# Patent

## Title
Charge pump

## Abstract

A charge pump exhibiting a voltage compensation function is provided. The charge pump includes: a first current generator, a first semiconductor device, a second current generator, a second semiconductor device, and a voltage regulator. The voltage regulator dynamically adjusts a voltage level at the gate of the first or second semiconductor device so as to adjust a first current or a second current outputted to a current output node. In addition, the voltage regulator provides a bias voltage at the current output node when both the first and second semiconductor devices are turned off.

## Background
FIELD OF THE INVENTION
The present invention relates to a charge pump, and more particularly to a charge pump exhibiting a voltage compensation function.
BACKGROUND OF THE INVENTION
FIG. 1A is a schematic functional block diagram illustrating a conventional phase locked loop. The phase locked loop (PLL) 10 includes a phase/frequency detector (PFD) 101, a charge pump (CP) 103, a low pass filter (LPF) 105 and a voltage control oscillator (VCO) 107. The phase locked loop 10 is optionally comprised of a frequency divider 109. The operating principle of the phase locked loop 10 will be illustrated as follows. Firstly, a divided signal Vdiv from the frequency divider 109 and an input signal Vin are received by the phase/frequency detector 101. Then, a phase difference between the divided signal Vdiv and the input signal Vin is detected. According to the phase difference, the frequency of an output signal Vout from the voltage control oscillator 107 is adjusted. The frequency of the output signal Vout is divided by the frequency divider 109, and the divided signal Vdiv is issued to the phase detector 101. Ideally, the frequency of the divided signal Vdiv is identical to that of the input signal Vin.
FIG. 1B is a schematic diagram illustrating the interconnection among the phase/frequency detector, the charge pump, and the low pass filter. After the phase/frequency detector 101 receives the input signal Vin and the divided signal Vdiv, the phase/frequency detector 101 outputs comparing signals (Vup, Vdown). The comparing signals (Vup, Vdown) are used for respectively controlling the switching states of the semiconductor devices (P1, N1) in the charge pump 103. Consequently, the low pass filter 105 is charged or discharged in response to the switching states of the semiconductor devices (P1, N1).
Charging/discharging the low pass filter 105 results in changes of the voltage level VCP at the current output node SCP, and further affects the frequency of the output signal Vout generated and outputted from the voltage control oscillator 107.
The operations of the phase/frequency detector 101, charge pump 103, low pass filter 105, and voltage control oscillator 107 will be further discussed below.
In a case that the frequency of the input signal Vin is greater than frequency of the divided signal Vdiv, the charge pump 103 charges the low pass filter 105 according to the first comparing signal Vup. After being charged, the voltage level VCP at the current output node SCP is increased, and so are the frequencies of the output signal Vout and the divided signal Vdiv.
Therefore, the increase of the voltage level VCP at the current output node SCP indirectly causes the increase of the frequency of the divided signal Vdiv. In spite the frequency of the divided signal Vdiv less than the frequency of the input signal Vin at the first, the frequencies of the output signal Vout and the divided signal, Vdiv become higher as the low pass filter 105 is charged. As a result, by increasing the voltage level VCP at the current output node SCP, the frequency of the divided signal Vdiv increases so as to approach the frequency of the input signal Vin.
In a case that the frequency of the input signal Vin is less than that of the divided signal Vdiv, the charge pump 103 discharges the low pass filter 105 according to the second comparing signal Vdown generated from the phase/frequency detector. After discharging, the voltage level VCP at the current output node SCP is decreased, and so are the frequencies of the output signal Vout and the divided signal Vdiv.
Therefore, the decrease of the voltage level VCP at the current output node SCP indirectly causes the decrease of the frequency of the divided signal Vdiv. In spite the frequency of the divided signal Vdiv is greater than the frequency of the input signal Vin at the first, the frequencies of the output signal Vout and the divided signal Vdiv become less as the low pass filter 105 is discharged. As a result, by decreasing the voltage level VCP at the current output node SCP, the frequency of the divided signal Vdiv decreases so as to approach the frequency of the input signal Vin.
In brief, since the voltage level VCP at the current output node SCP correlates to the frequencies of the output signal Vout and divided signal Vdiv, the control of the voltage level VCP at the current output node SCP facilitates the stabilization of the phase locked loop 10. It is shown that the control of the voltage level VCP is an important issue.
In details, with reference to FIG. 1B, an inverted first comparing signal Vup′ is generated by inverting the first comparing signal Vup. by an inverter 102a and received by the charge pump 103.
According to the inverted first comparing signal Vup′, the switching state of the first p-channel metal-oxide-semiconductor (PMOS) P1 is determined. In a case that the logic state of the first comparing signal Vup is logic “1”, then the logic state of the inverted first comparing signal Vup′ is logic “0”, and the first PMOS P1 is turned on. In such a case, the low pass filter 105 is charged by the charge pump 103 and the voltage level VCP at the current output node SCP is increased accordingly.
On the other hand, the second comparing signal Vdown is propagated via a transmission gate 102b. The propagated second comparing signal VdownΔ is received by the charge pump 103.
With the propagated second comparing signal VdownΔ, the switching state of the first n-channel metal-oxide-semiconductor (NMOS) N1 is determined. In a case that the logic state of the propagated second comparing signal VdownΔ is logic “1”, the first NMOS N1 is turned on. In such a case, the low pass filter 105 is discharged by the charge pump 103 and the voltage level VCP at the current output node SCP is decreased accordingly.
From the above discussions, in a case that logic states of the first and second comparing signals Vup, Vdown are logic “0”, the first PMOS P1 and the first NMOS N1 are both turned off. In such a case, the voltage level VCP at the current output node SCP becomes floating.
If the voltage control oscillator 107 receives the floating voltage level VCP at the current output node SCP, jitters are easily generated as noises might be occurred. Therefore, how to stabilize the voltage level VCP when both the comparing signals Vup, Vdown are high impedance is an important issue.
Ideally, the influences of the charging operation of the first and second PMOS, and the discharging operation of the first and second NMOS on the low pass filter 105 can be balanced. However, these two types of transistors are not completely symmetrical to each other in practice, and the intensities of the charging current and the discharging current are hard to completely equal to each other.
SUMMARY OF THE INVENTION
Therefore, an aspect of the present invention provides a charge pump capable of providing a bias voltage at the current output node.
Besides, another aspect of the present invention provides a charge pump capable of balancing the charging current from the PMOS and the discharging current from the NMOS whenever the voltage level VCP at the current output section SCP changes.
In accordance with an aspect, the present invention provides a charge pump, comprising: a first current generator electrically connected to a first voltage terminal, and providing a first current; a first semiconductor device electrically connected to the first current generator and a current output node, and optionally turned on to conduct flow of the first current to the current output node; a second current generator electrically connected to a second voltage terminal and providing a second current; a second semiconductor device electrically connected to the second current generator and the current output node, and optionally turned on to conduct flow of the second current to the current output node; and a voltage regulator electrically connected to the first and second semiconductor devices and the current output node for dynamically adjusting a voltage level at the gate of the first or second semiconductor device so as to adjust the first current or the second current outputted to the current output node.
In accordance with another aspect, the present invention provides a charge pump, comprising: a first current generator for providing a first current to a current output node; a first semiconductor device electrically connected to the first current generator and the current output node, and turned on in response to a specified state of a first signal inputted thereto so as to conduct flow of the first current to the current output node; a second current generator for providing a second current; a second semiconductor device electrically connected to the second current generator and the current output node, and turned on in response to a specified state of a second signal inputted thereto so as to conduct flow of the second current to the current output node; and a voltage regulator electrically connected to the first and second semiconductor device and the current output node, and configured to provide a bias voltage at the current output node.



BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
FIG. 1A is a schematic functional block diagram illustrating a conventional phase locked loop;
FIG. 1B is a schematic diagram illustrating the interconnection among the phase/frequency detector, the charge pump, and the low pass filter;
FIG. 2 is a schematic diagram illustrating the internal connections of a charge pump according to an embodiment of the present invention;
FIG. 3A is a schematic circuit diagram illustrating operations of an example of the charge pump as shown in FIG. 2 when the voltage level at the current output node increases;
FIG. 3B is a schematic circuit diagram illustrating operations of an example of the charge pump as shown in FIG. 2 when the voltage level at the current output node decreases; and
FIG. 4 is a schematic circuit diagram illustrating another example of the charge pump as shown in FIG. 2.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
For solving the incompatible current and jitter problem encountered by prior art, a charge pump according to an embodiment of the present invention, provides a small current between the voltage terminals Vdd and VGND so as to provide a bias voltage to the current output node SCP for voltage compensation.
FIG. 2 is a schematic diagram illustrating the internal connections of a charge pump according to an embodiment of the present invention. In the charge pump 203, a certain intensity of current is provided at the current output node SCP according to a set of comparing signals (Vup, Vdown) or a set of biasing voltage generated by a voltage regulator 2033 when the set of comparing signals (Vup, Vdown) are high impedance. The charge pump 203 includes a constant current source (CCSO) 2031, a constant current sink (CCSI) 2032, and the voltage regulator 2033. The CCSO 2031 includes a first current generator 2031a, and a first semiconductor device 2031b. The CCSI 2032 includes a second current generator 2032a, and a second semiconductor 2032b. The set of comparing signals (Vup, Vdown) are tri-state signals whose states are high voltage level, low voltage level or high impedance.
Please refer to FIG. 3A, which illustrates an example of the charge pump as shown in FIG. 2. The first current generator 2031a is electrically connected to a first voltage terminal Vdd and the current output node SCP. Based on a first bias control voltage Vb1, the first current generator 2031a provides a first current IP. On the other hand, the second current generator 2032a is electrically connected to the second voltage terminal VGND. Based on a second bias control voltage Vb2, the second current generator 2032a provides a second current IN.
The source and drain of the first semiconductor device 2031b are electrically connected to the first current generator 2031a and the current output node SCP, respectively. The first semiconductor device 2031b is turned on according to the first comparing signal Vup. If the first semiconductor device 2031b is turned on, the first current IP is provided to the current output node SCP. The first current IP serves as a charging current for charging a downstream low pass filter (not shown). When the first comparing signal Vup is high impedance, the first semiconductor device 2031b is biased according to a voltage level VS1.
The source and gate of the second semiconductor device 2032b are electrically connected to the second current generator 2032a and the current output node SCP, respectively. The second semiconductor device 2032b is turned on according to the second comparing signal Vdown. If the second semiconductor device 2032b is turned on, the second current IN is provided to the current output node SCP. The second current IN serves as a discharging current for discharging a downstream low pass filter (not shown). When the second comparing signal Vdown is high impedance, the second semiconductor device 2032b is biased according to a voltage level VS2.
As for the voltage regulator 203, it is electrically connected to the gates of the first and second semiconductor device 2031b, 2032b and the current output node SCP.
In a case that the set of comparing signals (Vup, Vdown) are high impedance, the voltage regulator 2033 provides a first bias voltage and a second bias voltage to the gates of the first and second semiconductor device 2031b, 2032b, respectively.
In a case that the set of comparing signals (Vup, Vdown) are high impedance, the voltage regulator 2033 dynamically adjusts the first or second bias voltage in response to changes of the voltage level VCP at the current output node SCP. By dynamically adjusting voltage levels at the first and second bias node S1, S2, the first current IP and the second current IN can be timely stabilized.
According to the present invention, the voltage regulator 2033 includes a first regulating unit 2033a and a second regulating unit 2033b. The first regulating unit 2033a is electrically connected between the first voltage terminal Vdd and the current output node SCP, and includes a third semiconductor device 33 and a fourth semiconductor device 34. The second regulating unit 2033b is electrically connected between the second voltage terminal VGND and the current output node SCP, and includes a fifth semiconductor device 35 and a sixth semiconductor device 36.
The first regulating unit 2033a is used together with the first current generator 2031a and the first semiconductor device 2031b to stabilize the first current IP provided by the first current generator 2031a by providing the first bias voltage to the gate of the first semiconductor device 2031b. 
The second regulating unit 2033b is used together with the second current generator 2032a and the second semiconductor device 2032b to stabilize the second current IN provided by the second current generator 2032a by providing the second bias voltage to the gate of the second semiconductor device 2032b. 
The first regulating unit 2033a is electrically connected to the first voltage terminal Vdd, the second voltage terminal VGND, and the current output node SCP. The first regulating unit 2033a and the first semiconductor device 2031b are both electrically connected to the first bias node S1. The first regulating unit 2033a generates and outputs a first compensated current IPC to the current output node SCP by means of the voltage level VS1 on the first bias node S1 when the set of comparing signals (Vup, Vdown) are high impedance.
The second regulating unit 2033b is electrically connected to the first voltage terminal Vdd, the second voltage terminal VGND, and the current output node SCP. The second regulating unit 2033b and the second semiconductor device 2032b are both electrically connected to the second bias node S2. The second regulating unit 2033b generates and outputs a second compensated current INC to the current output node SCP by means of the voltage level VS2 on the second bias node S2 when the set of comparing signals (Vup, Vdown) are high impedance.
In this example, the third semiconductor device 33 is an NMOS, whose drain and gate are electrically connected to the second voltage terminal VGND and the current output terminal SCP, respectively. Therefore, the voltage drop VGS-33 between the gate and source of the third semiconductor device 33 substantially equals to the voltage difference of the voltage level VCP at the current output node SCP and the voltage level VGND at the second voltage terminal.
On the other hand, the fourth semiconductor device 34 is a PMOS, whose source and gate are electrically connected to the first voltage terminal Vdd and the drain of the third semiconductor device 33, respectively. The gate of the fourth semiconductor device 34 is electrically connected to its own drain. Besides, the gate of the fourth semiconductor device 34 and the gate of the first semiconductor device 2031b are electrically connected to the first bias node S1.
Likewise, according to FIG. 3A, the fifth semiconductor device 35 is a PMOS, whose source and gate are electrically connected to the first voltage terminal Vdd and the current output node SCP, respectively. Therefore, the voltage drop VSG-35 between the gate and source of the fifth semiconductor device 33 substantially equals to the voltage difference of the voltage level Vdd at the first voltage terminal and the voltage level VCP at the current output node SCP.
The sixth semiconductor device 36 is an NMOS, whose source is electrically connected to the second voltage terminal VGND. The drain of the fifth semiconductor device 35 is electrically connected to the drain of the sixth semiconductor device 36. The gate of the sixth semiconductor 36 is electrically connected to its own drain. Besides, the gate of the sixth semiconductor device 36 and the gate of the second semiconductor device 2032b are electrically connected to the second bias node S2.
According to the present invention, the first regulating unit 2033a is considered as a compensation current source to output the voltage level VS1 on the first bias node S1 to the current output node SCP when the set of comparing signals (Vup, Vdown) are high impedance. Therefore, the first current generator 2031a, whose source-drain voltage is fixed in theorem, in the constant current source (CCSO) 2031 is considered as an independent current source for providing a constant current.
The second regulating unit 2033b is considered as a compensation current source to output the voltage level VS2 on the second bias node S2 to the current output node SCP when the set of comparing signals (Vup, Vdown) are high impedance. Therefore, the second current generator 2032a, whose drain-source voltage is fixed in theorem, in the constant current sink (CCSI) 2032 is considered as an independent current sink for receiving the constant current. A constant current generated by the CCSO 2031 flows to the CCSI 2032 consistently.
In a case that the set of comparing signals (Vup, Vdown) are high impedance, the current flows between the CCSO 2031 and the CCSI 2032 is kept constant. Since there is current constantly flowing to the current output node SCP, the voltage level VCP at the current output node SCP is maintained at a certain value (with a scale of nano-ampere). Hence the constant current is feasible to bias the voltage level VCP at the current output node SCP.
Therefore, when the set of comparing signals (Vup, Vdown) are high impedance, the voltage regulator 2033 provides a first compensation voltage generated by the first compensated currents ICP, that is the voltage level VS1, on the first bias node S1 and a second compensation voltage generated by the second compensated currents INC, that is the voltage level VS2, on the second bias node S2. Subsequently, the first current generator 2031a charges the downstream low pass filter with the first compensated current IPC, and the second current generator 2032a discharges the low pass filter with a second compensated current INC.
Accordingly, the first and second currents IP, IN are compensated. The current intensities of the first compensated current IPC and the second compensated current INC are equal and the charging/discharging of the low pass filter can be balanced.
The voltage regulator 2033 is capable of providing a bias voltage at the current output node SCP by means of the first and second compensated currents IPC, INC. Furthermore, the problem that the voltage level VCP at the current output node SCP is floating and accompanying disadvantages such as jitters can be solved.
As the intensities of the first and second compensated currents IPC, INC, are substantially equal, these compensated currents do not affect the charging/discharging of the low pass filter even if the set of comparing signals (Vup, Vdown) are high impedance.
The operations of the first regulating unit 2033a and the second regulating unit 2033b in response to the changes of the voltage level VCP at the current output node SCP are illustrated. The relationship between the first regulating unit 2033a and the first semiconductor device 2031b is first discussed, followed by discussions regarding the relationship between the second regulating unit 2033b and the second semiconductor device 2032b. 
For the first regulating unit 2033a, when the set of comparing signals (Vup, Vdown) are high impedance, the third semiconductor device 33 is regarded as a reference current source for providing a first compensated current IPC to the current output node SCP.
The gate and drain of the fourth semiconductor device 34 are electrically connected to each other, and thus the voltage levels thereat are both equal to the voltage level at the first bias node S1. The formula iDP=k(vSG-P−vt-P)2(1+λvSD-P) can be deduced to iD-P=k(vSG-P−vt-P)2(1+λvSG-P), where iDP is a current flowing through the fourth semiconductor device 34, k and λ are constants, vSG-P is the voltage drop between the source and gate of the fourth semiconductor device 34, and vt-P is the threshold voltage of the fourth semiconductor device 34. That is, the voltage drop VSG-34 of the source and gate of the fourth semiconductor device 34 is determined according to the first compensated current IPC.
Moreover, as the gates of the fourth and first semiconductor devices 2031b, 34 are electrically connected to the first bias node S1, the voltage drop VSG-34 is correlated to the voltage level VG-2031b at the gate of the first semiconductor device 2031b. 
According to the equation iD=k(vGS−vt)2(1+λvDS), both the voltage drop VGS and VDS are in direct proportion to the current intensity. That is, since the voltage drops VGS and VDS change in opposite ways, e.g. the voltage drop VGS increases while the voltage drop VDS decreases, and vice versa, the intensity of the charging current flowing through the first semiconductor device 2031b can be kept stable.
In brief, a change of the voltage drop VSG-2031b between the source and gate of the first semiconductor device 2031b is used to compensate the change of the voltage drop VSD-2031b between the source and drain of the same. Therefore, the charging current generated and outputted by the first current generator 2031a is not affected by the changes of the voltage level VCP at the current output node SCP.
For the second regulating unit 2033b, when the set of comparing signals (Vup, Ydown) are high impedance, the fifth semiconductor device 35 is regarded as a reference current source for providing a second compensated current INC to the current output node SCP .
As the gate and drain of the sixth semiconductor device 36 are electrically connected to each other, the voltage levels thereat are equal to the voltage level of the second bias node S2. The formula iDN=k(vGS-N−vt-N)2(1+λvDS-N) can be deduced to iDN=k(vGS-N−vt-N)2(1+λvGS-N), where iDN is a current flowing through the sixth semiconductor device 36, k and λ are constants, vGS-N is the voltage drop between the gate and source of the sixth semiconductor device 36, and vt-N is the threshold voltage of the sixth semiconductor device 34. That is, the voltage drop VGS-36 of the gate and source of the sixth semiconductor device 36 is determined according to the second compensated current INC.
Moreover, as the gates of both the sixth and the second semiconductor device 36, 2032b are electrically connected to the second bias node S2, the voltage drop VGS-36 correlates to the voltage level VG-2032b at the gate of the second semiconductor device 2032b. 
According to the equation iD=k(vGS−vt)2(1+λvDS), both the voltage drops VGS and VDS are in direct proportion to the current intensity. That is, since the voltage drops VGS and VDS change in opposite ways, e.g. the voltage drop VGS increases while the voltage drop VDS decreases, and vice versa, the intensity of the charging current flows through the second semiconductor device 2032b can be kept stable.
In brief, a change of the voltage drop VGS-2032b between the gate and source of the second semiconductor device 2032b is used to compensate the change of the voltage drop VDS-2032a between the drain and source of the same. Therefore, the discharging current generated and outputted by the second current generator 2032a is not affected by the changes of the voltage level VCP at the current output node SCP.
Meanwhile, the charge pump according to the present invention is capable of dynamically adjusting the voltage levels VS1, VS2 at the first and second bias nodes S1, S2 in response to the variation of the voltage level VCP at the current output node SCP. That is, the voltage level VS1 at the first bias node S1 is used to adjust the voltage drop VSG-2031b between the source and gate of the first semiconductor device 2031b. The voltage level VS2 at the second bias node S2 is used to adjust the voltage drop VGS-2032b between the gate and source of the second semiconductor device 2032b. 
Since the voltage drops VGS-2031b, VGS-2032b are changed in response to the changes of the voltage level VCP at the current output node SCP, the first current IP for charging and the second current IN for discharging become more stable as the first and second compensated currents IPC, INC are existed. In short, the voltage regulator 2033 exhibits a function of monitoring the variation of the voltage level VCP at the current output node SCP, and providing a negative feedback for diminishing that variation.
In the example of FIG. 3A, in a case that the set of comparing signals (Vup, Vdown) are high impedance, the voltage regulator adjusts the voltage levels at terminals of the semiconductor devices when the voltage level at the current output node increases. The operations of the first and second regulating units 2033a, 2033b are discussed below.
The internal operations of the first regulating unit 2033a are first discussed. When the voltage level VCP at the current output node SCP increases, the voltage drop VGS-33 also increases. The increase of the voltage drop VGS-33 causes the increase of the first compensated current IPC provided by the third semiconductor device 33.
The voltage drop VSG-34 between the source and gate of the fourth semiconductor device 34 varies with the current intensity of the first compensated current IPC. Therefore, the voltage drop VSG-34 increases if the first compensated current IPC increases.
Since the source of the fourth semiconductor 34 is electrically connected to the first voltage terminal Vdd, the increase of the voltage drop VSG is equivalent to the decrease of voltage level at the gate of the fourth semiconductor device 34. Due to the connection of the gates of the first and fourth semiconductor devices 2031b, 34, the voltage level at the gate of the first semiconductor device 2031b also decreases. Meanwhile, the voltage drop VSG-2031b between the source and gate of the first semiconductor device 2031b increases.
To sum up, the increase of the voltage level VCP at the current output node SCP causes the decrease of the voltage drop VSD-2031b but the increase of the voltage drop VSG-2031b.
Therefore, the voltage level at the conjunction of the first current generator 2031a and the first semiconductor device 2031b does not change with the increase of the voltage level VCP at the current output node SCP. As a result, the current provided by the first current generator 2031a is kept stable.
As the first semiconductor device 2031b shares the same base with the fourth semiconductor device 34, threshold voltages Vt of both the first and fourth semiconductor devices 2031b, 34 are equivalent. Besides, parameters related to material characteristics and operating temperatures of these two semiconductor devices 2031b, 34 are identical. Therefore, the first compensated current IPC conducted through the fourth semiconductor 34 is reflected to the first semiconductor device 2031b based on a current mirror structure.
Therefore, the relationship between changes of voltage levels discussed above can be explained from the viewpoint of current generation. That is, with the increasing of the voltage level VCP at the current output node SCP, the first compensated current IPC increases. In such case, the corresponding reflected current to the first semiconductor device 2031b also increases. The decrease of the charging current caused by increasing of the voltage level VCP at the current output node SCP is hence being diminished by the increasing of the reflected current. Therefore, the charging current provided to the current output node SCP is stabilized.
The internal operations of the second regulating unit 2033b are then discussed. When the voltage level VCP at the current output node SCP increases, the voltage drop VSG-35 decreases at meanwhile. The decrease of the voltage drop VSG-35 implies that the second compensated current INC provided by the fifth semiconductor device 35 decreases consequently.
The voltage drop VGS-36 between the gate and the source of the sixth semiconductor device 34 is depending on the current intensity of the second compensated current INC. Therefore, the voltage drop VGS-36 decreases if the second compensated current INC decreases.
Since the source of the sixth semiconductor 36 is electrically connected to the second voltage terminal VGND, the decrease of the voltage drop VGS-36 is equivalent to the decrease of voltage level at the gate of the sixth semiconductor device 36. Due to the connection of the gates of the second and sixth semiconductor device 2032b, 36, the voltage level at the gate of the second semiconductor device 2032b also decreases. At the meanwhile, the voltage drop VGS-2032b between the source and the gate of the second semiconductor device 2031b decreases.
To sum up, the increase of the voltage level VCP at the current output node SCP implies the increase of the voltage drop VDS-2032b but the decrease of the voltage drop VGS-2032b.
Therefore, the voltage level at the conjunction of the second current generator 2032a and the second semiconductor device 2032b does not change with the increase of the voltage level VCP at the current output node SCP. Furthermore, the current provided by the second current generator 2032a is kept stable.
As the second semiconductor device 2032b shares the same base with the sixth semiconductor device 36, threshold voltages Vt of both semiconductor devices 2032b, 36 are equivalent. Besides, parameters related to material characteristics and operating temperatures of these two semiconductor devices 2032b, 36 are identical. Therefore, the second compensated current INC conducted through the sixth semiconductor 36 is reflected to the second semiconductor device 2032b based on a current mirror structure.
Therefore, the relationship between changes of voltage levels discussed above can be explained from the viewpoint of current generation. That is, with the increase of the voltage level VCP, the second compensated current INC decreases. In such a case, the corresponding reflected current to the second semiconductor device 2032b also decreases. The increase of the discharging current caused by the increase of the voltage level VCP at the current output node SCP is hence being diminished by the decrease of the reflected current. Therefore, the discharging current provided to the current output node SCP is stabilized.
In the example of FIG. 3B, in a case that the set of comparing signals (Vup, Vdown) are high impedance, the voltage regulator adjusts the voltage levels at terminals of the semiconductor devices when the voltage level at the current output node decreases. The operations of the first and second regulating units 2033a, 2033b are discussed below.
The internal operations of the first regulating unit 2033a are first discussed. When the voltage level VCP at the current output node SCP decreases, the voltage drop VGS-33 also decreases. The decrease of the voltage drop VGS-33 causes the decrease of the first compensated current IPC provided by the third semiconductor device 33.
The voltage drop VSG-34 between the source and gate of the fourth semiconductor device 34 varies with the current intensity of the first compensated current IPC. Therefore, the voltage drop VSG-34 decreases if the first compensated current IPC decreases.
Since the source of the fourth semiconductor 34 is electrically connected to the first voltage terminal Vdd, the decrease of the voltage drop VSG is equivalent to the increase of voltage level at the gate of the fourth semiconductor device 34. Due to the connection of the gates of the first and fourth semiconductor device 2031b, 34, the voltage level at the gate of the first semiconductor device 2031b also increases. Meanwhile, the voltage drop VSG-2031b between the source and gate of the first semiconductor device 2031b decreases.
To sum up, the decrease of the voltage level VCP at the current output node SCP causes the increase of the voltage drop VSD-2031b but the decrease of the voltage drop VSG-2031b.
Therefore, the voltage level at the conjunction of the first current generator 2031a and the first semiconductor device 2031b does not change with the decrease of the voltage level VCP at the current output node SCP. As a result, the current provided by the first current generator 2031a is kept stable.
As the first semiconductor device 2031b shares the same base with the fourth semiconductor device 34, threshold voltages Vt of both semiconductor devices 2031b, 34 are equivalent. Besides, parameters related to material characteristics and operating temperatures of these two semiconductor device 2031b, 34 are identical. Therefore, the first compensated current IPC conducted through the fourth semiconductor 34 is reflected to the first semiconductor device 2031b based on the current mirror structure.
Therefore, the relationship between changes of voltage levels discussed above can be explained from the viewpoint of current generation. That is, with the decrease of the voltage level VCP, the first compensated current IPC decreases. In such case, the corresponding reflected current to the first semiconductor device 2031b also decreases. The increase of the charging current caused by the decrease of the voltage level VCP at the current output node SCP is hence being diminished by the decrease of the reflected current. Therefore, the charging current provided to the current output node SCP is stabilized.
The internal operations of the second regulating unit 2033b are then discussed. When the voltage level VCP at the current output node SCP decreases, the voltage drop VSG-35 increases at meanwhile. The increase of the voltage drop VSG-35 implies that the second compensated current INC provided by the fifth semiconductor device 35 increases consequently.
The voltage drop VGS-36 between the gate and the source of the sixth semiconductor device 34 is depending on the current intensity of the second compensated current INC. Therefore, the voltage drop VGS-36 increases if the second compensated current INC increases.
Since the source of the sixth semiconductor 36 is electrically connected to the second voltage terminal VGND, the increase of the voltage drop VGS-36 is equivalent to the increase of voltage level at the gate of the sixth semiconductor device 36. Due to the connection of the gates of the second and the sixth semiconductor devices 2032b, 36, the voltage level at the gate of the second semiconductor device 2032b also increases. At the meanwhile, the voltage drop VGS-2032b between the source and the gate of the second semiconductor device 2031b increases.
To sum up, the decrease of the voltage level VCP at the current output node SCP implies the decrease of the voltage drop VDS-2032b but the increase of the voltage drop VGS-2032b.
Therefore, the voltage level at the conjunction of the second current generator 2032a and the second semiconductor device 2032b does not change with the decrease of the voltage level VCP at the current output node SCP. Furthermore, the current provided by the second current generator 2032a is kept stable.
As the second semiconductor device 2032b shares the same base with the sixth semiconductor device 36, threshold voltages Vt of both semiconductor device 2032b, 36 are equivalent. Besides, parameters related to material characteristics and operating temperatures of these two semiconductor device 2032b, 36 are identical. Therefore, the second compensated current INC conducted through the sixth semiconductor 36 is reflected to the second semiconductor device 2032b based on a current mirror structure.
Therefore, the relationship between changes of voltage levels discussed above can be explained from the viewpoint of current generation. That is, with the decrease of the voltage level VCP, the second compensated current INC increases. In such case, the corresponding reflected current to the second semiconductor device 2032b also increases. The decrease of the discharging current caused by the decrease of the voltage level VCP at the current output node SCP is hence being diminished by the increase of the reflected current. Therefore, the discharging current provided to the current output node SCP is stabilized.
FIG. 4 is a schematic circuit diagram illustrating another example of the charge pump as shown in FIG. 2. According to FIG. 4, it is shown that extra components can be optionally used in the charge pump under a variety of considerations such as circuit matching.
While considering the voltage matching issue between the first and the fourth semiconductor device 2031b, 34, a seventh semiconductor device 37 is placed between the fourth semiconductor device 34 and the first voltage terminal Vdd. The gates of the first and fourth semiconductor devices 2031b, 34 are electrically connected to each other, but the first current generator 2031a is in between the first semiconductor device 2031b and the first voltage terminal Vdd while the fourth semiconductor device 34 is electrically connected to the first voltage terminal Vdd directly. Therefore, the seventh semiconductor device 37 is utilized to make the voltage levels at the gates of the fourth and the first semiconductor 34, 2031b switches match.
Similarly, an eighth semiconductor device 38 may be optionally used in between the sixth semiconductor device 36 and the second voltage terminal VGND, for compensating the voltage level at the gate of the second semiconductor device 203b. 
Moreover, a unit gain buffer (also referred to as a buffer amplifier) 2034 is optionally used in between the first semiconductor device 2031b, the second semiconductor device 2032b, and the voltage regulator 203. The unit gain buffer 2034 is an amplifier whose output end is electrically connected to its negative input end. The unit gain buffer 2034 passes the voltage level of the voltage signal VCP at the current output node SCP to the voltage regulator. Since the unit gain buffer 2034 has features of high input resistance, low output resistance etc., signal decay of the voltage regulator 203 is minimized.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

## Claims

1. A charge pump, comprising:
a first current generator electrically connected to a first voltage terminal, and providing a first current;
a first semiconductor device electrically connected to the first current generator and a current output node, and optionally conducting flow of the first current to the current output node;
a second current generator electrically connected to a second voltage terminal and providing a second current;
a second semiconductor device electrically connected to the second current generator and the current output node, and optionally conducting flow of the second current to the current output node; and
a voltage regulator electrically connected to the first and second semiconductor devices and the current output node for dynamically adjusting a voltage level at the gate of the first or second semiconductor devices so as to adjust the first current or the second current outputted to the current output node.

2. The charge pump according to claim 1, wherein the voltage regulator raises the voltage level at the gate of the first semiconductor device when the voltage level at the current output node increases.

3. The charge pump according to claim 1, wherein the voltage regulator lowers the voltage level at the gate of the first semiconductor device when the voltage level at the current output node decreases.

4. The charge pump according to claim 1, wherein the voltage regulator lowers the voltage level at the gate of the second semiconductor device when the voltage level at the current output node increases.

5. The charge pump according to claim 1, wherein the voltage regulator raises the voltage level at the gate of the second semiconductor device when the voltage level at the current output node decreases.

6. The charge pump according to claim 1, wherein the voltage regulator comprises:
a first regulating unit electrically connected to the first voltage terminal, the current output node and the first semiconductor device for adjusting the voltage level at the gate of the first semiconductor device according to a change of the voltage level at the current output node; and
a second regulating unit electrically connected to the second voltage terminal, the current output node, and the second semiconductor device for adjusting the voltage level at the gate of the second semiconductor device according to the change of the voltage level at the current output node.

7. The charge pump according to claim 6, further comprising:
a unit gain amplifier electrically connected to the current output node and the first and second regulating units for reflecting the voltage level at the current output node to the regulating units.

8. The charge pump according to claim 1, wherein the first semiconductor device is turned on in response to a specified state of a first comparing signal received from a phase/frequency detector disposed upstream of the charge pump, and the second semiconductor device is turned on in response to a specified state of a second comparing signal received from the phase/frequency detector.

9. The charge pump according to claim 1, wherein the first voltage terminal is coupled to a voltage source, and the second voltage terminal is coupled to ground.

10. The charge pump according to claim 1, wherein the voltage regulator electrically connected to gate electrodes of the first and second semiconductor devices, and the current output node.

11. A charge pump, comprising:
a first current generator for providing a first current to a current output node;
a first semiconductor device electrically connected to the first current generator and the current output node, and turned on in response to a specified state of a first signal inputted thereto so as to conduct flow of the first current to the current output node;
a second current generator for providing a second current;
a second semiconductor device electrically connected to the second current generator and the current output node, and turned on in response to a specified state of a second signal inputted thereto so as to conduct flow of the second current to the current output node; and
a voltage regulator electrically connected to the first and second semiconductor devices and the current output node, and configured to provide a bias voltage at the current output node when both the first and second signals are high impedance.

12. The charge pump according to claim 11, wherein the voltage regulator comprises:
a first regulating unit electrically connected to a first voltage terminal, where the first regulating unit is electrically connected to the current output node and the first semiconductor device, for outputting a first compensated current to the current output node; and
a second regulating unit electrically connected to a second voltage terminal, where the second regulating unit is electrically connected to the current output node, and the second semiconductor device, for outputting a second compensated current to the current output node,
wherein the bias voltage is generated at the current output node in response to the first and second compensated currents.

13. The charge pump according to claim 12, wherein the first voltage terminal is coupled to a voltage source, and the second voltage terminal is coupled to ground.

14. The charge pump according to claim 11, wherein the first and second regulating units are electrically connected to a filter disposed downstream of the charge pump for charging/discharge the filter with the first and second compensated currents, and intensities of the first and second compensated currents are substantially equal to each other.

15. The charge pump according to claim 11, further comprising
a unit gain amplifier electrically connected to the current output node and the first and second regulating units for reflecting the voltage level at the current output node to the regulating units.

16. The charge pump according to claim 11, wherein the first signal and the second signal are a first comparing signal and a second comparing signal, which are received from a phase/frequency detector disposed upstream of the charge pump.

17. The charge pump according to claim 11, wherein the voltage regulator electrically connected to gate electrodes of the first and second semiconductor devices, and the current output node.