JPH1013264A - Audio signal amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of component parts of an audio signal amplifier circuit by securing the high-pass active filter characteristic with respect to a 2nd audio signal for an amplifier transistor TR, which performs the shared amplification of both 1st and 2nd audio signals. SOLUTION: When the 1st audio signal selection voltage is supplied to a 1st audio signal selection voltage supply terminal 17, a 1st switching diode 10 is turned on. Then a 2nd switching diode 15 is turned on, when the 2nd audio signal selection voltage is supplied to a 2nd audio signal selection voltage supply terminal 18, and the selection voltage is amplified by an amplifier TR 1 and outputted to a signal output terminal 6. An audio signal amplifier circuit consists of the TR 1, the 1st and 2nd capacitors 12 and 13 and a feedback resistance 14 and has a high-pass active filter characteristic. Thus, the constitution is simplified, and the number of component parts for the amplifier circuit can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal amplifying circuit, and more particularly to amplification of a first audio signal obtained by demodulating an FM broadcast signal and removal of a stereo pilot signal from a second audio signal obtained by demodulating an AM broadcast signal. The present invention relates to an audio signal amplifying circuit in which amplifying with an audio signal is selectively performed.

[0002]

2. Description of the Related Art Generally, in an AM broadcast signal, when a stereo broadcast is performed, a stereo pilot signal indicating that the broadcast is a stereo broadcast is inserted. And
When an AM / FM broadcast receiver or the like receives an AM stereo broadcast signal, a 25 Hz frequency stereo pilot signal component remains in the demodulated audio signal.

For this reason, a conventional FM / AM broadcast receiver uses an audio signal amplifier circuit having a high-pass filter characteristic to remove a stereo pilot signal component when amplifying an audio signal obtained by demodulating an AM broadcast signal. I have.

FIG. 3 is a circuit diagram showing an example of a configuration of a conventional audio signal amplifier circuit having a high-pass filter characteristic.

[0005] Common emitter type amplifying transistor 1
Is a device that selectively amplifies an audio signal obtained by demodulating an FM broadcast signal (hereinafter referred to as a first audio signal) and an audio signal obtained by demodulating an AM broadcast signal (hereinafter referred to as a second audio signal). It is. The amplifying transistor 1 has an emitter connected to the ground via the ground resistor 2, and a collector connected to the power supply terminal 19 via the resistor 3.
And the signal output terminal 6 via the coupling capacitor 3, and the base is connected to the ground via the bias resistor 4. The first audio signal input terminal 7 is
Coupling capacitor 8 and first switching diode 10
And the connection point between the coupling capacitor 8 and the first switching diode 10 is connected to the first audio signal selection voltage supply terminal 17 via the resistor 9.

The common emitter type amplifying transistor 20 amplifies the second audio signal and constitutes a high-pass type active filter. The amplifying transistor 20 has an emitter connected to the ground via a ground resistor 21 and a collector connected via a resistor 23 to the second audio signal selection voltage supply terminal 18 and the coupling capacitor 2.
The base is connected to the second audio signal selection voltage supply terminal 18 via the bias resistor 24 and to the ground via the bias resistor 25, respectively. Have been. The second audio signal input terminal 11 includes first and second capacitors 12, 1 connected in series.
3 is connected to the base of the amplification transistor 20, and the connection point between the first and second capacitors 12 and 13 is connected to the emitter of the amplification transistor 20 via the feedback resistor 14. The connection point between the coupling capacitor 22 and the second switching diode 15 is connected to the second audio signal selection voltage supply terminal 18 via the resistor 16.
In this case, the amplification transistor 20, the first and second capacitors 12, 13 and the feedback resistor 14 constitute a high-pass active filter.

Now, the first audio signal selection voltage (FM _SW ) is supplied to the first audio signal selection voltage supply terminal 17 (at this time, no voltage is supplied to the second audio signal selection voltage supply terminal 18). Then, the first switching diode 10 is turned on. At this time, the first
The first audio signal supplied to the audio signal input terminal 7 is applied to the base of the amplifying transistor 1 via the coupling capacitor 8 and the first switching diode 10, and is amplified by the amplifying transistor 1. Is output from the signal output terminal 6 via

On the other hand, the second audio signal selection voltage (AM _SW ) is supplied to the second audio signal selection voltage supply terminal 18 (at this time, no voltage is supplied to the first audio signal selection voltage supply terminal 17). Then, the amplification transistor 20 is turned on and the second switching diode 15 is turned on. At this time, the second audio signal supplied to the second audio signal input terminal 11 is applied to the base of the amplifying transistor 20 via the first and second capacitors 12 and 13, and is amplified by the amplifying transistor 20. . Next, the second audio signal is applied to the base of the amplifying transistor 1 via the coupling capacitor 22 and the second switching diode 15, and after being amplified by the amplifying transistor 1, the signal output terminal 6 via the coupling capacitor 5. Output from

During the amplification of the second audio signal, the high-pass active filter including the amplifying transistor 20, the first and second capacitors 12, 13 and the feedback resistor 14 causes the component of the second audio signal to have a frequency of 25 Hz or less. Are attenuated and removed, and the output of the pilot signal component having a frequency of 25 Hz is suppressed.

[0010]

When the conventional audio signal amplifying circuit amplifies the second audio signal,
First, amplification is performed by the amplification transistor 20 constituting the high-pass type active filter, and then amplification is performed by the amplification transistor 1. Therefore, not only is the circuit configuration complicated, but also there are many components and the manufacturing cost is high. There is.

The present invention solves the above problems,
An object of the present invention is to provide an audio signal amplifier circuit which simplifies a circuit configuration, reduces components, and is inexpensive to manufacture.

[0012]

To achieve the above object, an audio signal amplifying circuit according to the present invention comprises first and second audio signal amplifying circuits.
When the second audio signal is amplified by the common-emitter amplification transistor that selectively amplifies the audio signal, a high-pass active filter for the second audio signal is configured including the amplification transistor.

According to the above configuration, the overall circuit configuration can be simplified by providing the high-pass type active filter characteristic for the second audio signal to the amplifying transistor for commonly amplifying the first and second audio signals. As a result, the number of components can be reduced, and an audio signal amplifier circuit with low manufacturing cost can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention, an audio signal amplifying circuit has a base to which a first or second audio signal is selectively inputted, an emitter grounded through a resistor, and a first collector connected to a collector. Or, an amplifying transistor for outputting a second audio signal, first and second capacitors connected in series between the second audio signal input terminal and the base of the amplifying transistor, and a connection point of the first and second capacitors. A feedback resistor connected between the emitter of the amplifying transistor and the amplifying transistor;
The first and second capacitors and the feedback resistor constitute a high-pass active filter for the second audio signal.

In a preferred example of the embodiment of the present invention, the audio signal amplifying circuit has a first and a second switching means connected in series between a first audio signal input terminal and a base of an amplifying transistor. The second switching means is connected between the two capacitors and the base of the amplifying transistor, and one of the first and second switching means is selectively driven to a conductive state. 2 audio signals are selectively amplified.

Further, in a specific example of the embodiment of the present invention, in the audio signal amplifying circuit, the first audio signal is a demodulated signal of an FM broadcast signal, and the second audio signal is a demodulated signal of an AM broadcast signal. The high-pass active filter removes a stereo pilot signal from a demodulated signal of an AM broadcast signal.

According to these embodiments, when the first and second audio signals are selectively amplified by the amplifying transistor, the first audio signal is amplified by the amplifying transistor. The second audio signal is amplified by one amplification stage using an amplification transistor having a high-pass active filter characteristic. That is, the second audio signal is amplified by an auxiliary amplification transistor having a high-pass type active filter characteristic as in the above-described audio signal amplification circuit, and further amplified by the amplification transistor. And it is not amplified by two amplification stages.

As a result, as compared with the conventional audio signal amplifier circuit of this type, the overall circuit configuration is simplified, whereby the number of components is reduced, and an audio signal amplifier circuit having a low manufacturing cost can be obtained.

[0019]

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

FIG. 1 is a circuit diagram showing a configuration of an embodiment of an audio signal amplifying circuit according to the present invention.

In the audio signal amplifying circuit of this embodiment shown in FIG. 1, the same components as those of the conventional audio signal amplifying circuit shown in FIG. 3 are denoted by the same reference numerals.

As shown in FIG. 1, in the audio signal amplifying circuit of this embodiment, the second audio signal (A
An audio signal obtained by demodulating an M broadcast signal) An input terminal 11 is connected to the base of the amplifying transistor 1 via first and second capacitors 12 and 13 and a second switching diode 15 connected in series. Capacitor 1
The connection point between 2 and 13 is connected to the emitter of the amplifying transistor 1 via a feedback resistor 14, and the connection point between the second capacitor 13 and the second switching diode 15 is connected via a resistor 16 to a second audio signal selection voltage supply terminal. 18 is connected. The amplifying transistor 1, the first and second capacitors 12, 13 and the feedback resistor 14 constitute a high-pass active filter. Further, in the audio signal amplifying circuit of this embodiment, the other parts than the circuit configuration are the same as those of the conventional audio signal amplifying circuit shown in FIG. Is omitted.

The audio signal amplifying circuit according to the present embodiment having the above configuration operates as follows.

The FM broadcast signal is received, and the first audio signal selection voltage (FM _SW ) is supplied to the first audio signal selection voltage supply terminal 17 (at this time, any signal is supplied to the second audio signal selection voltage supply terminal 18). Is not supplied), the first switching diode 10 is turned on. At this time, the first audio signal supplied to the first audio signal input terminal 7 is
The voltage is applied to the base of the amplifying transistor 1 via the switching diode 10, amplified by the amplifying transistor 1, and then output from the signal output terminal 6 via the coupling capacitor 5 to a subsequent circuit (not shown).

On the other hand, an AM broadcast signal is received,
When the second audio signal selection voltage (AM _SW ) is supplied to the second audio signal selection voltage supply terminal 18 (at this time, no voltage is supplied to the first audio signal selection voltage supply terminal 17), the second audio signal selection voltage (AM _SW ) is output. The switching diode 15 is turned on. At this time, the second audio signal supplied to the second audio signal input terminal 11 is applied to the base of the amplifying transistor 1 via the first and second capacitors 12 and 13 and the second switching diode 15 connected in series. After being amplified by the amplifying transistor 1, it is output from the signal output terminal 6 via the coupling capacitor 5 to a subsequent circuit (not shown). A part of the second audio signal is supplied from the emitter of the amplifying transistor 1 via the feedback resistor 14 to the first and second capacitors 12, 1 and 2.
3 is returned to the connection point.

Here, the first and second capacitors 12 and 13
Are respectively C1 and C2, and the resistance value of the feedback resistor 14 is R1, for example, C1 = 0.033 μF, C2 =
When 0.1 μF and R1 = 10 kΩ are selected, the frequency versus amplification characteristic of the amplification circuit portion having the high-pass type active filter characteristic including the amplification transistor 1, the first and second capacitors 12 and 13, and the feedback resistor 14 is as follows: For the first audio signal, the curve shown in FIG.
The result is as shown by the curve in FIG. 2 for the audio signal. Then, a stereo pilot signal component having a frequency of 25 Hz included in the second audio signal can be greatly attenuated.

As described above, according to this embodiment, the amplifying circuit having the high-pass active filter characteristic for the second audio signal by using the amplifying transistor 1 for selectively amplifying the first and second audio signals. , The circuit configuration is simplified, the number of components is reduced,
An audio signal amplifier circuit having a low manufacturing cost can be obtained.

[0028]

As described above, according to the present invention, an amplifying circuit having a high-pass active filter characteristic for a second audio signal using an amplifying transistor for selectively amplifying the first and second audio signals. As a result, the overall circuit configuration is simplified as compared with the conventional audio signal amplifier circuit of this type, thereby reducing the number of components and obtaining an audio signal amplifier circuit with low manufacturing cost. is there.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of an audio signal amplifying circuit according to the present invention.

FIG. 2 is a characteristic diagram showing a frequency versus signal amplification characteristic required in an audio signal amplification circuit.

FIG. 3 is a circuit diagram showing an example of a configuration of a conventional audio signal amplifier circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Amplification transistor 2 Ground resistance 7 1st audio signal input terminal 10 1st switching diode (1st switching means) 11 2nd audio signal input terminal 12 1st capacitor 13 2nd capacitor 14 Feedback resistance 15 2nd switching diode (1st 2 switching means)

Claims (3)

[Claims] An amplifying transistor to which a first or second audio signal is selectively input to a base, an emitter is grounded via a grounding resistor, and the first or second audio signal is output from a collector, First and second capacitors connected in series between a second audio signal input terminal and the base of the amplifying transistor, and connected between a connection point of the first and second capacitors and an emitter of the amplifying transistor. An audio signal amplifying circuit, comprising: a feedback resistor; and a high-pass active filter for the second audio signal configured by the amplifying transistor, the first and second capacitors, and the feedback resistor. 2. A first switching means between a first audio signal input terminal and a base of the amplifying transistor,
Second switching means is respectively connected between the first and second capacitors connected in series and the base of the transistor for amplification, and one of the first and second switching means is selectively driven to a conductive state. 2. The audio signal amplifier circuit according to claim 1, wherein the first audio signal or the second audio signal is selectively amplified by the amplification transistor. 3. The demodulated signal of an FM broadcast signal, the second audio signal is a demodulated signal of an AM broadcast signal, and the high-pass active filter is a demodulated signal of the AM broadcast signal. 3. The audio signal amplifier circuit according to claim 1, wherein the stereo pilot signal is removed.