KR101010451B1 - Low Dropout Regulator With Replica Load - Google Patents

Abstract

The low voltage drop regulator according to the present invention is connected to an output of a first amplifier and a first amplifier for receiving a reference voltage as a first input, amplifying a difference between the first input and the second input, and outputting the output voltage to a load. And an output unit providing an output unit, and a replica unit connected to an output of the first amplifier and providing a feedback voltage to a second input of the first amplifier. By maintaining a constant value irrespective of negative output voltage, stable output can be guaranteed even when external unstable power is supplied, and stable operation is possible regardless of capacitive load to be driven, thereby ensuring stable operation of the system.

Low Voltage Drop Regulator, Replica, Feedback, Gain, LDO

Description

Low Dropout Regulator With Replica Load}

The present invention relates to a low voltage drop regulator, and more particularly, to a low voltage drop regulator using a replica load having a constant feedback gain.

Low DropOut (LDO) regulator is a power supply device for analog and digital semiconductor circuits. It is a regulator that provides a stable DC voltage with a low output voltage value compared to its input, and operates precisely without malfunction of electronic devices. In order to guarantee the low voltage, a low voltage drop regulator is required to supply stable power to a circuit to be driven by receiving external power from a battery.

The low voltage drop regulator is mainly composed of semiconductor circuits used in wireless portable devices such as mobile phones and PDAs (Personal Digital Assistants), circuits constituting display devices such as monitors and TVs, drive circuits for driving light emitting diodes with adjustable constant brightness, It is used to supply a stable power supply circuit for the power supply circuit to supply the voltage used inside the biochip and other electronic devices that need a stable power supply.

Conventional low voltage drop regulators use a method of reducing the difference from the reference voltage by feeding back a feedback signal from the output voltage to the input. In the case of this feedback system, the stability of the system has become the biggest problem, and various compensation techniques have been proposed to secure the stability. However, this simple feedback system cannot accurately identify the capacitive load that the low-voltage drop regulator needs to drive. Therefore, even with a compensation scheme to ensure stability, only a limited range of capacitive loads can be driven. The problem still remains that the system becomes unstable when the capacitive load increases.

As a way to solve the problem of system instability when the capacitive load increases beyond a certain standard, a low voltage drop regulator using a replica load has been proposed. Figure 1 shows a low voltage drop regulator circuit using a conventional replica load. When using a replica load as shown in Figure 1, there is an advantage that the stability of the system can be secured regardless of the load to be operated by the regulator.

However, in the case of the voltage drop regulator circuit shown in FIG. 1, although the replica load is used, the voltage drop at the load is not reflected in the replica circuit. There was a problem that it could not adjust the output voltage because it did not detect.

To solve this problem, techniques for sensing the current supplied to the driving circuit have been proposed, one of which is a low voltage drop regulator circuit using a replica load to which a discontinuous mode compensation technique as shown in FIG. 2 is applied.

However, even in the circuit shown in Figure 2, if the output current changes to some extent can be expected to adjust the output voltage, as shown in Figure 2 due to the use of a comparator does not operate in a continuous mode (continuous mode), The problem is that the regulation characteristics are not good because of the operation in discrete mode. That is, in the circuit of FIG. 2, when the output current increases, the output voltage Vout decreases, so that the output of the comparator AMP2 becomes 1 and the switch MSW is brought into the ON state. The moment the switch MSW is turned on, the gain of the beta circuit eventually changes, resulting in a sudden increase in output voltage.

In order to solve the problem of the circuit as shown in FIG. 2, a low voltage drop regulator circuit using a replica load to which the continuous mode compensation technique as shown in FIG. 3 is applied has been proposed.

Referring to the regulation process in the circuit of FIG. 3, when the output current increases to decrease the output voltage Vout, the output of the second amplifier A2 increases, and accordingly, the I _BST increases to decrease vlb. Eventually Vout will increase. In other words, when the output current changes, the current I _BST value continuously changes accordingly, indicating continuous regulation characteristics for the output voltage. However, even in the circuit shown in FIG. 3, it can be seen that the feedback gain of the beta circuit changes as the I _BST value changes, causing an error in the output voltage and a problem in the stability of the circuit.

As described above, in the case of the low voltage drop regulator circuit, the regulation characteristics for the output voltage according to the change of the output current are different even if the feedback characteristics vary depending on the capacitive load or the stable feedback characteristics regardless of the capacitive load. There was a problem with poor or unsatisfactory feedback gains that made the system less stable and difficult to obtain the correct output voltage.

The present invention for solving the above-mentioned problems, by configuring an additional loop that reflects the output voltage as it is, providing a voltage equal to the output voltage to the input of the error amplifier, so that the same voltage as the output voltage It is an object of the present invention to provide a low voltage drop regulator using a replica circuit, which allows the comparison to maintain the characteristics of the entire system loop and output the correct voltage.

A low voltage drop regulator according to an aspect of the present invention for achieving the above object, the first amplifier for receiving a reference voltage as a first input, amplifying the difference between the first input and the second input, An output part connected to an output of the first amplifier and providing an output voltage to a load, and a replica part connected to an output of the first amplifier and providing a feedback voltage to the second input of the first amplifier. However, the feedback gain of the circuit composed of the first amplifier and the replica unit is maintained at a constant value regardless of the output voltage of the output unit.

The output unit includes a first transistor, a first resistance element connected in series to a source or a drain of the first transistor, and a second resistance element connected in series with the first resistance element, and the gate of the first transistor is It is characterized in that connected to the output terminal of the first amplifier.

The replica portion of the low voltage drop regulator according to the first aspect of the present invention includes a second transistor having a gate connected to the output of the first amplifier, a third resistor element, and a fourth resistor element connected in series with the third resistor element. Include.

The replica unit has one input terminal connected to the output voltage, and is connected to a second amplifier and the third resistor element to adjust the output by reflecting the change of the output voltage, and to the output of the second amplifier. And a compensation element coupled to provide a resistance value that varies with the output of the second amplifier.

The compensating element may be a transistor, in particular a MOS transistor.

The source or drain terminal of the compensation element is connected to the source or drain terminal of the second transistor, the gate of the compensation element is connected to the gate terminal of the second transistor, and the remaining source or drain terminal of the compensation element is It is connected to one end of the third resistor, characterized in that the remaining input terminal of the second amplifier is connected to the one end of the third resistor.

The node connected to the third resistor element and the fourth resistor element is connected to a second input of the first amplifier.

The replica portion of the low voltage drop regulator according to the second aspect of the present invention has a second transistor having a gate connected to the output of the first amplifier, a third resistor element connected in series with the second transistor, and a series with the third resistor element. And a fourth resistive element connected thereto.

The replica unit has one input terminal connected to the output voltage, and provides a second amplifier that adjusts the output by reflecting the change of the output voltage and provides a current value that varies according to the output voltage of the second amplifier. And a current providing element, wherein one end of the current providing element is connected to a source or drain terminal of the second transistor.

The other terminal of the second amplifier other than the input terminal connected to the output voltage may be connected to the second input of the first amplifier.

The current providing element may be a transistor, in particular, a MOS transistor.

The source or drain terminal of the current providing element is connected to the source or drain terminal of the second transistor, and the gate terminal of the current providing element is connected to the output of the second amplifier.

An integrated circuit according to another aspect of the present invention includes the low voltage drop regulator according to any one of claims 1 to 15. The present invention can be implemented as a portable terminal, an image processing apparatus, or the like including the low voltage drop regulator described above.

According to the low voltage drop regulator of the present invention implemented by adding one operational amplifier and one transistor, it operates as a stable voltage supply with low power consumption with almost no additional current consumption, and is stable even when an external unstable power supply is supplied. The output can be guaranteed and stable operation regardless of the capacitive load to be driven. Therefore, in view of the fact that the supply voltage also decreases as the semiconductor is integrated and miniaturized, the present invention provides a stable supply of the supply voltage to ensure stable operation of the system to be operated under the reduced supply voltage. The utility of the low voltage drop regulator will be very large.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant description of the same components is omitted.

4 is a block diagram of a feedback loop circuit applied to the present invention.

In the low voltage drop regulator according to the present invention, a feedback loop circuit as shown in FIG. 4 is applied. The output voltage Vout is represented by the relation between the input voltage Vin, the feedforward gain A, and the feedback gain β. It can be expressed as Equation 1.

[Equation 1]

Vout = A / (1 + Aβ) * Vin

Here, when Aβ is much larger than 1, that is, when Aβ >> 1, the output voltage Vout is expressed by Equation 2 below.

[Equation 2]

Vout = A / Aβ * Vin

     = Vin / β

That is, the low voltage drop regulator according to the present invention is a circuit capable of obtaining a constant output voltage when the feedback gain β is fixed. Therefore, in the low voltage drop regulator circuit according to the present invention, a compensation circuit capable of constantly controlling the feedback gain is added.

5 shows a first embodiment of a low voltage drop regulator circuit using a replica according to the present invention.

The low voltage drop regulator circuit according to the first embodiment of the present invention includes a first amplifier A1, a replica unit 510, and an output unit 520. In addition, the replica unit 510 and the output unit 520 include one transistor M2 and M1 and two resistors R3 and R4, R1 and R2, respectively, and the source of each transistor is an input voltage. (Vin), each gate is connected to the output (Vy) of the first amplifier (A1). In addition, the replica unit 510 further includes one transistor and one amplifier, which are the third transistor M3 and the second amplifier A2. The third transistor M3 and the second amplifier A2 are added to the present invention in comparison with the existing low voltage drop regulator circuit as shown in FIG. 1, and the low voltage drop regulator circuit according to the present invention is a conventional circuit. This is the biggest distinction compared to.

The reference voltage Vref is provided to the first input of the first amplifier A1. The voltage at N1, the node between the third resistor R3 and the fourth resistor R4 connected in series in the replica unit 510, is provided as a feedback signal to the second input of the first amplifier A1. The first amplifier A1 may be referred to as an error amplifier in the sense of amplifying a difference between the reference voltage Vref and the fed back signal, that is, an error. The output of the first amplifier A1 is connected to the gate of the second transistor M2 of the replica unit 510 and the gate of the first transistor M1 of the output unit 520. The drain of the second transistor M2 is connected to the source of the third transistor M3, and the gate of the third transistor M3 is connected to the output Vx of the second amplifier A2. In addition, the drain of the third transistor M3 is connected to the non-inverting input of the second amplifier A2 and one end of the third resistor R3, and the third resistor R3 and the fourth resistor R4 are connected in series. Connected. Meanwhile, the inverting input terminal of the second amplifier A2 is connected to the output terminal, and the output voltage is input to the inverting input terminal of the second amplifier A2.

The operation of the low voltage drop regulator circuit shown in FIG. 5 having such a configuration will be described.

When a change occurs in an external circuit connected to the low voltage drop regulator and the output current flowing toward the output stage increases, the output voltage Vout falls. Since the output voltage Vout is connected to the inverting input terminal of the second amplifier A2, the output voltage Vx of the second amplifier is increased. Accordingly, the ON resistance of the third transistor M3 increases and the voltage at the node N2 and the voltage at the node N1 decrease. Since the voltage at the node N1 is provided to the non-inverting input terminal of the first amplifier, the output voltage Vy of the first amplifier decreases, and as a result, the current flowing through the first transistor M1 of the output unit 520 increases and outputs the output. The voltage Vout is increased.

As described above, in the case of the low voltage drop regulator according to the first embodiment of the present invention, the change in the output voltage is reflected in the voltage at N2 as it is, and the feedback gain of the beta circuit is kept constant, thereby decreasing due to the increase in the output current. It can be seen that one output voltage is compensated by the replica unit.

6 shows a second embodiment of a low voltage drop regulator circuit using a replica according to the present invention.

The low voltage drop regulator circuit according to the second embodiment of the present invention includes a first amplifier A1, a replica unit 610, and an output unit 620. In addition, the replica unit 610 and the output unit 620 include one transistor M2 and M1 and two resistors R3 and R4, R1 and R2, respectively. Connected. In addition, the replica unit 610 further includes one transistor M3 and one amplifier A2, which is the part where the low voltage drop regulator circuit according to the present invention is most distinguished from the existing circuit. .

Since the replica unit 610 is used to better adjust the output voltage at the output terminal, it is preferable to consume the minimum power. For this purpose, the second transistor M2 of the replica unit 610 is an output unit ( It is smaller than the first transistor M1 of 620 and the third and fourth resistors R3 and R4 of the replica portion have a larger resistance value than the first and second resistors R1 and R2 of the output portion 620. It is desirable to design so that.

The first input of the first amplifier A1 is provided with a reference voltage Vref, and the voltage of the node N1 between the third resistor R3 and the fourth resistor R4 connected in series of the replica unit 620 is As a feedback signal, it is provided to the second input of the first amplifier A1. The output of the first amplifier A1 is connected to the gate of the second transistor M2 of the replica unit 610 and the gate of the first transistor M1 of the output unit 620. The drain of the second transistor M2 is connected to the drain of the third transistor M3 and one end of the third resistor, and the gate of the third transistor M3 is connected to the output of the second amplifier. The non-inverting input of the second amplifier A2 is connected to the other end of the third resistor R3 and one end of the fourth resistor R4. In addition, the inverting input of the second amplifier A2 is connected to the node N3 between the first resistor R1 and the second resistor R2 connected in series in the output unit.

In the circuit of FIG. 6, the third transistor is represented as an N-type metal oxide semiconductor (MOS) transistor, but may be implemented as a P-type MOS transistor. In this case, the polarity of the input terminal of the second amplifier A2 is shown in FIG. This is the opposite of that shown in the circuit of 6.

The operation of the low voltage drop regulator circuit shown in FIG. 6 having such a configuration will be described.

When a change occurs in an external circuit connected to the low voltage drop regulator and the output current flowing toward the output terminal increases, the output voltage Vout drops and thus the voltage at node 3 N3 also decreases. Since node 3 is connected to the inverting input terminal of the second amplifier A2, the output voltage of the second amplifier A2 increases. Accordingly, the current flowing through the third transistor M3 increases and the voltage Vx at the node N2 and the voltage at the node N1 decrease. Since the voltage at the node N1 is provided to the non-inverting input terminal of the first amplifier A1, the output voltage of the first amplifier A1 decreases, so that the current flowing through the first transistor M1 of the output unit 620 is The output voltage Vout is increased to increase. Here, it can be seen that the third transistor M3 is used as a voltage controlled current source.

In the circuit according to the second embodiment of the present invention, too, the change in the output voltage is reflected in the voltage at the node 1 (N1) as it is, and the feedback gain of the beta circuit is kept constant, resulting in a drop in output due to an increase in the output current. It can be seen that the voltage is compensated by the replica unit.

The low voltage drop regulator according to the present invention shown in FIGS. 5 and 6 is a circuit implemented by adding one operational amplifier and one transistor, and can operate as a stable voltage source having low power consumption with almost no additional current consumption. have.

Although the P-type MOS transistors are used for the first and second transistors of the circuits shown in FIGS. 5 and 6, it should be understood that the N-type MOS transistors may be used and the circuit can be changed accordingly.

In addition, although the MOS transistor is used in each of the circuits of FIGS. 5 and 6, the present invention is not limited thereto. The same function as that of the embodiment of the present invention, such as a bipolar junction transistor (BJT) and a complementary metal-oxide semiconductor (CMOS), is performed. The low voltage drop regulator according to the present invention may form part of an integrated circuit, and may be used to supply stable power by receiving power from a battery in a portable electronic device or the like. It may be used to stably drive a light emitting diode in an image processing apparatus.

7 is a graph illustrating the loop gain of the low voltage drop regulator according to the change of the capacitive load driven by the low voltage drop regulator circuit using the replica according to the present invention.

The horizontal axis of the graph shown in FIG. 7 is frequency (Hz), and the vertical axis represents loop gain (dB). Referring to the graph of FIG. 7, it can be seen that in the lower frequency, the loop gain remains one regardless of the capacitive load, but the loop gain also has various values from the point beyond 10 MHz according to the change of the capacitive load. have. More specifically, the frequency value at the point where the 0 dB gain, which is the basis for determining stability, meets the graph is between 1 MHz and 10 MHz, more precisely near 5 MHz, and the point where the loop gain begins to change is a much higher frequency. This is where you have it. In other words, it can be seen that the loop gain change due to the capacitive load of the regulator according to the present invention appears at a frequency much larger than the unit gain frequency. Accordingly, it can be seen from the graph of FIG. 7 that the low voltage drop regulator circuit according to the present invention can ensure stability regardless of the capacitive load it drives.

8 is a graph showing output current vs. output voltage of a low voltage drop regulator circuit using a replica according to the present invention.

8, the horizontal axis represents output current and the vertical axis represents output voltage. 8 shows that the output voltage is maintained at about 3.3V even when the output current changes. That is, in the low voltage drop regulator circuit using the replica according to the present invention, it can be confirmed that the change of the output voltage according to the output current hardly occurs.

As shown in Figures 7 and 8, according to the low voltage drop regulator circuit using the replica of the present invention, regardless of the capacitive load to be driven, it is possible to stably supply the voltage regardless of the output current.

1 is a circuit diagram of a low voltage drop regulator using a conventional replica load.

2 is a low voltage drop regulator circuit diagram using a replica load to which a conventional discontinuous mode compensation technique is applied.

3 is a circuit diagram of a voltage drop regulator using a replica load to which a conventional continuous mode compensation technique is applied.

4 is a block diagram of a feedback loop circuit applied to the present invention.

5 is a circuit diagram of a low voltage drop regulator using a replica according to a first embodiment of the present invention.

6 is a circuit diagram of a low voltage drop regulator using a replica according to a second embodiment of the present invention.

7 is a graph illustrating a loop gain of a low voltage drop regulator according to a change in a capacitive load driven by a low voltage drop regulator circuit using a replica according to the present invention.

8 is a graph showing output current vs. output voltage of a low voltage drop regulator circuit using a replica according to the present invention.

Claims (17)

A first amplifier receiving a reference voltage as a first input and amplifying and outputting a difference between the first input and a second input; An output unit including a first transistor, a first resistor element, and a second resistor element, the output unit being connected to an output of the first amplifier to provide an output voltage to a load; And A replica connected to an output of the first amplifier and providing a feedback voltage to the second input of the first amplifier, The replica unit, A second transistor having a gate connected to an output of the first amplifier; A second amplifier having one input terminal connected to the output voltage and adjusting its output to reflect a change in the output voltage; A third resistance element connected to the other input terminal of the second amplifier; A fourth resistance element connected in series with the third resistance element; And A compensation element connected to the output of the second amplifier and changing according to the output of the second amplifier, the compensation element being connected to the other end of the third resistance element, Supply a voltage as a feedback voltage to a second input of the first amplifier, The feedback drop of the circuit consisting of the first amplifier and the replica unit is maintained at a constant value irrespective of the output voltage of the output unit, low voltage drop regulator. The method of claim 1, The output unit, A first transistor; A first resistor element connected in series with the source or drain of the first transistor; And A second resistance element connected in series with the first resistance element, And a gate of the first transistor is connected to an output terminal of the first amplifier. delete delete The method of claim 1, The compensating element is a low voltage drop regulator, characterized in that the transistor. The method of claim 5, And the compensating element is a MOS transistor. The method of claim 6, A source or drain terminal of the compensation element is connected to a source or drain terminal of the second transistor, a gate of the compensation element is connected to an output of the second amplifier, And the remaining source or drain terminal of the compensation element is connected to one end of the third resistance element. The method of claim 7, wherein And a node to which the third resistance element and the fourth resistance element are connected is connected to a second input of the first amplifier. A first amplifier receiving a reference voltage as a first input and amplifying and outputting a difference between the first input and a second input; An output unit including a first transistor, a first resistor element, and a second resistor element, the output unit being connected to an output of the first amplifier to provide an output voltage to a load; And A replica connected to an output of the first amplifier and providing a feedback voltage to the second input of the first amplifier, The replica unit, A second transistor having a gate connected to an output of the first amplifier; A third resistance element connected to one end of the second transistor; A fourth resistance element connected in series with the third resistance element; A second input having a first input connected with the node between the third resistor element and the fourth resistor element, and a second input connected with the output voltage, and adjusting the output to reflect the change of the output voltage; amplifier; And It has a gate terminal connected to the output terminal of the second amplifier and provides a current value that changes according to the output voltage of the second amplifier, and has one end connected to a node to which the third and fourth resistance elements are connected. Including a current providing element, supplying a voltage that changes according to the change in the current value provided by the current providing element as a feedback voltage to the second input of the first amplifier, The feedback drop of the circuit consisting of the first amplifier and the replica unit is maintained at a constant value irrespective of the output voltage of the output unit. delete 10. The method of claim 9, And a first input terminal of the second amplifier is connected to a second input of the first amplifier. 10. The method of claim 9, And said current providing element is a transistor. The method of claim 12, Wherein said current providing element is a MOS transistor. The method of claim 13, The source or drain terminal of the current providing element, characterized in that connected to the source or drain terminal of the second transistor, low voltage drop regulator. An integrated circuit comprising the low voltage drop regulator according to any one of claims 1, 2, 5-9, and 11-14. A portable terminal comprising the low voltage drop regulator according to any one of claims 1, 2, 5 to 9, and 11 to 14. An image processing apparatus comprising the low voltage drop regulator according to any one of claims 1, 2, 5 to 9, and 11 to 14.

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