JPS61145907A - Negative feedback amplifier - Google Patents

Abstract

PURPOSE:To obtain a negative feedback amplifier excluding effect of both a feedback circuit and a load by providing the 1st output circuit extracting an output fed to the feedback circuit and the 2nd output circuit extracting an output fed to the load to the output side of the amplifier. CONSTITUTION:The 1st output circuit 24 extracting a feedback output and the 2nd output circuit 26 driving various loads are provided to the output side of the amplifier 22. That is, an input voltage ei to be amplified fed to an input terminal 28 is amplified by the amplifier 22, its output voltage eo is fed to the 1st and 2nd output circuits 24, 26, the voltage is extracted from an output terminal 30 of the 1st output circuit 24 as an output voltage eo1 and extracted from an output terminal 32 of the 2nd output circuit 26 as an output voltage eo2. A feedback element 34 is provided between the output terminal 30 of the 1st output circuit 24 and the input side of the amplifier 22 to form the feedback circuit 36 and the output voltage eo1 is fed negatively back to the input of the amplifier 22 at a prescribed rate via the feedback element 34. Thus, the effect of a load 38 onto the feedback circuit 36 is avoided to realize an ideal feedback amplification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a negative feedback amplifier that allows outputs to be individually taken out to be supplied to a feedback circuit and a load.

[Conventional technology]

Generally, a negative feedback amplifier obtains a feedback signal from an output point to which a load is connected and supplies it to the input side, as shown in FIG. That is, a driver 4 is installed on the output side of the amplifier 2, and the input signal at to be amplified applied to the input terminal 6 is
After being amplified by the amplifier 2, the output signal eo is taken out from the output terminal 8 via the driver 4. This output signal eO is fed back to the input side of the amplifier 2 via the feedback element 10, and is also fed back to the load 12 connected to the output terminal 8.
supplied to In this case, the driver 4 installed on the output side of the amplifier 2 is installed to drive the load 12.

In such a negative feedback amplifier, if the amplification gain of the amplifier 2 is AO1, and the feedback constant of the feedback element 10 is β, the ideal input/output characteristic is eo=Ao−ei/(1+Ao・β)...( 1) becomes.

[Problem that the invention seeks to solve]

In such a negative feedback amplifier, a feedback signal is taken out from the drive output terminal 8 which provides the drive output to the load 12, and the output signal eo applied to the load 12 is fed back to the input side of the amplifier 2 at a specific ratio. There is. This is excellent in terms of improving the linearity of amplifier 2, but the feedback characteristics
2 impedance etc. have an influence. That is, strictly speaking, it is necessary to consider the impedance of the load 12 in the feedback constant β of the feedback element 10, and it is extremely difficult to consider the characteristics that affect feedback, such as the impedance of the load 12, for each load 12. It is troublesome.

Therefore, the present invention aims to provide a negative feedback amplifier that eliminates the mutual influence of the feedback circuit and the load.

[Means for solving problems]

That is, in the present invention, a first output circuit that takes out an output to be supplied to a feedback circuit and a second output circuit that takes out an output to be supplied to a load are installed on the output side of an amplifier.

[For production]

Therefore, in the present invention, the output of the amplifier is taken out from the first and second output circuits, the first output circuit drives the feedback circuit of the amplifier, and the second output circuit drives the load.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the negative feedback amplifier of the present invention.

In FIG. 1, a first output circuit 24 for taking out a feedback output is installed on the output side of an amplifier 22, and a second output circuit 26 for driving various loads is installed. That is, the input voltage ei applied to the input terminal 28 to be amplified is amplified by the amplifier 22, and its output voltage eo is applied to the first and second output circuits 24, 26, and the output voltage eo of the first output circuit 24 is amplified by the amplifier 22. Output voltage e from output terminal 30
ol is taken out from the output terminal 32 of the second output circuit 26 as an output voltage eo2.

A feedback circuit 36 is formed by installing a feedback element 34 between the output terminal 30 of the first output circuit 24 and the input side of the amplifier 22. Negative feedback is provided to the input side of the amplifier 22.

A load 3 is connected to the output terminal 32 of the second output circuit 26.
8 is connected, and the output voltage eog of the second output circuit 26 is supplied to the load 38.

The first and second output circuits 24 and 26 are configured to have arbitrary amplification gains, and their input/output relationships are configured to be independent of each other in terms of electrical characteristics such as impedance.

The operation will be explained based on the above configuration.

The input voltage ei applied to the input terminal 28 is applied to the amplifier 22
The output voltage eo is applied to the first and second output circuits 24 and 26, and the output voltage eo obtained from the first output circuit 24 is amplified by the amplifier 22 via the feedback element 34. The output voltage eo2 fed back to the input side and obtained by the second output circuit 26 is supplied to the load 38.

Since the first and second output circuits 24 and 26 do not affect each other, the feedback voltage of the feedback circuit 36 and the load 38
are driven independently of each other.

Here, the amplification gain in the open loop of the amplifier 22 is A
o, the feedback constant of the feedback element 34 is β, the first output circuit 24
The amplification gain of the amplifier constituting the circuit is 1, and the second output circuit 26
Assuming that the amplification gain of the amplifier constituting is n (usually n=1), the output voltage eo2 of the second output circuit 26 is eo! = n i eO = n -e i -Ao/ (1+Ao-β)...
(2) becomes.

In this way, the feedback circuit 36 and the load 38 are
If the output circuits 24 and 26 are driven individually so as to be independent of each other, the influence of the load 38 on the feedback circuit 36 can be avoided, and ideal feedback amplification can be realized.

Further, by arbitrarily setting the feedback constant β, the driving conditions of the load 38 can be arbitrarily and freely changed, and it is possible to easily adapt to different amplification forms such as a voltage amplifier and a current amplifier, for example.

Such operation is performed by the first and second output circuits 24.2
The same thing can be done by adjusting the drive ability of 6.

Therefore, such a feedback amplifier can provide the current versus frequency characteristics required for a so-called recording (current) amplifier that amplifies the recording current of a magnetic head, and can be used in this type of amplifier.

FIG. 2 shows a current amplifier which is a specific embodiment of the negative feedback amplifier of the present invention, and the same parts as in the negative feedback amplifier shown in FIG. 1 are given the same reference numerals.

In FIG. 2, amplifier 22 is transistor 40.42.
A non-inverting input terminal 2 is formed on the base of the transistor 400 and is composed of a differential amplifier consisting of a constant current source 44 and a constant current source 44.
A signal source 46 is connected to 8a to which an input voltage ei to be amplified is applied, and an inverting input terminal 28b formed at the base of the transistor 42 is connected to a feedback element 34 from an output terminal 30 of the first output circuit 24. The output voltage eo is fed back from the feedback circuit 36 in which the output voltage eo is installed.

The first output circuit 24 includes a diode 50, a transistor 52, and a constant current source 54 installed between the collector of the transistor 42 and the positive line where the power supply terminal 48 is formed.
The output terminal 30 is formed on the collector side of the transistor 52. That is, the diode 50 and the transistor 52 constitute a current mirror circuit that extracts the differential current flowing through the transistor 42 , and the difference current between the differential current flowing through the transistor 52 and the constant current flowing through the constant current source 54 is transferred to the feedback element 34 . flows.

Feedback element 34 includes resistor 56,58 and capacitor 60.
It consists of

The second output circuit 26 includes a diode 50, a transistor 62 forming a current mirror circuit, and a constant current source 64.
An output terminal 32 is formed on the collector side of the transistor 62, and a load 38 is connected between the output terminal 32 and a ground terminal 66.

According to such a configuration, the output of the amplifier 22 is taken out from the first and second output circuits 24, 26 by the differential current flowing through the transistor 42 without affecting each other due to the current mirror effect, and 38 can be supplied.

Moreover, FIG. 3 shows an embodiment of a voltage amplifier which is another specific embodiment of the negative feedback amplifier of the present invention, and the same parts as in the embodiment shown in FIG. 2 are given the same reference numerals. .

The amplifier 22 is a differential amplifier made up of transistors 40, 42 and a constant current source 44, to which a current mirror circuit made up of a diode 68 and a transistor 70 as an active load is added. The collector of the transistor 42.70 is set at the output point of the amplifier 22, and the differential current flowing to this output point is applied to the first and second output circuits 24.26.

The first output circuit 24 is composed of a transistor 52 and a constant current source 54, and the second output circuit 26 is composed of a transistor 62 and a constant current source 64, so that the differential current flowing to the output point of the amplifier 22 is added to the base.

In this way, the output stage can be configured as a voltage drive circuit, and by arbitrarily setting the feedback elements constituting the feedback circuit 36, the load 38 can be driven with an arbitrary voltage waveform.

〔Effect of the invention〕

As explained above, according to the present invention, the feedback circuit and the load can be driven separately, the influence of the load on the feedback circuit can be removed, ideal feedback amplification can be achieved, and the feedback constant of the feedback circuit can be reduced. Load drive conditions can be adjusted freely by adding or subtracting.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the negative feedback amplifier of the present invention, Figs. 2 and 3 are circuit diagrams showing a specific embodiment of the negative feedback amplifier of the invention, and Fig. 4 is a general circuit diagram. FIG. 2 is a block diagram showing a negative feedback amplifier. 22... Amplifier, 24... First output circuit, 26...
...Second output circuit, 36...Feedback circuit, 38...
load. Figure 1 Figure 3 Figure 4

Claims (2)

[Claims] (1) A negative feedback amplifier characterized in that a first output circuit for extracting an output to be supplied to a feedback circuit and a second output circuit for extracting an output to be supplied to a load are installed on the output side of the amplifier. . (2) The negative feedback amplifier according to claim 1, wherein the first and second output circuits are configured by current mirror circuits installed on the output side of the amplifier.