JPH06164264A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit without being affected by an input signal level by providing third and fourth transistors to which the collector output of first and second transistors are applied, and fifth and sixth transistors whose bases are connected to a reference power source commonly. CONSTITUTION:This circuit is equipped with the fifth transistor 24 whose emitter is connected to the collector of the first transistor 5 and whose collector to the ground and whose base to a first reference power source VREF, respectively, and the sixth transistor 25 whose emitter is connected to the collector of the second transistor 6 and whose collector to the ground and whose base to the first reference power source VREF, respectively. An input signal Vin applied between input terminals A, B is differentially amplified by the first and second transistors 5, 6, and furthermore, a signal applied between the bases of the third and fourth transistors 10, 11 is amplified by a differential amplifier circuit consisting of the third and fourth transistors 10, 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a differential amplifier circuit, and particularly to provide a differential amplifier circuit suitable for use in a gyrator (equivalent L circuit).

[0002]

2. Description of the Related Art Conventionally, a gyrator as shown in FIG. 2 has been known. This gyrator includes an input terminal 1, a first amplifier circuit 2 having a positive input terminal connected to the input terminal 1 and a negative input terminal connected to ground, and a capacitor connected to an output terminal of the first amplifier circuit 2. 3 and the negative input terminal is the first amplifier circuit 2
The positive input terminal is connected to the ground, and the output terminal is connected to the positive input terminal of the first amplifying circuit 2. Then, using the circuit of FIG. 2, when viewed from the input terminal 1, C / (G1 × G2)
(However, C is the capacitance of the capacitor 3, G1 is the mutual conductance of the first amplifier circuit 2, and G2 is the mutual conductance of the second amplifier circuit 4.) Since an equivalent L is obtained, the phase shift circuit is integrated into a circuit. It is often used for etc.

The first and second amplifier circuits 2 and 4 in FIG. 2 are required to have characteristics such as a wide input dynamic range and stable and large mutual conductance.
For example, a differential amplifier circuit as shown in FIG. 3 has been conventionally used. In FIG. 3, the input stage consists of first and second transistors 5 and 6 which are differentially connected. The collectors of the first and second transistors 5 and 6 have a constant voltage source 7 at their bases.
The emitters of the third and fourth transistors 8 and 9 that are connected to the load are connected. The collectors of the first and second transistors 5 and 6 are connected to the bases of the fifth and sixth transistors 10 and 11, respectively, which form the next stage differential amplifier circuit. The base of the output transistor 12 is connected to the collector of the sixth transistor 11.

In the differential amplifier circuit of FIG. 3, a constant current source 1
The currents flowing in 3 and 14 are I ₁ , respectively, and the constant current source 15
Let I ₂ be the current flowing through the resistor and R _{E be} the resistance value of the resistor 16,
The mutual conductance G is I ₂ / (2I ₁ R _E ).
The differential amplifier circuit of FIG. 3 is often used because of its excellent characteristics, but the base amplifiers of the third and fourth transistors 8 and 9 are used.
Since the base-emitter voltage V _BE of the emitter voltage V _BE and the fifth and sixth transistors 10 and 11 are required, can not be used in the device of low power supply voltage as in the case of using a battery of 1.5V There was a problem.

The differential amplifier circuit of FIG. 4 is obtained by improving the differential amplifier circuit of FIG. 3 so that it operates at a low power supply voltage. In FIG. 4, the first and second transistors 5 and 6
Collector current is extracted via the first and second current mirror circuits 17 and 18 , and is supplied to the load resistors 19 and 20. The terminal voltage of the load resistor 19 is applied to the base of the transistor 11, and the terminal voltage of the load resistor 20 is applied to the base of the transistor 10 and differentially amplified by the transistors 10 and 11. The output signals differentially amplified by the transistors 10 and 11 are output to the output terminal 21.

[0006]

The differential amplifier circuit shown in FIG. 4 can operate at a sum voltage V _BE + 2V _CE of a transistor base-emitter voltage V _BE and a collector-emitter voltage V _CE. Therefore, it can be used for equipment with low power supply voltage. However, in the circuit of FIG. 4, the collector currents of the first and second transistors 5 and 6 are composed of PNP transistors, and the first and second current mirror circuits 17 are provided.
And 18 must be removed using a deteriorated frequency characteristic, there is a problem that does not operate at high frequencies.
Further, since the input levels of the transistors 10 and 11 forming the output stage are determined by the input signal level to the input stage and the gain of the input stage, there is a problem that the transconductance of the entire circuit changes depending on the input signal level. It was Therefore, the differential amplifier circuit of FIG. 4 has limited applications.

[0007]

The present invention has been made in view of the above points, and provides a differential amplifier circuit which operates at a low power supply voltage and whose mutual conductance does not change depending on an input signal level. Differentially connected to the first and second transistors connected to each other and the current loads connected to the collectors of the first and second transistors, respectively, and the collector outputs of the first and second transistors are applied to the bases, respectively. And a fifth and a sixth transistor whose emitters are respectively connected to the bases of the third and fourth transistors and whose bases are commonly connected to a reference power source. To do.

In the present invention, the emitters are connected to the collectors of the first and second transistors, the bases are commonly connected to the second reference power source, and the collectors are connected to the bases of the third and fourth transistors, respectively. It is characterized in that the seventh and eighth transistors are provided.

[0009]

According to the present invention, a current load is arranged as a load of the input stage composed of the first and second transistors, and the input end of the output stage composed of the third and fourth transistors is directly connected to the output end of the input stage. Since they are connected, a differential amplifier circuit that operates at a low voltage can be provided. In addition, since the fifth and sixth transistors are provided to reduce the input impedance of the output stage, it is possible to provide a circuit that is not affected by the input signal level.

Further, the first and second transistors and the third transistor
If a seventh and an eighth transistor to which a reference voltage that changes according to the power supply voltage is applied are provided between the base and the fourth transistor, the collectors of the seventh and the eighth transistor according to the fluctuation of the power supply voltage. Since the voltage between the emitters can be changed and the mutual conductance can be kept constant by keeping the voltage drop of the current load constant, it is possible to provide a differential amplifier circuit that is resistant to fluctuations in the power supply voltage.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
In the figure, 22 is a constant current source connected to the collector of the first transistor 5 as a current load, 23 is a constant current source connected to the collector of the second transistor 6 as a current load, and 24 is an emitter of the first transistor 5. 5, the collector is grounded, the base is the first reference power supply V _REF
The fifth transistor and the second transistor 25, which are respectively connected to, are a sixth transistor having an emitter connected to the collector of the second transistor 6, a collector connected to ground, and a base connected to the first reference power source.

The other circuit elements in FIG. 1 are designated by the same reference numerals as those in FIG. 4, and the description thereof is omitted. Next, the operation will be described. The input signal ΔV _in applied between the input terminals A and B first receives the first and second transistors 5 and 6.
Is differentially amplified by. The current flowing through the constant current sources 13 and 14 is I ₁ , the current flowing through the constant current source 15 is I ₂ , and the constant current source 22 is
If the current flowing through I and I is I ₃ , the collector current Δi ₁ of the first transistor 5 is as shown in the equation (1).

[0013]

[Equation 1]

Here, re is the resistance value of the emitter resistance of the transistor, and R _E is the resistance value of the emitter resistance. Also,
The collector current I ₃ of the fifth transistor 24 is I ₃ = I ₄
Since it becomes −I ₁ , the base-to-base voltage ΔV ₂ of the third and fourth transistors 10 and 11 is expressed by the equation (2).

[0015]

[Equation 2]

The signal applied between the bases of the third and fourth transistors 10 and 11 is further amplified by the differential amplifier circuit composed of the third and fourth transistors 10 and 11. Therefore, the output current I _out obtained at the collector of the fourth transistor 11 is expressed by the equation (3).

[0017]

[Equation 3]

However, V _T is a temperature coefficient. Input voltage Δ
The relationship between V _in and the output current ΔI _out , that is, the mutual conductance G is as shown in the formula (4), and as is clear from the formula (4), the mutual conductance G is stable regardless of the input signal level. Becomes

[0019]

[Equation 4]

On the other hand, the circuit of FIG. 1 has constant current sources 15 and 2
Since it operates with a power supply voltage equal to or higher than the sum voltage (V _BE + 2V _CE ) of the voltage drop (V _CE ) of 2 and the base-emitter voltage V _BE of the transistor 10, a differential amplifier circuit that can operate with a low power supply voltage Can be provided. By the way, in the circuit of FIG. 1, when the power supply voltage changes, the collector-emitter voltage of the constant current source 22 changes accordingly, and the base voltages of the third and fourth transistors 10 and 11 change. Although this voltage change is minute, it becomes a problem when more accurate transconductance is obtained.

FIG. 5 is a further improvement of the operational amplifier circuit of FIG. 1, in which the mutual conductance can be maintained at a predetermined value even if the power supply voltage fluctuates. 5, the circuits corresponding to the constant current sources 22 and 23 of FIG. 1 are composed of transistors 26 to 28, resistors 29 to 31 and a constant current source 32. The collector-emitter paths of the seventh and eighth transistors 33 and 34 are connected between the collectors of the first and second transistors 5 and 6 and the bases of the third and fourth transistors 10 and 11, respectively. . The seventh and eighth transistors 33
A reference voltage V _REF1 that changes according to the power supply voltage is applied to the bases of the and 34.

In the circuit of FIG. 5, the base voltages of the seventh and eighth transistors 33 and 34 change according to the power supply voltage, and the transistors 27 and 28 forming a constant current source.
Since the voltage between the emitter and collector of is kept substantially constant, the emitter currents of the fifth and sixth transistors 24 and 25 can be kept substantially constant. As a result, the base voltages of the third and fourth transistors can be kept stable against changes in the power supply voltage, and more accurate transconductance can be obtained.

[0023]

As described above, according to the present invention, it is possible to provide a differential amplifier circuit which operates with a low power supply voltage. Further, according to the present invention, it is possible to provide a differential amplifier circuit in which the gain of the next-stage amplifier circuit is not affected by the input signal level. Further, according to the present invention, it is possible to provide a differential amplifier circuit that is stable against fluctuations in power supply voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional gyrator.

FIG. 3 is a circuit diagram showing a conventional differential amplifier circuit.

FIG. 4 is a circuit diagram showing a conventional differential amplifier circuit.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

 5 ... 1st transistor 6 ... 2nd transistor 10 ... 3rd transistor 11 ... 4th transistor 13, 14, 15 ... Constant current source 22, 23 ... Current load 24 ... 5th transistor 25 ... 6th transistor 33 ... 7th transistor 34 ... 8th transistor

Claims (2)

[Claims] 1. A differentially connected first and second transistor, a current load respectively connected to the collectors of the first and second transistors, and a differentially connected base to which the first and second transistors are connected, respectively. Third and fourth transistors to which collector outputs of the transistors are applied, and fifth and sixth transistors whose emitters are connected to the bases of the third and fourth transistors, respectively, and whose bases are commonly connected to a reference power source, And a differential amplifier circuit configured to obtain an output signal at the collector of the third transistor or the fourth transistor. 2. An emitter connected to the collectors of the first and second transistors, respectively, and a base commonly connected to a second reference power supply whose output voltage changes in response to changes in the power supply voltage. An eighth transistor is provided, and the seventh transistor
2. The differential amplifier circuit according to claim 1, wherein collectors of the eighth and eighth transistors are connected to bases of the third and fourth transistors, respectively.