JP5993263B2 - Operational amplifier - Google Patents

Description

  The present invention relates to an operational amplifier, and more particularly to an operational amplifier that improves the sink current capability of an operational amplifier capable of rail-to-rail operation.

As an operational amplifier configured by a bipolar transistor and capable of rail-to-rail output, for example, there is one proposed in Patent Document 1 or the like.
FIG. 5 shows a conventional circuit example simplified for easy understanding of the circuit configuration example disclosed in Patent Document 1. Hereinafter, the conventional circuit will be described with reference to FIG. .
This operational amplifier is roughly divided into a voltage amplifier A1, a pre-driver transistor Q1, a push-pull output stage 102A, and an idling current supply circuit 104A.

In such a configuration, when a differential voltage signal is input between the input terminals + IN and -IN of the voltage amplifier A1, the amplified voltage output is applied to the base of the pre-driver transistor Q1, and is converted into a current at the emitter. Output as a current signal.
This current signal drives the push-pull output stage 102A constituted by the transistors Q2 and Q3.
The idling current of the push-pull output stage 102A is supplied by the idling current supply circuit 104A. The idling current supply circuit 104A is composed of fourth and fifth transistors Q4 and Q5, two constant current sources I1 and I2, and two constant voltage sources Vb1 and Vb2.

Japanese Patent Publication No. 6-91379 (page 3-4, FIGS. 1 to 3)

  By the way, in the above-described conventional circuit, when a large voltage difference is generated between two inputs of the voltage amplifier A1 and the output potential of the voltage amplifier A1 is extremely lowered, a large source current is caused to flow by the Darlington configuration including the transistors Q1 and Q2. However, in the case of a sink current, it is difficult to obtain a large current like a source current.

The source current capability in the conventional circuit will be described below.
First, when a large voltage difference occurs between the two inputs of the voltage amplifier A1, and the output potential of the voltage amplifier A1 rises extremely, the transistor Q1 is turned off.
Correspondingly, all the current of the current source I1 is supplied to the base of the transistor Q3 and the current source I2 via the transistors Q4 and Q5. This state is a condition in which the current supplied to the base of the transistor Q3 is maximized and the collector current of the transistor Q3 is maximized, that is, the sink current of the operational amplifier is maximized.
Therefore, the sink current capability ISink is expressed by the following equation 1.

  Isink≈βQ3 × (I1-I2) Equation 1

Here, βQ3 is the current amplification factor of the transistor Q3, I1 is the current value of the current source I1, and I2 is the current value of the current source I2.
As represented by Equation 1, in the configuration shown in FIG. 5 previously, the sink current capability is determined by the process constant β and the current values of the current sources I1 and I2.

Therefore, in the configuration shown in FIG. 5, in order to improve the sink current capability, it is necessary to increase the current value I1.
For example, if 10 mA is required as the sink current capability, assuming that the value of βQ3 is 100, I1 needs to be 100 μA or more.
As described above, the conventional circuit shown in FIG. 5 has a problem that a high sink current capability cannot be obtained when specifications are made with a low current consumption.

  The present invention has been made in view of the above circumstances, and an operational amplifier capable of securing a high sink current capability while maintaining a rail-to-rail operation and a high source current capability even under a low current consumption. Is to provide.

In order to achieve the above object of the present invention, an operational amplifier according to the present invention comprises:
A differential amplifier circuit for performing differential amplification on an input signal; a pre-driver circuit for converting the output of the differential amplifier circuit into a voltage / current; and an output stage driven by the output of the pre-driver circuit; Comprising
The output stage includes a PNP-type first output stage transistor and an NPN-type second output stage transistor, and is provided so that a sink current flows into the second output stage transistor. An amplifier,
A sink current auxiliary circuit configured to monitor an operating state of a pre-driver transistor constituting the pre-driver circuit and to control current supply to the base of the second output stage transistor according to the monitoring result Is provided ,
The sink current auxiliary circuit is a PNP type, and includes a current detection circuit for detecting a current of the pre-driver transistor having an emitter connected to a base of the first output transistor, and the pre-driver using the current detection circuit. If the collector current of the pre-driver transistor is detected while the base current of the second output stage transistor is suppressed to a certain level or less, the collector current of the pre-driver transistor is detected. And a current auxiliary circuit configured to be able to supply the current to the base current of the second output stage transistor,
The current detection circuit includes a PNP-type current detection circuit transistor and a current detection circuit constant current source, and a base of the current detection circuit transistor is connected to a base of the pre-driver transistor and is connected to a collector. The second power supply voltage can be applied, while the emitter of the current detection circuit transistor is connected to one terminal of the current detection circuit constant current source, and the other of the current detection circuit constant current source is connected. The terminal is configured to be able to apply the first power supply voltage,
The current auxiliary circuit includes an NPN-type first current auxiliary circuit transistor, a PNP-type second current auxiliary circuit transistor, and a current auxiliary circuit bias constant voltage source. The base of the current auxiliary circuit transistor is connected to the emitter of the current detection circuit transistor, and a first power supply voltage can be applied to the collector, while the emitter of the first current auxiliary circuit transistor is Connected to the emitter of the second current auxiliary circuit transistor, the collector of the second current auxiliary circuit transistor is connected to the base of the second output stage transistor, while for the second current auxiliary circuit The base of the transistor is connected to the negative side of the current auxiliary circuit bias constant voltage source and to the positive side of the current auxiliary circuit bias constant voltage source In which the first power supply voltage, which are configured to be applied.

  According to the present invention, since the base current of the transistor constituting the push-pull stage in which the sink current flows according to the operation state of the circuit can be significantly increased by the sink current auxiliary circuit as compared with the conventional case, low power consumption is achieved. The effect is that a high sink current capability can be maintained even under a current.

It is a circuit diagram which shows the example of a basic circuit structure of the operational amplifier in embodiment of this invention. FIG. 2 is a circuit diagram showing a specific circuit configuration example of a sink current auxiliary circuit in the basic circuit configuration example shown in FIG. 1. FIG. 3 is a circuit diagram showing a more specific circuit configuration example in the circuit configuration example shown in FIG. 2. It is a characteristic diagram which shows the simulation result of the relationship between the sink current of the operational amplifier and the output terminal voltage in the embodiment of the present invention. It is a circuit diagram of a conventional circuit.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.
The members and arrangements described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
First, an example of a basic circuit configuration of an operational amplifier according to an embodiment of the present invention will be described with reference to FIG.
This operational amplifier includes a voltage amplifier (noted as “A1” in FIG. 1) 20 as a differential amplifier circuit, a pre-driver circuit 101, a push-pull output stage 102, a sink current auxiliary circuit 103, and an idling current supply. The circuit is roughly divided into circuits 104.
The voltage amplifier 20 corresponds to a difference between signals applied to the non-inverting input terminal (indicated as “+ IN” in FIG. 1) 35 and the inverting input terminal (indicated as “−IN” in FIG. 1) 36 from the outside. It is configured to output a voltage signal.

The pre-driver circuit 101 uses a PNP-type first transistor (indicated as “Q1” in FIG. 1) 1 as a pre-driver transistor, and converts the output voltage of the voltage amplifier 20 into a push-pull output. The stage 102 is driven.
Specifically, the base of the first transistor 1 is connected to the output terminal of the voltage amplifier 20 so that the output voltage of the voltage amplifier 20 is applied.
A first constant current source 21 is connected in series between the emitter of the first transistor 1 and the first power supply line 41, and the emitter of the first transistor 1 has a push-pull output. The collector is connected to the second power supply line 42 while being connected to the base of the second transistor (denoted as “Q2” in FIG. 1) 2 constituting the stage 102.
Note that a predetermined first power supply voltage is applied to the first power supply line 41, and a predetermined second power supply voltage is applied to the second power supply line 42.

The push-pull output stage 102 includes a PNP-type second transistor (first output-stage transistor) 2 and an NPN-type third transistor (denoted as “Q3” in FIG. 1) 3. , AB class output stage.
That is, the collectors of the second and third transistors 2 and 3 are connected to each other and to the output terminal 37.
The emitter of the second transistor 2 is connected to the first power supply line 41, and the emitter of the third transistor (second output stage transistor) 3 is connected to the second power supply line 42.

The idling current supply unit 104 supplies idling current to the second and third transistors 2 and 3, and includes a PNP type fourth transistor (indicated as “Q4” in FIG. 1) 4, an NPN type The fifth transistor (denoted as “Q5” in FIG. 1) 5, two constant voltage sources 31, 32, and a second constant current source 22.
Specifically, the emitter of the fourth transistor 4 and the collector of the fifth transistor 5 are both connected to the base of the second transistor 2 while the collector of the fourth transistor 4 and the collector of the fifth transistor 5 are connected. Both emitters are connected to the base of the third transistor 3.
The second constant current source 22 is connected between the collector of the fourth transistor 4 and the second power supply line 42.

Further, the negative electrode side of the first constant voltage source 31 is connected to the base of the fourth transistor 4, and the positive electrode side of the first constant voltage source 31 is connected to the first power supply line 41.
The base of the fifth transistor 5 is connected to the positive side of the second constant voltage source 32, and the negative side of the second constant voltage source 32 is connected to the second power supply line 42.

The sink current auxiliary circuit 103 monitors the operating state of the first transistor 1 and can control the current supply to the base of the third transistor 3 according to the monitoring result. The current supply to the base of the third transistor 3 can be controlled according to the operating state of one transistor 1.
That is, the sink current auxiliary circuit 103 suppresses the supply current to the base of the third transistor 3 below a certain level while the collector current ICQ1 of the first transistor 1 flows, while the collector current ICQ1 is interrupted. Only, the boosted current is supplied to the base of the third transistor 3.
The boost of the output current at the output terminal 37 is performed by supplying the boosted current to the base of the third transistor 3 only in such an operation of the sink current auxiliary circuit 103, particularly in a state where the collector current ICQ1 is interrupted. It is supposed to be.

FIG. 2 shows a circuit configuration example in which the sink current auxiliary circuit 103 is embodied as a specific circuit. This circuit will be described below with reference to FIG.
The same components as those in the circuit configuration example shown in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and different points will be mainly described below.
In this circuit configuration example, the sink current auxiliary circuit 103 includes a current detection circuit 103A and a current auxiliary circuit 103B.

The current detection circuit 103A is configured to monitor the operation state of the first transistor 1, and in this configuration example, a PNP-type sixth transistor (denoted as “Q6” in FIG. 2) 6 And a third constant current source (constant current source for current detection circuit) 23.
That is, the base of the sixth transistor (current detection transistor) 6 is connected to the output terminal of the voltage amplifier 20, while the third constant current source 23 is connected in series between the emitter and the first power supply line 41. The collector is connected to the second power supply line 42.

The current auxiliary circuit 103B can control the current supply to the base of the third transistor 3 according to the operation of the current detection circuit 103A, in other words, according to the monitored operation state of the first transistor 1. It is configured.
The current auxiliary circuit 103B includes an NPN-type seventh transistor (indicated as “Q7” in FIG. 2) 7, a PNP-type eighth transistor (indicated as “Q8” in FIG. 2) 8, 3 constant voltage sources (current auxiliary circuit bias constant voltage source) 33.

That is, the seventh transistor (first current auxiliary circuit transistor) 7 and the eighth transistor (second current auxiliary circuit transistor) 8 are connected to each other, while the collector of the seventh transistor 7 is connected. Is connected to the first power supply line 41, and the collector of the eighth transistor 8 is connected to the base of the third transistor 3.
The base of the seventh transistor 7 is connected to the emitter of the sixth transistor 6, while the base of the eighth transistor 8 is connected to the negative side of the third constant voltage source 33. The positive electrode side of the third constant voltage source 33 is connected to the first power supply line 41.

Next, FIG. 3 shows a more specific circuit configuration example of the first to third constant voltage sources 31 to 33. Hereinafter, this circuit configuration example will be described with reference to FIG. The same components as those in the circuit configuration example shown in FIGS. 1 and 2 are denoted by the same reference numerals, detailed description thereof is omitted, and different points are mainly described below. .
In this circuit configuration example, a first constant voltage generation unit 105 and a second constant voltage generation unit 106 are provided, and the first constant voltage generation unit 105 is shown in FIG. The second constant voltage generator 106 functions as the first constant voltage source 31 and the third constant voltage source 33, and the second constant voltage generation unit 106 functions as the second constant voltage source 32 shown in FIG. It has become something that fulfills.

The first constant voltage generator 105 includes PNP-type ninth and tenth transistors (represented as “Q9” and “Q10” in FIG. 3, respectively) 9 and 10, and a diode (“D1” in FIG. 3). ”) And a fourth constant current source 24.
That is, first, the emitter of the ninth transistor 9 is connected to the collector and base of the tenth transistor 10, and the emitter of the tenth transistor 10 is connected to the first power supply line 41.

The base and collector of the ninth transistor 9 are both connected to the base of the fourth transistor 4 and to the anode of the diode 15.
A fourth constant current source 24 is connected in series between the cathode of the diode 15 and the second power supply line 42, and the cathode of the diode 15 is connected to the base of the eighth transistor 8. .

The eighth transistor 8 is connected to the NPN type thirteenth and fourteenth transistors (referred to as “Q13” and “Q14” in FIG. 3, respectively) 13 and 14 through a current mirror. 1 transistor 1 is connected.
That is, the thirteenth and fourteenth transistors 13 and 14 are both connected to the base of the fourteenth transistor 14 and to the collector of the first transistor 1 while the collector and base of the thirteenth transistor 13 are both connected. .
The collector of the fourteenth transistor 14 is connected to the collector of the eighth transistor 8, while the emitters of the thirteenth and fourteenth transistors 13 and 14 are both connected to the second power supply line 42. .

The second constant voltage generation unit 106 includes NPN-type eleventh and twelfth transistors (indicated as “Q11” and “Q12” in FIG. 3) 11 and 12, a fifth constant current source 25, It is comprised and comprises.
That is, first, a fifth constant current source 25 is connected in series between the collector of the eleventh transistor 11 and the first power supply line 41, and the collector and base of the eleventh transistor 11 are connected to each other. Both are connected to the base of the fifth transistor 5.
The emitter of the eleventh transistor 11 is connected to the collector and base of the twelfth transistor 12, and the emitter of the twelfth transistor 12 is connected to the second power supply line 42.

Next, the operation in this configuration will be described.
First, the eighth transistor 8 constituting the current auxiliary circuit 103B functions as a current buffer. If the seventh and eighth transistors 7 and 8 are in a range where they normally operate as transistors, the emitter current of the seventh transistor 7 is applied to the base of the third transistor 3 regardless of the collector potential of the eighth transistor 8. A current substantially equivalent to IEQ 7 is output via the eighth transistor 8.

If there is no eighth transistor 8 and the emitter of the seventh transistor 7 is directly connected to the base of the third transistor 3, the power supply voltage, that is, the first power supply line 41 The value of the potential difference between the potential and the potential of the second power supply line 42 is limited to 3 × Vbe only.
This is because the emitter of the seventh transistor 7 is 2 × from the first power supply line 41 by the base-emitter voltage of the first and second transistors 1, 2, sixth and seventh transistors 6, 7. This is because the base of the third transistor 3 is fixed to a voltage higher by 1 × Vbe from the second power supply line 42 by the base-emitter voltage of the third transistor 3. .

On the premise of the action of the eighth transistor 8 on the base of the third transistor 3, the overall circuit operation will be described below.
First, when the potential difference between the two inputs + IN and -IN of the voltage amplifier 20 is small and the first transistor 1 is operating and the collector current is flowing, the sixth transistor 6 is also operated. At this time, since the current I3 of the third constant current source 23 almost flows into the emitter of the sixth transistor 6, the base current IBQ7 of the seventh transistor 7 becomes very small. At the same time, the collector current ICQ1 of the first transistor 1 is mirrored as ICQ14 by the current mirror formed by the thirteenth and fourteenth transistors 13 and 14, so that a current equivalent to ICQ1 is the third transistor. Out of 3 bases.

  As a result, when the potential difference between the two inputs + IN and −IN of the voltage amplifier 20 is small and the first transistor 1 is operating, the voltage is supplied from the sink current auxiliary circuit 103 to the base of the third transistor 3. Since the generated current is reduced, the idling current is suppressed.

Next, when the potential difference between the two inputs + IN and −IN of the voltage amplifier 20 increases and the output potential of the voltage amplifier 20 rises extremely, both the first and sixth transistors 1 and 6 are turned off.
When the first transistor 1 is turned off, its collector current ICQ1 and current mirror current ICQ14 become zero, and all the current I1 of the first constant current source 21 is supplied to the base of the third transistor 3. Inflow. At the same time, since the sixth transistor 6 is turned off, all the current I3 of the third constant current source 23 flows into the base of the seventh transistor 7, so that I3 = IBQ7.

Therefore, the emitter current IEQ7 of the seventh transistor 7 is a current obtained by multiplying the current I3 by (β + 1). Here, β is the current amplification factor of the seventh transistor 7.
Therefore, the base current of the third transistor 3 is expressed by the following formula 2, and the sink current of the third transistor 3 at this time, that is, the collector current ISink is expressed by the following formula 3. .

  IBQ3≈ (βQ7 + 1) × I3 + (I1-I2) Equation 2

  Isink≈βQ3 × {(βQ7 + 1) × I3 + (I1−I2)} Equation 3

FIG. 4 shows the result of simulating the relationship between the sink current and the output voltage in the above circuit configuration under the conditions of I1≈3 μA, I2≈1 μA, and I3≈1 μA, which is similar to that of the conventional circuit (see FIG. 5). This is shown together with the simulation results, and will be described below.
In FIG. 4, the horizontal axis represents the sink current, and the vertical axis represents the output terminal voltage. The dotted characteristic line (characteristic line with the symbol A) represents the simulation result of the conventional circuit, and the solid characteristic line. (Characteristic lines to which reference sign B is attached) indicate the simulation results of the circuit in the embodiment of the present invention. According to FIG. 4, it can be confirmed that the sink current capability of the circuit according to the embodiment of the present invention is remarkably improved as compared with the conventional circuit.

  The present invention can be applied to an operational amplifier in which a high sink current capability is desired while maintaining a rail-to-rail output and a high source current capability.

DESCRIPTION OF SYMBOLS 101 ... Pre-driver circuit 102 ... Push pull output stage 103 ... Sink current auxiliary circuit 103A ... Current detection circuit 103B ... Current auxiliary circuit 104 ... Idling current supply circuit 105 ... First constant voltage generation part 106 ... Second constant voltage generation Part

Claims (1)

A differential amplifier circuit that differentially amplifies an input signal; a pre-driver circuit that outputs the output of the differential amplifier circuit by voltage-current conversion; and an output stage driven by the output of the pre-driver circuit; Comprising
The output stage includes a PNP-type first output stage transistor and an NPN-type second output stage transistor, and is provided so that a sink current flows into the second output stage transistor. An amplifier,
A sink current auxiliary circuit configured to monitor an operating state of a pre-driver transistor constituting the pre-driver circuit and to control current supply to the base of the second output stage transistor according to the monitoring result Is provided,
The sink current auxiliary circuit is a PNP type, and includes a current detection circuit for detecting a current of the pre-driver transistor having an emitter connected to a base of the first output transistor, and the pre-driver using the current detection circuit. If the collector current of the pre-driver transistor is detected while the base current of the second output stage transistor is suppressed to a certain level or less, the collector current of the pre-driver transistor is detected. And a current auxiliary circuit configured to be able to supply the current to the base current of the second output stage transistor,
The current detection circuit includes a PNP-type current detection circuit transistor and a current detection circuit constant current source, and a base of the current detection circuit transistor is connected to a base of the pre-driver transistor and is connected to a collector. The second power supply voltage can be applied, while the emitter of the current detection circuit transistor is connected to one terminal of the current detection circuit constant current source, and the other of the current detection circuit constant current source is connected. The terminal is configured to be able to apply the first power supply voltage,
The current auxiliary circuit includes an NPN-type first current auxiliary circuit transistor, a PNP-type second current auxiliary circuit transistor, and a current auxiliary circuit bias constant voltage source. The base of the current auxiliary circuit transistor is connected to the emitter of the current detection circuit transistor, and a first power supply voltage can be applied to the collector, while the emitter of the first current auxiliary circuit transistor is Connected to the emitter of the second current auxiliary circuit transistor, the collector of the second current auxiliary circuit transistor is connected to the base of the second output stage transistor, while for the second current auxiliary circuit The base of the transistor is connected to the negative side of the current auxiliary circuit bias constant voltage source and to the positive side of the current auxiliary circuit bias constant voltage source Computation amplifier you characterized in that the first power supply voltage, which are configured to be applied.

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