JPH0249050B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention provides an extremely suitable amplifier for electronic equipment.
In particular, the present invention relates to an integrated circuit amplifier that can be used as a linear amplifier.

(b) Prior art In general, electronic equipment uses linear amplifiers and pulse amplifiers as amplifiers, and the former in particular consists of various components to amplify input signals faithfully and without distortion. (referred to as IC).

One example is Tokyo SANYO Semiconductor Product Catalog No. 286B from Tokyo SANYO Electric Co., Ltd.'s Semiconductor Division Light Emission.
(LA3115, 3122) is a three-stage directly connected low frequency amplifier shown in FIG. The configuration is such that an output signal V ₀ which is applied to the base of the output signal V 0 and amplified by the amplification transistors 4 and 5 is obtained from the output terminal 7 via the coupling capacitor 6 .

In the above configuration, in order to amplify low frequencies, the gain in the open loop is generally increased and negative feedback is used to achieve the purpose.
An emitter resistor 8 and a bypass capacitor 9 are provided on the emitter side of the amplifying transistor 4 in each stage to increase the gain of the amplifying transistor 4.

(c) Problems to be Solved by the Invention In the conventional configuration described above, in the low frequency range, the impedance of the bypass capacitor increases, the gain in the open loop decreases, and the distortion rate worsens. When converting a circuit into an integrated circuit (IC), there is a problem in that the IC requires one pin for connection to the bypass capacitor.

Therefore, the bypass capacitor mentioned above is made unnecessary,
The present invention provides a new amplifier circuit that improves low-frequency characteristics and prevents an increase in the number of pins and parts when integrated into an IC.

(D) Means for Solving the Problem The present invention provides a method for connecting first and second differential amplifiers and emitter follower transistors in series, and connecting the second differential amplifier and the first differential amplifier to each other. , and a third feedback resistor is connected between the emitter follower transistor and the first differential amplifier.

(E) Effect The base bias of the first differential amplifier is determined by the emitter of the second differential amplifier whose emitter is connected to a resistor or a constant current source.
First and second feedback resistors are connected to the emitters of the differential amplifier, and are applied via the first and second feedback resistors, and the first and second feedback resistors are connected to the emitters of the differential amplifier.
The amplified input signal is supplied from the output terminal of the differential amplifier, and a high voltage gain is obtained in the first and second differential amplifiers, and a bypass capacitor is not particularly required.

(F) Embodiment The present invention will be described with reference to the drawings. FIG. 1 shows a circuit diagram of an amplifier for an integrated circuit according to the present invention, in which reference numeral 10 indicates a pair of transistors 11 and 12, a resistor 13 commonly connected to the emitters, Load transistor 14,1
A first differential amplifier 16 includes a pair of transistors 17, 18 and 19, 20, and a second differential amplifier 22, 21 includes a constant current transistor 21.
3 are transistors and diodes for the first current mirror, 24 are emitter follower transistors, 25, 26, 27, and 28 are transistors and diodes for the second current mirror, and 29, 30, and 31 are transistors and diodes for the second current mirror, respectively. 1 second and third feedback resistors, 32 an emitter load, and 33 a load.

Next, to explain the operation of the integrated circuit amplifier of the present invention, the input signal Vi is passed through the coupling capacitor 2 to the transistor 1 of the first differential amplifier 10.
1 and to the second differential amplifier 16 via load transistors 14 and 15. In this case Darlington connected transistor 1
The amplified output is applied to the bases of transistors 17 and 18 via transistors 9 and 20, and the amplified output is introduced from one end of a load resistor 34 and applied to the base of an emitter follower transistor 24. An output signal appears at the output terminal 7 from one end of the emitter load 32 of the emitter follower transistor 24 via the coupling capacitor 6.

Here, signals of opposite polarity from the load transistors 14 and 15 are applied to the bases of the transistors 19 and 20 of the second stage differential amplifier 16, so that
The second differential amplifier 16 provides a high voltage gain. For feedback from the second differential amplifier 16 to the first differential amplifier 10, if the resistance values of the first feedback resistor 29 and the second feedback resistor 30 are made equal, the same amount of feedback will be transmitted to the second differential amplifier 10. It is applied to the base of each transistor of differential amplifier 10, thereby providing base bias for said transistor.

The transistor 22, the diode 23 and the resistor 38 operate as a constant current source for the constant current transistor 21, and the transistor 25, the diode 26, 2
7, 28 and resistors 35, 39, 40 constitute a second current mirror, and the load transistor 1
4, 15 and the base of the transistor 22 are biased.

Since the third feedback resistor 31 is connected to one end of the coupling capacitor 6 and the emitter of the first differential amplifier 10, AC negative feedback is provided in the configuration of the embodiment.

If the voltage gain at this time is Av, it is determined by Av=R _E +R ₃ /R ₃ .

In the figure, a resistor 36 is a resistor for suppressing the voltage gain of the first differential amplifier 10, and a capacitor 37 is a MOS capacitor for preventing parasitic oscillation. Therefore, according to the embodiment shown in FIG. 1, the signal applied to the input terminal 1 is amplified by the first and second differential amplifiers 10 and 16, and is output from the emitter side of the emitter follower transistor 24. V ₀ is obtained.

As an example, good results were obtained as a low frequency amplifier circuit by using the following resistance values: R ₁ =R ₂ =16KΩ R _E =150Ω R ₃ =15KΩ. In the above embodiment, a constant current transistor is used as the emitter of the second differential amplifier, but a resistor may also be used.

(g) Effects of the Invention According to the present invention, when configuring a direct-coupled amplifier as in the past, it is necessary to provide one terminal pin outside the IC for a bypass capacitor that bypasses the emitter resistance of the transistor connected to the collector load. In contrast, the first and second differential amplifiers and the emitter follower transistor constitute a direct-coupled amplifier, and in order to obtain sufficient voltage gain, a Darlington connection is used as in the embodiment. There is no need to connect a bypass capacitor outside the IC.

Therefore, according to the present invention, the terminal pin for connecting the capacitor is not required, and the number of terminal pins can be reduced by one compared to the conventional method, and the present invention is extremely suitable for IC implementation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an amplifier for integrated circuits according to the present invention;
FIG. 2 shows a circuit diagram of the conventional amplifier. Explanation of main figure numbers, 1... Input terminal, 10... First differential amplifier, 16... Second differential amplifier, 2
4... Emitter follower transistor, 29...
First feedback resistor, 30...Second feedback resistor, 31
...Third feedback resistor, 33...Load.

Claims (1)

[Claims] 1 a first differential amplifier consisting of a pair of transistors whose emitters are commonly connected to a resistor; a second differential amplifier consisting of a pair of transistors whose emitters are commonly connected to a resistor or a constant current source; an emitter follower transistor whose base is connected to the output terminal of one transistor of the second differential amplifier; a common emitter of the second differential amplifier and each transistor of the first differential amplifier; and a third feedback resistor connected between the emitter of the emitter follower transistor and the common emitter of the first differential amplifier. 1. An amplifier for an integrated circuit, wherein the first and second differential amplifiers and the emitter follower transistor are sequentially DC-coupled.