JP4647130B2 - Reference voltage generation circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reference voltage generation circuit, and more particularly to a technique for shortening a rise time of an output voltage at start-up while reducing a noise voltage superimposed on an output voltage.
[0002]
[Prior art]
FIG. 4 is a diagram showing a conventional reference voltage generating circuit, where 1 is a reference voltage source, 2 is an amplifier, 3 is an intermediate terminal, 4 is an output terminal, C1 is a capacitor, R1 is a resistor, and D1 is a diode. The amplifier 2 inputs the voltage of the reference voltage source 1 to the input node 2a, and feeds back the voltage appearing at the output node 2c to the feedback node 2b, so that a constant reference voltage obtained by amplifying the voltage of the reference voltage source 1 is an intermediate terminal. 3 is output. The capacitor C1 and the resistor R1 constitute a low-pass filter, and reduce the effective value of the noise voltage due to the thermal noise generated in the resistor elements constituting the reference voltage source 1 and the amplifier 2 superimposed on the voltage of the output terminal 4. . The diode D1 is connected so as to bypass the resistor R1. When the voltage Va of the intermediate terminal 3 gradually increases from 0V when the power is turned on, the resistor D1 is bypassed to charge the capacitor C1, and the voltage of the output terminal 4 is Raise Vb quickly.
[0003]
[Problems to be solved by the invention]
However, in order for the diode D1 to pass a current, it is necessary to apply a voltage for turning it on between the anode and the cathode. In the case of a silicon semiconductor, this voltage is required to be about 0.7V. For this reason, as shown in FIG. 5B, the rise of the voltage Vb at the output terminal 4 in FIG. 4 is fast until a certain voltage, but the diode D1 is turned off in the middle. Is charged through the resistor R1, and the rise of the voltage Vb is delayed.
[0004]
If the value of the resistor R1 is reduced, the rise will be quicker, but the cut-off frequency of the low-pass filter composed of R1 and C1 will be increased, and the effective value of the noise voltage at the output terminal 4 will increase.
[0005]
The present invention has been made in view of the above points, and an object of the present invention is to provide a reference voltage generation circuit that quickly rises the output voltage while reducing the effective value of the output noise voltage.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention of claim 1, an amplifier that amplifies the voltage of the reference voltage source and outputs the voltage of the output node that feeds back to the feedback node and controls the voltage of the output node to be constant, In a reference voltage generating circuit comprising: a first resistor connected between an intermediate terminal connected to a feedback node of the amplifier and an output terminal; and a capacitor connected between the output terminal and ground. An NPN-type first transistor having a collector and base connected to the output node of the amplifier and an emitter connected to the feedback node of the amplifier, an emitter connected to the output node of the amplifier, and a base connected to the output terminal And a second resistor connected between the collector of the second transistor and the feedback node of the amplifier. It was a quasi-voltage generation circuit.
[0007]
The invention of claim 2 is characterized in that, in the invention of claim 1, the second resistor is replaced by a diode having an anode connected to the collector of the second transistor and a cathode connected to the feedback node. A reference voltage generation circuit was used.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram of a reference voltage generating circuit according to one embodiment of the present invention, and FIG. 2 is a detailed circuit diagram of FIG. In FIG. 1, 1 is a reference voltage source, 2 is an amplifier, 3 is an intermediate terminal, 4 is an output terminal, C1 is a capacitor, R1 and R2 are resistors, Q1 is an NPN transistor (diode connection), and Q2 is a PNP type. It is a transistor. The resistor R1 and the capacitor C1 constitute a low pass filter.
[0009]
As shown in FIG. 2, the reference voltage source 1 and the amplifier 2 are configured by a band gap type reference voltage generating unit including PNP type transistors Q3, Q4, Q5, NPN type transistors Q6, Q7, and resistors R3, R4. Has been. The reference voltage is set by the emitter ratio of the transistors Q6 and Q7 and the resistance ratio of the resistors R3 and R4. That is, the sum of the base-emitter voltage Vbe7 of the transistor Q7 and the voltage generated in the resistor R4 is set to a band gap voltage (1.205 V). Transistors Q4 and Q5 constitute a current mirror circuit for supplying the same current to transistors Q6 and Q7. Transistor Q3 is for output.
[0010]
When the power supply voltage Vcc is turned on and the circuit starts operating, the transistor Q3 starts to supply current to the intermediate terminal 3 via the transistors Q1 and Q2. The voltage Va at the intermediate terminal 3 is negatively fed back from the feedback node 2b to the transistors Q6 and Q7, and the whole operates so that the voltage Va becomes constant. In this way, the voltage Va at the intermediate terminal 3 rises to a certain voltage V1 due to the current from the transistor Q3. However, since the voltage Vb of the output terminal 4 has to be stored in the capacitor C1 through the resistor R1, it takes time until the voltage rises to a predetermined value compared to the intermediate terminal 3.
[0011]
Assuming that the voltage Va of the intermediate terminal 3 instantaneously reaches a certain voltage V1, the process in which the charge of the capacitor C1 is accumulated by the current flowing through the resistor R1 and the voltage Vb of the output terminal 4 increases is as follows.
Vb = Va [1-exp {-t / (C1 · R1)}] (1)
Is represented by From this equation, it can be seen that no matter how fast the voltage Va of the intermediate terminal 3 rises, the rise of the voltage Vb of the output terminal 4 becomes slower than that of the intermediate terminal 3 as the values of R1 and C1 are increased.
[0012]
Here, after the power is turned on, the voltage Va at the intermediate terminal 3 rises to a certain voltage e1, but the voltage Vb at the output terminal 4 rises only to a voltage e2 lower than the voltage Va. At this time, the potential difference between the base and emitter of the transistor Q2 is
Vbe2 = e1 + Vbe1-e2 (2)
It becomes. Here, Vbe1 is a potential difference between the base and emitter of the transistor Q1, and when the collector current of the transistor Q1 is Ic1,
Vbe1 = V _T · ln (Ic1 / Is) (3)
It becomes. Where V _T = K · T / q, Is: junction saturation current, K: Boltzmann constant, T: absolute ambient temperature, q: charge amount of electrons.
[0013]
This potential difference Vbe1 varies with the collector current Ic1, but in the case of a silicon semiconductor, it is about 0.7 V at room temperature. Due to the potential difference Vbe1 expressed by the equation (3), the transistor Q2 has a collector current Ic2 = Is [exp Vbe2 / V _T ] as shown below (4)
Try to flow.
[0014]
However, because of the resistance R2, the potential difference Vec2 between the emitter and collector of the transistor Q2 is
Vec2 = Vbe1−R2 ・ Ic2 (5)
become that way. From this equation (5), when the collector current Ic2 reaches a certain value, the potential difference Vec2 between the emitter and the collector of the transistor Q2 cannot be sufficiently obtained, and the operation of the transistor Q2 becomes a saturation region. In particular, when the value of the resistor R2 is large, the operation of the transistor Q2 enters the saturation region even if the collector current of the transistor Q2 is small.
[0015]
In the bipolar transistor, the current amplification factor decreases and the collector current decreases in the saturation region. For this reason, most of the current flowing from the emitter of the transistor Q2 becomes the base current of the transistor Q2. Since this current flows directly into the capacitor C1 without going through the resistor R1, the charge in the capacitor C1 is rapidly accumulated, and the voltage Vb at the output terminal 4 rises rapidly.
[0016]
When the potential Vb of the output terminal 4 rises and approaches the potential Va of the intermediate terminal 3, the potential difference Vbe2 decreases and the collector current Ic2 also decreases. As a result, the potential difference Vec2 also increases, so that the transistor Q2 leaves the operation in the saturation region, most of the current flowing from the emitter becomes the collector current Ic2, and the base current decreases. In this state, the capacitor C1 is charged only with the current flowing through the resistor R1, and the increase in the voltage Vb at the output terminal 4 approaches the voltage Va at the intermediate terminal 3 according to the equation (1).
[0017]
This is shown in FIGS. FIG. 5 (a) shows a change in the voltage Va at the intermediate terminal 3 in the conventional circuit of FIG. 4, and shows that the voltage Va suddenly rises to a certain voltage value V1 at a certain time t0. FIG. 5B shows a change in the voltage Vb of the output terminal 4 in FIG. In the case of the conventional circuit, since the charging diode D1 is ON until the voltage Vb of the output terminal 4 rises to 0 to V2, it rises relatively quickly, but the diode D1 is OFF until V2 to V1. Therefore, since the capacitor C1 is charged via the resistor R1, the rate of increase of the voltage value is slow according to the equation (1). The potential difference from V2 to V1 is about 0.7 V in the case of a silicon semiconductor.
[0018]
FIG. 6 shows the rise of the voltage Va at the intermediate terminal 3 and the voltage Vb at the output terminal 4 in the embodiment of the present invention (FIGS. 1 and 2). In the present embodiment, the voltage Va of the output terminal 4 rises rapidly from 0 to V3 (V3> V2) because the capacitor C1 is charged by the base current of the transistor Q2, and thereafter reaches the voltage V1 via the resistor R1. The voltage gradually approaches the voltage V1 due to the current flowing into the capacitor C1. However, the value of the voltage V3 is higher than that of the voltage V2 of FIG. 5, and continues until the PNP transistor Q2 of FIG. For this reason, the time until the voltage Vb of the output terminal 4 reaches around V1 becomes very fast.
[0019]
When the voltage Va at the intermediate terminal 3 and the voltage Vb at the output terminal 4 reach a certain value V1, the base current Ib2 from the base of the transistor Q2 to the output terminal 4 has a current amplification factor in the non-saturated region of the transistor Q2. If β is
Ib2 = Ic1 / β (6)
It becomes. Since β is usually about 100, the value of the base current Ib2 becomes very small and hardly affects the change of the voltage Vb at the output terminal 4.
[0020]
FIG. 3 is a diagram showing a reference voltage generating circuit according to another embodiment of the present invention, in which the resistor R2 in FIGS. 1 and 2 is replaced with a diode D2. In FIG. 1 and FIG. 2, the potential difference is generated between the intermediate terminal 3 and the collector of the transistor Q2 by the collector current of the resistor R2 and the transistor Q2, but this is replaced with the ON voltage of the diode D2. Works the same way.
[0021]
In the above description, the reference voltage is generated by the band gap type circuit. However, the present invention is not limited to this, and it is needless to say that the reference voltage can be applied to a circuit that generates the reference voltage by other methods.
[0022]
【The invention's effect】
From the above, according to the present invention, the capacitance of the output terminal can be quickly charged by bypassing this resistor while starting up while reducing the noise appearing in the voltage of the output terminal by increasing the value of the noise reducing resistor. Can get up quickly. As a result, it is possible to realize a reference voltage generation circuit that starts up quickly with low noise. By providing such a feature, the present invention is suitable for an application that requires a low output noise voltage while repeating ON / OFF frequently in order to reduce current consumption during standby.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a reference voltage generation circuit according to an embodiment of the present invention.
FIG. 2 is a more detailed circuit diagram of the reference voltage generation circuit of FIG.
FIG. 3 is a circuit diagram of a reference voltage generation circuit according to another embodiment of the present invention.
FIG. 4 is a circuit diagram of a conventional reference voltage generation circuit.
5 is a characteristic diagram of voltages Va and Vb of the reference voltage generation circuit of FIG. 4. FIG.
6 is a characteristic diagram of voltages Va and Vb of the reference voltage generation circuit of FIGS. 1 and 2. FIG.
[Explanation of symbols]
1: Reference voltage source, 2: Amplifier, 3: Intermediate terminal, 4: Output terminal

Claims (2)

An amplifier that amplifies the voltage of the reference voltage source and outputs the voltage of an output node that is fed back to a feedback node to control the voltage of the output node to be constant, and an intermediate terminal connected to the feedback node of the amplifier and an output In a reference voltage generating circuit comprising a first resistor connected between the output terminal and a capacitor connected between the output terminal and ground, a collector and a base are connected to an output node of the amplifier. An NPN-type first transistor having an emitter connected to a feedback node of the amplifier; a PNP-type second transistor having an emitter connected to the output node of the amplifier and a base connected to the output terminal; And a second resistor connected between a collector of the transistor and a feedback node of the amplifier. In claim 1,
2. A reference voltage generating circuit according to claim 1, wherein the second resistor is replaced with a diode having an anode connected to the collector of the second transistor and a cathode connected to the feedback node.

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