JPH06125227A - Audio equipment containing battery and audio signal amplifier circuit - Google Patents

Abstract

PURPOSE:To provide an audio equipment containing a battery and an audio signal amplifier circuit so as to amplify the audio signals with no distortion even at a low power voltage level. CONSTITUTION:A control current generating circuit 3 generates a control current Im of a level accordant with the power voltage Vcc and the reference voltage VB. The current Im is applied to the feedback input terminal (-) of an amplifier 1. Thus the base potential of the transistor of the first stage is held at a prescribed level as a precondition for operation of the amplifier 1. Furthermore the base current is controlled. Then the operating point voltage of an output signal B is set at the middle level (Vcc/2) of the voltage Vcc. Thus it is possible to amplify an audio signal A with no distortion even at a low power voltage as well as at a high power voltage level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device with a built-in battery and an audio signal amplifier circuit. The present invention relates to an audio signal amplifier circuit suitable for headphone stereo, etc., and an audio device with a built-in battery including the audio signal amplifier circuit.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional audio signal amplifier circuit compatible with a low power supply voltage. Where 1 is the input signal A
2 is a reference voltage generating circuit for generating a reference voltage VB. The first stage transistor of amplifier 1 is
Normally, it is connected to the grounded-emitter type, and the base receives an input signal. Therefore, in order for the amplifier 1 to operate, the input signal must be at least 1 VF (0.6 to 0.7).
V) or higher. However, under a low power supply voltage, the operating point voltage of the input signal, that is, the bias voltage of the base cannot be secured simply by dividing the power supply voltage into two.

Therefore, the reference voltage generating circuit 2 is provided in the circuit corresponding to the low power supply voltage, and the reference voltage VB is usually set to about 0.9V in consideration of the amplitude of the input signal and the like. As a result, the operating point voltage of the non-inverting input terminal and the inverting input terminal of the amplifier 1 and the output signal B is fixed to the reference voltage VB, and the signal value fluctuates around this operating point voltage. Therefore, the audio signal can be amplified even under a standard battery with a supply voltage of 1.5 V or less. This output signal is output as sound through headphones, earphones, or the like.

[0004]

As described above, in the conventional audio device with a built-in battery and the audio signal amplifier circuit, the reference voltage VB is used as the operating point voltage of the output signal B regardless of the value of the power supply voltage Vcc (see FIG. 4 (a)). Therefore, while the battery is new and the value of the power supply voltage Vcc is large (see Vcc1 in FIG. 4B) and the output voltage of the amplifier 1 has a margin, the output signal B has a sufficient amplitude centered on the reference voltage VB. It can have (see waveform Bc in FIG. 4B). However, when the value of the power supply voltage Vcc decreases as the battery discharges, the power supply voltage Vcc and the reference voltage Vcc
The difference from B disappears (see Vcc2 in Fig. 4 (c)). Then, there is no margin in the output voltage of the amplifier 1, and the output signal B swinging around the reference voltage VB is
The waveform on the power supply voltage side is limited to the voltage Vcc2 or less, and the power supply side cannot swing with a sufficient amplitude (see the waveform Bd in FIG. 4C).

For this reason, although it operates for a while even when the power supply voltage is lowered, in that case, the waveform of the output signal is greatly distorted. This is inconvenient because the sound is disturbed and the listener is uncomfortable. An object of the present invention is to solve the above-mentioned problems of the prior art, and an audio device with a built-in battery and an audio signal amplifier having a configuration capable of amplifying an audio signal without distortion even under a low power supply voltage. It is to realize the circuit.

[0006]

The structure of the audio device with a built-in battery according to the present invention for achieving the above object is as follows.
The following audio signal amplification circuit is provided.
The configuration of the audio signal amplifier circuit of the present invention which achieves such an object is such that the base of the differential transistor pair in the first stage is provided with an amplifier having a feedback resistance for receiving an input signal, and the received audio signal is amplified and output. In an audio signal amplifier circuit that outputs a signal, a reference voltage generation circuit that generates a reference voltage of a predetermined voltage value and supplies it as a bias voltage of the base, and a control in which the voltage is controlled to the same voltage value as the reference voltage. A line, a first resistor having a resistance value about twice that of the feedback resistor and connected between a power supply voltage line and the control line, and flowing a first current; and about twice the feedback resistor. A second resistor having a resistance value of, connected between the control line and the ground line, and flowing a second current;
A control current generation circuit that outputs a difference current between the second current and the first current as a control current, the control current being connected to the feedback resistor in the transistor pair. By being added to the base current of the other transistor, the operating point voltage of the output signal is controlled to a voltage value that is approximately half the power supply voltage while maintaining the input bias voltage of the amplifier at the reference voltage. is there.

[0007]

In the audio device with built-in battery and the audio signal amplifying circuit of the present invention having the above-mentioned structure,
The operating point voltage of the non-inverting input signal and the inverting input signal of the amplifier is maintained at the reference voltage, that is, the bias voltage of the base of the differential transistor pair is maintained at the required value for transistor operation. Therefore, the amplifier can perform the differential amplification operation of the input signal. Furthermore, since the operating point voltage of the output signal of the amplifier is controlled to a voltage value that is almost half the power supply voltage, the output signal can have a sufficiently large amplitude when the power supply voltage is high, and the power supply voltage drops to almost the standard value. The output signal can swing to the power supply side and the ground side almost symmetrically even when the voltage becomes as low as the voltage. Therefore, the audio signal can be amplified without being distorted not only under a high power supply voltage but also under a low power supply voltage.

[0008]

1 is a circuit diagram of an embodiment of an audio signal amplifier circuit according to the present invention. Here, 1 is a differential amplifier that non-inverts and amplifies the audio signal component of the input signal A and outputs an output signal B, 2 is a reference voltage generation circuit that generates a reference voltage VB, and 3 is a power supply voltage Vcc and a reference It is a control current generation circuit that generates a control current Im according to the voltage VB. The amplifier 1 is a differential transistor pair in which the first-stage circuit is connected to the grounded-emitter type, and its base receives an input signal via a non-inverting input terminal and an inverting input terminal.

The reference voltage generating circuit 2 generates a reference voltage VB of about 0.9V by the forward voltage (1VF) of the diode and the voltage drop (set to about 2Vsat) at the resistor.
This reference voltage VB is applied to the non-inverting input terminal (+) of the amplifier 1 as the operating point voltage of the audio signal A via the resistor Rp.
Be transmitted to. Further, it is also transmitted to the inverting input terminal (-) of the amplifier 1 via the resistor Rm. Since the inverting input terminal (-) is virtually short-circuited to the non-inverting input terminal (+) by the function of the amplifier 1 to which the feedback resistor Rf is connected, it also receives the input signal having the reference voltage VB as the operating point voltage.
As a result, the input signal received by both the input terminals of the amplifier 1 is 1 VF (0.6 to 0.6) which is necessary as the bias voltage between the base and the emitter even when the amplitude of the input signal is taken into consideration.
A voltage of 0.7 V) or higher is secured. So amplifier 1
There is no hindrance to the operation of.

The control current generating circuit 3 is composed mainly of all feedback amplifiers, and has a reference voltage V as one input signal.
The voltage of the other input signal is controlled so that it follows B. The other input signal is the line of the power supply Vcc and the ground G.
It is given as the voltage at the connection point between the resistors connected in series with the ND line. In other words, the control line 3a
Are controlled so that the voltage becomes the same as the reference voltage VB. As a result, the resistance on the power supply Vcc side (resistance value 2 × Rf)
A current I1 = ((Vcc-VB) / (2 * Rf)) flows through the resistor and a current I is applied to the resistance (resistance value 2 * Rf) on the ground GND side.
2 = (VB / (2 * Rf)) flows. Therefore, from this connection point, the difference current Im ′ = (I1−I2) =
(((Vcc / 2) -VB) / Rf) is obtained. This difference current follows the difference voltage between the half of the power supply voltage and the reference voltage, and the direction of the current is inverted and output as the control current Im.

The control current Im is applied to the connection point between the inverting input terminal (-) of the amplifier 1 and the resistor Rp for transmitting the reference voltage and the feedback resistor Rf (shown in the drawing in the direction indicated by the reference numeral in FIG. 1). Has been). Since the inverting input terminal (-) of the amplifier 1 is virtually short-circuited to the non-inverting input terminal (+) and the voltage at the connection point is not influenced by the control current Im, this control current Im passes through the feedback resistor Rf. Flowing. Due to the voltage drop across the resistor Rf, the voltage level of the output signal B transitions by Im * Rf, that is, ((Vcc / 2) -VB).

Then, since there was no control current Im, the voltage level of the output signal B was Vm, so that the operating point voltage VB 'of the output signal B was (Vcc / 2 due to the addition of the control current Im. ) (See FIG. 2A). Therefore, if the battery is new and the value of the power supply voltage Vcc is large (see Vcc1 in FIG. 2B) and the output voltage of the amplifier 1 has a margin, the output signal B is naturally centered on the operating point voltage VB '. Can have sufficient amplitude (Fig. 2
(See waveform Ba in (b)).

Not only that, the value of the power supply voltage Vcc becomes smaller as the battery discharges, and there is no difference between the power supply voltage Vcc and the reference voltage VB (Vcc in FIG. 2C).
2), even when the output voltage of the amplifier 1 is running low, the output signal B swinging around the operating point voltage VB 'does not distort the waveform on the power supply voltage side, Can also swing symmetrically to the ground side (see waveform Bb in FIG. 2C). Therefore, even when the supply voltage of the battery drops to about 0.9V (1VF + 2Vsat), the audio signal can be amplified without distortion. As a result, clear sound is output from the headphones or earphones. It should be noted that the embodiment of the audio device with a built-in battery of the present invention is provided with the above-mentioned audio signal amplifier circuit, and the operation and effect thereof are similar.

[0014]

As can be understood from the above description, in the present invention, a control current having a current value corresponding to the power supply voltage is generated and applied to the feedback side input terminal of the amplifier. As a result, even when the power supply voltage drops, the base current can be adjusted while holding the base potential of the first-stage transistor, which is a prerequisite for the amplifier operation, at a predetermined value. Therefore, the operating point voltage of the output signal becomes the midpoint voltage of the power supply voltage. As a result, the audio signal can be amplified without distortion even under a high power supply voltage as well as under a low power supply voltage.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram thereof, (a) is a graph showing a voltage relationship, and (b) and (c) are waveform examples.

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

FIG. 4 is an explanatory diagram of a conventional example,
(A) is a graph showing a voltage relationship, and (b) and (c) are waveform examples.

[Explanation of symbols]

 1 Amplifier 2 Reference voltage generation circuit 3 Control current generation circuit

Claims (2)

[Claims] 1. A built-in battery having an audio signal amplifier circuit in which the base of a first-stage differential transistor pair includes an amplifier which receives an input signal and which has a feedback resistance, and which outputs an output signal obtained by amplifying the received audio signal. In an audio device, a reference voltage generating circuit for generating a reference voltage having a predetermined voltage value and supplying it as a bias voltage for the base, a control line whose voltage is controlled to the same voltage value as the reference voltage, and the feedback resistor. Has a resistance value about twice that of the first resistance and has a resistance value about twice that of the feedback resistance, and a first resistance connected between the line of the power supply voltage and the control line and flowing a first current. A second resistor connected between the control line and the ground line to allow a second current to flow, and a difference current between the second current and the first current is output as a control current. Control power And a holding circuit for holding the input bias voltage of the amplifier at the reference voltage by adding the control current to the base current of the transistor to which the feedback resistor is connected in the transistor pair. An audio device with a built-in battery, comprising an audio signal amplifier circuit in which an operating point voltage of the output signal is controlled to a voltage value which is approximately half the power supply voltage. 2. An audio signal amplifier circuit, wherein the base of a first-stage differential transistor pair comprises an amplifier which receives an input signal and has a feedback resistor, and which outputs an output signal obtained by amplifying the received audio signal. A reference voltage generating circuit for generating a reference voltage having a predetermined value and supplying it as the bias voltage of the base, a control line for controlling the voltage to the same voltage value as the reference voltage, and a resistance value about twice that of the feedback resistor. A first resistor connected between a power supply voltage line and the control line to flow a first current; and a control line and a ground line having a resistance value about twice that of the feedback resistor. A second resistor connected between the first current and the second resistor, the control current generating circuit outputting a difference current between the second current and the first current as a control current. Equipped with the control current By being added to the base current of the transistor of the pair of transistors to which the feedback resistor is connected, the operating point voltage of the output signal is equal to the power supply voltage while holding the input bias voltage of the amplifier at the reference voltage. An audio signal amplifying circuit characterized by being controlled to almost half the voltage value.