JP3138124B2 - amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an OCL (Output)
Condenserless) type amplifier,
In particular, the present invention relates to an amplifier suitable for use in a small device such as a headphone stereo.

[0002]

2. Description of the Related Art In general, there is a small device such as a headphone stereo which mutes an audio signal and generates a beep indicating an operation state of the small device. An amplifier used in such a small device is shown in FIG. It is configured as follows. In FIG. 2, in the case of the normal operation, since no control signal is applied to the mute circuits (1) and (1 '), the mute circuits (1) and (1') do not perform the mute operation. The left and right audio signals applied through the input terminals (2) and (2 ') are amplified by the amplifiers (3) and (3'), and then the DC components are added to the capacitors (4) and (4 '). Be cut. Then, the left and right audio signals are applied to the headphones (5) and (5 ') via the mute circuits (1) and (1'), and sound is generated from the headphones (5).

In the case of a beep sound, the mute circuits (1) and (1 ') perform a mute operation, and the left and right audio signals generated from the amplifiers (3) and (3') are muted at the same time. A beep signal is applied to the headphones (5) and (5 ') and the headphones (5) and (5')
Produces a beep. When the beep is finished,
The mute operation of the mute circuits (1) and (1 ') is stopped, and the left and right audio signals are again applied to the headphones (5) and (5').

The muting operation is performed by operating the mute circuits (1) and (1 '), but cannot be completely muted only by providing the mute circuits (1) and (1'). Therefore, mute circuit (1)
At the same time as (1) and (1 ') are operated, for example, the amplifiers (3) and (3') are deactivated to more completely mute.

[0005]

However, in the circuit of FIG. 2, when the mute is released, the amplifiers (3) and (3 ') are changed from the non-operating state to the operating state. ′) Causes an output fluctuation, and at the same time, the mute circuits (1) and (1 ′) stop the mute operation. Therefore, the output fluctuation is applied to the headphones (5) and (5 ′), and the headphone (5) is output. ) And (5 ') generate a shock sound.

Further, the circuit of FIG. 2 requires a capacitor for blocking direct current and a mute circuit, and when it is formed into an IC, it must be external to the IC. Therefore, the circuit of FIG. In addition, there is a problem that the number of external parts increases and the size cannot be reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a first aspect for amplifying a left audio signal.
An amplifier, a second amplifier for amplifying the right audio signal,
An OCL type amplifier including a center amplifier that generates a DC voltage equal to the output DC voltage of the first and second amplifiers, amplifies the beep signal and supplies the amplified signals to the output terminals of the first, second and center amplifiers. Beep amplifier,
Attenuating means for attenuating a beep signal supplied from the beep amplifier to the output terminal of the center amplifier; and disabling the beep amplifier during operation of the first, second and center amplifiers, and operating the beep amplifier. , The first and second
And control means for disabling the center amplifier.

The beep amplifier includes an input amplifier for amplifying an input signal, and first, second and third output signals for generating first, second and third output signals in accordance with an output of the input amplifier.
And a third output circuit, and a current source for generating an operation current of the input amplifier circuit.

[0009]

According to the present invention, when the first, second and center amplifiers are operated and the beep amplifier is deactivated, the first and second amplifiers amplify the left and right audio signals, and the center amplifier operates in the middle. A point DC voltage is generated, and sound is generated from headphones connected between the output terminals of the first and second amplifiers and the output terminal of the center amplifier. Conversely, when the beep amplifier is operated and the first, second and center amplifiers are deactivated, the beep signal is amplified by the beep amplifier, and
It occurs at the output terminals of the second and center amplifiers. Since the beep signal generated at the output terminal of the center amplifier is attenuated by the attenuating means, a sound corresponding to the difference between the output terminals of the first and second amplifiers and the beep signal generated at the output terminal of the center amplifier is generated from the headphones. .

[0010] The beep amplifier includes an input amplifier circuit,
First, second, and third output circuits are provided, and the first, second, and third output circuits generate first, second, and third output signals, respectively, according to the output of the input amplifier circuit. Then, the outputs of the first, second and third output circuits are supplied to the output terminals of the first, second and center amplifiers.

[0011]

FIG. 1 shows an embodiment of the present invention.
(37) is a left power amplifier, (38) is a right power amplifier, (39) is a center amplifier, (44) is a beep amplifier for amplifying a beep signal, (45) is a left power amplifier (37), and a right power amplifier ( 38), a control circuit for generating control signals for controlling the operations of the center amplifier (39) and the beep amplifier (44). (46), (4)
7) and (48) are oscillation prevention circuits each including a capacitor and a resistor.

In FIG. 1, during normal operation, the control circuit (4
5) Left, right, center and beep amplifier (37),
A control signal of "1" or "0" is applied to the current sources of (38), (39) and (44). For example, a control signal of "1" is applied to the current sources of the left, right and center amplifiers (37), (38) and (39) to turn on the current sources,
The current source of the beep amplifier (44) to which the control signal of "0" is applied is turned off. That is, the left, right and center amplifiers (37), (38) and (39) operate, and the beep amplifier (44) does not operate. Input terminals (42) and (4
The left and right audio signals applied to 3) are amplified by left and right power amplifiers (37) and (38), and then applied to headphones (40) and (41), and headphones (40) and (41). Produces sound. At this time, the center amplifier (39) connects the left and right power amplifiers (37) and (38) to the connection point between the speakers (40) and (41).
Generates a midpoint DC voltage equal to the DC voltage generated.
Oscillation prevention circuits (46), (47) and (48) are connected to the output terminals of the left, right and center amplifiers (37), (38) and (39) so that no oscillation occurs.
The capacity of the capacitor of the oscillation prevention circuit (47) is set to be larger than the capacity of the capacitors of the other oscillation prevention circuits (46) and (48).

When a beep sound is to be generated, the beep amplifier (44) is operated by the control signal of "1" generated from the control circuit (45), and the control signal of "0" is applied to the left side. , Right and center amplifier (37), (3
8) and (39) become inactive. Since the left, right and center amplifiers (37), (38) and (39) are not operating, the left and right audio signals applied to the input terminals (42) and (43) are left and right power amplifiers (37). )
And (38), and the center amplifier (3
9) does not generate the midpoint DC voltage. Thereafter, the beep signal applied to the input terminal (31) is transmitted to the beep amplifier (4
4) amplified by left, right and center amplifier (37),
It is supplied to the output terminals of (38) and (39). The beep signals generated at the output terminals of the left and right power amplifiers (37) and (38) are attenuated by the oscillation prevention circuits (46) and (48), and the beep signals generated at the output terminals of the center amplifier (39) are oscillated. It is attenuated by the prevention circuit (47). The amount of attenuation of the oscillation prevention circuit (47) is determined by the oscillation prevention circuits (46) and (4).
Since the attenuation amount is larger than the attenuation amount of 8), a difference occurs between the beep signal levels at both ends of the headphones 40 and 41, and a beep sound is generated from the headphones 40 and 41 at a volume corresponding to the difference. Since the beep sound is a single-frequency sound, the beep sound becomes unpleasant sound by increasing the volume, so that the beep sound is generated by the method described above,
The volume of the sound by the left and right audio signals of the headphones (40) and (41) is lower than the volume of the sound, so that unpleasant sound can be prevented.

Thereafter, when the mute is released, the left, right and center amplifiers (37), (38) and (39) operate, and the beep amplifier (44) does not operate. FIG. 3 is a specific circuit example of the beep amplifier (44) of FIG.
(6) is an input amplifier circuit composed of a differential amplifier composed of transistors (9) and (8) and a differential amplifier composed of transistors (7) and (10), and (11) is a transistor (12) ) And (13) and the transistor (1)
A first output circuit composed of a current mirror circuit (16) composed of 4) and (15), and (17) is composed of transistors (18) and (19), and transistors (20) and (2).
(2) a second output circuit composed of a current mirror circuit (22) composed of the transistors (24) and (25) and a current mirror circuit composed of the transistors (26) and (27); 28) and a third output circuit composed of a resistor (29), and (30) is a current source.

Next, the operation of FIG. 3 will be described. Control circuit (4
When the current source (30) is turned on by the control signal generated from 4), the input signal applied via the input terminal (31) is amplified in the input amplifier circuit (6), and the transistors (7) and (8) are amplified. An output signal is generated from the collector of ()). The output signal of the transistor (8) is
3) and (19), a collector current is generated in the transistors (13) and (19) according to the output signal. The collector currents of transistors (13) and (19) are generated at the collectors of transistors (14) and (20) via current mirror circuits (16) and (22), respectively. The output signal of the transistor (7) is applied to the bases of the transistors (12) and (18), and a collector current is generated in the transistors (12) and (18) according to the output signal. And the transistor (14)
An output signal corresponding to the difference between the collector currents of the transistors (12) and (12) is generated from the output terminal (32), and an output signal corresponding to the difference between the collector currents of the transistors (18) and (20) is output from the output terminal (33). Arising from

Further, depending on the collector currents of the transistors (7) and (8), the transistors (24) and (2)
5) A collector current is generated. Transistor (25)
Is generated at the collector of the transistor (27) via the current mirror circuit (28). A current corresponding to the collector currents of the transistors (24) and (27) is generated from the output terminal (34) via the resistor (29), and the transistors (8) and (1) via the resistor (35).
0) is applied to the base.

When the current source (30) is turned off, the differential amplifier circuit (6) does not operate and does not generate an output signal. Therefore, the first, second and third output circuits (11), (17) and (2)
No output signal is generated from 3). Since the first, second and third output circuits (11), (17) and (23) have the same configuration, the output signals of the output terminals (32), (33) and (34) are the same.

[0018]

As described above, according to the present invention, since the power amplifier and the center amplifier are turned on and off at the same time, output fluctuations occur at both ends of the headphone, so that the shock noise can be reduced. Further, since the configuration of the OCL type amplifier is employed, it is not necessary to add a mute circuit and a DC blocking capacitor, which is suitable for IC.

Further, by attenuating the beep signal, the operation state can be determined based on the beep sound without making the beep sound unpleasant.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a circuit diagram showing a specific circuit example of a beep amplifier of the present invention.

[Explanation of symbols]

 (37) Left power amplifier (38) Right power amplifier (39) Center amplifier (44) Beep amplifier (45) Control circuit

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/00-3/72

Claims (2)

(57) [Claims] 1. A first amplifier for amplifying a left audio signal, a second amplifier for amplifying a right audio signal, and a center amplifier for generating a DC voltage equal to an output DC voltage of the first and second amplifiers. In the OCL system amplifier, a beep amplifier for amplifying a beep signal and supplying the amplified signal to output terminals of the first, second, and center amplifiers, and an output terminal of the first, second, and center amplifiers, respectively. Control means for disabling the beep amplifier during the operation of the first, second and center amplifiers, and disabling the first, second and center amplifiers during the operation of the beep amplifier; The attenuation amount of the attenuation means connected to the center amplifier,
An amplifier characterized in that the attenuation is set to be larger than the amount of attenuation of attenuation means connected to the first and second amplifiers. 2. The beep amplifier comprises: an input amplifier circuit for amplifying an input signal; and first, second and third output signals for generating first, second and third output signals in accordance with an output of the input amplifier circuit. A three-output circuit, and a current source for generating an operating current of the input amplifier circuit, wherein output terminals of the first, second, and third output circuits are the first, second, and third output circuits.
2. The amplifier according to claim 1, wherein the amplifier is connected to the output terminals of the second and center amplifiers.