JP2003110373A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit having a large input impedance. SOLUTION: A resistor R1 is connected in between transistors 1, 2, whose gate electrodes are respectively connected to a positive and a negative input terminals. Currents, having the same value, are passed to both ends of the resistor R1 by constant current sources 10, 11. The voltage at the positive and negative input terminals are the same as the voltage of both the ends of the resistor R1. The current, flowing through the resistor R1, is extracted by using current mirror transistors 4, 6 and current mirror transistors 3, 5, 7, 8. Since a current having the same value as that in the resistor R1 flows through the resistor R2, a voltage (potential difference between the positive and negative input terminals multiplied by R2/R1) is outputted to an output terminal. Since the positive and negative input terminals are connected to the gate electrodes of the transistors, the circuit has a large impedance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit that greatly amplifies a small electric signal in an electronic circuit. More specifically, the present invention relates to an amplifier circuit that amplifies a voltage difference between positive and negative input terminals with an amplification factor according to a resistance ratio and outputs the voltage difference as a voltage difference between an output terminal and a reference potential such as GND. Furthermore, since the amplifier circuit can be configured only with MOS transistors and resistors, it relates to an integrated amplifier circuit.

[0002]

2. Description of the Related Art First, a conventional amplifier circuit will be described to clarify the background of the present invention. FIG. 2 shows an amplifier circuit that has been widely used conventionally. The amplifier circuit of FIG. 2 is called a so-called differential amplifier circuit.

In the circuit of FIG. 2, it is assumed that R1 = R3 and R2 = R4. The voltage difference between the positive input terminal and the negative input terminal is the resistance ratio = R
It is amplified by the amplification factor of 2 / R1, and the output terminal and the reference voltage V
It is output as the voltage difference between b.

[0004]

The circuit shown in FIG. 2 has the following problems or problems. A resistor R1 is connected between the negative input terminal and the negative input terminal of the operational amplifier 14, and the input impedance of the negative input terminal is R1.
The input impedance of the positive input terminal is R3 + R
It becomes 4. Therefore, when connecting the outputs of other circuits to the positive input terminal and the negative input terminal, it is necessary to have the ability to drive the input impedance sufficiently.

[0005]

In order to solve the problems of the prior art, the present invention employs the means shown in FIG. That is, in the first transistor, the drain electrode is commonly connected to the drain electrode and gate electrode of the third transistor, and the gate electrode of the fifth transistor, the gate electrode is connected to the positive input terminal, and the source electrode is connected to one end of the resistor R1. And constant current source 10
Commonly connected to one end of. In the second transistor, the drain electrode is commonly connected to the gate electrode and drain electrode of the fourth transistor, and the gate electrode of the sixth transistor, the gate electrode is connected to the negative input terminal, and the source electrode is connected to the resistor R1.
Are commonly connected to the other end of the constant current source 11. Third,
The source electrode of transistor No. 4 was connected to the GND potential. In the fifth transistor, the drain electrode was commonly connected to the gate electrode and drain electrode of the seventh transistor and the gate electrode of the eighth transistor, and the source electrode was connected to the GND potential. The drain electrode of the sixth transistor is the drain electrode of the eighth transistor and the operational amplifier circuit 14
The inverting input terminal and the one end of the resistor R2 are commonly connected, and the source electrode is connected to the GND electrode. The source electrodes of the seventh and eighth transistors were connected to the power supply.

The other ends of the constant current sources 10 and 11 are connected to a power source. The reference voltage source Vb has one end connected to the positive input terminal of the operational amplifier and the other end connected to the GND potential. The other end of the resistor R2 is commonly connected to the output terminal and the output of the operational amplifier.

In the circuit of FIG. 1, the potential difference between the positive and negative input terminals is substantially equal to the potential difference of the resistor R1. Transistors 3, 4, 5, 6 are all the same size
And 8 are equal in size. Since the current flowing through the resistor R1 is equal to the current flowing through the resistor R2, a voltage difference that is R2 / R1 times the potential difference between the positive and negative inputs occurs at both ends of the resistor R2. That is, the circuit of FIG. 1 amplifies the voltage difference between the positive and negative input terminals. The positive and negative input terminals are connected to the gate electrodes of the transistor 1 and the transistor 2, respectively. The transistors 1 and 2 are so-called MOS transistors, and the input impedance of the gate electrode is extremely large. Therefore, the input impedance of the amplifier circuit of FIG. 1 is extremely large, and it hardly affects the driving capability of the preceding circuit to be connected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a concrete circuit configuration of an amplifier circuit according to the present invention. In the circuit of FIG. 1, the potential difference between the positive and negative input terminals is substantially equal to the potential difference of the resistor R1.
It is assumed that the transistors 3, 4, 5 and 6 have the same size, and the transistors 7 and 8 have the same size. Since the current flowing through the resistor R1 is equal to the current flowing through the resistor R2, a voltage difference that is R2 / R1 times the potential difference between the positive and negative inputs occurs at both ends of the resistor R2. That is, the circuit of FIG. 1 is an amplifier circuit for the voltage difference between the positive and negative input terminals.

[0009]

EXAMPLE FIG. 1 shows an example of the present invention. In the transistor 1, the drain electrode is commonly connected to the drain electrode and the gate electrode of the transistor 3 and the gate electrode of the transistor 5, the gate electrode is connected to the positive input terminal, and the source electrode is connected to one end of the resistor R1 and one end of the constant current source 10. Connected in common. In the transistor 2, the drain electrode is commonly connected to the gate electrode and the drain electrode of the transistor 4 and the gate electrode of the transistor 6, the gate electrode is connected to the negative input terminal, and the source electrode is the other end of the resistor R1 and one end of the constant current source 11. Commonly connected to. The source electrodes of the transistors 3 and 4 were connected to the GND potential. The transistor 5 has a drain electrode, a gate electrode of the transistor 7, a drain electrode, and a transistor 8
, And the source electrode was connected to the GND potential. In the transistor 6, the drain electrode is commonly connected to the drain electrode of the transistor 8, the inverting input terminal of the operational amplifier circuit 14 and one end of the resistor R2, and the source electrode is connected to GND.
It was connected to the electrode. The source electrodes of the transistors 7 and 8 were connected to the power supply.

The other ends of the constant current sources 10 and 11 were connected to a power source. The reference voltage source Vb has one end connected to the positive input terminal of the operational amplifier and the other end connected to the GND potential. The other end of the resistor R2 is commonly connected to the output terminal and the output of the operational amplifier.

In the circuit of FIG. 1, constant current sources 10, 11
The same current is applied to both. First, the case where the voltage difference between the positive and negative input terminals is 0 will be described. The currents flowing through the transistors 1 and 2 are equal, and the currents flowing through the transistors 3 and 4 are also equal. If the currents flowing through the transistors 1 and 2 are equal,
Since the voltage Vgs between the gate electrode and the source electrode of the transistors 1 and 2 is equal, and the voltage across the resistor R1 is also equal,
No current flows through the resistor R1. The gate electrodes of the transistors 5 and 6 are commonly connected to the gate electrodes of the transistors 3 and 4, respectively, to form a so-called current mirror circuit.
Therefore, the current flowing through the transistors 5 and 6 is the current flowing through the transistors 3 and 4 multiplied by the transistor size ratio. Similarly, since the gate electrodes of the transistors 7 and 8 are commonly connected to form a so-called current mirror circuit, the current flowing through the transistor 8 is the current flowing through the transistor 7 multiplied by the transistor size ratio.

Here, it is assumed that the sizes of the transistors 3, 5, 5, 4, 6 and 7, 8 are equal to each other. If the currents flowing through the transistors 3 and 4 are equal,
The currents flowing through the transistors 5 and 6 are equal. A current equal to the current flowing through the transistor 5 flows through the transistors 7 and 8. Since the current flowing through the transistor 8 is equal to the current flowing through the transistor 6, no current flows through the resistor R2. Therefore, the output of the operational amplifier 14 is equal to the value of the reference voltage Vb.

Next, the case where the positive input terminal is higher than the voltage of the negative input terminal by a (Volt) will be described. Assuming that the Vgs of the transistors 1 and 2 are substantially equal, the voltage of the source electrode of the transistor 1 becomes higher than the voltage of the source electrode of the transistor 2 by a. Therefore, the potential difference across the resistor R1 is a, and the current flowing through the resistor R1 is a / R1.
become. Since the current values of the constant current sources 10 and 11 are equal, the current flowing through the transistor 2 is larger than the current flowing through the transistor 1 by a / R1. The current flowing through the transistor 4 is a / R1 larger than the current flowing through the transistor 3,
The current flowing through the transistor 6 is a / R1 larger than the current flowing through the transistor 5. Since the current flowing through the transistor 8 is smaller than the current flowing through the transistor 6 by a / R1, a current of a / R1 flows through the resistor R2 from the output terminal of the operational amplifier 14 to the inverting input terminal of the operational amplifier 14. The potential difference across the resistor R2 becomes a * R2 / R1 by multiplying the resistance value R2 by the current value a / R1.

With respect to Vb as a reference, the output terminal has a *
A voltage of R2 / R1 is generated. That is, an output obtained by multiplying the potential difference a between the positive and negative input terminals by R2 / R1 can be obtained. When the positive and negative input terminals have a potential difference of −a (Volt), which is the opposite of the above, the output has a voltage value of −a * R2 / R1.

In the circuit of FIG. 1, positive and negative input terminals are connected to the gate electrodes of the transistors 1 and 2, respectively. The gate electrode generally has high impedance and hardly passes direct current. Therefore, a circuit having a small driving capability can be connected to the front stage of the circuit shown in FIG.

The circuit of FIG. 3 is the constant current source 1 of the circuit of FIG.
0 and 11 are realized by transistors 10 and 11 whose gate electrodes are connected to a constant voltage value Vc. The source electrodes of the transistors 10 and 11 are connected to the power supply terminal, and the drain electrodes are commonly connected to the source electrodes of the transistors 1 and 2, respectively. Since the gate voltage is constant in the transistors 10 and 11, a substantially constant current flows. Since the circuit of FIG. 3 is composed of only a transistor and a resistor, it is suitable for an integrated circuit.

The circuit of FIG. 4 is obtained by adding transistors 21, 22, 23 and 24 to the circuit of FIG. The drain electrode of the transistor 21 is connected to the power supply, the gate electrode is connected to the positive input terminal, and the source electrode is commonly connected to the gate electrode of the transistor 1 and the drain electrode of the transistor 23. The drain electrode of the transistor 22 is connected to the power supply terminal, the gate electrode is connected to the negative input terminal, and the source electrode is the gate electrode of the transistor 2 and the transistor 24.
Is commonly connected to the drain electrode of. Transistor 2
The gate electrode of 3 is commonly connected to the gate electrode and drain electrode of the transistor 4 and the gate electrode of the transistor 6, and the source electrode thereof is connected to the GND potential. The gate electrode of the transistor 24 is commonly connected to the gate electrode and drain electrode of the transistor 3 and the gate electrode of the transistor 5, and the source electrode thereof is connected to the GND potential. The parts other than the transistors 21, 22, 23, and 24 are the same as the circuit of FIG. 1, and each circuit element performs the same operation as the circuit of FIG.

In the circuit of FIG. 4, the size of the transistor 24 and the size of the transistor 3 are the same, and the size of the transistor 23 and the size of the transistor 4 are the same. Since the gate electrodes of the transistors 23 and 4 and the transistors 24 and 3 are commonly connected, the currents flowing through the transistors 23, 4, and 24 and 3 are equal. Voltage-current conversion coefficient (β) of transistors 1, 2, 21, 22
Set the sizes so that they are equal.

First, the case where the voltage difference between the positive and negative input terminals is 0 will be described. The currents flowing through the transistors 1 and 2 are equal, and the currents flowing through the transistors 3 and 4, the currents flowing through the transistors 23 and 24, and the currents flowing through the transistors 21 and 22 are equal. Since the currents are equal, transistor 2
Since the voltage Vgs between the gate electrodes and the source electrodes of the transistors 2 and 21 and the transistors 1 and 2 is equal, and the voltage across the resistor R1 is also equal, no current flows through the resistor R1. The gate electrodes of the transistors 5 and 6 are commonly connected to the gate electrodes of the transistors 3 and 4, respectively, to form a so-called current mirror circuit. Therefore, the current flowing through the transistors 5 and 6 is the current flowing through the transistors 3 and 4 multiplied by the transistor size ratio. Similarly, since the gate electrodes of the transistors 7 and 8 are commonly connected to form a so-called current mirror circuit, the current flowing through the transistor 8 is the current flowing through the transistor 7 multiplied by the transistor size ratio.

Next, the case where the positive input terminal is higher than the voltage of the negative input terminal by a (Volt) will be described. In the description of FIG. 1, it is assumed that the Vgs of the transistors 1 and 2 are almost equal, but in reality, the Vgs of the transistors 21, 22 and 1 are slightly different because the flowing currents are different.

The current-voltage conversion coefficient of the transistor is β,
Id is the current flowing through the transistor, and transistors 1 and 2 are
Assuming that the difference between the current flowing through the transistor and the current flowing through the transistors 21 and 22 is ΔId and the threshold voltage of the transistor is Vth, the current flowing through the transistor is generally Id = (β / 2) * (Vgs−Vth) ** 2 (** 2 represents the square) (1) can be expressed as
The difference between the Vgs of the transistors 21 and 22 and ΔVgs is ΔVgs = √ ((Id + ΔId) / (2 * β)) − √ (Id / (2 * β), assuming that a large amount of ΔId flows in one transistor. ) (2)

Since the currents flowing through the constant current sources 10 and 11 are equal, the difference between the currents flowing through the transistors 1 and 2 is the resistance R
It becomes the electric current which flows into 1. Since the voltage at the positive input terminal is higher than the voltage at the negative input terminal by a (V), the transistor 21
Is higher than the voltage of the source electrode of the transistor 22 by a, and the voltage of the source electrode of the transistor 1 is higher by a than the voltage of the source electrode of the transistor 2. Since both ends of the resistor R1 are connected to the source electrodes of the transistors 1 and 2, the potential difference between both ends of the resistor R1 is a. Since the current of a / R1 flows through the resistor R1,
The transistor 2 has a larger ΔId current. Since the difference in Vgs between the transistor 2 and the transistor 1 can be expressed by the equation (2), the Vgs of the transistor 2 is larger than the Vgs of the transistor 1 by ΔVgs of the equation (2).

The current flowing through the transistor 2 is equal to the current flowing through the transistors 4, 23 and 21, and the current flowing through the transistor 1 is equal to the current flowing through the transistors 3, 24 and 22. Therefore, the current difference ΔId flowing between the transistor 21 and the transistor 22 is
Is equal to the current difference ΔId. That is, in the transistor 21,
A current larger than that of the transistor 22 by ΔId is flowing. Similarly, the difference in Vgs between the transistors 21 and 22 can be expressed by the equation (2), and the transistor 21 has a larger Vgs by ΔVgs.

When the voltage difference between the positive and negative input terminals is a, the potential difference between the source electrodes of the transistors 21 and 22 is exactly a
The potential difference between the gate electrodes of the transistors 1 and 2, which is + ΔVgs, is naturally a + ΔVgs, and
The potential difference of the source electrode of is a minus ΔVgs
Becomes In the absence of the transistors 21, 22, 23, and 24, to be precise, a voltage of a + Vgs is applied across the resistor R1 and an error of ΔVgs is generated. In the circuit of FIG. 4, the ΔVgs of the transistors 21 and 22 is increased. However, since ΔVgs of the transistors 1 and 2 is canceled, the potential difference between both ends of the resistor R1 and the potential difference between the positive and negative input terminals are exactly equal. The circuit of FIG. 4 can provide an amplifier circuit with less error than the circuit of FIG.

The circuit operation of the latter half of the circuit shown in FIG. 4 will be described. It is exactly the same as the circuit of FIG. The current flowing through the transistor 2 is a
/ R1 is large. The current flowing through the transistor 4 is a / R1 larger than the current flowing through the transistor 3, and the current flowing through the transistor 6 is a / R1 larger than the current flowing through the transistor 5.
/ R1 increases. Since the current flowing through the transistor 8 is smaller than the current flowing through the transistor 6 by a / R1, the resistor R2 is connected to the operational amplifier 1 through the output terminal of the operational amplifier 14.
The current of a / R1 flows in the direction of the inverting input terminal of No. 4. The potential difference between both ends of the resistor R2 is calculated by adding the current value a / R1 to the resistance value R2.
Multiply a * R2 / R1.

At the output terminal, when Vb is the reference, a *
A voltage of R2 / R1 is generated. That is, an output obtained by multiplying the potential difference a between the positive and negative input terminals by R2 / R1 can be obtained. When the positive and negative input terminals have a potential difference of −a (Volt), which is the opposite of the above, the output has a voltage value of −a * R2 / R1.

The circuit of FIG. 5 differs from the circuit of FIG. 1 in that transistors 31, 32, 33 and 34 and transistors 41, 42 and 4 are included.
3,44 is added.

The drain electrode of the transistor 31 is GND
The gate electrode is connected to the potential, the gate electrode is connected to the positive input terminal, and the source electrode is commonly connected to the gate electrode of the transistor 1 and the drain electrode of the transistor 32. The gate electrode of the transistor 32 is commonly connected to the gate electrode and drain electrode of the transistor 33 and the drain electrode of the transistor 34, and the source electrode is connected to the power supply terminal. The source electrode of the transistor 33 is connected to the power supply. The gate electrode of the transistor 34 is commonly connected to the drain electrode and the gate electrode of the transistor 4, and the source electrode is connected to the GND potential. The drain electrode of the transistor 41 is connected to the GND potential, the gate electrode is connected to the negative input terminal, and the source electrode is commonly connected to the gate electrode of the transistor 2 and the drain electrode of the transistor 42. The gate electrode of the transistor 42 is commonly connected to the gate electrode and drain electrode of the transistor 43 and the drain electrode of the transistor 44, and the source electrode is connected to the power supply terminal. The source electrode of the transistor 43 is connected to the power supply. The gate electrode of the transistor 44 is commonly connected to the drain electrode and the gate electrode of the transistor 5, and the source electrode is connected to the GND potential.

Transistors 31, 32, 33, 34, 4
The circuits other than 1, 42, 43 and 44 are exactly the same as those in FIG. 1, and the same elements perform the same functions.

Transistors 3 and 44, Transistors 4 and 34, Transistors 33 and 32, Transistors 43 and 4
2 have the same size, and transistors 1, 2, 31, 41
Have the same size and β have the same size. Transistors 3 and 44,
The gate electrodes of the transistors 4 and 34, the transistors 33 and 32, and the transistors 43 and 42 are commonly connected to each other, and the Vgs are equal, so that the flowing currents are equal to each other.
Therefore, the same current as the transistor 2 flows through the transistor 31, and the same current as the transistor 1 flows through the transistor 41.

The circuit of FIG. 5 is a so-called source follower circuit composed of the transistors 21, 22, 23 and 24 in the circuit of FIG.
And transistors 41, 42, 43 and 44. In the circuit of FIG. 5, since the transistors 31 and 41 of the source follower circuit have the same polarity as the transistors 1 and 2, β can be easily made equal by making the sizes equal. The circuit of FIG. 5 is functionally equivalent to that of FIG.
Performs the same operation as the circuit.

It is assumed that a potential difference of a (V) is generated across the resistor R1 and the voltage of the source electrode of the transistor 1 is higher than the voltage of the source electrode of the transistor 2. Resistance R1
, A current of a / R1 flows. On the other hand, constant current sources 10 and 1
Since the current value of 1 is the same, the current value of transistor 2 is larger than that of transistor 1 by a / R1. Transistor 1,
Assuming that the current difference of 2 is ΔId = a / R1, the potential difference ΔVgs of Vgs of the transistors 1 and 2 can be obtained by the equation (2). Therefore, the potential difference between the gate electrodes of the transistors 1 and 2 is a + ΔVgs. The current flowing through the transistor 31 is equal to the current flowing through the transistors 2 and 4,
Since the current flowing through the transistor 41 is equal to the current flowing through the transistors 1 and 3, the current flowing through the transistor 31 is larger by ΔId = a / R1 than the current flowing through the transistor 41. Therefore, the potential difference ΔVgs of Vgs of the transistors 31 and 41 can be similarly obtained from the equation (2) and has the same value as ΔVgs of the transistors 2 and 1.

The source electrodes of the transistors 31 and 41 are
Since they are connected to the gate electrodes of the transistors 1 and 2, respectively, the potential difference is a + ΔVgs. As described above, since ΔVgs of the transistors 31 and 41 is equal to ΔVgs of the transistors 1 and 2, the voltage between the positive and negative input terminals is a. That is, in the circuit of FIG. 5, like the circuit of FIG. 4, the voltage between the positive and negative input terminals becomes equal to the voltage of the resistor R1 and is not affected by the difference in current flowing through the transistor.

The circuit operation of the latter half of the circuit of FIG. 5 will be described. It is exactly the same as the circuit of FIG. The current flowing through the transistor 2 is a
/ R1 is large. The current flowing through the transistor 4 is a / R1 larger than the current flowing through the transistor 3, and the current flowing through the transistor 6 is a / R1 larger than the current flowing through the transistor 5.
/ R1 increases. Since the current flowing through the transistor 8 is smaller than the current flowing through the transistor 6 by a / R1, the resistor R2 is connected to the operational amplifier 1 through the output terminal of the operational amplifier 14.
The current of a / R1 flows in the direction of the inverting input terminal of No. 4. The potential difference between both ends of the resistor R2 is calculated by adding the current value a / R1 to the resistance value R2.
Multiply a * R2 / R1.

The output terminal has a *
A voltage of R2 / R1 is generated. That is, an output obtained by multiplying the potential difference a between the positive and negative input terminals by R2 / R1 can be obtained. When the positive and negative input terminals have a potential difference of −a (Volt), which is the opposite of the above, the output has a voltage value of −a * R2 / R1.

The circuit of FIG. 6 is obtained by replacing the resistor 13, the operational amplifier 14, and the reference voltage Vb of the circuit of FIG. 4 with a capacitor C. From the drain electrodes of the transistors 8 and 6, a current of a / R1 proportional to the potential difference a at the positive and negative input terminals is output. The voltage generated at both ends of the output terminal, that is, the capacitance C is obtained by dividing the current value a / R1 by time and dividing it by the capacitance value C. In the circuit of FIG. 6, as described in the circuit of FIG. 4, the potential difference between the positive and negative input terminals is exactly equal to the potential difference across the resistor R1. The output current is not affected by the difference between the currents flowing through the transistors 1 and 2.

In the circuit of FIG. 6, circuits other than the capacitor C can be generally used as the VI conversion circuit 50 (voltage current conversion circuit). That is, the potential difference (voltage difference) between the positive and negative input terminals can be accurately converted into a current.

The circuit shown in FIG. 7 is the VI conversion circuit 50 shown in FIG.
Is used instead of the resistance of the filter. Input the input signal to the positive input terminal. The negative input terminal is connected to the output terminal. The VI conversion circuit 50 of FIG. 7 outputs a current proportional to the potential difference between the positive input terminal and the output terminal. The conversion coefficient of voltage and current becomes R1. That is, the VI conversion circuit 50 in FIG. 7 has the same function as the resistor R1. Further, if the circuit of FIG. 6 is used as the VI conversion circuit 50, the potential difference between the positive and negative input terminals can be accurately converted into a current without being affected by the Vgs difference of the internal transistor, and therefore, when used as a filter resistor. ， The resistance value can be realized accurately.

[0039]

As described above, according to the present invention,
Since the positive and negative input terminals are connected to the gate electrode of the transistor, it is possible to provide an amplifier circuit having an extremely large input impedance. Further, by adding a source follower circuit, an error caused by a difference in current flowing through the transistor is canceled out, so that an accurate amplification factor can be obtained.

In the circuit of FIG. 1, assuming that the voltage between the positive and negative input terminals is a, to be precise, a + ΔV is present across the resistor R1.
A voltage of gs is generated. ΔVgs is the transistor 1,
It is the difference in Vgs due to the current difference ΔId of 2 and can be obtained by the equation (2). In the circuit of FIG. 4, the output voltage is (a + ΔVgs) × R2 /
It becomes R1 and an error occurs.

On the other hand, in the circuit of FIG.
It is assumed that the potential difference of (V) is generated and the voltage of the source electrode of the transistor 1 is higher than the voltage of the source electrode of the transistor 2. A current of a / R1 flows through the resistor R1.
On the other hand, since the constant current sources 10 and 11 have the same current value, the transistor 2 has a larger current value a / R1 than the transistor 1. Assuming that the current difference between the transistors 1 and 2 is ΔId = a / R1, the potential difference ΔVgs between the Vgs of the transistors 1 and 2 is ΔVgs.
Is calculated by the equation (2). Therefore, the potential difference between the gate electrodes of the transistors 1 and 2 is a + ΔVgs.

The source electrodes of the transistors 21 and 22 are
Since they are commonly connected to the gate electrodes of the transistors 1 and 2, the potential difference is a + ΔVgs. ΔVgs of the transistors 21 and 22 is ΔVgs of the transistors 1 and 2.
Since it is equal to gs, the voltage between the positive and negative input terminals is a. That is, in the circuit of FIG. 4, the voltage between the positive and negative input terminals is
It becomes equal to the voltage of the resistor R1 and is not affected by the difference in current flowing through the transistor. Therefore, the output voltage is exactly the voltage a * R2 / R1 between the input terminals.

[Brief description of drawings]

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

FIG. 2 is an amplifier circuit according to the related art.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a circuit diagram showing an embodiment of the present invention.

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

FIG. 6 is a circuit diagram showing an embodiment of the present invention.

FIG. 7 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

1,2,3,4,5,6,7,8 transistors 21,22,23,24 transistors 31, 32, 33, 34 transistors 41, 42, 43, 44 transistors 10, 11 constant current source 14 Operational amplifier 12, 13, 16, 17 resistance C capacity 50 VI conversion circuit

Continued front page    F term (reference) 5J066 AA01 AA12 CA72 CA88 FA20                       HA10 HA17 HA25 HA29 KA01                       KA05 KA09 MA02 MA21 ND01                       ND12 ND25 PD01 TA01                 5J091 AA01 CA72 CA88 FA15 HA10                       HA17 HA19 HA25 HA29 KA01                       KA02 KA05 KA09 KA31 KA41                       MA02 MA08 MA21 TA01                 5J500 AA01 AA12 AC72 AC88 AF15                       AF20 AH10 AH17 AH19 AH25                       AH29 AK01 AK02 AK05 AK09                       AK31 AK41 AM02 AM08 AM21                       AT01 DN01 DN12 DN25 DP01

Claims (3)

[Claims] 1. A drain electrode is commonly connected to a drain electrode and a gate electrode of a third transistor, and a gate electrode of a fifth transistor, a gate electrode is connected to a positive input terminal, and a source electrode is connected to one end of a first resistor. The first transistor commonly connected to one end of the first constant current source and the drain electrode are connected to the gate electrode and drain electrode of the fourth transistor and the sixth transistor.
A second transistor commonly connected to the gate electrode of the transistor, the gate electrode connected to the negative input terminal, and the source electrode commonly connected to the other end of the first resistor and one end of the second constant current source; A third transistor whose source electrode is connected to the GND potential, a fourth transistor whose source electrode is connected to the GND potential, and a drain electrode which is the gate electrode and drain electrode of the seventh transistor and a gate electrode of the eighth transistor. A fifth transistor, which is commonly connected and whose source electrode is connected to the GND potential, and a drain electrode, which is commonly connected to the drain electrode of the eighth transistor, the inverting input terminal of the operational amplifier circuit, and one end of the second resistor, and the source electrode GN
A sixth transistor connected to the D electrode, a seventh transistor whose source electrode is connected to the power source, an eighth transistor whose source electrode is connected to the power source, and the first constant current whose other end is connected to the power source Source, the second constant current source having the other end connected to the power supply, the reference voltage source having one end connected to the positive input terminal of the operational amplifier and the other end connected to the GND potential, and the other end to the output terminal and the operation. An amplifier circuit configured by the second resistor commonly connected to the output of the amplifier and the operational amplifier circuit. 2. A twenty-first transistor having a drain electrode connected to a power supply terminal, a gate electrode connected to a positive input terminal, and a source electrode commonly connected to the gate electrode of the first transistor and the drain electrode of the twenty-third transistor. , The drain electrode is connected to the power supply terminal, the gate electrode is connected to the negative input terminal, and the source electrode is connected to the gate electrode of the second transistor and the second
Second connected in common to the drain electrodes of the four transistors
The second transistor, the 24th transistor in which the gate electrode is commonly connected to the gate electrode of the third transistor and the source electrode is connected to the GND potential, and the gate electrode is commonly connected to the gate electrode of the fourth transistor in the source A twenty-fourth transistor whose electrode is connected to the GND potential, a drain electrode commonly connected to the drain electrode and the gate electrode of the third transistor, and a gate electrode of the fifth transistor, and a source electrode to one end of the first resistor and a first resistor. The first transistor commonly connected to one end of the first constant current source and the drain electrode are connected to the gate electrode and the drain electrode of the fourth transistor and the sixth transistor.
The second transistor having the source electrode commonly connected to the gate electrode of the first transistor and the source electrode commonly connected to the other end of the first resistor and one end of the second constant current source
The third transistor connected to the electric potential and the source electrode are G
A fourth transistor connected to the ND potential, and a fifth transistor having a drain electrode commonly connected to the gate electrode and drain electrode of the seventh transistor and a gate electrode of the eighth transistor, and a source electrode connected to the GND potential. , The drain electrode of the eighth transistor, the inverting input terminal of the operational amplifier circuit and one end of the second resistor are commonly connected, and the source electrode is connected to the GND electrode and the sixth transistor is connected to the power source. A connected seventh transistor, an eighth transistor having a source electrode connected to a power supply, the first constant current source having the other end connected to a power supply, and a second constant current having the other end connected to a power supply Source, a reference voltage source having one end connected to the positive input terminal of the operational amplifier and the other end to the GND potential, and the other end commonly connected to the output terminal and the output of the operational amplifier. A second resistor, the amplifier circuit constituted by said operational amplifier circuit. 3. A 31st transistor in which a drain electrode is connected to a power supply terminal, a gate electrode is connected to a positive input terminal, and a source electrode is commonly connected to a gate electrode of a first transistor and a drain electrode of a 32nd transistor. , The drain electrode is connected to the power supply terminal, the gate electrode is connected to the negative input terminal, and the source electrode is connected to the gate electrode of the second transistor and the fourth electrode.
4th commonly connected to the drain electrodes of the 2nd transistor
1st transistor, 32nd transistor in which the gate electrode is commonly connected to the drain electrode and gate electrode of the 33rd transistor, and the drain electrode of the 34th transistor, and the source electrode is connected to the power supply terminal, and the source electrode is the power supply terminal Connected to the 33rd transistor, the 34th transistor whose gate electrode is commonly connected to the gate electrode of the 4th transistor and whose source electrode is connected to the GND potential, and its gate electrode is the gate electrode and drain of the 43rd transistor Of the transistor and the drain electrode of the forty-fourth transistor and the source electrode connected to the power supply terminal, the forty-second transistor, the source electrode connected to the power supply terminal, the forty-third transistor, and the gate electrode of the third transistor. The 44th transistor connected commonly to the gate electrode and the source electrode to the GND potential And the drain electrode of the third transistor are commonly connected to the drain electrode and gate electrode of the third transistor and the gate electrode of the fifth transistor, and the source electrode is commonly connected to one end of the first resistor and one end of the first constant current source. First connected
Transistor and drain electrode are commonly connected to the gate electrode and drain electrode of the fourth transistor and the gate electrode of the sixth transistor, and the source electrode is the other end of the first resistor and one end of the second constant current source. The second transistor commonly connected to the third transistor and the third transistor having the source electrode connected to the GND potential.
Transistor, a fourth transistor having a source electrode connected to the GND potential, and a drain electrode commonly connected to the gate electrode and the drain electrode of the seventh transistor and the gate electrode of the eighth transistor, and the source electrode to the GND potential. The connected fifth transistor and drain electrode are commonly connected to the drain electrode of the eighth transistor, the inverting input terminal of the operational amplifier circuit, and one end of the second resistor, and the source electrode is connected to G
A sixth transistor connected to the ND electrode, a seventh transistor whose source electrode is connected to a power source, an eighth transistor whose source electrode is connected to a power source, and the first constant current whose other end is connected to a power source Source, the second constant current source having the other end connected to the power supply, the reference voltage source having one end connected to the positive input terminal of the operational amplifier and the other end connected to the GND potential, and the other end to the output terminal and the operation. An amplifier circuit configured by the second resistor commonly connected to the output of the amplifier and the operational amplifier circuit.