JPH0563463A - Arithmetic amplifier - Google Patents

Abstract

PURPOSE:To provide the arithmetic amplifier with the input voltage range widened on both grounding and power supply sides. CONSTITUTION:The emitters of transistors Q22 and Q23 are commonly connected to a current source Q21, and the bases of the transistors Q22 and Q23 are connected to the input terminal. The collectors of transistors Q24 and Q25 are connected to each collector. The common current source is connected to the bases of the transistors Q24 and Q25. The collector potential of the transistors Q24 and Q25 is set to 0.4V lower by 0.3V than the base potential.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operational amplifier having an expanded common mode input range.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit diagram of a conventional operational amplifier. In this circuit, PNP transistors Q1 and Q2 whose emitters are commonly connected to a constant current source 1 are connected to current mirror connection NPN transistors Q3 and Q4 as active loads, and further, PNP transistors Q5 and Q6 are connected to Darlington connections to the transistors Q1 and Q2. Differential amplification section configured as described above, PNP transistor Q7, NPN transistor Q
8, Q9, and an output circuit composed of constant current sources 2 and 3. 4 is an inverting input terminal, 5 is a non-inverting input terminal,
6 is an output terminal.

In this circuit, the transistors Q3, Q4, Q7, etc. operate without being saturated even when the input terminals 4, 5 become 0V. For the collector voltage V _C3 of the transistor Q3, the forward voltage between its base and emitter is V _{BE 3} (= 0.7
v), V _C3 = V _{BE 3} .

Further, the emitter voltage V of the transistor Q1
_When the base-emitter forward voltage of the transistors Q5 and Q1 is V _{BE 5} (= 0.6v) and V _{BE 1} (= 0.65v) when the base of the transistor Q5 is 0v, _E1 is V _{E1 = V bE 5 + V bE} 1 = is 1.25v.

Therefore, the collector-emitter voltage V _{CE 1} of the transistor Q1 is V _{CE 1} = V _E1 -V _C3 = 1.25-0.7 = 0.55 v. As a result, the transistor Q1 operates in the current limiting region (non-saturation region). The same applies to the other transistor Q2 which is differentially connected to this.

For these transistors Q1 and Q2, the collector-emitter voltages V _{CE 1} and V _{CE 2} work as a current limiting region up to about 0.3 v, so that 0.55-0.3 = 0. Input voltages V ₄ and V ₅ applied to the input terminals 4 and 5 by 0.25 V
Can be reduced. As a result, in this circuit, the input terminal 4,
It operates even if the voltage of 5 drops from 0v to -0.25v.

[0007]

However, when the power supply voltage is V _CC , the maximum voltage that can be input to the power supply side is the collector-emitter voltage of the transistor constituting the constant current source 1 which is V _CE (= 0. 3 v), the input voltage V ₄ applied to the input terminal 4 is V ₄ = V _CC − (V _CE + V _{BE 1} + V _{BE 5} ) = V _CC − (0.3 + 0.65 + 0.6) = V _CC − It becomes 1.55v, and only a value lower than V _CC by 1.55v can be input. This is the input voltage V ₅ applied to the input terminal _5.
Is also the same.

By connecting the transistors Q5 and Q6 in this way, the input voltage range on the ground side is expanded to the negative side, but the input voltage range on the V _CC side is between the base and emitter of the transistors Q5 and Q6. Forward voltage V _BE
5 and V _{BE 6} (= 0.6v).

In the above circuit, the transistor Q
There is also a problem that the noise of 5 and Q6 cannot be ignored and is not suitable for a low noise circuit.

The object of the present invention is to avoid the problem of noise,
Another object is to provide an operational amplifier having a wide input voltage range on both the ground side and the power supply side.

[0011]

Therefore, the present invention provides the first aspect of the present invention.
A first and a second transistor having emitters commonly connected to a current source; and third and fourth transistors having collectors respectively connected to the collectors of the first and second transistors and having the same base potential. In the operational amplifier that takes out the output from one of the collectors of the third and fourth transistors,

The bases of the first and second transistors are connected to the input terminal, and the collector potentials of the third and fourth transistors are set lower than the base potential.

[0013]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a circuit diagram of an operational amplifier of the embodiment. Q21
Is a multi-collector type PNP transistor and functions as a constant current source. The resistor R1 is a resistor that determines its current value. The PNP transistors Q22 and Q23 are differential connection transistors whose operating current is determined by the transistor Q21, and their bases are directly connected to the inverting input terminal 4 and the non-inverting input terminal 5. NPN transistor Q
24 and Q25 are current mirrors to which the base current is supplied from the transistor Q22.
It works as an active load for Q23. The resistors R2 and R3 are Gm of a Gm amplifier composed of transistors Q21 to Q25.
The reducing resistors, the resistors R4 and R5, and the diode D1 are resistors for reducing the collector voltage of the transistors Q24 and Q25. NPN transistor Q26 is for emitter follower, PNP transistor Q27 is for output, PN
The P transistor Q28 is for a constant current source. The NPN transistor Q29 is a transistor forming a current mirror circuit with the transistors Q21 and Q28, the NPN transistors Q30 and Q31, the FET transistor Q32, the diodes D2 and D3, the resistors R8 and R9 are the transistors Q2.
A bias circuit that determines the current flowing through the collector of 9 is configured.

Now, assuming that the collector currents of the four collectors of the transistor Q21 are 20 μA, the transistor Q21
A current of 40 μA flows through the common emitter of 22 and Q23. Here, assuming that the values of the resistors R4 and R5 are 15 KΩ,
The voltages V _R4 and V _R5 generated in the resistors 4 and R5 are V _R5 and V _R5 = 20 μA × 15 KΩ = 0.3 v.

Further, the collector voltage V _{C2 2} of the transistor Q22 is a voltage obtained by subtracting the voltage V _R4 of the resistor R4 from the base-emitter of the transistor Q24 forward voltage _{V BE 2 4 (= 0.7V)} . In other words, the _{V C2 2 = V BE 2 4} -V R4 = 0.7-0.3 = 0.4v.

[0016] Similarly, the collector voltage V _{C2 3} of the transistor Q23, the transistor Q26, the order between the base and emitter of Q27 direction voltage _{V BE 2 6, V BE 2} 7 sum (= 1.4V)
From the voltage V _{R5 of the} resistor R5 and the forward voltage V _F1 (= 0.7v) of the diode D1. _{That, V C2 3 = V BE 2} 6 + V BE 2 7 - (V R5 + V F1) = 0.7 + 0.7- (0.3 + 0.7) = a 0.4 v.

Here, the collector-emitter voltages V _{CE 2 2} and V _{CE 2 3} of the transistors Q22 and Q23 are set to at least 0.3 v.
Up to the current limit region, and the same transistors Q22 and Q23
If between the base-emitter forward voltage _{V BE 2 2, V BE 2} 3 respectively and 0.7 v, the voltage V ₄ of the input terminal 4, 5, V ₅
Is V ₄ = V _{C2 2} + V _{CE 2 2} −V _{BE 2 2} = 0.4 + 0.3−0.7 = 0 v V ₅ = V _{C2 3} + V _{CE 2 3} −V _{BE 2 3} = 0.4 + 0.3 -0.7 = 0v. That is, it is possible to input the ground voltage to the input terminals 4 and 5.

On the other hand, on the power supply side, the transistor Q
Saturated collector-emitter voltage of _{21 V CE 2 1 (= 0} .
3 v), the voltage V ₄ of the input terminal 4 is V ₄ = V _CC − (V _{CE 2 2} + V _{BE 2 2} ) = V _CC − (0.3 + 0.7) = V _CC −1v of the input terminal 5. Similarly, the voltage V _{5 is} also V ₄ = V _CC − (V _{CE 2 3} + V _{BE 2 3} ) = V _CC − (0.3 + 0.7) = V _CC −1v. This means that the input voltage range on the power supply side is expanded by about 0.55v as compared with the conventional case.

From the above, the input voltages V ₄ and V ₅ can be applied within the range of 0 ≦ (V ₄ , V ₅ ) ≦ (V _CC −1).

Further, as described above, the transistor Q2
Since one collector of 1 supplies the base current to the transistors Q24 and Q25, it is possible to provide a wide input voltage range even under the usage condition of the gain of +1.
The noise characteristics do not deteriorate.

In the above embodiment, the transistor Q21 works as three current sources, but this can be replaced with individual current source transistors. Further, since the diode D1 only needs to generate a voltage of 0.7 V there, it can be replaced with a resistor. Also,
In this embodiment, the resistors R4 and R5, the diode D1 and the like are used to lower the collector potential of the transistors Q24 and Q25 by 0.3v below the base potential. It is not something that can be done.

[0022]

As described above, according to the present invention, since the Darlington connection transistor is not required for the differential connection transistor, a wide input voltage range can be provided, so that the noise characteristic is also excellent. Then, even in the low power supply voltage operation (V _CC ≦ 5v), a large input voltage signal can be handled. For example, with a 5v power supply, a 4v signal can be passed even with a gain of 1.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an operational amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional operational amplifier.

[Explanation of symbols]

1-3: constant current source, 4: inverting input terminal, 5: non-inverting input terminal, 6: output terminal.

Claims (5)

[Claims] 1. A first and a second transistor having emitters commonly connected to a first current source, and third and fourth transistors having collectors respectively connected to collectors of the first and second transistors and having the same base potential. A transistor is provided, and the third and fourth
In an operational amplifier that extracts an output from one collector of a transistor, the bases of the first and second transistors are connected to an input terminal, and the collector potentials of the third and fourth transistors are set lower than the base potential. Characteristic operational amplifier. 2. A second current source connected in common to the bases of the third and fourth transistors, a first resistor connected between the base and collector of the third transistor, and a diode in the collector of the fourth transistor. Second connected via
A resistor, a fifth transistor of emitter follower connection whose base is connected to the other end of the second resistor, a third current source connected to the base of the fifth transistor, and an output for receiving the output of the fifth transistor. 6. The operational amplifier according to claim 1, further comprising: 3. The operational amplifier according to claim 2, wherein the first to third current sources are composed of one multi-collector transistor. 4. The operational amplifier according to claim 2, wherein the first and second resistors have the same value. 5. The operational amplifier according to claim 2, wherein the diode is replaced with a resistor.