JPH09162666A - Limiter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the limiter circuit in which a temperature characteristic of an upper limit voltage is improved with a few number of components and the upper limit itself is revised. SOLUTION: A base of a transistor(TR) Q11 connects to a constant voltage source 7, its collector connects to ground and its emitter connects to a collector of an NPN TR Q9. A constant current source 25 and an output terminal OUT are connected to an emitter of a TR Q10. An emitter follower is configured for the TR Q10 to increase an output current, a temperature characteristic of the TR Q10 is cancelled with that of the TR Q11 to set the temperature characteristic of an upper limit voltage to be equal to that of a constant voltage source 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving the temperature characteristic of the output upper limit voltage in an operational amplifier IC or the like.

[0002]

2. Description of the Related Art Conventionally, an example of a single power supply type operational amplifier used in a limiter circuit such as a microphone amplifier will be described with reference to FIG. In FIG. 4, two pairs of transistors T
An input circuit 101 composed of 1, T2, T3, T4 and having an in-phase input terminal IN (+) and an inverting input terminal IN (-), and a current mirror circuit 102 composed of a pair of transistors T5, T6. The differential input section 103 is formed by and.

The output of the differential input section 103 is the intermediate amplification section.
Transistor via transistors T7 and T8 at 104
Output section 105 as a limiter circuit amplified by T9
It is output from the output terminal OUT via the transistor T10 of. The transistor T10 has an emitter follower structure so that a large output current can be taken out. In an IC such as an operational amplifier of a single power supply system, an NPN transistor is used as a transistor forming the emitter follower of the output section. Therefore, in the following, the transistor forming the emitter follower of the output section is referred to as an NPN transistor. The explanation will be limited.

In the above configuration, the common mode input terminal IN (+)
If a predetermined bias voltage and signal are superimposed and applied to the output terminal OUT and the inverting input terminal IN (-) is connected with an appropriate negative feedback resistor, etc. The amplified signal is output. Then, when the amplitude of the input signal exceeds a predetermined level, the output signal is limited by the upper and lower limiter voltages and acts as a limiter circuit. In the circuit of FIG. 4, the upper limit voltage is Vmax, the lower limit voltage is Vmin, the power supply voltage is Vcc, and the transistor is
If the junction voltage between the base and emitter of T10 is VBE (10), then Vmax = Vcc-VBE (10) Vmin = 0.

[0005]

Since the base-emitter junction voltage of a transistor fluctuates under the influence of temperature changes, the circuit shown in FIG. 4 has excellent temperature characteristics of the power supply voltage. However, the upper limit voltage fluctuates under the influence of temperature change. The lower limit voltage is 0 and does not change. Therefore, even if the input signal has a vertically symmetrical waveform with respect to the bias voltage, in the signal appearing at the output terminal, only the upper limit voltage is affected by temperature, and the waveform of the output voltage is not vertically symmetrical.

As described above, the conventional limiter circuit has a problem that the upper limit voltage is greatly affected by the temperature change. Also, the upper limit voltage is Vmax = Vcc
-Become VBE (10), so power supply voltage and transistor T10
It is fixed at the base-emitter junction voltage of, and it is difficult to set the desired voltage without changing the power supply voltage.

As an example of a circuit configuration capable of changing the upper limit voltage, there is a circuit example in which operational amplifiers as shown in FIG. 5 are combined. In the case of this circuit, by adding an ideal diode circuit having a dead zone composed of the operational amplifier A2 and the diodes D1 and D2 to the inverting amplifier circuit composed of the operational amplifier A1, the upper and lower limits are set by the external control voltage ViN. It is configured to control the voltage of.

However, in this case, the number of parts increases,
There is a problem that it becomes difficult to operate stably up to a high frequency due to an increase in power consumption, an increase in heat generation, and the influence of the capacitive component of the junction and the rotation of the phase.

Therefore, the present invention has been made for the purpose of providing a limiter circuit capable of changing the upper limit voltage while improving the temperature characteristic of the upper limit voltage with a small number of parts.

[0010]

In order to solve the above-mentioned problems, according to the invention of claim 1, a base is connected to a power supply voltage via a constant current source, and an emitter is an NPN transistor connected to an output terminal. In a limiter circuit of a single power supply system having a configuration in which the upper limit voltage is the power supply voltage minus the junction voltage between the base and emitter of the NPN transistor, the base is connected to a constant voltage source, the collector is grounded, and the emitter is By providing the PNP transistor connected to the base of the NPN transistor, the temperature characteristic of the upper limit voltage of the signal input to the base of the NPN transistor and output from the output terminal is improved to the same level as that of the constant voltage source.

According to the second aspect of the present invention, the upper limit voltage can be changed by providing the voltage changing means for changing the voltage of the constant voltage source.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 showing a case where it is applied to the circuit configuration of an operational amplifier IC.
It will be described based on. In FIG. 1, reference numeral 1 denotes an in-phase input terminal IN which is composed of two pairs of transistors Q1, Q2, Q3 and Q4.
The input circuit 2 having (+) and the inverting input terminal IN (-),
The current mirror circuit is composed of a pair of transistors Q5 and Q6, and 3 is a differential input section composed of these input circuit 1 and current mirror circuit 2. 21,22,23
Is a constant current source for driving each transistor with a constant current.

Reference numeral 4 denotes an intermediate amplifying section composed of transistors Q7, Q8 and Q9. A constant current source 24 is connected to the emitter of the transistor Q7 and a constant current source 26 is connected to the collector of the transistor Q9. . Reference numeral 5 denotes an output section. A constant current source 25 and an output terminal OUT are connected to the emitter of the transistor Q10, and the amplified current signal is taken out from the output terminal OUT. The transistor Q10 has an emitter follower structure in order to increase the output current.

The above structure is similar to the conventional structure. 6
Is a limiter control circuit including a constant voltage source 7 and a PNP transistor Q11. The base of the transistor Q11 is connected to the constant voltage source 7, the collector is grounded, and the emitter is connected to the collector of the NPN transistor Q9. As the constant voltage source 7, a constant voltage source having excellent temperature characteristics using a Zener diode or the like is used.

The output section 5 and the limiter control circuit 6 constitute the limiter circuit of claim 1.

In the operational amplifier IC having the configuration shown in FIG. 1, a predetermined bias voltage and an input signal are superimposed and applied to the in-phase input terminal IN (+), and the output terminal OUT and the inverting input terminal IN (-) are applied.
If and are connected by an appropriate negative feedback resistor or the like, the signal amplified around the bias voltage is output from the output terminal OUT.

When the amplitude of the input signal exceeds a predetermined level, the output signal is limited by the upper and lower limiter voltages and acts as a limiter circuit. In the circuit of FIG. 1, the upper limit voltage is Vmax, the power supply voltage is Vcc, and the constant voltage source 7
Is V1, the junction voltage between the base and emitter of transistor Q10 is VBE (10), the base of transistor Q11 is
Assuming that the junction voltage between the emitters is VBE (11), Vmax + VBE (10) = V1 + VBE (11) holds, so that Vmax = V1 + VBE (11) -VBE (10).

If the lower limit voltage is Vmin, then Vmin = 0. Where transistor Q11 and transistor Q10
Is a device that is generated at the same time in the same IC, so the junction voltage VBE (1
The temperature characteristics of 1) and VBE (10) are almost the same. Therefore,
The upper limit voltage Vmax becomes equal to the voltage V1 of the constant voltage source 7,
The temperature characteristic has the same stability as that of the constant voltage source 7.

Conventionally, even if the temperature characteristic of the power supply voltage Vcc is excellent, the base
Since the temperature characteristic of the junction voltage between the emitters is about -2.2 mV / ° C, the temperature characteristic of the upper limit voltage is also about 2.2 mV / ° C, but in the case of Fig. 1, + VBE (11) and -VBE (10 Since the fluctuation due to the temperature change is canceled by the above, the temperature characteristic of the upper limit voltage is improved to about ± several mV (-10 ° C to 60 ° C) like the temperature characteristic of the constant voltage source 7.

An embodiment of the limiter circuit according to claim 2 will be described with reference to FIG. Constant voltage source 7 shown in FIG.
2 is used as the variable constant voltage source 71 as shown in FIG. 2A or the voltage switching type constant voltage source as shown in FIG. 2B.
By changing to 72, it becomes possible to change the upper limit voltage without changing the power supply voltage. Again,
The temperature characteristic of the upper limit voltage is the same as that of the constant voltage source 7.

The variable constant voltage source 71 or the voltage switching type constant voltage source 72 corresponds to the voltage changing means of claim 2.

The differential input circuit may be constructed as shown in FIG. The differential input circuit 11 shown in FIG. 3 includes an input circuit 12 including a pair of transistors Q21 and Q22, a constant current source 16 arranged on the power supply line thereof, and a constant current source 13 connected to the collector of the transistor Q21. It consists of The current value of the constant current source 13 is set to one half of the current value of the constant current source 16. A resistor 15 is connected to the emitter of the transistor Q23 of the intermediate amplification unit 14.

According to the circuit of FIG. 3, since the transistors of the input circuit 12 have a one-stage structure, the upper limit of the input voltage can be made higher than that of the circuit of FIG. Also, since the configuration is one-stage, the distortion near the input voltage of 0V increases, so instead of the current mirror circuit, connect the constant current source 13 to the collector of the transistor Q21 to collect the collector of the transistor Q21 near the input voltage of 0V. Secured the current.

Further, since the differential input section 12 has a one-stage configuration, the base voltage and the emitter voltage of the transistor Q23 of the intermediate amplification section 14 become low, and the output voltage of the transistor Q9 rises near the input voltage of 0V. Phenomenon occurs, the emitter of transistor Q23
By raising the voltage of the emitter of the transistor Q8 by about 0.1 to 0.3V by the resistor 15 connected between the emitters of the Q8, the transistor Q8, Q near the input voltage 0V
Stabilize the operation of 9.

Also in the circuit of FIG. 3, transistors Q8 and Q
The configurations and operations of 9, Q10, Q11 and the constant voltage source 7 are the same.
According to the circuit of FIG. 3, it is possible to obtain an effect that the temperature characteristic of the upper limit voltage can be improved with a smaller number of components. Since the operational amplifier IC realized by such a small number of parts is less affected by the phase rotation and the like, it is easy to configure a circuit that can be used up to high frequencies.

The present invention can be applied not only to the operational amplifier IC but also to various circuits such as a microphone amplifier which requires a limiter circuit.

[0027]

According to the first aspect of the present invention, the temperature characteristics of the junction voltage between the base and the emitter of the two transistors are offset, so that the temperature characteristics of the upper limit voltage have a junction between the base and the emitter. It is not affected by the voltage and has a temperature characteristic equivalent to that of the constant voltage source.

Moreover, since such an effect can be realized only by adding one transistor and a constant voltage source, excellent temperature characteristics can be realized with a small number of circuit components. in addition,
Since the number of parts is small, it consumes less power and can be used with a high mounting density in small equipment. Further, since the number of parts is small and the influence of the capacitance component of the junction portion of the transistor and the rotation of the phase is small, it is possible to configure an operational amplifier that can be used even at a high frequency.

According to the second aspect, the upper limit voltage can be set to a desired voltage without changing the power supply voltage, so that it is possible to construct an amplifier circuit having a wider adaptive range than the conventional one.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of an operational amplifier IC using a limiter circuit according to claim 1 of the present invention.

FIG. 2 is an equivalent circuit diagram of a main part of a limiter circuit according to claim 2 of the present invention.

FIG. 3 is an equivalent circuit diagram of another operational amplifier IC using the limiter circuit of the present invention.

FIG. 4 is an operational amplifier IC using a conventional limiter circuit.
3 is an equivalent circuit diagram of FIG.

FIG. 5 is a configuration example of a limiter circuit using a conventional operational amplifier.

[Explanation of symbols]

 Q10 NPN transistor Q11 PNP transistor 25,26 Constant current source 5,6 Limiter circuit 7 Constant voltage source 71 Variable constant voltage source (voltage changing means) 72 Voltage switching type constant voltage source (voltage changing means) Vcc Power supply voltage OUT output terminal

Claims (2)

[Claims] 1. A base is connected to a power supply voltage via a constant current source, an emitter is provided with an NPN transistor connected to an output terminal, and an upper limit voltage subtracts the junction voltage between the base and emitter of the NPN transistor from the power supply voltage. In a limiter circuit of a single power supply system having a different voltage, the base of the NPN transistor is connected to a constant voltage source, the collector is grounded, and the emitter is connected to the base of the NPN transistor. A limiter circuit in which temperature characteristics of an upper limit voltage of a signal input to a base and output from an output terminal are improved to be equal to those of the constant voltage source. 2. The limiter circuit according to claim 1, wherein the limiter circuit is configured so that the upper limit voltage can be changed by including voltage changing means for changing the voltage of the constant voltage source.