its source terminal electronically coupled to its drain terminal, but not limited to this implementation. Actually, any electric device or circuit with capacity value can be a voltage-boost capacitor. The first voltage-boost capacitor  330   a  has its source electronically coupled to its drain to be a twelfth node Node 12 , and the second voltage-boost capacitor  330   b  has its source electronically coupled to its drain to be a thirteenth node Node 13 . The twelfth node Node 12  is the connection of source and drain of the third voltage-boost capacitor  330   c , and the thirteenth node Node 13  is the connection of source and drain of the fourth voltage-boost capacitor  330   d . The nodes Node 12  and Node 13  respectively connect first impulse signal φ 1  and second impulse signal φ 2 , which are mutual reverse to each other. The signal source&#39;s high and low level is reciprocal, and the low level is 0 and high level is Vφ. However the low level and high level can be adjusted according to the specification. The gates of voltage-boost capacitors  330  are respectively connected to the first node Node 1 , the second node Node 2 , the third node Node 3  and the fourth order&#39;s output Vout. 
         [0033]    Accordingly, the 4-order charge-pump circuit&#39;s  300  operation is described below: 
         [0034]    The  FIG. 4  discloses an equivalent circuit of 4-order charge-pump circuit in first input state according to  FIG. 3 . In first input state, an input voltage signal Vin is transferred to the charge-pump circuit  300 , φ 1  is 0 (ground) or low voltage and φ 2  is high voltage V φ. In the reverse current cut-off circuit  310 , the switch pair turn on or turn off according to the input voltage signal Vin, thus forming two conductive paths. The depletion NMOS transistor with the equivalent diodes  320   a  and  320   c  has its gate and source diode-connected to form a closed loop. The depletion NMOS transistor with the equivalent diodes  320   b  and  320   d  makes its gate and source open, thus the depletion NMOS transistor is not diode-connected and the equivalent diodes  320   b  and  320   d  are disable in the first input state. 
         [0035]    The depletion NMOS transistor in the equivalent diode  320   a  is closed, thus the input voltage Vin generates charge current I 1  to the capacitor  330   a  until the Node 1 &#39;s voltage Vnode 1 =Vin. 
         [0036]    The  FIG. 5  discloses an equivalent circuit of 4-order charge-pump circuit  300  in second input state according to  FIG. 3 . In second input state, an input voltage signal Vin is transferred to the charge-pump circuit  300 , φ 1  is V φ and φ 2  is 0 (ground or low level). In the reverse current cut-off circuit  310 , the switch pair turn on or turn off according to the input voltage signal Vin, thus forming two conductive paths. The depletion NMOS transistor with the equivalent diodes  320   b  and  320   d  has its gate and source forming closed loop and is diode-connected. The depletion NMOS transistor with the equivalent diodes  320   a  and  320   c  has its gate and source open, thus the depletion N-channel transistor is not diode-connected and the equivalent diodes  320   a  and  320   c  are disable in the second input state. The first impulse signal φ 1  is input to the Node 12 , so the voltage of first voltage-boost capacitor  330   a  is raised a V φ level and the voltage Vnode 1  in Node 1  is raised to Vin+V φ level. The second equivalent diode  320   b  is conducted owing to diode-connected, and through the loop to generate a charge current I 2  to the capacitor  330   b , then the voltage Vnode 2  is raised to Vin+V φ. Most noticeably, in the conventional circuits since the voltage of Vnode 1  is greater than Vin, a reverse current Iq is occurred in the charge-pump circuit  300 . in this embodiment the gate of depletion NMOS transistor is coupled to the ground because of the switch pair. If a reverse current is generated, the depletion NMOS transistor&#39;s source in the equivalent diode  320   a  is the voltage Vin of node owing to the direction of reverse current Iq. The depletion NMOS transistor&#39;s source in the equivalent diode  320   a  has gate-source voltage Vgs 1 =−Vin. If gate-source voltage of the depletion NMOS transistor smaller than its threshold voltage Vt, means Vgs 1 &lt;Vt, no reverse current happens. That is the way the charge-pump circuit  300  enhances the efficiency and reduces the cost. 
         [0037]    Referring the  FIG. 6  is the 4-order charge-pump circuit in first input state after second input state, and the second pulse signal φ 2 =V φ. Node 2  will be raised a V φ voltage level in the same operation described before, so Vnode 2 =Vin+ 2 V φ. The third diode equivalent network in the depletion NMOS transistor turns on or off according to the third reverse current cut-off circuit  310   c  switching, thus forming two conductive paths. Through this loop a charge current charges the capacitor  330   c  to Vnode 3 =Vin+ 2 V φ. Besides, as the voltage of Vnode 1  backs to Vin (Vgs 2 =−Vin), the gate-source voltage of the depletion NMOS transistor smaller than its threshold voltage Vt, means Vgs 1 &lt;Vt, no reverse current occurs. The second equivalent diode  320   b  turns off and sustains the voltage of Node 2  and Node 3 . 
         [0038]    Referring the  FIG. 7  is the 4-order charge-pump circuit in second input state after first input state, and the second pulse signal φ 1 =V φ. The first pulse signal φ 1 =V φ is input to node Node 12  and the voltage of third voltage-boost capacitor is raised a V φ level, the voltage of Node 3  Vnode 3  also raised to Vin+ 3 V φ. The depletion NMOS transistor in the fourth equivalent diode  320   d  is diode-connected, Through this loop a charge current I 4  charges the capacitor  330   d  from Vout to Vin+ 3 V φ. 
         [0039]    When the pulse signal retunes back to the second pulse signal, the capacitor  330   d  is raised a voltage V φ and causes output voltage being boosted to Vout=Vin+ 4 V φ. 
         [0040]    Most noticeably, the reverse current cut-off circuit may utilize any electrical device or circuit with conductive characteristic similar to those mentioned above. That electrical device or circuit is capable of changing conduction path in response to the input pulse signal for avoiding the reverse current leakage. Therefore, the present invention implements the reverse current cut-off circuit by using an enhancement-type NMOS transistor and an enhancement-type PMOS transistor, but it is not only embodiment for the present invention. 
         [0041]    The present invention uses the switch with opposite electricity to form a reverse current cut-off circuit. This can avoid the reverse current caused by raising voltage, save electrical energy and promote the reliability. 
         [0042]    This is summarized as follows: the output voltage of a N-order charge-pump circuit is showed in equation (2-1) 
         [0000]        V out= V in+ N*Vφ   (2-1) 
         [0043]    The N-order charge-pump circuit&#39;s  300  order in series can be adjusted upon the requirements until the Pumping Voltage Gain reach to the saturation. In other words, before the Pumping Voltage Gain reaches to the saturation, the charge-pump circuit&#39;s orders are adjusted according the specification. The 4-order charge-pump circuit is not the only embodiment for the present invention. 
         [0044]    The present invention can avoid the threshold voltage of conventional charge-pump circuit and the reverse current which causes inefficiency to the system. The disclosed charge-pump circuit utilizes the pulse signal of the circuit to switch the conductive path in order to cut off the reverse current without complicate design in the manufacturing process for the circuit. Therefore, the present invention can fit in the Mobile/Hand-Held Device, which is in need of power management for low voltage and limited power supply, to save electrical energy and increase the efficiency of raising voltage and promote the reliability. 
         [0045]    Most noticeably, the charge-pump circuit  300  can connect a regulator to the input to receive a stable input voltage. When the input power supply decay or vary, the charge-pump circuit  300  still can have a stable input voltage. 
         [0046]    Besides, previous described circuits and elements in compound of charge-pump circuit are just to show the preferred embodiments and not to limit the spirit of the present invention. For example, any equivalent network composed of number of elements should belong to the scope of the present invention. In addition, the skilled in the art should understand the network topology disclosed has other implementation with the idea that the reverse current cut-off circuit combined with equivalent diode. For instance, the depletion N-channel transistor may use the JFET instead. In some system, the present invention can be a relative ground for a negative charge-pump circuit, whose input voltage is a negative input voltage, and a depletion P-channel transistor is used in the present invention. 
         [0047]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.