JPH06338727A - Amplifying circuit - Google Patents

Abstract

PURPOSE:To prevent a signal from being outputted in a first state, in which the signal is not outputted to the outside, with respect to the amplifying circuit used in an audio amplifier or the like. CONSTITUTION:This amplifying circuit is provided with an input amplifying means 11 which amplifies an input signal to output it to first and second amplifying means 12 and 13, a first amplifying means 12 which is operated in the first state to feed back the amplified input signal to the input amplifying means 11, a second amplifying means 13 which is operated in a second state, in which the signal is outputted to the outside, and amplifies the amplified input signal to output it to the outside, and a potential fixing means 14 which fixes the reference potential of the first amplifying means 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, and more particularly to improvement of an amplifier circuit used in audio amplifiers and the like.

[0002]

2. Description of the Related Art A conventional amplifier circuit will be described below with reference to the drawings. The amplifier circuit according to the conventional example is an audio amplifier that prevents pop noise by switching circuits according to the mute mode and the play mode. In the mute mode, the audio device (for example, stereo) including the amplifier circuit is powered on, and current is flowing through the amplifier circuit (for example, from the speaker).
In the state where no sound is output to the outside, the play mode refers to a state in which a current flows through the amplifier circuit and a sound is output to the outside. The pop noise will be described later.

The circuit is, as shown in FIG. 3, an input amplifier (1), a mute mode amplifier (2), a play mode amplifier (3), a switching circuit (4), a switching circuit (5) and a current amplifier (IA). The audio signal (SI) is input to itself, amplified, and output to an external speaker or the like. The input amplifier (1) is composed of a differential amplifier (1A) and a current mirror circuit (1B), inputs an audio signal (SI) into itself, amplifies and amplifies the mute mode amplifier (2), and the play mode amplifier (3). ) Is output to.

The mute mode amplifier (2) comprises a differential amplifier (2A) and a current mirror circuit (2B) and is connected to a positive power source (+ Vcc) via a switching circuit (4). When the switching circuit (4) is turned on, it operates to amplify the audio signal (SI) amplified by the input amplifier (1), and a negative feedback circuit (NF) is provided to one input side of the input amplifier (1). Is output via.

The play mode amplifier (3) comprises a differential amplifier (3A) and a current mirror circuit (3B) and is connected to a positive power source (+ Vcc) via a switching circuit (SW2). Further, the switching circuit (5) is turned on to operate, and further amplifies the audio signal (SI) amplified by the input amplifier (1) and outputs it to the current amplifier (IA).

The switching circuit (4) has a resistor (R
1), a transistor (Q14), a constant current source (TS1) and a switch (SW1), which is a circuit for supplying / not supplying a constant current to the mute mode amplifier (2). The switching circuit (4), like the switching circuit (5), is a circuit for supplying / not supplying a constant current to the mute mode amplifier (2). The detailed circuit configuration is omitted in the figure.

The current amplifier (IA) further amplifies the amplified signal output from the play mode amplifier (3) and outputs the amplified signal to an external speaker. The operation of the circuit will be described below. In the mute mode, the switching circuit (4) is turned on by turning on the switch (SW1) in the circuit, and a constant current is supplied to the mute mode amplifier (2). At this time, the switching circuit (SW2) is turned off, and only the mute mode amplifier (2) operates.

First, the audio signal (S) is input to the base of the transistor (Q4) which is the input terminal of the input amplifier (1).
When I) is input, it is amplified and output to the mute mode amplifier (2) and the play mode amplifier (3). At this time, the differential amplifier (3A) of the play mode amplifier (3)
Of the differential amplifier (2A) of the mute mode amplifier (2) is always kept at the same potential as that of the input signal of the mute mode amplifier (2), and the audio signal (SI) input to the mute mode amplifier (2) is Is the mute mode amplifier (2)
And a transistor (Q which is one input terminal of the input amplifier (1) via the negative feedback circuit (NF).
Since it is input to the base of 5), the amplified audio signal (SI) is not output to the outside, and therefore no sound is output from the external speaker.

Next, the circuit is switched from the mute mode to the play mode, the switching circuit (4) that has been turned on is turned off, and the switching circuit (5) that has been turned off is turned on. Then, the mute mode amplifier (2) which has been operating up to now does not operate, and the play mode amplifier (3) operates instead, so that the audio signal (SI) amplified by the input amplifier (1) becomes
It is amplified by the play mode amplifier (3) and output to the current amplifier (IA).

Then, the current amplifier (IA) further amplifies the amplified signal from the play mode amplifier (3) and outputs it to the outside, so that a sound is output from an external speaker or the like.

[0011]

However, according to the amplifier circuit of the conventional example, the mute mode amplifier (2) is used.
The switch transistor (Q14) related to the power supply of
Since it is used only for ON / OFF operation and corresponds to the mute mode, a transistor with low power consumption and relatively low driving capability is used.

In the normal mute mode, a constant current is supplied from the collector of the transistor (Q14) to the mute mode amplifier (2) by the switching circuit (4), but the transistor (Q14) having a low driving capability is used. Therefore, the transistor (Q14) that has that constant current
The collector current of can only pass a relatively low current.

For this reason, the switching transistor (Q
14) Positive audio signal (SI) exceeding the driving capability of
Is the transistor (Q6,
When input to Q7), the transistor (Q6, Q
Transistor (Q14) that regulates the emitter current of 7)
Since the collector current of is a relatively low current, the output voltage of the mute mode amplifier (2) is not sufficiently output according to the input voltage, so that the transistor (Q7) is driven by the negative feedback and the transistor (Q7) The DC potential of the base drops significantly.

The DC potential of the base of the transistor (Q7) must not fluctuate, but when used in the above conditions,
The base potential of the transistor (Q7) fluctuates sharply in a rectangular wave shape, and the voltage fluctuation is differentiated by the phase correction capacitor (C1) connected to the base of the transistor (Q7), and the high frequency component thereof is a current amplifier (IA). Is amplified and output to the outside.

This sound leakage is caused by the switch transistor (Q
The smaller the driving capacity of 14) becomes, the more remarkable it becomes.
When using a transistor with a very low drive capacity,
It became so remarkable that sound leakage always occurred in the mute mode regardless of the amplitude of the audio signal (SI).

[0016]

The present invention has been made in view of the above-mentioned drawbacks of the prior art. As shown in FIG. 1, the first and second amplifying means (12, 13) are provided by amplifying an input signal. And an input amplifying means (11) for outputting to the outside, and a first amplifying means (12) for operating in a first state in which no signal is output to the outside and feeding back the amplified input signal to the input amplifying means (11).
A second amplifying means (13) which operates in a second state of outputting a signal to the outside, amplifies the amplified input signal and outputs the amplified input signal to the outside, and a first amplifying means (12). By providing the potential fixing means (14) for fixing the reference potential, the present invention provides an amplifier circuit capable of suppressing the pop noise and suppressing the high frequency sound leakage as much as possible.

[0017]

[Operation] According to the amplifying circuit of the present invention, as shown in FIG. 1, the input amplifying means (11) and the first amplifying means (1
2), the second amplification means (13), and the potential fixing means (1
4) and are provided. For example, input amplification means (11)
The input signal is amplified by and is output to the first and second amplifying means (12, 13), and the input signal amplified by the first amplifying means (12) in the first state in which the signal is not output to the outside is In the second state in which the signal is fed back to the input amplifying means (11) and is output to the outside, the input signal amplified by the second amplifying means (13) is amplified and output to the outside, and the potential fixing means (14). ) By the first amplification means (1
The reference potential of 2) is fixed.

Therefore, the reference potential of the first amplifying means (12) is fixed by the potential fixing means (14),
As in the conventional case, the reference potential of the first amplifying means (12) fluctuates, so that a signal should not be output to the outside.
In this state, it is possible to prevent the signal from being output to the outside. In the amplifier circuit according to the present invention, the first amplifier means (12) includes a transistor circuit including first and second transistors, and a diode, for example, between the base and emitter of the first transistor. Potential fixing means (14) is provided.

For this reason, the emitter potentials of the first and second transistors of the first amplifying means (12) are easily fixed by the potential fixing means (14) composed of diodes. By changing the emitter potential of the second transistor, it is possible to realize that the signal is output to the outside in the first state with a simple circuit configuration.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amplifier circuit according to an embodiment of the present invention will be described below with reference to the drawings. The amplifier circuit shown in FIG. 2 is an audio amplifier, and the pop noise is prevented by switching the amplifier inside the circuit according to two modes of a mute mode and a play mode. Note that the mute mode is an example of the first state, in which a current is flowing through the amplifier circuit, but an amplified signal such as sound is not output to the outside (for example, from a speaker), The play mode is an example of the second state and is a state in which a current flows through the amplifier circuit and an amplified signal such as sound is output to the outside.

The circuit is, as shown in FIG. 2, an input amplifier (11), a mute mode amplifier (12), a play mode amplifier (13), a current amplifier (IA1), a diode (14) and a switching circuit (15, 16). ), An audio signal (SI) is input to itself, amplified, and output to an external speaker or the like. The input amplifier (11) is an example of an input amplifying means, and includes a first differential amplifier (11A) and a first current mirror circuit (1).
1B), the audio signal (SI) is input to itself, amplified, and output to the mute mode amplifier (12) and the play mode amplifier (13).

The mute mode amplifier (12) is an embodiment of the first amplifying means, and is a transistor (Q26,
The second differential amplifier (12
A) and a second current mirror circuit (12B), and a positive power source (+ Vc) via a switching circuit (15).
c), which operates when the switching circuit (15) is turned on in the mute mode and amplifies the audio signal (SI) amplified by the input amplifier (11) to input the input amplifier (11). It outputs to the one input side via a negative feedback circuit (NF). The transistors (Q26, Q27) are an example of the first and second transistors.

The play mode amplifier (13) is an embodiment of the second amplifying means, and is the third differential amplifier (13).
A) and a third current mirror circuit (13B),
Positive power supply (+ Vcc) via switching circuit (16)
The audio signal (SI) amplified by the input amplifier (11) is operated by turning on the switching circuit (16) in the play mode.
Is further amplified and output to the current amplifier (IA1).

The current amplifier (IA1) further amplifies the amplified signal output from the play mode amplifier (13) and outputs it to an external speaker. The diode (14) is one example of the potential fixing means, and is connected between the emitter and the base of the transistor (Q26) that constitutes the second differential amplifier (12A) of the mute mode amplifier (12). As a result, the emitter potentials of these transistors (Q26, Q27) are fixed at a constant potential.

The switching circuit (15) has a resistor (R1
1), transistor (Q34), constant current source (TS11)
And a switch (SW11), which is a circuit for supplying / not supplying a constant current to the mute mode amplifier (12).
The switching circuit (16) is a switching circuit (1
Similar to 5), it is a circuit for supplying / not supplying a constant current to the play mode amplifier (13). The detailed circuit configuration is omitted in the figure.

The operation of the circuit will be described below. First, the operation in the mute mode will be described. At this time, first, the switch (SW11) is turned on to turn on the switching circuit (15), and the switching circuit (16) is turned off to make the mute mode amplifier (12).
Supply a constant current to. Next, when the audio signal (SI) is input to the base of the transistor (Q24) which is the input terminal of the input amplifier (11), the audio signal (SI) is amplified by the input amplifier (11), and the mute mode amplifier (12) and the play mode amplifier. (13) is output to.

At this time, only the mute mode amplifier (12) is operating, and the potential of the input portion of the second differential amplifier (12A) of the mute mode amplifier (12) is the play mode amplifier (12). The audio signal (SI) which is kept at the same electric potential as the electric potential of the input section of the third differential amplifier (13A) of 13) and which is amplified by the mute mode amplifier (12) is passed through the negative feedback circuit (NF). Since it is input to one input terminal of the input amplifier (11), that is, the base of the transistor (Q25), the externally amplified audio signal (SI) is not output, and therefore no sound is output from the external speaker.

Next, the operation in the play mode will be described. Switching circuit (15) that was turned on when switching from mute mode to play mode
Is turned off, and the switching circuit (1
6) is turned on to supply a constant current to the play mode amplifier (13). Then, since the switching circuit (15) that has been turned on is turned off, the mute mode amplifier (12) that has been operating up to now does not operate, and the play mode amplifier (13) operates instead. Therefore, the input amplifier ( 11) Audio signal (SI) amplified by
Is amplified by the play mode amplifier (13) and output to the current amplifier (IA1).

Next, the current amplifier (IA1) further amplifies the amplified signal from the play mode amplifier (13) and outputs the amplified signal, so that sound is output from an external speaker or the like. By the way, in this circuit, since the transistor (Q34) of the switching circuit (15) relating to the power supply of the mute mode amplifier (12) is used only for ON / OFF operation, low power consumption and so large driving capability are required. Not using a transistor.

Further, in this circuit, unlike the prior art, the diode (14) is connected between the emitter and the base of the transistor (Q26) and the diode (1
4) is connected to the collector of the transistor (Q22). Therefore, a positive audio signal (S) exceeding the driving capability of the transistor (Q14), which has been a problem in the past, is used.
1) is the transistor (Q) of the miute mode amplifier (2)
6, Q7), the base DC potential of the transistor (Q7) tends to decrease due to negative feedback.
In the present invention, at this time, since the diode (14) which is in the reverse bias state in the normal state is forward biased, the emitter potential of the transistor (Q7) is positive (+ V).
From cc), the potential drop is only 3 stones in total including 2 stones of the transistors (Q22) and (Q23) and 1 stone of the diode (14), and is fixed at a constant potential near the positive power supply (+ Vcc).

As a result, since the DC potential of the base of the transistor (Q27) hardly changes as in the conventional case, the leakage of the differentiated high frequency component to the current amplifier (IA) is prevented, and the current amplifier (IA) is prevented. ), It is possible to suppress the phenomenon that the unnecessary component is output to the outside by being amplified. Therefore, in the mute mode, it is possible to prevent leaking of high-pitched sound, which is the high frequency band of the audio signal (SI), from the external speaker.

[0032]

As described above, according to the amplification circuit of the present invention, the input amplification means (11), the first amplification means (12), the second amplification means (13), and the potential Fixing means (14). Therefore, the potential of the first amplifying means (12) is fixed to a constant value by the potential fixing means (14), and therefore the first amplifying means (1
The potential of 2) does not change. Therefore, it is possible to prevent the signal from being output to the outside in the first state in which the signal is not output to the outside.

In the amplifying circuit according to the present invention, the first amplifying means (12) includes a transistor circuit including first and second transistors, and for example, between the base and emitter of the first transistor, A potential fixing means (14) composed of a diode is provided. Therefore, the first
Of the first and second transistors of the amplifying means (12) of (1) are fixed potential means (1
Since it is easily fixed by 4), it becomes possible to output the signal to the outside in the first state with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a principle diagram of an amplifier circuit according to the present invention.

FIG. 2 is a circuit diagram of an amplifier circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of an amplifier circuit according to a conventional example.

Claims (3)

[Claims] 1. An input amplifying means (11) for amplifying an input signal and outputting the amplified signal to first and second amplifying means (12, 13), and operating in a first state in which no signal is externally output, A first amplifying means (12) for feeding back the amplified input signal to the input amplifying means (11) and a second state for outputting a signal to the outside to amplify the amplified input signal. An amplifying circuit comprising: a second amplifying means (13) for outputting to the outside; and a potential fixing means (14) for fixing the reference potential of the first amplifying means (12). 2. An input amplifying means (11) for amplifying an input signal and outputting it to the first and second amplifying means (12, 13), and operating in a first state in which no signal is output to the outside, A first amplifying means (12) for feeding back the amplified input signal to the input amplifying means (11) and a second state for outputting a signal to the outside to amplify the amplified input signal. It comprises a second amplifying means (13) for outputting to the outside, and a potential fixing means (14) for fixing the reference potential of the first amplifying means (12), and the first amplifying means (12). An amplifier circuit comprising a transistor circuit including first and second transistors, wherein the potential fixing means (14) is provided between a base and an emitter of the first transistor. 3. An input amplifying means (11) for amplifying an input signal and outputting it to the first and second amplifying means (12, 13), and operating in a first state where no signal is output to the outside, A first amplifying means (12) for feeding back the amplified input signal to the input amplifying means (11) and a second state for outputting a signal to the outside to amplify the amplified input signal. It comprises a second amplifying means (13) for outputting to the outside, and a potential fixing means (14) for fixing the reference potential of the first amplifying means (12), and the first amplifying means (12). , A transistor circuit including first and second transistors, the potential fixing means (14) is provided between the base and the emitter of the first transistor, and the potential fixing means (14) is composed of a diode. An amplifier circuit characterized in that.