阅读说明：本技术 低压差稳压器以及调节低压差稳压器的方法 (Low dropout voltage regulator and method for regulating low dropout voltage regulator ) 是由 金正雄 于 2020-11-09 设计创作，主要内容包括：本发明提供一种调节低压差(LDO)稳压器的方法。方法包含：通过从低压差稳压器的输出节点接收反馈来产生反馈电压；通过接收反馈电压和参考电压来产生用以驱动传输元件的控制信号；通过检测电路来检测第一节点的电压且根据检测结果来控制第一开关的切换操作。当低压差稳压器在主动模式下操作时,第一开关接通以使第一节点与传输元件的控制端连接,且当低压差稳压器在待机模式下操作时,第一开关断开以使第一节点与传输元件的控制端断开连接。还提供一种低压差(LDO)稳压器。(The present invention provides a method of regulating a Low Dropout (LDO) regulator. The method comprises the following steps: generating a feedback voltage by receiving feedback from an output node of the low dropout regulator; generating a control signal to drive a transmission element by receiving a feedback voltage and a reference voltage; the voltage of the first node is detected by a detection circuit and the switching operation of the first switch is controlled according to the detection result. When the low dropout regulator operates in the active mode, the first switch is turned on to connect the first node with the control terminal of the transmission element, and when the low dropout regulator operates in the standby mode, the first switch is turned off to disconnect the first node from the control terminal of the transmission element. A Low Dropout (LDO) regulator is also provided.)

1. A low dropout regulator, comprising:

a transmission element connected between a power supply voltage and an output node of the low dropout regulator;

a feedback circuit configured to receive feedback from the output node and generate a feedback voltage;

an error amplifier configured to receive the feedback voltage and a reference voltage to generate a control signal to drive the pass element;

a compensation capacitor comprising a first terminal and a second terminal, wherein the first terminal is coupled to a first node and the second terminal is coupled to the output node of the LDO; and

a detection circuit configured to detect a voltage of the first node and control the first switch according to a detection result,

wherein when the LDO is operating in an active mode, the first switch is turned on to connect the first node to the control terminal of the transmission element, and when the LDO is operating in a standby mode, the first switch is turned off to disconnect the first node from the control terminal of the transmission element.

2. The low dropout regulator of claim 1, further comprising:

a driver circuit configured to charge and discharge the first node; and

a second switch configured to connect the driver circuit and the first node.

3. The low dropout regulator of claim 1, wherein the first switch is coupled between the first node and the control terminal of the pass element, and when the first switch changes from on to off, a transition detection pulse is generated to initialize the first node with a first predetermined voltage by the driver circuit.

4. The low drop-out regulator of claim 3, wherein the detection circuit compares the voltage of the first node to the first predetermined voltage when the transition detection pulse is generated.

5. The low drop-out regulator of claim 4, wherein the driver circuit discharges the first node when the voltage of the first node is above the first predetermined voltage and charges the first node when the voltage of the first node is below the first predetermined voltage.

6. The low drop-out regulator of claim 5, wherein the driver circuit comprises a diode-connected PMOS configured to charge the first node to the first predetermined voltage during charging.

7. The low dropout regulator according to claim 6, wherein the detection circuit is coupled to the driver circuit to detect the voltage of the diode-connected PMOS.

8. A method of regulating a low dropout regulator, comprising:

generating a feedback voltage by receiving feedback from an output node of the LDO;

generating a control signal to drive a transmission element by receiving the feedback voltage and a reference voltage; and

the voltage of the first node is detected by the detection circuit and the switching operation of the first switch is controlled according to the detection result,

wherein when the LDO is operating in an active mode, the first switch is turned on to connect the first node to the control terminal of the transmission element, and when the LDO is operating in a standby mode, the first switch is turned off to disconnect the first node from the control terminal of the transmission element.

9. The method of regulating a LDO of claim 8, further comprising:

performing a charging operation and a discharging operation on the first node.

10. The method of regulating a LDO of claim 8, wherein said first switch is coupled between said first node and said control terminal of said pass element, and when said first switch changes from on to off, a transition detection pulse is generated to initialize said first node with a first predetermined voltage by said driver circuit.

11. The method of regulating a low dropout voltage regulator according to claim 10, wherein said detection circuit compares a voltage of said first node with said first predetermined voltage when said transition detection pulse is generated.

12. The method of regulating a low dropout voltage regulator according to claim 11, wherein said driver circuit discharges said first node when said voltage of said first node is above said first predetermined voltage and charges said first node when said voltage of said first node is below said first predetermined voltage.

13. The method of regulating a low dropout voltage regulator of claim 12, wherein the driver circuit comprises a diode-connected PMOS configured to charge the first node to the first predetermined voltage during charging.

14. The method of regulating a low dropout voltage regulator according to claim 13, wherein the detection circuit is coupled to the driver circuit to detect the voltage of the diode-connected PMOS.

Technical Field

The present invention relates to voltage regulators, and more particularly, to an on-chip active Low Dropout (LDO) regulator with improved wake-up time and a method of regulating the LDO regulator.

Background

On-chip (on-chip) LDO regulators are commonly employed today in conventional DRAM and NAND memory devices. The LDO regulator has an active mode and a standby mode based on a load condition in the memory device. During a mode transition from standby mode to active mode, LDO regulators tend to suffer from long wake-up times. This is due to the slow speed of the loop response during wake-up due to the high RC time constant associated with the large compensation capacitance in the feedback loop in the LDO regulator. On the other hand, if the load current is drained (draw) before the LDO regulator settles to a constant value, the voltage at the output node of the LDO regulator drops further, which results in errors in data transfer in the memory device.

With the desire to address longer wake-up times during mode transitions from standby mode to active mode, it may be desirable to develop an LDO regulator with improved wake-up response for certain applications in the art.

Disclosure of Invention

A Low Dropout (LDO) regulator of the present disclosure includes a transmission element, a feedback circuit, an error amplifier, a compensation capacitor, and a detection circuit. The transmission element is connected between a power supply voltage and an output node of the LDO regulator. The feedback circuit is configured to receive feedback from the output node and generate a feedback voltage. The error amplifier is configured to receive the feedback voltage and the reference voltage to generate a control signal to drive the pass element. The compensation capacitor includes a first terminal and a second terminal, wherein the first terminal is coupled to the first node and the second terminal is coupled to the output node of the LDO regulator. The detection circuit is configured to detect a voltage of the first node and control the first switch according to a detection result. The first switch is turned on to connect the first node to the control terminal of the transmission element when the LDO regulator operates in the active mode, and is turned off to disconnect the first node from the control terminal of the transmission element when the LDO regulator operates in the standby mode.

A method of regulating a Low Dropout (LDO) regulator is provided. The method comprises the following steps: generating a feedback voltage by receiving feedback from an output node of the LDO regulator; generating a control signal to drive a transmission element by receiving a feedback voltage and a reference voltage; the voltage of the first node is detected by a detection circuit and the switching operation of the first switch is controlled according to the detection result. The first switch is turned on to connect the first node to the control terminal of the transmission element when the LDO regulator operates in the active mode, and is turned off to disconnect the first node from the control terminal of the transmission element when the LDO regulator operates in the standby mode.

Based on the above, in the embodiments of the present disclosure, when the LDO regulator operates in the active mode, the first switch is turned on to connect the first node with the transmission element, and when the LDO regulator operates in the standby mode, the first switch is turned off to disconnect the first node from the transmission element. Thus, the discharge time of the output of the error amplifier is improved due to charge sharing, thereby improving the wake-up response of the LDO regulator and reducing the voltage drop/undershoot voltage of the LDO regulator.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

FIG. 1 is a circuit diagram of an LDO regulator according to an embodiment of the present invention;

FIG. 2A is a circuit diagram of an enable pulse generator according to an embodiment of the present invention;

FIG. 2B is a waveform illustrating the operation of the enable pulse generator according to an embodiment of the present invention;

FIG. 3 illustrates operation waveforms of the LDO regulator according to an embodiment of the present invention;

FIG. 4 is a method for regulating an LDO regulator according to an embodiment of the present invention.

Detailed Description

It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms "connected," "coupled," and "mounted," and variations thereof herein, are used broadly and encompass direct and indirect connections, couplings, and mountings.

Fig. 1 is a circuit diagram of an LDO regulator according to an embodiment of the present invention. Referring to fig. 1, LDO regulator 100 includes a pass element 110, a feedback circuit 120, an error amplifier 130, a compensation capacitor Cc 140, an output capacitor CL 150, a load resistor RL 160, a parasitic capacitor Cpar 170, a detection circuit 180, a driver circuit 190, a first switch 191, and a second switch 192.

The transmission element 110 is a PMOS transistor including a source terminal, a drain terminal, and a control terminal. The source terminal is coupled to a supply voltage VEXT. The drain terminal is coupled to the output node VINT of the LDO regulator 100. The control terminal of the pass element 110 is coupled to the output node of the error amplifier 130. The transfer element 110 is also defined as a transfer transistor Pass Tr.

The feedback circuit 120 is configured to receive feedback from the output node VINT of the LDO regulator 100. The feedback circuit 120 includes a first feedback resistor R_FB1And a second feedback resistor R_FB2. First feedback resistor R_FB1A second feedback resistor R coupled to the output node VINT of the LDO regulator 100_FB2In the meantime. Similarly, a second feedback resistor R_FB2Coupled to the first feedback resistor R_FB1And a ground potential VSS. The feedback circuit 120 generates a feedback voltage VFB that is sent to the error amplifier 130 based on the voltage at the output node VINT of the LDO regulator 100.

The error amplifier 130 is configured to receive the feedback voltage VFB and the reference voltage VREF to generate a control signal for driving the transmission element 110. Error amplifier 130 is an operational amplifier having two inputs and one output. In other words, there are inverting and non-inverting terminals and an output terminal. Error amplifier 130 receives a feedback voltage VFB at the non-inverting terminal and a reference voltage VREF at the inverting terminal. The reference voltage VREF is a predetermined voltage and is defined by the user.

The compensation capacitor Cc 140 includes a first terminal and a second terminal. The first terminal is coupled to the first node VCC and the second terminal is coupled to the output node VINT of the LDO regulator 100. The compensation capacitor Cc 140 is also defined as the Miller capacitance used for frequency compensation in the voltage regulator. The compensation capacitor/miller capacitance Cc 140 is well known in the art and therefore, a description is omitted.

Output capacitor C_L150 is coupled between the output node VINT of the LDO regulator and the ground potential VSS. Output capacitor 150 is also defined as load capacitor CL.

Similarly, a load resistor R_L160 is coupled between the output node VINT of the LDO regulator and the ground potential VSS.

The parasitic capacitor Cpar 170 is coupled between the control terminal of the transmission element 110 and the ground potential VSS.

The detection circuit 180 is configured to detect a voltage at the first node VCC and a voltage at the driver circuit 190 and control the first switch 191 according to the detection result.

The detection circuit 180 includes a transistor M51, a transistor M52, a transistor M53, and a detection resistor R_DETECTAnd an inverter INV 1. The transistor M51 and the transistor M52 are PMOS transistors. The transistor M53 is an NMOS transistor.

The transistors M51, M52, and M53 include source, drain, and control terminals. A source terminal of the transistor M51 and a source terminal of the transistor M52 are coupled to the power supply voltage VEXT, and a drain terminal of the transistor M51 and a drain terminal of the transistor M52 are connected to each other. The control terminal of the transistor M51 and the control terminal of the transistor M53 are coupled to the enable signal Enb _ TD.

Detection resistor R_DETECTThe input terminal of the inverter INV1 is coupled to the drain terminal of the transistor M53. The source terminal of transistor M53 is coupled to ground potential VSS. An output of the inverter INV1 is coupled to the driver circuit 190.

In some embodiments, an N-type transistor is used instead of the sense resistor R_DETECT。

The driver circuit 190 is configured to charge and discharge the first node VCC. The driver circuit 190 includes a transistor M61, a transistor M62, a transistor M63, and a resistor R_BLEED. The transistors M61, M62, and M63 include source, drain, and control terminals. The transistor M61 and the transistor M62 are PMOS transistors. The transistor M63 is an NMOS transistor.

The transistor M61 is a diode-connected PMOS. In detail, a control terminal of the transistor M61 is coupled to a drain terminal of the transistor M61. The source terminal of transistor M61 is coupled to the supply voltage VEXT.

The source terminal of transistor M62 is coupled to the drain terminal of transistor M61, and the drain terminal of transistor M62 is coupled to resistor R_BLEEDTo one end of (a). The control terminal of the transistor M62 is controlled by the enable signal EN. Resistor R_BLEEDThe other terminal thereof is coupled to the drain terminal of the transistor M63, and the source terminal of the transistor M63 is coupled to the ground potential VSS. A control terminal of the transistor M63 is coupled to the output terminal of the inverter INV1 of the detection circuit 180.

In some embodiments, an N-type transistor is used instead of resistor R_BLEED。

The second switch 192 is coupled to the first node VCC and the drain terminal of the transistor M62. The second switch 192 is configured to connect the first node VCC with the driver circuit 190 during charging and discharging of the first node VCC.

The first switch 191 is coupled between the first node VCC and the output terminal of the error amplifier 130. In other words, the first switch 191 is coupled between the control terminal of the transmission element 110 and the first node VCC.

The detection circuit 180 is configured to detect a voltage of the first terminal of the compensation capacitor Cc 140 and the driver circuit 190, and control the first switch 191 and the second switch 192 to connect the compensation capacitor Cc 140 to the control terminal of the transmission element 110 in the active mode and disconnect the compensation capacitor Cc 140 from the control terminal of the transmission element 110 in the standby mode, so as not to increase the tail current I of the error amplifier 130_BIASThe discharge time of the transfer element 110 is improved.

In detail, when EN ═ 0, the first node VCC is connected to the driver circuit 190 and precharged at a predetermined voltage VEXT- | Vthp |, by the diode-connected PMOS transistor M61. It should be noted that the predetermined voltage VEXT- | Vthp | is the same as the voltage at the transfer element 110. When EN is 1, the LDO regulator 100 is turned on, and then the first node VCC is connected to the control terminal of the transmission element 110. During this condition, a charge sharing process occurs and the voltage at the control terminal of the transfer element 110 is due to the compensation capacitorCc 140 is larger than parasitic capacitor Cpar 170 and falls to a predetermined voltage VEXT- | Vthp | in a short time. Typically, compensation capacitor Cc 140 is larger than parasitic capacitor Cpar 170 in LDO regulator 100. This reduces the discharge time of the transfer element 110 by Cc | Vthp |/I_BIAS. The first node VCC is initialized to a first predetermined voltage VEXT- | Vthp | during EN-0 to prevent overshoot at the output of the LDO regulator 100 during the wake-up process.

Fig. 2A is a circuit diagram of an enable pulse generator according to an embodiment of the invention. The enable pulse generator 200 includes an inverter 210, a pulse generator tD 220, an inverter 230, and a logic gate 240.

The inverter 210 is configured to receive the enable signal EN and generate the enable signal ENb. The delay of the enable signal ENb is determined by the number of inverters. In this embodiment, an inverter 210 is used to generate the enable signal ENb.

The pulse generator tD 220 receives the enable signal ENb and generates an output that is sent to the inverter 230. Inverter 230 receives the output of pulse generator tD 220 and generates a delayed signal that is provided to logic gate 240.

The logic gate 240 is a 2-input AND gate (AND gate). One input of the and gate is an enable signal ENb and the other input is a delayed signal from the inverter 230 and generates an enable signal ENb _ TD.

In some embodiments, the logic gate 240 may be an and gate, an OR gate (OR), a NOT gate (NOT), an exclusive OR gate (EXOR), an exclusive OR gate (EXNOR), a flip-flop, OR the like. The logic gate 240 in the present disclosure is not limited thereto.

Fig. 2B illustrates an operation waveform of an enable pulse generator according to an exemplary embodiment of the present disclosure. Referring to fig. 2A, when the enable signal EN goes to logic high "1", the enable signal EN _ b goes to logic low "0" at time t 0. Note that the enable signal EN and the enable signal EN _ b are inverted signals.

When the enable signal ENb _ b reaches a logic low "0" to a logic high "1" at time t1, the enable signal ENb _ TD goes from a logic low "0" to a logic high "1" for a short time TD. The time tD is also defined as the transition detection pulse. Note that the enable signal EN, the enable signal EN _ b, and the enable signal ENb _ TD are used for referring to the detection circuit 180 of fig. 1.

FIG. 3 is an operation waveform of the LDO regulator according to an embodiment of the invention. Like elements in fig. 3 have the same reference numerals as the LDO regulator 100 in fig. 1.

Referring to fig. 1 and 2B, the enable signal EN goes from high to low during a mode transition from the standby mode to the active mode. After that, a transistor detection pulse having a pulse width tD is generated. The transition detection pulse tD is a short pulse for initializing the first node VCC with a predetermined voltage VEXT- | Vthp |. In other words, the enable signal ENb _ TD is high during the transition detection pulse TD, and the detection circuit 180 detects the voltage at the first node VCC. The detection circuit 180 compares the voltage of VCC with a predetermined voltage VEXT- | Vthp |. If the voltage at the first node VCC is higher than the predetermined voltage VEXT- | Vthp |, the driver circuit 190 drives the first node VCC to discharge the voltage at the first node VCC. In contrast, if the voltage at the first node VCC is lower than the predetermined voltage VEXT- | Vthp |, the diode-connected PMOS M61 in the driver circuit 190 charges the first node VCC.

In detail, during the mode transition from standby mode to active mode, the voltage at the transfer element 110 starts to be discharged from the power supply voltage VEXT to the predetermined voltage VEXT | Vthp | at time t 0. After that, at time t1, the transfer element 110 starts to discharge from the first predetermined voltage VEXT- | Vthp | to Vb at time Δ t, where Δ t is the discharge time of the transfer element 110. It should be noted that the time 411a taken for the transmission element 110 to discharge from VEXT to Vb is much higher in the conventional LDO than the time 411b taken for the transmission element 110 to discharge from VEXT to Vb. The undershoot voltage 421b at the output node VINT of the LDO regulator 100 is therefore much smaller than the undershoot voltage 421a of the conventional LDO regulator.

Typically, the compensation capacitor Cc 140 is larger than the parasitic capacitor 170. The Slew Rate (SR) and the discharge time (Δ t) of the transmission element 110 are calculated as:

if C is present_C＞＞C_par→ (1)

After the enable signal EN goes from logic high to logic low, the transition detection pulse tD is generated. At this time, the first node VCC is charged to VEXT at time t2, and then the detector compares the voltage at the first node VCC with a predetermined voltage VEXT- | Vthp |. If it is detected at time t3 that the first node VCC is higher than the predetermined voltage VEXT | Vthp | then the driver circuit 190 discharges the first node VCC to VEXT | Vthp | at time t 4. In contrast, if the first node VCC is lower than the predetermined voltage VEXT- | Vthp |, the diode-connected PMOS M61 charges the first node VCC.

Based on the above, during the standby mode, the compensation capacitor Cc 140 is precharged to the predetermined voltage VEXT- | Vthp | so that the compensation capacitor Cc 140 starts to discharge from the predetermined voltage VEXT- | Vthp | to the voltage Vb (which is lower than VEXT), thereby improving the wake-up time in the LDO regulator 100.

FIG. 4 is a method for regulating an LDO regulator according to an embodiment of the present invention. The method for regulating the LDO voltage regulator comprises the following steps: a feedback voltage is generated by receiving feedback from an output node of the LDO regulator in step S401. In step S402, a control signal to drive the transmission element is generated by receiving the feedback voltage and the reference voltage. In step S403, the voltage of the first node is detected by the detection circuit and the switching operation of the first switch is controlled according to the detection result. In step S404, when the LDO regulator operates in the active mode, the first switch is turned on to connect the first node with the control terminal of the transmission element. In step S405, when the LDO regulator operates in the standby mode, the first switch is turned off to disconnect the first node from the control terminal of the transmission element.

Summarizing the embodiments of the present disclosure, during the standby mode, the compensation capacitor Cc is precharged to the predetermined voltage VEXT | Vthp | so that the compensation capacitor Cc starts to discharge from the predetermined voltage VEXT | Vthp | to the voltage Vb (which is lower than the supply voltage VEXT), thereby improving the wake-up time in the LDO regulator.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.