JPH0730389A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain the differential amplifier circuit of one-stage constitution which inputs a single-phase analog signal and obtains outputs of both phases having a small phase error from an amplitude error and a 180 deg. phase difference. CONSTITUTION:A feedback circuit is connected fro differential outputs 1 and 2 to the base of a current source transistor(TR) 7 through output feedback resistance 9 and 10 and a DC cut capacitance 11. Consequently, even when the outputs 1 and 2 become unbalance at the time of high-frequency input, feedback is applied to the current source and then the collector current of switching TRs 3 and 4 are fed back to decrease the amplitude error between outputs 1 and 2 of both phrases and the phase error from a 180 deg. phase difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier circuit,
The present invention relates to a differential amplifier circuit which can output two signals having the same amplitude and a phase difference of 180 ° different from each other with a particularly simple configuration.

[0002]

2. Description of the Related Art In a conventional differential amplifier circuit, as shown in FIG. 4, when a differential amplifier including a transistor 23 for inputting a single-phase analog signal and a transistor 22 for inputting a DC bias is formed, each of them will be described. There is no feedback circuit at the base of the current source transistor 27 from the collector, and in order to obtain a signal with the same amplitude and a phase difference of 180 °, the transistor 2
The collectors of the transistors 3 and 24 are connected to the bases of the emitter follower transistors 29 and 30, respectively.
The emitters of 9 and 30 are respectively connected to the bases of the switching transistors 37 and 38 of the second differential amplifier circuit, and the output signal is obtained from the contact point between the load resistors 35 and 36 and the collectors of the switching transistors 37 and 38. There is. In the first differential amplifier circuit, an AC signal is input,
Since the collector output amplitude of the transistor 23 and the collector output amplitude of the transistor 24 to which the DC bias is input are different, inputting to the second differential amplifier circuit via the emitter follower circuit causes a small amplitude difference and a phase difference. Vessel 1
I was getting two output signals close to 80 °.

[0003]

In this conventional differential amplifier, when it is configured by only one stage, the amplitude error between the two output signals and the error from the 180 ° phase difference are large. Further, in order to obtain a signal with a small error, it is necessary to configure at least two stages of differential amplifier circuits, which increases the circuit current,
There is also a problem that the layout area is also large.

[0004]

In a differential amplifier circuit of the present invention, a first transistor having an input terminal for inputting a single-phase analog signal connected to a base, and a collector of the first transistor is a first transistor. A high-potential source via a load resistor of 1, a base of the second transistor is connected to a DC source, and a collector of the second transistor is connected to the high-potential source via a second load resistor; The transistor collector is the first
To the output terminal of the second transistor, the collector of the second transistor is connected to the second output terminal, the emitter of the first transistor is connected to the third resistor, and the emitter of the second transistor is connected to the fourth resistor. The other ends of the third and fourth resistors are connected to each other, and the contact point between the third and fourth resistors is connected to the collector of the third transistor. The emitter of the third transistor is connected to the fifth resistor. In a differential amplifier circuit in which a base is connected to a DC source, which is grounded through a resistor,
A sixth resistor is connected to the output terminal of the third resistor, a seventh resistor is connected to the second output terminal, the other ends of the sixth and seventh resistors are connected to each other, and the third resistor is connected via a capacitor. It is provided with a feedback circuit connected to the base of the transistor.

[0005]

Embodiments of the present invention will now be described with reference to the drawings. [Embodiment 1] FIG. 1 is a circuit diagram of an embodiment of the present invention. An AC signal is input from one base of the switching transistors 3 and 4 forming the differential amplifier circuit, and a DC bias is applied to the other base. Load resistors 1 and 2 are connected to the collectors of the switching transistors 3 and 4, and outputs 1 and 2 are obtained from the collectors, respectively. When the input frequency becomes higher, the amplitude of the output 1 becomes larger than that of the output 2, and the phase difference of the output 2 with respect to the output 1 lags behind 180 °. This is because the delay time until the input signal is transmitted to the emitter of the transistor 3, further inverted to the emitter of the transistor 4 and transmitted to the collector output of the transistor 4 with respect to the input frequency,
Because it cannot be ignored.

In the present invention, output feedback resistors 9 and 10 are connected between the outputs 1 and 2, and D is connected from the contact point of the resistors.
AC feedback is applied to the base of the current source transistor 7 via the C-cut capacitor 11. If there is an amplitude difference between the outputs 1 and 2, the contacts of the resistors 9 and 10 change in phase with the output 1.
When this signal is input to the base of the transistor 7, for example, when the output 1 is high (H) level, the current of the transistor 7 increases, the current of the switching transistor 4 increases, and the output 2 becomes lower (L). Displace to level. The reverse occurs when the output 1 is at the (L) level, so that the outputs 1 and 2 have the same amplitude. Further, since the delay of the switching operation of the switching transistor 4 can be compensated by changing the current flowing through the current source transistor 7, the phase difference also approaches 180 °. Figure 2
Load resistors 1 and 2 are 500Ω, output feedback resistors 9 and 10 are 1
9 is a simulation result showing the gain of the differential amplifier when KΩ and the DC cut capacitance 11 are set to 2 pF.
As a reference, when compared with a differential one-stage amplifier without a feedback circuit, when the input frequency is 1 GHz or higher, the gain at the collector of the signal input side transistor is smaller than the gain at the collector of the other transistor. Has been improved.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention. Similar effects can be obtained in the FET. When the bipolar transistor is replaced with the FET as in the first embodiment, the gate of the current source FET 14 is connected to the gate of the current feedback FET 14 through the DC feedback capacitor 11 from the contact of the output feedback resistors 9 and 10.
By applying the C feedback, the amplitude and phase errors of the outputs 1 and 2 can be reduced by the same principle as in the first embodiment.

[0008]

As described above, according to the present invention, the two output terminals of the single-phase input differential amplifier circuit, which are out of phase with each other, are connected by a resistor, and the DC-cutting capacitor is connected from the middle point. Through the AC feedback to the base of the current source transistor through the effect, it is possible to reduce the amplitude error of the output signals of both phases and the phase error from the 180 ° phase difference in the one-stage differential amplifier circuit configuration. Is played.

[Brief description of drawings]

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

FIG. 2 is a frequency characteristic of gain of the amplifier shown in FIG.

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

FIG. 4 is a circuit diagram of a conventional example.

[Explanation of symbols]

1, 2, 21, 22, 35, 36. Load resistance 3, 4, 23, 24, 37, 38. Switching transistors 5, 6, 25, 26, 39, 40. Emitter feedback resistors 7, 27, 31, 32, 41. Current source transistors 8, 28, 33, 34, 42. Current source resistance 9, 10. Output feedback resistor 11. DC cut capacity 29, 30. Emitter follower transistor 12, 13. Switching FET 14. Current source FE
T

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[Procedure amendment]

[Submission date] January 7, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

[0004]

In a differential amplifier circuit of the present invention, a first transistor having an input terminal for inputting a single-phase analog signal connected to a base, and a collector of the first transistor is a first transistor. A high-potential source via a load resistor of 1, a base of the second transistor is connected to a DC source, and a collector of the second transistor is connected to the high-potential source via a second load resistor; The transistor collector is the first
To the output terminal of the second transistor, the collector of the second transistor is connected to the second output terminal, the emitter of the first transistor is connected to the third resistor, and the emitter of the second transistor is connected to the fourth resistor. The other ends of the third and fourth resistors are connected to each other, and the contact point between the third and fourth resistors is connected to the collector of the third transistor. The emitter of the third transistor is connected to the fifth resistor. In a differential amplifier circuit in which a base is connected to a DC source, which is grounded through a resistor,
A sixth resistor is connected to the output terminal of the third resistor, a seventh resistor is connected to the second output terminal, the other ends of the sixth and seventh resistors are connected to each other, and the third resistor is connected via a capacitor. It is provided with a feedback circuit connected to the base of the transistor. In addition, the third transistor of the differential amplifier circuit is a FET
The differential amplifier circuit is characterized in that AC feedback is applied to the gate of the current source FET from the contact of the output feedback resistor through the DC cutting capacitor.

Claims (1)

[Claims] 1. A first transistor having an input terminal for inputting a single-phase analog signal connected to a base, and the first transistor.
The collector of the transistor of is connected to the high potential source through the first load resistor, and the base of the second transistor is
A DC source is connected, a collector is connected to the high potential source via a second load resistor, a collector of the first transistor is connected to the first output terminal, and a collector of the second transistor is connected to the second output terminal. The emitter of the first transistor is directly connected to the emitter of the second transistor, or the emitter of the second transistor is connected to the emitter of the first transistor by connecting the third resistor to the emitter of the first transistor. To a fourth resistor, the other ends of the third and fourth resistors are connected to each other, and a contact between the emitters of the first and second transistors, or a contact between the third and fourth resistors is connected. ,
The differential amplifier circuit is connected to the collector of the third transistor, the emitter of the third transistor is grounded through the fifth resistor, and the base is connected to the DC source.
A sixth resistor is connected to the output terminal of the third resistor, a seventh resistor is connected to the second output terminal, the other ends of the sixth and seventh resistors are connected, and the third resistor is connected via a capacitor. A differential amplifier circuit characterized by being connected to the base of a transistor.