JPH0250513A - Triangular wave generating circuit - Google Patents

Abstract

PURPOSE:To attain high speed and to improve the temperature characteristic by executing temperature compensation of a threshold voltage having a hysteresis characteristic to determine an oscillation frequency and using an emitter follower output circuit. CONSTITUTION:The collector output voltage of differential transistors Q3 and Q4 to execute a voltage comparing action is supplied to the base of transistors Q1 and Q2 to constitute respective emitter follower output circuits. At the emitter of a transistor Q1, a constant current transistor Q8 is provided and at the emitter of a transistor Q2, a constant current source transistor Q6 is provided. A band gap circuit to form a constant current having a positive temperature characteristic to cancel the temperature dependency having the voltage between the base and the emitter of an output transistor is used. Through the second emitter follower output circuit of the collector output of the other differential transistor, a switching control to reset a capacitor to constitute the time constant circuit of one differential transistor is executed. Thus, high speed can be attained and the temperature characteristics can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a triangular wave generation circuit, and relates to a technique that is effective for use in, for example, a switching regulator.

[Conventional technology]

A triangular wave generating circuit is used, for example, in a switching regulator. A switching regulator forms a pulse width modulation signal from a triangular wave and a reference voltage corresponding to the output voltage and performs switching control to obtain a desired output voltage corresponding to the pulse duty of the pulse width modulation signal. It is.

As an example of a triangular wave generation circuit, for example, June 3, 1981
Published on 0th “Integrated Circuit Application Handbook 1 page 150-1
There are 51.

[Problem to be solved by the invention]

In order to obtain a triangular wave generation circuit that achieves high speed (high frequency), an emitter follower output circuit with low output impedance may be used. However, in this case, the temperature characteristics deteriorate due to the temperature dependence of the voltage between the base and emitter of the transistor.

It is an object of the present invention to provide a triangular wave generation circuit that achieves high speed and improved temperature characteristics.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the output transistor is used as a first emitter follower output circuit that receives the collector output of one differential transistor that performs a voltage comparison operation and feeds it back to the base of the other differential transistor to form a reference voltage with hysteresis characteristics. A constant current transistor with positive temperature characteristics that cancels out the temperature dependence of the voltage between the base and emitter is provided, and the collector output of the other differential transistor is connected to one of the differential transistors through a second emitter follower output circuit. Controls the switch of the transistor that resets the capacitor that constitutes the time constant circuit provided at the base of the transistor.

[For production]

According to the above means, it is possible to perform temperature compensation for the threshold voltage having hysteresis characteristics that determines the oscillation frequency, so it is possible to improve the temperature characteristics while increasing the speed by using the emitter follower output circuit. .

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment of a triangular wave generating circuit according to the present invention. Each circuit element in the figure is formed on a single semiconductor substrate such as single-crystal silicon by a known semiconductor integrated circuit manufacturing technique, except for the resistor and capacitor that constitute the time constant circuit, although this is not particularly limited. Ru.

Differential transistors Q3 and 04 perform a voltage comparison operation.

A constant current transistor Q7 through which an operating current flows is provided at the common emitter of the differential transistors Q3 and 04. A load resistor R1 is connected to the collectors of the differential transistors Q3 and Q4.
and R2 are provided, respectively. The collector output voltages of the differential transistors Q3 and Q4 are respectively supplied to the bases of transistors Q1 and Q2 forming emitter follower output circuits. A constant current transistor Q8 is provided at the emitter of the transistor Q1 via a resistor R3.

Since the emitter of the transistor Q2 constitutes a zero oscillation circuit in which a constant current source transistor Q6 is provided via a resistor R4, the collector output of the differential transistor Ql is connected to the emitter follower output transistor Ql and the other via the emitter resistor R3. is supplied to the base of the differential operation transistor Q4. A time constant circuit consisting of a charging resistor RT and a capacitor CT is connected to the base of the differential transistor Q1 via an external terminal, and a reset transistor Q5 is connected in parallel to the capacitor CT. , the other differential transistor Q4
The output signal of the emitter follower output circuit provided corresponding to the collector output of is supplied.

Transistor Q whose emitter is connected to the circuit ground potential
Between the base and collector of 9 is a transistor QIO.
The emitter and base of are combined.

The collector of the transistor QIO is supplied with the operating voltage VR. A constant current source is provided at the collector of the transistor Q9. As a result, the above transistor Q
9, a constant current 11 formed by a constant current source is caused to flow therethrough.

In the oscillation circuit O8C, when the differential transistor Q4 is on and the differential transistor Q3 is off, the reference voltage VA supplied to the base of the differential transistor Q4 is expressed by the following equation (1).

VA=VR-VIEOI-R3・12・・
−・・(llHere, ■□.1 is the transistor Q1
base of.

is the emitter voltage. In this way, the differential transistor Q
4 is on, transistor Q5 has VRVm
A voltage of tot I 1 (R2+R4) is applied to turn it off. Therefore, a charging operation is performed on the capacitor CT via the resistor RT.

When the potential of the capacitor CT reaches the reference voltage VA (VLH) shown in equation 11 above, the differential transistor Q3 is switched on and the differential transistor Q4 is switched off. Therefore, the reference voltage VA changes as shown in the following equation (2).

VA"'VCVIIEGI R1・II R3・I
2... (2) Therefore, depending on the off state of the transistor Q4, its output level increases by the voltage drop of ll-R2,
Transistor Q5 is turned on and the capacitor CT is discharged.

Due to the discharging operation of the capacitor CT, the base potential of the differential transistor Q3 increases to the reference voltage VA (
VTL), the differential transistor Q4 is turned on and the differential transistor Q3 is turned off again. An example of the changes in the voltages VA and VB as described above is shown in the waveform diagram in FIG.
The voltage VB at is a triangular wave.

The reference voltage VA supplied to the base of the differential transistor Q4 has a hysteresis characteristic such that equation (1) is combined with the high-level threshold voltage VT) and the voltage in (2) is set as the low-level threshold voltage VTL. In this embodiment, in order to increase the speed, an emitter follower output circuit is used, so the above threshold voltage VTH
VTL includes the base-to-emitter voltage VIE, I of the emitter follower output transistor Q1, and has temperature dependence.

In this embodiment, in order to improve the temperature dependence as described above, the transistor Q8 that forms the constant current I2 that determines the reference voltage VA (VTR, VTL) has an emitter with respect to the input current mirror transistor Q9. The area is increased and an emitter resistor R5 is provided to form a so-called bandgap circuit, so that the constant current I2 has a positive temperature coefficient. As a result, the current increase Δ■2 due to the positive temperature coefficient of the constant current ■2, the voltage drop across the resistor R3, and the voltage between the base and emitter of the transistor Ql ■□
. The negative temperature coefficient of 1 can be canceled out.

As a result, when the temperature ranges from -20"C to 85°C, frequency fluctuations can be kept to around 5% at most.

Thereby, it is possible to obtain a triangular wave generation circuit that achieves high-speed operation (higher frequency) and improved temperature characteristics by performing the switching operation of the voltage comparator circuit through the emitter follower output circuit as described above.

The triangular wave VB is compared with the reference voltage 0, which is used to form a pulse width modulation signal PWM.
For example, in a switching regulator, a switch element is controlled in accordance with the pulse width modulation signal PWM, and an output voltage level formed by smoothing the switch output voltage is controlled.

The effects obtained from the above examples are as follows. (1) As a first emitter follower output circuit that receives the collector output of one differential transistor that performs a voltage comparison operation and feeds it back to the base of the other differential transistor to form a reference voltage with hysteresis characteristics. A bandgap circuit is used that forms a constant current with positive temperature characteristics that cancels out the temperature dependence of the voltage between the base and emitter of the output transistor, and the collector output of the differential transistor is used as the second emitter follower output. A transistor switch is controlled via a circuit to reset a capacitor forming a time constant circuit provided at the base of one of the differential transistors. In this configuration, it is possible to perform temperature compensation for the threshold voltage with hysteresis characteristics that determines the oscillation frequency, so it is possible to improve the temperature characteristics while increasing the speed by using an emitter follower output circuit. You can get the effect that you can.

(2) By using a bandgap circuit in which the emitter area of the current mirror output transistor is increased as the constant current circuit with the above positive temperature coefficient,
The effect is that a high-speed and highly stable triangular wave generation circuit can be obtained with a simple configuration.

(3) By using the charging resistor and capacitor for obtaining the above-mentioned triangular wave as external components, it is possible to use ones with small temperature dependence and variation, so it is possible to obtain a highly accurate triangular wave generation circuit. is obtained.

(4) Since a highly accurate triangular wave can be obtained according to (11) above, it is possible to obtain an effect that a high-speed and highly accurate switching regulator can be obtained.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above-mentioned Examples, and can be modified in various ways without departing from the gist thereof. For example, an emitter follower circuit used in an oscillation circuit may use a Darlington-type output transistor. Operating voltage V
Although R is not particularly limited, it is desirable to configure it with a stabilized power supply circuit. The capacitor and resistor constituting the time constant circuit may be built into the semiconductor integrated circuit. The configuration of the constant current source circuit that causes constant current 11 to flow through transistor Q9 can take various embodiments.

It goes without saying that the triangular wave generating circuit according to the present invention can be used not only to form triangular waves in a narrow sense used for pulse width modulation as described above, but also as a highly stable oscillation circuit that is temperature compensated. Probably.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. That is, the output transistor is used as a first emitter follower output circuit that receives the collector output of one differential transistor that performs a voltage comparison operation and feeds it back to the base of the other differential transistor to form a reference voltage with hysteresis characteristics. Using a bandgap circuit that forms a constant current with positive temperature characteristics that cancels out the temperature dependence of the voltage between the base and emitter, the collector output of the differential transistor is connected via a second emitter follower output circuit. A switch M of a transistor that resets a capacitor forming a time constant circuit provided at the base of one of the differential transistors is controlled. In this configuration, it is possible to perform temperature compensation for the threshold voltage with hysteresis characteristics that determines the oscillation frequency.
By using an emitter follower output circuit, it is possible to increase the speed and improve the temperature characteristics.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, No. 21!
I is a waveform diagram for explaining the operation. 01~QIO...transistor, R1-R5...resistance,
RT: External resistor, CT: External capacitor

Claims (1)

[Claims] 1. A reference voltage having hysteresis characteristics is formed by receiving the collector output of one differential transistor and feeding it back to the base of the other differential transistor, and an emitter follower output transistor, its base, a first emitter follower output circuit including a constant current transistor having a positive temperature characteristic that cancels the temperature dependence of the emitter voltage; and a first emitter follower output circuit that receives the collector output of the other differential transistor; A triangular wave generating circuit comprising: a second emitter follower output circuit that switches and controls a transistor that resets a capacitor in a time constant circuit that includes a charging resistor and a capacitor provided at the base of the triangular wave generating circuit. 2. The constant current transistor with positive temperature characteristics provided in the first emitter follower output circuit is a current mirror type output side transistor, and has a band gap whose emitter area is set larger than that of the input side transistor. 2. The triangular wave generating circuit according to claim 1, wherein the triangular wave generating circuit is comprised of a circuit. 3. What are the capacitors and resistors that make up the above time constant circuit?
A triangular wave generation circuit characterized in that it is connected via an external terminal.