JPH10161760A - Constant voltage generation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant voltage generation circuit obtaining a band gap voltage without being influenced by the fluctuation of a power source voltage even if it fluctuates. SOLUTION: The two transistors Q1 and Q2 of a BG (band gap reference) circuit are supplied with current from respectively different first and second current mirror circuits 11 and 12 and the circuits 11 and 12 are connected to a third current mirror circuit 13 as a common active load so that equal currents may easily flow through the transistors Q1 and Q2. In addition. The circuit 13 is successively connected with an emitter ground amplifier circuit 15 and first and second emitter follower circuits 16 and 17 and the output of double ends are taken out as the output of a single end. In order to prevent the generation of the difference of currents supplied for the transistors Q1 and Q2 of the BG circuit, negative feedback is executed by these circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage generating circuit using a band gap reference circuit (hereinafter, referred to as a BG circuit), and more particularly to a constant voltage generating circuit which is hardly affected by fluctuations in power supply voltage.

[0002]

2. Description of the Related Art Since a bandgap voltage obtained from a BG circuit is hardly affected by a change in temperature, a constant voltage generating circuit for obtaining a desired voltage from the voltage is often used. But,
The BG circuit has a disadvantage that it is easily affected by the fluctuation of the power supply voltage V _CC . FIG. 2 shows a circuit diagram of a general BG circuit. This BG circuit is composed of a multi-emitter transistor Q1 and a transistor Q2 whose bases are connected to each other, and resistors R3 and R4 connected to the emitters of the transistor Q1 and the transistor Q2. The bandgap voltage V _BG is obtained at the terminal 3 when the collector currents of both transistors are formed equal and the values of the resistors R3 and R4 are selected so as to cancel the negative temperature coefficient of the transistor Q2. Transistor Q20 and transistor Q21 form a current mirror circuit for flowing the same current to transistor Q1 and transistor Q2.

However, the circuit when the band gap voltage V _BG is obtained is such that the collector-emitter voltage of the diode-connected transistor Q21 has a base-emitter voltage of 0.6 V (V _CC ─0.6). , The collector-emitter voltage of transistor Q21 is (V _CC ─V _BG )
Are different voltages as represented by Therefore, when the power supply voltage V _CC applied to the terminal 1 fluctuates up and down, the emitter-collector voltages of the transistors Q20 and Q21 change in different states, and the accuracy of the current mirror circuit deteriorates due to the Early effect. .

[0004]

An object of the present invention is to provide a power supply.
Even if the voltage fluctuates, the two transistors in the BG circuit
New current flows and is not affected by fluctuations in the power supply voltage.
Band gap voltage V _BGConstant voltage generator that can obtain
It is to provide a raw circuit.

[0005]

A constant voltage generating circuit according to the present invention includes first and second transistors having bases connected to each other, and a band gap from the base by equalizing collector currents of both transistors. A bandgap reference circuit for obtaining a voltage, a third and a fourth transistor cascade-connected to the first and second transistors, and bases connected to each other, each serving as an active load of the first and second transistors; First and second current mirror circuits having input terminals connected to the third and fourth transistors, a third current mirror circuit serving as an active load of the first and second current mirror circuits, and a third current mirror A common emitter amplifier circuit to which the output of the circuit is added, a first emitter follower circuit to which the output of the common emitter amplifier circuit is added, a first emitter A second emitter follower circuit to which an output of the follower circuit is applied and obtains a desired voltage from an output terminal; the first and second current mirror circuits each have two output terminals; 3, and the remaining output terminals are connected to each other and connected to the common-emitter amplifier circuit as a load.
The first emitter follower circuit is connected to a constant current source as a load, and further provided with a fourth current mirror circuit so that the current of the constant current source flows to the ground side without flowing to the preceding circuit. In the emitter follower circuit, the first and second resistors are connected as a load, and the first resistor is connected to a connection point between the resistors.
And the base of the second transistor are connected, and the third
And a desired voltage is obtained from the output terminal connected to the base of the fourth transistor.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A constant voltage generating circuit according to the present invention has a BG
Two transistors of the circuit are supplied with current from separate first and second current mirror circuits, respectively, and the first and second current mirror circuits
Is connected to the third current mirror circuit as a common active load, thereby facilitating the flow of current equal to the transistor. The third current mirror circuit is sequentially connected to the common emitter amplifier circuit, the first and second emitter follower circuits, and the double-ended output from the third current mirror circuit is taken out as a single-ended output. Then, by these circuits connected to the third current mirror circuit, negative feedback is applied to the BG circuit so as not to cause a difference between the currents supplied to the two transistors of the BG circuit.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a constant voltage generating circuit according to the present invention. The same parts as those in FIG. 2 are denoted by the same reference numerals. In FIG. 1, the bases of the first and second multi-emitter transistors Q1 and Q2 are connected, the emitters are connected via a resistor R3, and the emitter of the transistor Q2 is grounded via a resistor R4. These circuit elements form a BG circuit. The emitters of a third transistor Q3 and a fourth transistor Q4 whose bases are connected to each other are connected to the collectors of the transistors Q1 and Q2, respectively. That is, the transistor Q3
And the transistor Q4 are cascaded to the transistors Q1 and Q2.

The transistors Q7, Q8 and Q9 form a first current mirror circuit 11, the emitter is commonly connected to the terminal 1 to which the power supply voltage V _cc is applied, and the collector of the transistor Q9 as an input terminal is a transistor. Q3
Connected to the collector. The current mirror circuit 11 is connected as an active load of the transistor Q1. The transistors Q10, Q11, Q12 form a second current mirror circuit 12, the emitters of which are commonly connected to the terminal 1,
The collector of the transistor Q10, which is the input terminal, is connected to the collector of the transistor Q4. The current mirror circuit 12 is connected as an active load of the transistor Q2.
The collectors of the transistors Q8 and Q11, which are one output terminal of the current mirror circuit 11 and the current mirror circuit 12, are connected to the collectors of the transistors Q13 and Q14, respectively.

A transistor Q1 whose emitter is grounded
3, Q14 form a third current mirror circuit 13, and the current mirror circuit 11 and the current mirror circuit 12
Acts as an active load. The transistor Q15 forms a common-emitter amplifier circuit 15. The base is connected to the collector of the transistor Q14. The collectors of the transistors Q7 and Q12 connected to each other are connected as a load. The collectors of the transistors Q7 and Q12 are the remaining output terminals of the current mirror circuits 11 and 12, respectively.
Reference numeral 15 is provided with two emitters in order to make the emitter current density the same as the surrounding transistors.

The transistors Q5 and Q6 connected in series and the transistor Q forming the fourth current mirror circuit 14
16, Q17 form a first emitter follower circuit 16. The base of the transistor Q5 which is an input terminal is connected to the collector of the transistor Q15, and the collector is connected to the current source S1 connected to the terminal 1 of the power supply voltage V _CC as a load. The emitter of the transistor Q6 is grounded, and the base is connected to the collector of the transistor Q16, which is the input terminal of the current mirror circuit 14. The collector of the transistor Q17, which is the output terminal of the current mirror circuit 14,
Connected to the base of transistor Q5, the emitter is grounded.

The transistor Q18, the first resistor R1, and the second resistor R2 form a second emitter follower circuit 17. The collector of the transistor Q18 is connected to terminal 1 of the power supply voltage V _CC, the base is connected to the collector of the transistors Q5, connected to the base of the transistor Q3, Q4 with the emitter which is the output terminal is grounded through a resistor R1, R2 I do. The connection point P between the resistors R1 and R2 is a transistor Q
1. Connect to the base of Q2. 2 is a terminal connected to the emitter of the transistor Q18 which is the output terminal of the emitter follower circuit 17. This constant voltage generating circuit includes a BG circuit as a center, a current mirror circuit 11 as a load thereof,
The current mirror circuit 12 and the current mirror circuit 13 which is a common load of both are formed substantially symmetrically.

Next, the operation of the constant voltage generating circuit will be described. In the constant voltage generating circuit, two transistors Q of the BG circuit
1, a current mirror circuit 1 formed similarly
Currents are supplied from the current mirror circuits 1 and 12, respectively, and a common current mirror circuit 13 is connected to the current mirror circuits 11 and 12 as a load. Therefore, the current of the two transistors of the BG circuit is unlikely to cause a difference. That is,
Assuming that a current flowing from the current mirror circuits 11 and 12 to the current mirror circuit 13 is I, (2I /
The current of β) flows. Therefore, transistor Q13
, A collector current of (I− (2I / β)) flows.

On the other hand, a collector current of (2I) flows through the transistor Q15 of the common-emitter amplifier circuit 15, and (2I)
I / β). As a result, a collector current of (I− (2I / β)) also flows through the transistor Q14. Here, β is the transistor Q13, Q1
4. Current amplification factor of Q15. In this way, since the currents of the current mirror circuits 11 and 12 are the same, the current of the two transistors of the BG circuit hardly causes a difference. The cascaded transistors Q3 and Q4 prevent the characteristics of the transistors Q1 and Q2 from deteriorating due to the Early effect. The double-ended output of the third current mirror circuit 13 is converted to a single-ended output by the common-emitter amplifier 15.

[0014] Now, it is assumed that the collector current of the transistor Q2 due to fluctuations in the power supply voltage V _CC becomes greater than that of the transistor Q1, the band gap voltage V _BG is no longer obtained. At this time, the collector current of the transistor Q11 becomes larger than that of the transistor Q8. Transistor Q15
Although the base current increases and the collector current increases, the collector current is increased by the transistors Q7 and Q1.
Since there is almost no change due to the current of (2I) from 2, the base current of the transistor Q5 of the emitter follower circuit 16 increases. Then, the emitter current of the transistor Q5 increases, the base current of the transistor Q18 of the emitter follower circuit 17 decreases, and the collector current also decreases, so that the voltage at the connection point P decreases.

Therefore, the current of the BG circuit decreases.
When the current decreases, the multi-emitter transistor Q
One collector current flows more than the transistor Q2. This means that the transistor Q1 is supplied with a current from the current mirror circuit 11, so that the current in the current mirror circuit 11 increases. On the other hand, if the bandgap voltage V _BG cannot be obtained because the collector current of the transistor Q2 becomes smaller than that of the transistor Q1, the common emitter amplifier circuit 15, the emitter follower circuit 16, and the emitter follower circuit 17 operate in reverse. As the voltage at the connection point P increases, the current of the BG circuit increases. When the current of the BG circuit increases, the collector current of the transistor Q2 becomes larger than that of the transistor Q1, which acts to increase the current of the current mirror circuit 12.

Thus, the transistors Q1, Q2
Of the power supply voltage V _CC always acts in a balanced and equal manner regardless of the fluctuation of the power supply voltage V _CC . That is, a negative feedback is applied to the connection point P between the resistors R1 and R2 so that the bandgap voltage _VBG is always obtained, and a desired voltage _VOUT set by the resistors R1 and R2 is applied from the bandgap voltage _VBG. Terminal 2 can be obtained. The current mirror circuit 14 allows the current flowing from the current source S1 to the emitter follower circuit 16 to flow to the ground side, and prevents the current from flowing into the preceding transistor Q15 via the base of the transistor Q5.

[0017]

As described above, in the constant voltage generating circuit according to the present invention, the current mirror circuits are respectively connected so that the currents supplied to the two transistors of the BG circuit become the same. When a difference occurs in the current of the circuit, the difference is detected by a common-emitter amplifier circuit, the first and second emitter follower circuits, and a negative feedback is applied, so that a band is always connected to the connection point of the resistor of the second emitter follower circuit. A gap voltage is obtained. Therefore, even if the current flowing through the two transistors of the BG circuit changes due to the fluctuation of the power supply voltage or the like, the voltage obtained at the output terminal is not affected by the change and a stable voltage can be obtained. Further, the constant voltage generating circuit of the present invention has an advantage that it is less affected by variations in transistor characteristics during manufacturing.
This is because three current mirror circuits are formed substantially symmetrically around the BG circuit, and if the characteristics of all the transistors are uniform, the influence of the variation hardly appears in the operation. In the case of forming an integrated circuit, the characteristics of the transistor vary in a uniform state, which is advantageous.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a constant voltage generation circuit according to the present invention.

FIG. 2 is a circuit diagram of a conventional band gap reference circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st current mirror circuit 12 2nd current mirror circuit 13 3rd current mirror circuit 15 Common emitter amplifier circuit 16 1st emitter follower circuit 17 2nd emitter follower circuit

Claims (2)

[Claims] 1. A bandgap reference circuit comprising a first and a second transistor having a base connected to each other, wherein a bandgap voltage is obtained from the base by equalizing collector currents of both transistors.
Third and fourth transistors cascade-connected to a second transistor and a base, and the first and second transistors are connected to each other.
And the input ends of the third and fourth transistors
First and second current mirror circuits connected to the first transistor, a third current mirror circuit serving as an active load of the first and second current mirror circuits, and a common emitter to which the output of the third current mirror circuit is applied An amplifier circuit, a first emitter follower circuit to which the output of the common emitter amplifier circuit is added, and a second emitter follower circuit to which an output of the first emitter follower circuit is added and a desired voltage is obtained from an output terminal. And the second current mirror circuit each have two output terminals, one output terminal of each of which is connected to the third current mirror circuit, and the other output terminals of which are connected to each other so that the load is applied to the common emitter amplifier circuit. The first emitter follower circuit is connected to a constant current source as a load, and further connected without the current of the constant current source flowing to the preceding circuit. A fourth current mirror circuit is provided so as to flow to the side, and the second emitter follower circuit is connected to first and second resistors as loads, and the first and second transistors are connected to a connection point between the resistors. A constant voltage generating circuit having a base connected thereto, wherein a desired voltage is obtained from the output terminal connected to the bases of the third and fourth transistors. 2. A first emitter floor circuit comprising: a fifth transistor having an input terminal connected to a common-emitter amplifier circuit;
6. A sixth transistor connected in series to the fifth transistor, and a fourth current mirror circuit having an input terminal connected to the base of the sixth transistor and an output terminal connected to the base of the fifth transistor. Constant voltage generation circuit.