JPS63269608A - Differential amplifier - Google Patents

Abstract

PURPOSE:To amplify linearly a differential current by connecting a 3rd registor for amplification between controlled electrodes each of 2nd and 4th transistors (TRs) having a differential voltage. CONSTITUTION:A base potential of TRs Q3, Q4 is not fluctuated even when the collector currents of TRs Q1, Q2 are changed and the emitter potential of TRs Q6, Q7 is fluctuated by the increased/decreased current. In this case, a base-emitter voltage VBE of the TRs Q6, Q7 is changed by the increased and decreased current, but no effect is given onto a voltage signal generated in resistors R11, R12 and a signal of opposite phase is generated to each emitter of the TRs Q6, Q7. A resistor 9 is interposed between the emitters of the TRs Q6, Q7 to amplify the changed current. In this case, since an output current signal of the differential pair circuit is generated linearly as a voltage signal, the output voltage Vout has very low distortion. Thus, the output current of the differential pair circuit is amplified linearly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a differential amplifier that handles signals from an audio frequency band to a video frequency band, and particularly relates to improving its output distortion characteristics.

(Prior Art) A differential amplifier that handles signals from the audio frequency band to the video frequency band is basically configured as shown in FIG.

That is, transistors Ql, Q2 and emitter resistance R
1 and R2 is biased by a constant current source 11. Transistor Ql.

A bias current from a constant voltage source E1 is applied to each base of Q2 via a base resistor R3°R4. Also, a capacitor CI is connected to the base of the transistor Q2.
An input signal Vin is applied via.

The collector current of transistor Q1 is input to the input terminal of a second current mirror circuit consisting of diode D1, resistors R5, R7, ) transistor Q3, and the collector current of transistor Q2 is input from diode D2, resistors Re, R8, ) transistor Q4. It is input to the input terminal of the second current mirror circuit. Transistor Q3. A resistor R9 is connected between the emitter of Q4.

The output current of the first current mirror circuit is the diode D3.
The output current of the second current mirror circuit is added to the output current of the third current mirror circuit and is input to the load resistor RIG. This load resistance RIO
A bias voltage v2 is applied to by a constant voltage source E2.

In the above configuration, the input signal Vin is voltage-to-current converted by the differential pair circuit, and appears as a differential current signal at the collectors of the transistors Ql and Q2.

By converting each collector current into a reverse current in the first and second current mirror circuits, and further converting it into a reverse current in the third current mirror circuit, the differential current signal is made single-ended. The amount of changing current is doubled. This current signal flows through the load resistor RIO, where it is converted into current and voltage and output as an output voltage V out.

Here, transistor Q3. A resistor R9 connected between the emitters of Q4 is for amplifying the above changing current. That is, since the emitter potentials of the transistors Q3 and Q4 change differentially, the midpoint of the resistor R9 becomes a virtual ground point. At this time, the resistance applied to the emitter of transistor Q3 is the parallel resistance of R7 and R9/2, and the resistance applied to the emitter of transistor Q4 is the parallel resistance of R8 and R9/2.
It is equivalent to the parallel resistance of , and as the variable current increases, the resistance value decreases. In other words, the mirror ratios of the output side transistors Q3゜Q4 of the first and second current mirror circuits have become isometrically larger, and the signal current output from the differential pair circuits has become larger than the first and second current mirror circuits. This means that the signal is amplified by the current mirror circuit No. 2.

However, the conventional differential amplifier as described above has the following problems. That is, the base-emitter voltage VBE of the transistor is expressed by an exponential function, and increases as the current increases. However, in FIG. 2, if we consider the case where the collector current of transistor Ql increases linearly, the collector current of transistor Q2 also increases.
Due to the above-mentioned reason, the collector potential of Q2 does not change linearly and cannot fall completely. Conversely, transistor Q1
If the collector current of transistor Q2 decreases, the collector potential of transistor Q2 will not be able to rise completely. Therefore, the current output signal mainly has odd-order distortion components, which affect the output voltage v out and cause distortion.

(Problems to be Solved by the Invention) As stated above, conventional differential amplifiers generate distortion in the output voltage because the output current of the differential -5 pair circuit is not proportional to the change in input voltage. There was a problem.

This invention was made to solve the above problem.
It is an object of the present invention to provide a differential amplifier that can linearly amplify from an audio frequency band to a video frequency band with extremely low distortion.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a differential amplifier according to the present invention includes a differential pair circuit that divides and outputs a constant current according to an input voltage, and a differential pair circuit that divides and outputs a constant current according to an input voltage. The output current of one side of the dynamic pair circuit is input, a current in the opposite direction is generated by the first transistor, and this reverse direction current and the bias current are added to control the second transistor. One non-control electrode
A first current mirror circuit connected to the control electrode of the first transistor through a resistor and the other output current of the differential pair circuit are inputted, and a third transistor generates a current in the opposite direction. A fourth transistor is controlled by adding this reverse current and a bias current, and one non-control electrode of the fourth transistor is connected to the control electrode of the third transistor via a second resistor. The second one connected
a current mirror circuit, a resistor connected between one of the controlled electrodes of the second and fourth transistors, and a current output from the other controlled electrode of the second transistor. a third current mirror circuit that generates and outputs a current; and an output circuit that adds and outputs the folded current of the third current mirror circuit and the current output from the other controlled electrode of the fourth transistor. It is equipped with and configured.

(Function) In the differential amplifier having the above configuration, in the first and second current mirror circuits, the second transistor and the first resistor, and the fourth transistor and the second resistor constitute a negative feedback circuit. , the current from the differential pair circuit is the first, third
After being converted into a reverse current by the transistor, negative feedback is provided via the second and fourth transistors and the first and second resistors.

At this time, the voltage generated by the current flowing through the first and second resistors does not depend on the controlled/controlled amount voltage of the first and third transistors, and changes linearly with the output current of the differential pair circuit. do. Therefore, by connecting a third resistor for amplification between the controlled electrodes of each of the second and fourth transistors where the differential voltage is generated, the differential current can be linearly amplified.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a configuration in which the present invention is applied to the differential amplifier shown in FIG. In Figure 1, the second
Components that are the same as those in the figures are designated by the same reference numerals, and their explanations will be omitted.

This differential amplifier connects the collector of the transistor Q3, which is the output terminal of the first current mirror circuit, to the constant current source I2.
and supplies the collector current of Q3 to the base of transistor Q6.

The collector of the transistor Q4, which is the output end of the second current mirror circuit, is biased by the constant current source I3, and the Q
A collector current of 4 is supplied to the base of transistor Q7. The emitter of transistor Q6 is connected to the base of Q3 via resistor RLI to form a negative feedback path, and the collector is connected to the collector of transistor Q5, which is the output end of the third current mirror circuit. The emitter of transistor Q7 is connected to the base of Q4 via resistor R12 to form a negative feedback path, and the collector is connected to the base of transistor Q5, which is the input end of the third current mirror circuit. The resistor R9 is connected between the emitters of the transistors QB and Q7.

That is, the first current mirror circuit consists of the transistor Q
6 and a resistor R11, and the second current mirror circuit includes a transistor Q7 and a resistor R12. Therefore, the output current of the differential pair circuit is the same as that of transistor Q6. Appears in the collector of Q7. However, Q6. Q
7 collector current is Q3. Since the phase is opposite to the collector current of Q4, the collector current of Q7 is supplied to the input terminal of the third current mirror circuit, and the collector current of Q6 is added to the output current of the third current mirror circuit to generate the load. An internal force is applied to the resistor R10.

Now, regarding the first current mirror circuit, most of the current from constant current source 2 flows through resistor R7 and transistor Q3, and if the mirror ratio is 1=1, diode Di
The same current flows through.

Since the current flowing through the diode D1 becomes the collector current of the transistor Q1, a difference current between the current of the constant current source I2 and the collector current of the transistor Q1 flows through the resistor R7 and the transistor Q3.

Here, if the forward current amplification factor β of each transistor is sufficiently large, the current flowing through transistor Q3 and diode DI will be constant, and the current flowing through transistor Q6 will also increase or decrease in response to an increase or decrease in the collector current of transistor Q1. . Their magnitudes are equal and their phases are opposite. This also applies to the second current mirror circuit.

From the above, transistor Q3. The base potential of Q4 does not change even if the collector currents of transistors Ql and Q2 change; The emitter potential of 6°Q7 fluctuates depending on the increased or decreased current. At this time, transistor Q8. Although the base-emitter voltage VBF of Q7 changes depending on the increase or decrease in current, it does not have the same effect on the voltage signal generated across resistors RLI and R12. That is, signals of opposite phases are generated at the emitters of transistors Q6 and Q7, respectively. In this state, resistor R9 is connected to transistors QB, Q
By interposing it between the emitters of 7, the changing current is amplified. In this case, since the output current signal of the differential pair circuit is linearly generated as a voltage signal, the output voltage V ou
t also has extremely low distortion compared to the conventional one.

Therefore, since the differential amplifier having the above configuration can linearly amplify the output current of the differential pair circuit, distortion of the output voltage can be sufficiently reduced.

By the way, when the same load resistance is driven by a large number of differential amplifiers, conventionally, the resistor R9 is omitted from the circuit shown in FIG. 2, and the gain is increased by the current mirror ratio. However, with this method, the input/output current can only be made linear when the mirror ratio is an integer ratio, and if the voltage/current conversion rate of the differential pair circuit is constant, only discrete gain values can be obtained. Can not. Furthermore, output distortion increases, which is not preferable. If the differential amplifier according to the present invention is used, the gain can be set as a continuous value by appropriately setting the values of the resistors R9, RIL, R12 and constant current sources I2, 13, and there is a degree of freedom in setting the gain. , is extremely effective in increasing the gain of a certain single stage amplifier.

In the above embodiment, even if the diodes D1 and D2 are omitted and the resistors R5 and R[f are set to appropriate values, the same effect can be obtained as long as the temperature is constant.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a differential amplifier capable of linearly amplifying from the audio frequency band to the video frequency band with extremely low distortion.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a differential amplifier according to the present invention, and FIG. 2 is a circuit diagram showing the configuration of a conventional differential amplifier to which the present invention is applied. Q1 to Q7...Transistor, R1-R12...Resistor, ■1 to ■3... Constant current source, El, E2... Constant voltage source, Vin... Input voltage, V out... Output voltage.

Claims (1)

[Claims] A differential pair circuit that divides and outputs a constant current according to the input voltage,
One output current of this differential pair circuit is input, a current in the opposite direction is generated by the first transistor, and the second transistor is controlled by adding this reverse direction current and the bias current. a first current mirror circuit formed by connecting one non-control electrode of the transistor to the control electrode of the first transistor through a first resistor, and inputting the output current of the other of the differential pair circuit; A third transistor generates a reverse current, the reverse current and a bias current are added together to control a fourth transistor, and one non-control electrode of the fourth transistor is connected through a second resistor. a second current mirror circuit connected to the control electrode of the third transistor; a resistor connected between the controlled electrodes of one of the second and fourth transistors;
a third current mirror circuit that inputs the current output from the other controlled electrode of the transistor and generates and outputs a current in the opposite direction; A differential amplifier comprising an output circuit that adds and outputs the current output from the other controlled electrode.