Low Dropout Regulator

Abstract

To provide a low dropout regulator.SOLUTION: The low dropout regulator includes a gain stage module, an output setting stage, and a detection circuit. The gain stage module generates a gain stage signal, the output setting stage is electrically connected to the gain stage module, and the output setting stage outputs a load current to an output terminal in response to the gain stage signal. The detection circuit is electrically connected to the gain stage module and the output setting stage, and the detection circuit includes a monitoring circuit and a compensation circuit. The monitoring circuit is electrically connected to the output terminal. The monitoring circuit compares a charge-up duration of the signal at the output terminal with a preset threshold duration and generates a comparison signal accordingly. The compensation circuit is electrically connected to the gain stage module and the output terminal, and the compensation circuit performs frequency compensation in response to the comparison signal selectively.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a low dropout regulator that can detect the location of a dominant pole and selectively perform frequency compensation. [Background technology]

[0002] In electronic equipment, linear regulators are used to stabilize the power supply voltage Vdd and convert it into a stable output voltage Vout. A low dropout (LDO) regulator is a type of linear regulator that has the advantages of low cost, low noise, and high speed voltage conversion.

[0003] 1 is a schematic diagram illustrating an embodiment of an LDO regulator used in a conventional electronic device. The electronic device 10 includes an LDO regulator 13a and a load circuit 15. The LDO regulator 13a converts a power supply voltage Vdd to an output voltage Vout, and supplies the output voltage Vout to the load circuit 15. The value of the output voltage Vout is preset and determined by the requirements of the load circuit 15. Summary of the Invention [Problem to be solved by the invention]

[0004] A voltage source 12 (e.g., a battery) supplies a power supply voltage Vdd. However, since the power supply voltage Vdd is unstable, an LDO regulator 13a is used. A load capacitor Cld is electrically connected to an output terminal Nout and a ground terminal Gnd. For ease of understanding, terminals and their signals are denoted by the same symbols in this specification. For example, a ground voltage and a ground terminal are both denoted by Gnd in this specification.

[0005] In practical applications, the load capacitor Cld is integrated into the LDO regulator 13a (i.e., it is an on-chip capacitor), but it may be mounted separately outside the LDO regulator 13a (i.e., it is an off-chip capacitor). The use of an off-chip capacitor provides frequency compensation and ensures stability. When the output resistance is large, the load current becomes small (light load condition) and the output pole starts to move toward low frequency. This means that the phase margin decreases, and stability needs to be monitored. For this reason, a large off-chip capacitor is adopted to make the output pole the dominant pole. However, the off-chip capacitor requires a large area. On the other hand, the off-chip capacitor is not necessarily required under medium or heavy load conditions, so the cost of the circuit can be reduced by omitting the off-chip capacitor.

[0006] In practical applications, the LDO regulator 13a also operates under different load conditions. Under light load conditions, it employs off-chip capacitors to ensure stability and required load transient performance. Under medium to heavy load conditions, it does not use off-chip capacitors to maintain stability and load transient performance.

[0007] As is well known, the dominant pole affects the stability of the LDO regulator 13a, and the position of the pole is clearly modified by using an off-chip capacitor. However, it is not possible to know in advance whether the LDO regulator 13a has an off-chip capacitor. Therefore, it is necessary to develop an LDO regulator 13a that has the feasibility of selectively performing or not performing frequency compensation according to the position of the dominant pole.

[0008] Therefore, the inventors believed that the above-mentioned drawbacks could be improved, and as a result of extensive research, they came to propose the present invention, which rationally and effectively improves the problems.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an LDO regulator having a function for detecting the dominant pole position, and selectively compensating the LDO regulator based on the result of the detection. [Means for solving the problem]

[0010] The various aspects of the present invention for achieving the above object are as follows. In order to solve the above problem, a low dropout regulator according to one aspect of the present invention includes a gain stage module, an output setting stage, and a detection circuit. The gain stage module generates a gain stage signal. The output setting stage is electrically connected to the gain stage module. The output setting stage outputs a load current toward an output terminal in response to the gain stage signal. The detection circuit is electrically connected to the gain stage module and the output setting stage. The detection circuit includes a monitoring circuit and a compensation circuit. The monitoring circuit is electrically connected to the output terminal. The monitoring circuit compares a charging duration of a signal present at the output terminal with a preset threshold period, and generates a comparison signal accordingly. The compensation circuit is electrically connected to the gain stage module and the output terminal. The compensation circuit selectively performs frequency compensation in response to the comparison signal.

[0011] In the following detailed description, for the purposes of explanation, numerous specific details are provided to facilitate a thorough understanding of the disclosed embodiments. However, it will be apparent that one or more embodiments may be practiced without these specific details. In other embodiments, simplified diagrams of structures and equipment are shown in schematic form to familiarize the public. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of an LDO regulator used in conventional electronic equipment. [Diagram 2]1 is a block diagram illustrating an LDO regulator according to an embodiment of the present invention. [Figure 3A] 4 is a schematic diagram illustrating a change in an output voltage Vout when a process is installed in an LDO regulator according to an embodiment of the present invention. FIG. [Figure 3B] FIG. 2 is a schematic diagram illustrating the relationship between the position of the dominant pole and the change in the output voltage Vout when a process is set in an LDO regulator according to an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing an exemplary design of a pole detection circuit in accordance with an embodiment of the present invention. [Figure 5A] 4 is a flowchart illustrating an operation state of an LDO regulator according to an embodiment of the present invention during a ramp phase (PH1). [Figure 5B] 1 is a flowchart illustrating an operation state of an LDO regulator according to an embodiment of the present invention during a steady state phase (PH2). [Figure 6] FIG. 2 is a schematic diagram illustrating an exemplary capacitor-less LD0 regulator in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the low dropout regulator of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and the members, materials, etc. described below can be modified in various ways within the spirit and scope of the present invention.

[0014] 2 is a block diagram illustrating an LDO regulator according to an embodiment of the present invention. The LDO regulator 20 includes a gain stage module 22, a pole detection circuit 27, an output setting stage 28, a reference generator 29, a bias stage 21, and a load capacitor Cld. The gain stage module 22 includes a first gain stage 23 and a second gain stage 25, and the pole detection circuit 27 includes a monitoring circuit 271 and a compensation circuit 273.

[0015] The load capacitor Cld is electrically connected to the output terminal Nout and the ground terminal Gnd, and the load capacitor Cld may be on-chip or off-chip.

[0016] The following describes the elements and connections of the LDO regulator 20. The second gain stage 25 accounts for the total loop gain when the LDO regulator 20 operates under heavy load conditions.

[0017] The output setting stage 28 is basically a flipped voltage follower (hereinafter, abbreviated as FVF). The output setting stage 28 is electrically connected to the output terminal Nout, the first gain stage 23, the second gain stage 25, and a reference generator 29. The output setting stage 28 outputs a load current Ild to the output terminal Nout, and generates a stable output voltage Vout at the output terminal Nout.

[0018] The bias stage 21 is electrically connected to the first gain stage 23, the second gain stage 25, and the output setting stage 28. The reference generator 29 is electrically connected to the bias stage 21, the first gain stage 23, and the output setting stage 28.

[0019] In the pole detection circuit 27, the monitoring circuit 271 and the compensation circuit 273 are both electrically connected to the output terminal Nout, and the compensation circuit 273 is electrically connected to the first gain stage 23 and the second gain stage 24 via the gain stage terminal Ng1. The monitoring circuit 271 is electrically connected to the compensation circuit 273, and transmits a comparison signal Scmp to the compensation circuit 273.

[0020] An exemplary implementation of the monitoring circuit 271 and the compensation circuit 273 is shown in Figure 4. An exemplary internal design of the bias stage 21, the first gain stage 23, the second gain stage 25, the power setting stage 28, and the reference generator 29 is shown in Figure 6.

[0021] 3A is a schematic diagram illustrating the change in the output voltage Vout when a process is installed in an LDO regulator according to an embodiment of the present invention, where the vertical axis represents the output voltage Vout and the horizontal axis represents time.

[0022] Waveform WF1 shows the change of output voltage Vout during the setting process. The setting process involves a ramp phase (PH1) and a steady-state phase (PH2). In the ramp phase (PH1), the output voltage Vout starts from the ground voltage Gnd (i.e., the power-on time t_on in FIG. 3A) and gradually increases to the preset output voltage. In the steady-state phase (PH2), the output voltage Vout is held at a constant voltage (at the preset output voltage). The duration of the ramp phase (PH1) is defined as the charging duration Tch, and the charging time Tch changes according to the position of the dominant pole (see FIG. 3B).

[0023] 3B is a schematic diagram illustrating the relationship between the position of the dominant pole and the change in the output voltage Vout when a process is set in the LDO regulator according to an embodiment of the present invention, where the vertical axis represents the output voltage Vout and the horizontal axis represents time.

[0024] Waveform WF2a shows how the output voltage Vout changes during a settling process starting from the power-on time t_on when the dominant pole is located inside the gain stage module 22. The charging duration corresponding to waveform WF2a is shown as charging duration Tch_a.

[0025] The waveform WF2b shows how the output voltage Vout changes during the settling process starting from the power-on time t_on when the dominant pole is located at the output terminal Nout. The charging duration corresponding to the waveform WF2b is shown as another charging duration Tch_b.

[0026] The slew rate of the waveform W2a is fast. The fast slew rate of the waveform W2a means that the load capacitor Cld corresponding to the waveform W2a can be charged quickly and has a small capacitance. Therefore, the dominant pole is located inside the LDO regulator 20 and between the first gain stage 23 and the second gain stage 25.

[0027] On the other hand, the slow slew rate of the waveform W2b means that the load capacitor Cld corresponding to the waveform W2a cannot be charged quickly and has a large capacitance, so that the dominant pole is located at the output terminal Nout.

[0028] Based on the waveforms WF2a and WF2b, the conclusion is that the charging duration Tch_a is short when the dominant pole is located inside the LDO regulator 20. Moreover, when the dominant pole is located at the output terminal Nout, the charging duration Tch_b is even longer.

[0029] According to an embodiment of the present invention, a preset threshold period Tth is defined and used to distinguish the position of the dominant pole. First, the monitoring circuit 271 detects the charging duration Tch. Then, the charging duration Tch detected by the monitoring circuit 271 is compared with the preset threshold period Tth to identify the position of the dominant pole.

[0030] 3B, since the charging duration Tch_a is shorter than the preset threshold duration Tth, the dominant pole corresponding to the waveform WF2a is identified as being located inside the gain stage module 22. Meanwhile, since the charging duration Tch_b is longer than the preset threshold Tth, the dominant pole corresponding to the waveform WF2b is identified as being located at the output terminal Nout.

[0031] 4 is a schematic diagram showing an exemplary design of a pole detection circuit in accordance with an embodiment of the present invention.

[0032] The monitoring circuit 271 includes a measuring circuit 271a, a threshold setting circuit 271e, and a comparing circuit 271c. The measuring circuit 271a and the threshold setting circuit 271e are electrically connected to the comparing circuit 271c. The measuring circuit 271a measures a charging duration Tch, and the threshold setting circuit 271e provides a preset threshold period Tth.

[0033] The implementation of the measuring circuit 271a, the threshold setting circuit 271e, and the comparing circuit 271c is not limited. For example, the measuring circuit 271a may be a digital counter that counts the number of cycles required to charge the load capacitor Cld. The threshold setting circuit 271e may be a recorder that records a count value representing a preset threshold duration Tth, and the comparing circuit 271c may be a comparator.

[0034] In another example, the measurement circuit 271a may include a charging circuit (e.g., a charge pump), and the comparison circuit 271c may be an analog comparator. When the charging circuit charges the output terminal Nout, the charging duration Tch increases at the same time. The aforementioned analog comparator 271c detects the output terminal Nout and determines whether to charge and when to stop charging based on a comparison between the output terminal Nout and a threshold voltage Vth. The threshold voltage Vth corresponds to a preset threshold period Tth. Once the output terminal Nout reaches the threshold voltage Vth, the charging circuit stops charging. The preset threshold voltage Vth is provided by a bandgap circuit (see FIG. 6 described below).

[0035] In another example, the measurement circuit 271a includes a digital counter and a digital-to-analog converter (DAC) (not shown). The digital counter calculates a cumulative number indicative of the charging duration Tth, and the DAC converts the cumulative number into a cumulative comparison voltage Vcmp.

[0036] An analog circuit is further used to realize the monitoring circuit 271. In practical application, the monitoring circuit 271 only needs to detect the charging duration Tch of the LDO regulator and accurately generate the comparison signal Scmp to identify whether the charging duration Tch is greater than or equal to the preset threshold period Tth. The design of the monitoring circuit 271 is not limited.

[0037] The compensation circuit 273 has connection terminals Nc1 and Nc2. One of the connection terminals Nc1 and Nc2 is electrically connected to the output terminal Nout, and the other of the connection terminals Nc1 and Nc2 is electrically connected to the gain stage terminal Ng1. The compensation circuit 273 is also electrically connected to the comparison circuit 271c.

[0038] The compensation circuit 273 includes one mirror capacitance Cm and one switch sw, and the switch sw is controlled by the comparison signal Scmp. The mirror capacitance Cm is used for frequency compensation. The mirror capacitance Cm is connected between the gain stage terminal Ng1 and the output terminal Nout, and is used to compensate the frequency when the switch sw is turned on. Alternatively, when the switch sw is turned off, the terminal of the mirror capacitance Cm is in a floating state, and the mirror capacitance Cm stops the compensation frequency.

[0039] 5A is a flowchart illustrating an operation state of an LDO regulator according to an embodiment of the present invention during the ramp phase (PH1). First, the comparison circuit 271c obtains a preset threshold period Tth and a preset charging duration Tch from the threshold setting circuit 271e and the measurement circuit 271a, respectively, and compares the preset charging duration Tch with the preset threshold period Tth (step S31a).

[0040] When the charging duration Tch is equal to or longer than a preset threshold period Tth (Tch ≧ Tth), the dominant pole is regarded as being outside the LDO regulator 20 (step S31c). A long charging duration Tch means that the load capacitor Cld may have an even larger capacitance value. In such a situation, the comparison circuit 271c sets the comparison signal Scmp to a logic low level (Scmp = L) to disable the compensation circuit 273 (step S31e), and the LDO regulator 20 operates without frequency compensation.

[0041] When the charging duration Tch is shorter than the preset threshold period Tth (Tch < Tth), the dominant pole is regarded as being inside the LDO regulator 20 (step S31g). A short charging duration Tch means that the load capacitor Cld may have a small capacitance value. In such a situation, the comparison circuit 271c sets the comparison signal Scmp to a logic high level (Scmp = H) to enable the compensation circuit 273 (step S31i), and the LDO regulator 20 operates with frequency compensation. After steps S31e and S31i, the LDO regulator 20 proceeds to the steady-state phase (PH2).

[0042] FIG. 5B is a flowchart for explaining the operation status of the LDO regulator according to an embodiment of the present invention at the steady-state phase (PH2). During the steady-state phase (PH2) period, the operation of the LDO regulator 20 is related to the load conditions (step S33a).

[0043] When the LDO regulator 20 faces a light load condition, the load current Ild decreases and an overshoot occurs. In other words, the increase in the output voltage Vout temporarily stops. In such a situation, the second gain stage 25 is disabled and the output voltage Vout is pulled down to eliminate the overshoot (step S33c). By doing so, the output voltage Vout is maintained at a constant voltage during the steady-state phase (PH2) period.

[0044] When the LDO regulator 20 faces a heavy load condition, the load current Ild increases and an undershoot occurs. In other words, the decrease in the output voltage Vout pauses. In such a situation, the second gain stage 25 is enabled to increase the output voltage Vout and eliminate the undershoot (step S33e). In this way, the output voltage Vout is held constant during the steady-state phase (PH2).

[0045] 6 is a schematic diagram of an exemplary capacitorless LDO regulator in accordance with one embodiment of the present invention, with reference to Figures 2 and 6. The internal components of bias stage 21, first gain stage 23, second gain stage 25, and reference generator 29 are each described below.

[0046] The bias stage 21 includes bias transistors Qb1, Qb2, and Qb3, a current source 211, a resistor R, and a high-pass capacitor Ch. The bias transistor Qb3 is a PMOS transistor, and the bias transistors Qb1 and Qb2 are NMOS transistors.

[0047] In the bias stage 21, a current source 211 continuously supplies a sink bias current Ibias and generates a mirror current Imb through the bias transistors Qb2 and Qb3 by replicating the sink bias current Ibias. The high-pass capacitor Ch and resistor R together provide a high-pass function to prevent the sink bias current Ibias from being affected by overshoot at the output terminal Nout.

[0048] The first gain stage 23 includes first stage transistors Q1a and Q1b. The first stage transistor Q1a is a PMOS transistor, and the first stage transistor Q1b is an NMOS transistor. The bias transistor Qb3 and the first stage transistor Q1a form a current mirror, and the first stage current I1 is generated by the mirror current Imb. The first stage current I1 flows through the first stage transistor Q1b, and the signal at the gain stage terminal Ng2 (the source terminal of the first stage transistor Q1b) affects the first stage current I1.

[0049] The second gain stage 25 includes second stage transistors Q2a, Q2b, Q2c, and Q2d. The second stage transistors Q2a and Q2b are PMOS transistors, and the second stage transistors Q2c and Q2d are NMOS transistors. The second stage transistor Q2a may be a voltage-to-current converter, and the second stage transistor Q2a is controlled by a signal at the gain stage terminal (i.e., a gain stage signal) Ng1. Based on the current structure of the second stage transistor Q2b and the bias transistor Qb3, the second stage transistor Q2b is held in an on state. The second stage transistors Q2c and Q2d jointly form another current mirror.

[0050] When only second stage transistor Q2a is on, the second gain stage 25 is enabled and the on of second stage transistor Q2a is associated with first stage current I1. When second stage transistor Q2a is on, second stage current I2a flows through second stage transistors Q2a, Q2c, and second stage transistor Q2d replicates second stage current I2a from bias transistor Q2c to generate second stage current I2b.

[0051] The output setting stage 28 includes power transistors Qp1 and Qp2, an output setting transistor Qos, and output bias transistors Qob1 and Qob2. The power transistors Qp1 and Qp2 and the output setting transistor Qos are PMOS transistors, and the output bias transistors Qob1 and Qob2 are NMOS transistors. The power transistors Qp1 and Qp2 are controlled by the outputs of the first gain stage 23 and the second gain stage 25, respectively. When the LDO regulator 20 faces a light load condition, the power transistor Qp1 is turned on and the power transistor Qp2 is turned off. When the LDO regulator 20 faces a heavy load condition, the power transistor Qp1 is turned off and the power transistor Qp2 is turned on.

[0052] The aspect ratio of the power transistor Qp2 is larger than that of the power transistor Qp1. For example, the aspect ratio of the power transistor Qp2 is 10 times that of the power transistor Qp1. Thus, when the LDO regulator 20 faces a heavy load condition, the power transistor Qp2 turns on and conducts a larger load current Ild, and when the LDO regulator 20 faces a light load condition, the power transistor Qp1 turns on and conducts a lower load current Ild.

[0053] The aspect ratio of the output bias transistor Qob1 is larger than the aspect ratio of the output bias transistor Qob2, so that the output bias current Iob flowing through the output bias transistor Qb1 is larger than the output set current Ios2 flowing through the output bias transistor Qob2.

[0054] The reference generator 29 includes a bandgap circuit 291, reference transistors Qr1, Qr2, and Qr3, and an operational amplifier 293. The bandgap circuit 291 outputs a stable reference voltage Vref to the inverting input terminal (-) of the operational amplifier 293 and to the gate terminal of the first stage transistor Q1b. In this way, the first stage transistor Q1b is maintained on, and the first stage current I1 is continuously conducted to the gain stage terminal Ng2.

[0055] When the reference transistor Qr2 and the output setting transistor Qos form a current mirror, the output setting current Ios1 flowing through the output setting transistor Qos replicates the reference current Iref flowing through the reference transistor Qr2. Also, based on the current mirror structure, the signal at the output terminal Nout becomes equivalent to the non-inverting input terminal (+) of the operational amplifier 293.

[0056] Due to the virtual short circuit characteristic of the operational amplifier 293, the output voltage Vout becomes equivalent to the reference voltage Vref (Nout = Vref), so that the LDO regulator 20 continuously outputs the constant output voltage Vout.

[0057] As mentioned above, LDO regulator 20 may or may not be used with an off-chip capacitor, depending on the load conditions. To assist in operation under different load conditions, LDO regulator 20 needs a mechanism to detect whether the output terminal is connected to a large load capacitor. By utilizing pole detection circuit 27, LDO regulator 20 can determine whether output terminal Nout forms a dominant pole. Once this is determined, LDO regulator 20 will take appropriate action to adjust frequency compensation.

[0058] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the claims that such modifications and improvements can also be included in the technical scope of the present invention. [Explanation of symbols]

[0059] 10 Electronic equipment 12 Voltage Source 13a Low Dropout Regulator 15 Load circuit 20 Low Dropout Regulator 21 Bias Stage 211 Current source 22 Gain Stage Module 23 1st gain stage 25 2nd gain stage 27 Pole detection circuit 271 Monitoring circuit 271a Measuring circuit 271c comparison circuit 271e Threshold setting circuit 273 Compensation circuit 28 Output Setting Stage 29 Reference Generator 291 Bandgap Circuit 293 Operational Amplifiers Cld Load capacitor Cm Mirror Capacity CMP Comparator Ch High Pass Capacitor Gnd Earth terminal (ground voltage) I1 First stage current I2a Second stage current I2b Second stage current Ibias Sink bias current Ild load current Imb Mirror bias current Iob Output bias current Ios1 Output setting current Ios2 Output setting current Iref Reference current Nc1 connection terminal Nc2 connection terminal Ng1 gain stage terminal Ng2 gain stage terminal Nout Output terminal PH1 Ramp phase PH2 Steady state phase Q1a First stage transistor Q1b First stage transistor Q2a Second stage transistor Q2b Second stage transistor Q2c Second Stage Transistor Q2d Second stage transistor Qb1 bias transistor Qb2 bias transistor Qb3 Bias transistor Qp1 Power transistor Qp2 power transistor Qob1 output bias transistor Qob2 output bias transistor Qos output setting transistor Qr1 Reference Transistor Qr2 Reference Transistor Qr3 Reference Transistor R resistor sw switch Scmp comparison signal Tch charge time Tch_a Charge time Tch_b Charge time Tth Pre-set threshold period t_on Power on time Vdd power supply voltage Vout Output voltage Vref Reference voltage WF1 waveform WF2a waveform WF2b waveform S31a Step S31c Step S31g Step S31e Step S31i Step S33a Step S33c Step S33e Step

Claims

1. a gain stage module for generating a gain stage signal; an output setting stage electrically connected to the gain stage module for outputting a load current toward an output terminal in response to the gain stage signal; a detection circuit electrically connected to the gain stage module and the output setting stage; The detection circuit includes: a monitoring circuit electrically connected to the output terminal for comparing a charging duration of a signal present at the output terminal with a preset threshold period and correspondingly generating a comparison signal; a compensation circuit electrically connected to the gain stage module and the output terminal, the compensation circuit selectively performing frequency compensation in response to the comparison signal.

2. The compensation circuit includes: Mirror capacitance, 2. The low dropout regulator according to claim 1, further comprising: a switch electrically connected to the mirror capacitance and the monitoring circuit, the switch being selectively turned on by the comparison signal.

3. 3. The low dropout regulator of claim 2, wherein when the switch is turned on, the compensation circuit performs the frequency compensation using the Miller capacitance, and when the switch is turned off, the compensation circuit stops performing the frequency compensation.

4. The monitoring circuit includes: a measurement circuit for measuring the charging duration; a threshold setting circuit for providing the preset threshold period; 2. The low dropout regulator of claim 1, further comprising: a comparison circuit electrically connected to the measurement circuit and the threshold setting circuit for comparing the charging duration and the preset threshold period and generating the comparison signal correspondingly.

5. 5. The low dropout regulator of claim 4, wherein the comparison signal is set to a first logic potential if the charging duration is greater than or equal to the preset threshold period.

6. 5. The low dropout regulator of claim 4, wherein the comparison signal is set to a second logic potential if the charging duration is less than the preset threshold period.

7. 5. The low dropout regulator of claim 4, wherein the measurement circuit is an analog circuit or a digital counter.

8. 2. The low dropout regulator of claim 1, wherein a dominant pole of the low dropout regulator is located within the gain stage module when the charging duration is less than the preset threshold period.

9. 9. The low dropout regulator of claim 8, wherein the compensation circuit performs the frequency compensation when the dominant pole of the low dropout regulator is located within the gain stage module.

10. 2. The low dropout regulator of claim 1, wherein a dominant pole of the low dropout regulator is located at the output terminal when the charging duration is equal to or greater than the preset threshold period.

11. 11. The low dropout regulator of claim 10, wherein the compensation circuit stops performing the frequency compensation when the dominant pole of the low dropout regulator is located at the output terminal.

12. 2. The low dropout regulator of claim 1, wherein when the low dropout regulator is operating in a ramp phase, the signal present at the output terminal increases gradually and when the low dropout regulator is operating in a steady state phase, the signal present at the output terminal is held constant, the steady state phase being after the ramp phase.

13. 13. The low dropout regulator of claim 12, wherein the charging duration represents the duration for the signal present at the output terminal to rise from a ground voltage to a preset output voltage.

14. 2. The low dropout regulator of claim 1, wherein a load capacitor is electrically connected to the output terminal, the load capacitor being an on-chip capacitor.

15. 2. The low dropout regulator of claim 1, wherein a load capacitor is electrically connected to said output terminal, said load capacitor being an off-chip capacitor.

16. 2. The low dropout regulator of claim 1, wherein the load current decreases when the low dropout regulator experiences a light load condition, and the load current increases when the low dropout regulator experiences a heavy load condition.

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