Linear voltage stabilizer and configuration method thereof

Abstract

The invention discloses a linear voltage stabilizer and a configuration method thereof. The linear voltage stabilizing device comprises a digital-to-analog converter, an operational amplifier, a switcher and a resistor. The digital-to-analog converter provides a controlled current according to the control signal. The inverting input end of the operational amplifier is coupled to the digital-to-analog converter. The output end of the operational amplifier is the output end of the linear voltage stabilizing device. The input end of the switcher receives a plurality of reference voltages. The control end of the switcher receives a control signal. The output end of the switcher is coupled with the non-inverting input end of the operational amplifier. The resistor is coupled between the output end and the inverting input end of the operational amplifier. The current reversal point of the linear voltage regulator is determined by one of a plurality of reference voltages corresponding to the control signal and the controlled current.

Description

Technical Field

[0001] The present invention relates to a corresponding technology of a low voltage difference regulator, and in particular to a linear voltage stabilizing device and a configuration method thereof. Background Art

[0002] Low-dropout regulator (LDO) can provide a stable DC voltage and is often used in technologies such as battery management and device wake-up. LDO can be implemented in a variety of forms. Transimpedance LDO uses current adjustment as the output voltage adjustment. In applications where the output voltage needs to be changed, the output needs to be adjusted accurately to have a higher resolution. In addition, when adjusting the current of the transimpedance LDO, special attention should be paid to issues such as linearity and output offset. Summary of the invention

[0003] The present invention provides a linear voltage regulator and a configuration method thereof, which controls the current reversal point of the linear voltage regulator by adjusting the fixed current value in a digital-to-analog converter and selecting the reference voltage of an operational amplifier, so as to simplify the circuit area of ​​the linear voltage regulator while meeting the system application.

[0004] The linear voltage regulator of the present invention comprises: a digital-to-analog converter, which provides a controlled current according to a control signal; an operational amplifier, whose inverting input terminal is coupled to the digital-to-analog converter, and whose output terminal is the output terminal of the linear voltage regulator; a switch, whose input terminal receives a plurality of reference voltages, whose control terminal receives the control signal, and whose output terminal is coupled to the non-inverting input terminal of the operational amplifier; and a resistor, which is coupled between the output terminal and the inverting input terminal of the operational amplifier, wherein the current reversal point of the linear voltage regulator is determined by one of the plurality of reference voltages corresponding to the control signal and the controlled current.

[0005] The configuration method of the linear voltage regulator device of the present invention includes the following steps: setting multiple reference voltages and multiple current values ​​according to multiple current reversal points in the linear voltage regulator device; and enabling a digital-to-analog converter in the linear voltage regulator device to provide a controlled current to an inverting input terminal of an operational amplifier in the linear voltage regulator device according to a control signal, wherein the controlled current corresponds to one of the multiple current values, and selectively coupling one of the multiple reference voltages to a non-inverting input terminal of the operational amplifier according to the control signal, wherein the linear voltage regulator device further includes a resistor coupled between an output terminal and the inverting input terminal of the operational amplifier, wherein the current reversal point of the linear voltage regulator device is determined by one of the multiple reference voltages corresponding to the control signal and the controlled current.

[0006] Based on the above, the linear voltage regulator and its configuration method described in the embodiment of the present invention are based on the perspective of system application, by adjusting the fixed current value in the digital-to-analog converter and selecting the reference voltage of the operational amplifier, to correspondingly control the current reversal point of the linear voltage regulator, so that these relationship points between the input signal and the output voltage in the linear voltage regulator can perform accurate linear voltage conversion. When the number of the aforementioned relationship points is small, the function of the linear voltage regulator can not only meet the system application, but also simplify the circuit area of ​​the linear voltage regulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a block diagram of a linear voltage regulator device according to an embodiment of the present invention;

[0008] Figure 2 is a flow chart of a configuration method of a linear voltage regulator device according to an embodiment of the present invention;

[0009] Figure 3A and Figure 3B is a schematic diagram of a linear voltage stabilizing device when the reference voltage is 1.0V in one embodiment of the present invention;

[0010] Figure 4A and Figure 4B is a schematic diagram of a linear voltage stabilizing device when the reference voltage is 2.0V in one embodiment of the present invention;

[0011] Figure 5 is a circuit diagram of a digital-to-analog converter in one embodiment of the present invention. DETAILED DESCRIPTION

[0012] The embodiment of the present invention designs a low dropout regulator (LDO) from the perspective of system application. In different system applications, it may not be necessary for the LDO to have a very accurate linear relationship between all input signals and output voltages, but it is only necessary to perform accurate linear voltage conversion at a few specific relationship points between the input signal and the output voltage. Therefore, the embodiment of the present invention first determines the multiple relationship points at which the LDO needs to accurately perform linear voltage conversion from the perspective of system application, and designs the LDO based on these multiple relationship points. When the number of the aforementioned relationship points is small, the LDO function can be made to meet the system application while simplifying the circuit area of ​​the LDO, and the linearity and output drift of the LDO at the aforementioned relationship points can be effectively improved. The following is a detailed description of each embodiment consistent with the present invention.

[0013] Reference Figure 1, the linear voltage regulator 100 of this embodiment can be a circuit structure such as a low dropout regulator (LDO), a linear voltage regulator, etc. The linear voltage regulator 100 includes a digital-to-analog converter (DAC) 110, an operational amplifier (OPAMP) 120, a switch 140, and a resistor Res. The linear voltage regulator 100 may also include a plurality of reference voltage generators, and here two reference voltage generators 130-1 and 130-2 are taken as examples. The reference voltages Vref1 and Vref2 in this embodiment are constant under different temperatures and power supply voltages. In this embodiment, a bandgap reference voltage generator is used to implement the reference voltage generators 130-1 and 130-2. The switch 140 can be implemented using a multiplexer.

[0014] In general specifications, the power supply voltages in flash memory are more commonly 3.3 volts (V) and 1.8V. If the voltage changes under different temperatures are taken into account, the voltage operating range of the 3.3V power supply voltage is approximately between 2.5V and 3.8V; the voltage operating range of the 1.8V power supply voltage is approximately between 1.65V and 1.95V. The embodiment of the present invention uses a reference voltage generator to generate reference voltages Vref1 and Vref2, so that the reference voltages Vref1 and Vref2 are constant within the power supply voltage operating range, so as to minimize the influence of different temperatures and environments.

[0015] The DAC 110 provides a controlled current Ic according to the control signal CS. The DAC 110 of the present embodiment can be implemented by a variety of circuit structures, such as a voltage output type current source, a current output type current source, a binary weighted resistance type current source (referred to as a binary current source), or a thermometer type current source. The embodiment of the present invention implements the DAC 110 with a circuit structure of a binary current source. The DAC 110 also receives a current control signal SCI so that the DAC 110 generates a corresponding current as the controlled current Ic.

[0016] The inverting input terminal Vin- of the operational amplifier 120 is coupled to the DAC 110. The output terminal OUT of the operational amplifier 120 is also the output terminal of the linear voltage regulator 100. The input terminal of the switch 140 receives a plurality of reference voltages (here, two reference voltages Vref1 and Vref2 are taken as an example). The control terminal of the switch 140 receives the control signal CS. The output terminal of the switch 140 is coupled to the non-inverting input terminal Vin+ of the operational amplifier 120. The resistor Res is coupled between the output terminal OUT and the inverting input terminal Vin- of the operational amplifier 120. When the operational amplifier 120 is in operation, the inverting input terminal Vin- and the non-inverting input terminal Vin+ are virtual short circuits.

[0017] Please refer to Figure 1From the perspective of system application, the linear voltage regulator 100 does not need to make the relationship points between each input signal (e.g., current control signal SCI) and output voltage (e.g., voltage at output terminal OUT) very accurate, as long as multiple relationship points with specific applications can accurately perform voltage conversion. It is assumed here that the number of the aforementioned relationship points is N, and N is a positive integer greater than 1. The configuration method for the linear voltage regulator 100 proposed in the embodiment of the present invention can also be called "N-point alignment method". Refer to Figure 2 , Figure 2 can be Figure 1 The circuit structure is realized. Figure 1 The number of relationship points in is 2 (ie, N is equal to 2). Figure 1 The reference current Iref is used to drive the DAC 110 and the operational amplifier 120 to make them operate normally. In this embodiment, the value of the reference current Iref may be 4 μA.

[0018] Please refer to Figure 1 and Figure 2 In step S210, since the number of relation points is N, the embodiment of the present invention uses the N relation points as the corresponding N current reversal points in the linear voltage regulator 100, and sets a plurality of reference voltages (e.g., N reference voltages) and a plurality of current values ​​(e.g., N current values) according to the plurality of current reversal points (e.g., N current reversal points) in the linear voltage regulator 100. Each relation point is a corresponding current reversal point in the linear voltage regulator 100, and each relation point corresponds to 1 reference voltage and 1 current value. In this embodiment, the N relation points for accurate linear voltage conversion are equal to the corresponding reference voltage values.

[0019] The "N current values" are calculated by the voltage values ​​of the aforementioned N reference voltages, the circuit structure of the operational amplifier 120 and the resistor Res. The purpose of designing the aforementioned "N current values" is to hope that the voltage output range corresponding to the output voltage at the output terminal OUT of the linear voltage regulator 100 and the multiple steps in the output voltage will not be changed by the aforementioned reference voltage being selected by the control signal CS, which will be described later. The embodiment of the present invention also provides a circuit structure of a DAC 110, so that the current value provided by the DAC 110 will be adjusted according to the aforementioned "N current values".

[0020] When the linear voltage regulator 100 is desired to output one of the aforementioned N relationship points, a current source corresponding to a current value corresponding to each of the aforementioned relationship points (the current source is provided by the DAC 110) can be provided to the operational amplifier 120 through the switching signal CS. On the other hand, when the linear voltage regulator 100 is desired to output one of the aforementioned N relationship points, a reference voltage (e.g., one of the reference voltages Vref1 and Vref2) corresponding to the aforementioned N relationship points can be provided to the operational amplifier 120 through the switching signal CS through the switch 140, so that the overall system of the linear voltage regulator 100 can accurately perform linear voltage conversion at one of the selected N relationship points, and so on. That is to say, in step S220, the linear voltage regulator device 100 can enable the DAC 110 in the linear voltage regulator device 100 to provide a controlled current Ic to the inverting input terminal Vin- of the operational amplifier 120 in the linear voltage regulator device 100 according to the control signal CS, wherein the controlled current Ic corresponds to one of the aforementioned multiple current values, and the linear voltage regulator device 100 selectively couples one of the aforementioned multiple reference voltages to the non-inverting input terminal Vin+ of the operational amplifier 120 according to the control signal CS.

[0021] Therefore, when Figure 1 When the reference voltage of the linear voltage regulator 100 is changed by adjusting the control signal CS, as long as the corresponding current value of the DAC 110 is properly designed, the voltage output range corresponding to the output voltage at the output terminal OUT and the multiple steps in the output voltage can be made similar to the situation before the reference voltage is changed. Figure 1 The linear voltage regulator 100 may not be affected by the voltage output range and the output voltage step in the output voltage changing based on the selection of a plurality of reference voltages.

[0022] For example, if the linear voltage regulator device 100 is applied to a non-volatile memory (NVM), two voltage values ​​in the NVM (e.g., a read voltage and a verify voltage) are the relationship points that need to be accurately converted to voltage, that is, the aforementioned N is equal to 2. This embodiment assumes that the read voltage of the NVM is 1.0V and the verify voltage is 2.0V. Therefore, the embodiment of the present invention selectively sets two reference voltages and two current values ​​according to two current reversal points in the linear voltage regulator device 100.

[0023] Reference Figure 3A , Figure 3AThe first current reversal point (the first relationship point between the input signal and the output voltage) is 1.0V. When the voltage output range corresponding to the output voltage of the output terminal OUT falls between 0.05V and 1.00V (that is, when the output voltage of the output terminal OUT is less than the selected reference voltage 1.0V), the controlled current Ic will flow from the DAC 110 to the output terminal OUT.

[0024] In detail, assuming that the resistance value of the resistor Res is 396.4 kΩ and the minimum step current of the linear voltage regulator 100 is 0.125 μA, the voltage difference of each step is approximately 50 mV (approximately 396.4 kΩ multiplied by 0.125 μA), and the switch 140 is controlled by the control signal CS to couple the reference voltage Vref1 (whose voltage value is 1.0 V) to the non-inverting input terminal Vin+ of the operational amplifier 120. In this way, the starting value Vstrt1 of the voltage output range in the output voltage can be calculated based on the above information, as shown in the following equation (1). It can be clearly seen from equation (1) that the starting value Vstrt1 is approximately 0.05 V. In equation (1), "2.5 μ-0.125 μ" is the controlled current Ic provided by the DAC 110.

[0025] Vstrt1=1.0-(396.4k×(2.5μ-0.125μ))=0.05855V…(1)

[0026] Reference Figure 3B , Figure 3B It also presents that the first current reversal point (the first relationship point between the input signal and the output voltage) is 1.0V, and when the voltage output range corresponding to the output voltage of the output terminal OUT falls between 1.00V and 6.30V (that is, when the output voltage of the output terminal OUT is greater than the selected reference voltage 1.0V), the controlled current Ic will flow from the output terminal OUT to the DAC 110. In detail, as in the above assumption, the end value Vend1 of the voltage output range in the output voltage can be calculated from the above information, see the following equation (2). It can be clearly seen from equation (2) that the end value Vend1 is approximately 6.30V. In equation (2), "15.875μ-2.5μ" is the controlled current Ic provided by the DAC 110.

[0027] Vend1=1.0+(396.4k×(15.875μ-2.5μ))=6.30185V…(2)

[0028] from Figure 3A and Figure 3BIt can be seen that when the output voltage of the output terminal OUT is close to the reference voltage Vref1 (1.0V), its voltage conversion will be close to accuracy, and the direction of the controlled current will be reversed. The starting value Vstrt1 and the ending value Vend1 of the voltage output range in the output voltage are 0.05V and 6.30V respectively.

[0029] Reference Figure 4A , Figure 4A When the second current reversal point (the second relationship point between the input signal and the output voltage) is 2.0V and the voltage output range corresponding to the output voltage of the output terminal OUT falls between 0.05V and 2.00V (that is, when the output voltage of the output terminal OUT is less than the selected reference voltage 2.0V), the controlled current Ic flows from the DAC 110 to the output terminal OUT.

[0030] In detail, as previously assumed, the voltage difference of each step is approximately 50 mV (approximately 396.4 kΩ multiplied by 0.125 μA), and the starting value Vstrt2 of the voltage output range in the output voltage can be calculated from the aforementioned information, as shown in the following equation (3). It can be clearly seen from equation (3) that the starting value Vstrt2 is approximately 0.05 V. In equation (3), "5.0 μ-0.125 μ" is the controlled current Ic provided by the DAC 110.

[0031] Vstrt2=2.0-(396.4k×(5.0μ-0.125μ))=0.06755V…(3)

[0032] Reference Figure 4B , Figure 4B It also presents that the second current reversal point (the second relationship point between the input signal and the output voltage) is 2.0V, and when the voltage output range corresponding to the output voltage of the output terminal OUT falls between 2.00V and 6.30V (that is, when the output voltage of the output terminal OUT is greater than the selected reference voltage 2.0V), the controlled current Ic will flow from the output terminal OUT to the DAC 110. In detail, as in the above assumption, the end value Vend2 of the voltage output range in the output voltage can be calculated from the above information, see the following equation (4). It can be clearly seen from equation (4) that the end value Vend2 is approximately 6.30V. In equation (4), "15.875μ-5.0μ" is the controlled current Ic provided by the DAC 110.

[0033] Vend2=2.0+(396.4k×(15.875μ-5.0μ))=6.30185V…(2)

[0034] from Figure 4A and Figure 4BIt can be seen that when the output voltage of the output terminal OUT is close to the reference voltage Vref2 (2.0V), its voltage conversion will be close to accuracy, and the direction of the controlled current will be reversed. The starting value Vstrt2 and the ending value Vend2 of the voltage output range in the output voltage are 0.05V and 6.30V respectively, which is consistent with the above Figure 3A and Figure 3B The starting value Vstrt1 of the corresponding voltage output range is similar to the ending value Vend1. Figure 1 Even if the reference voltage of the linear regulator 100 is changed or switched to Vref1 or Vref2, the voltage output range (0.05V to 6.30V) corresponding to the output voltage at the output terminal OUT and the multiple steps of the output voltage (the voltage difference of each step is about 50mV) will not change.

[0035] Figure 5 1 is a circuit diagram of a digital-to-analog converter 110 in an embodiment of the present invention. The present invention provides a circuit structure of a DAC 110, so that the current value provided by the DAC 110 is adjusted according to the aforementioned “N current values”. Figure 5 The DAC 110 includes a plurality of controlled current sources 510 , a first fixed current source 520 , and a second fixed current source 530 . Figure 5 The DAC 110 further includes a reference current source 540 and a current mirror circuit 550 .

[0036] The controlled current source 510 includes a plurality of transistors N0 to N6 as switches and transistors MB0 to MB6 as current sources. The control terminals of the transistors N0 to N6 receive signals SCI0 to SCI6 in the current control signal SCI to selectively direct the current generated by the corresponding transistors MB0 to MB6 to the output terminal DACout of the DAC 110 .

[0037] The first fixed current source 520 includes a transistor MS1, and the current mirror circuit 550 includes transistors P0 and P1. The first fixed current source 520 and the current mirror circuit 550 are used to provide a first fixed current to the output terminal DACout of the DAC 110. The second fixed current source 530 includes a transistor MS2 and a switch NCS. The control terminal of the switch NCS receives a control signal CS. Therefore, the second fixed current source 530 is controlled by the control signal CS to selectively generate a second fixed current. The current mirror circuit 550 acts as a sink and a source of the control current.

[0038] The reference current source 540 receives the reference current Iref to drive the entire DAC 110. The reference current source 540 includes a transistor Mref. The reference current source 540, the controlled current source 510, the first fixed current source 520, and the second fixed current source 530 form a current mirror circuit, and the size of the transistor Mref and the transistors MB0 to MB6, MS1, and MS2 have a specific ratio to each other, so that the transistors MB0 to MB6, MS1, and MS2 can provide current values ​​of different sizes. For example, in this embodiment, the size ratio of the transistor Mref and the transistors MB0 to MB6, MS1, and MS2 is shown in the following equation (5).

[0039]

[0040] Therefore, when the current value of the reference current Iref is 4μA, the current values ​​that can be provided by transistors MB0 to MB6, MS1, and MS2 are 0.125μA, 0.25μA, 0.5μA, 1.0μA, 2.0μA, 4.0μA, 8.0μA, 2.5μA, and 2.5μA, respectively.

[0041] Therefore, when the control signal CS is disabled, it means Figure 1 The linear voltage regulator 100 uses the reference voltage Vref1 (1.0V) as the current reversal point. At this time, the second fixed current source 530 does not provide the second fixed current, and the controlled current Ic provided by the output terminal DACout of the DAC 110 is determined by the multiple sub-currents provided by the controlled current source 510 and the first fixed current provided by the first fixed current source 520. That is, the controlled current Ic at this time is the sum of these sub-currents and the first fixed current. In other words, when the control signal CS is disabled, the second fixed current provided by the second fixed current source 530 is not needed.

[0042] When the control signal CS is enabled, it indicates Figure 1 The linear voltage regulator 100 uses the reference voltage Vref2 (2.0V) as the current reversal point. At this time, the second fixed current source 530 provides a second fixed current, and the controlled current Ic provided by the output terminal DACout of the DAC 110 is determined by the sub-currents provided by the controlled current source 510, the first fixed current provided by the first fixed current source 520, and the second fixed current provided by the second fixed current source 530. That is, the controlled current Ic at this time is the sum of these sub-currents, the first fixed current, and the second fixed current. In other words, when the control signal CS is enabled, the fixed current of the DAC 110 increases from the original 2.5μA (first fixed current) to 5.0μA (the sum of the first fixed current and the first fixed current).

[0043] because Figure 5The DAC 110 is used in Figure 1 In this embodiment, N is equal to 2, so the number of the second fixed current sources is 1. If the number of reference voltages in this embodiment is N, an additional second fixed current source is provided in the DAC 110, and the number of the second fixed current sources is (N-1).

[0044] In summary, the linear voltage regulator and its configuration method described in the embodiment of the present invention are based on the perspective of system application, by adjusting the fixed current value in the digital-to-analog converter and selecting the reference voltage of the operational amplifier to correspondingly control the current reversal point of the linear voltage regulator, so that these relationship points between the input signal and the output voltage in the linear voltage regulator can perform accurate linear voltage conversion. When the number of the aforementioned relationship points is small, the function of the linear voltage regulator can not only meet the system application, but also simplify the circuit area of ​​the linear voltage regulator.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A linear voltage stabilizing device, characterized in that: include: A digital-to-analog converter provides a controlled current according to a control signal; An operational amplifier, whose inverting input terminal is coupled to the digital-to-analog converter, and whose output terminal is the output terminal of the linear voltage regulator; A switch, whose input terminal receives a plurality of reference voltages, whose control terminal receives the control signal, and whose output terminal is coupled to the non-inverting input terminal of the operational amplifier; as well as a resistor coupled between the output terminal and the inverting input terminal of the operational amplifier, Wherein, the current reversal point of the linear voltage regulator is determined by one of the reference voltages corresponding to the control signal and the controlled current.

2. The linear voltage regulator according to claim 1, characterized in that: The digital-to-analog converter comprises: A plurality of controlled current sources, controlled by a current control signal to generate a plurality of sub-currents; A first fixed current source generates a first fixed current; and at least one second fixed current source, controlled by the control signal to selectively generate a second fixed current, When the control signal is disabled, the controlled current is determined by the sub-current and the first fixed current. When the control signal is enabled, the controlled current is determined by the sub-current, the first fixed current, and the second fixed current.

3. The linear voltage regulator according to claim 2, characterized in that: The digital-to-analog converter further comprises: Reference current source, The reference current source, the plurality of controlled current sources, the first fixed current source and the at least one second fixed current source form a current mirror circuit.

4. The linear voltage regulator according to claim 2, characterized in that: The number of the multiple reference voltages is N, the number of the at least one second fixed current source is N-1, and N is a positive integer greater than 1.

5. The linear voltage regulator according to claim 1, characterized in that: When the operational amplifier is operating, the inverting input terminal and the non-inverting input terminal of the operational amplifier are virtually short-circuited.

6. The linear voltage regulator according to claim 1, characterized in that: The current reversal point of the linear voltage regulator is a selected reference voltage selected by the control signal from the plurality of reference voltages, When the output voltage of the output terminal is greater than the selected reference voltage, the controlled current flows from the output terminal to the inverting input terminal of the operational amplifier. When the output voltage of the output terminal is less than the selected reference voltage, the controlled current flows from the inverting input terminal of the operational amplifier to the output terminal.

7. The linear voltage regulator according to claim 1, characterized in that: The voltage output range corresponding to the output voltage in the output terminal and the plurality of steps in the output voltage are not changed by the selection of the plurality of reference voltages by the control signal.

8. A method for configuring a linear voltage regulator, characterized in that: include: Setting multiple reference voltages and multiple current values ​​according to multiple current reversal points in the linear voltage regulator; as well as According to a control signal, a digital-to-analog converter in the linear voltage regulator device provides a controlled current to an inverting input terminal of an operational amplifier in the linear voltage regulator device, wherein the controlled current corresponds to one of the plurality of current values, and, according to the control signal, one of the plurality of reference voltages is selectively coupled to a non-inverting input terminal of the operational amplifier, wherein the linear voltage regulator device further comprises a resistor coupled between an output terminal of the operational amplifier and the inverting input terminal, The current reversal point of the linear voltage regulator is determined by one of the reference voltages corresponding to the control signal and the controlled current.

9. The configuration method according to claim 8, characterized in that: The digital-to-analog converter comprises: A plurality of controlled current sources, controlled by a current control signal to generate a plurality of sub-currents; A first fixed current source generates a first fixed current; and at least one second fixed current source, controlled by the control signal to selectively generate a second fixed current, When the control signal is disabled, the controlled current is determined by the sub-current and the first fixed current. When the control signal is enabled, the controlled current is determined by the sub-current, the first fixed current, and the second fixed current.

10. The configuration method according to claim 8, characterized in that: The current reversal point of the linear voltage regulator is a selected reference voltage selected by the control signal from the plurality of reference voltages, When the output voltage of the output terminal is greater than the selected reference voltage, the controlled current flows from the output terminal to the digital-to-analog converter. When the output voltage of the output terminal is less than the selected reference voltage, the controlled current flows from the digital-to-analog converter to the output terminal.

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