JP3014557B2 - Audio device with built-in battery and audio signal amplifier circuit - Google Patents

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 amplifying circuit. The present invention relates to an audio signal amplifying circuit suitable for a headphone stereo or the like, and an audio device with a built-in battery including the audio signal amplifying 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. Here, 1 is the input signal A
And a reference voltage generating circuit 2 for generating a reference voltage VB. The first transistor of the amplifier 1 is
Usually, they are connected to a common 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).
V) or higher. However, under a low power supply voltage, the operating point voltage of the input signal, that is, the base bias voltage cannot be secured simply by dividing the power supply voltage into two.

Therefore, a reference voltage generating circuit 2 is provided in a circuit corresponding to a low power supply voltage, and the reference voltage VB is usually set to about 0.9 V in consideration of the amplitude of an 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 at 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 having 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, as long as 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 around the reference voltage VB. (See waveform Bc in FIG. 4B). However, when the value of the power supply voltage Vcc decreases as the battery discharge proceeds, the power supply voltage Vcc and the reference voltage Vcc are reduced.
The difference from B disappears (see Vcc2 in FIG. 4C). Then, the output voltage of the amplifier 1 has no margin, and the output signal B swinging around the reference voltage VB becomes
The waveform on the power supply voltage side is limited to the voltage Vcc2 or less and cannot swing with sufficient amplitude on the power supply side (see waveform Bd in FIG. 4C).

[0005] For this reason, even if the power supply voltage is lowered, the device operates for the time being, but in that case, the waveform of the output signal is greatly distorted. This is inconvenient because the sound is disturbed and gives the listener discomfort. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to provide an audio device with a built-in battery and an audio signal amplifier configured to amplify an audio signal without distortion even under a low power supply voltage. It is to realize a circuit.

[0006]

The configuration of an audio device with a built-in battery according to the present invention that achieves the above object is as follows.
It has the following audio signal amplifier circuit.
In order to achieve the above object, the audio signal amplifier circuit according to the present invention has an amplifier in which the base of a first-stage differential transistor pair has an amplifier having a feedback resistor for receiving an input signal, and an amplified output of the received audio signal. A reference voltage generating circuit for generating a reference voltage of a predetermined voltage value and supplying the same as a bias voltage of the base in an audio signal amplifier circuit for outputting a signal; and control for controlling a voltage to the same voltage value as the reference voltage line and a first resistor passing a first current is connected between the line and the control line substantially the power supply voltage has twice the resistance value of the feedback resistor, substantially of the feedback resistor A second resistor having a resistance value that is twice as high and connected between the control line and the ground line to flow a second current; the second current and the first current Current difference And a control current generating circuit for outputting a current, a, by the control current is applied to the base connection of the transistor towards said feedback resistor in said transistor pair is connected to the base input bias of the amplifier The operating point voltage of the output signal is controlled to substantially half the voltage value of the power supply voltage while maintaining the voltage at the reference voltage.

[0007]

In the audio device with a built-in battery and the audio signal amplifying circuit of the present invention having such a configuration,
The operating point voltages of the non-inverting input signal and the inverting input signal of the amplifier are kept at the reference voltage, that is, the bias voltage at the base of the differential transistor pair is kept at a value required for transistor operation. Therefore, the amplifier can perform a differential amplification operation of the input signal. Furthermore, since the operating point voltage of the output signal of the amplifier is controlled to substantially half the voltage value of the power supply voltage, when the power supply voltage is high, the output signal can have a sufficiently large amplitude, and the power supply voltage decreases. Even when the voltage becomes almost as low as the reference voltage, the output signal can swing substantially symmetrically to the power supply side and the ground side.
Therefore, the audio signal can be amplified without distortion even under a low power supply voltage as well as under a high power supply voltage.

[0008]

FIG. 1 is a circuit diagram of an embodiment of an audio signal amplifying 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 generating circuit that generates a reference voltage VB, and 3 is a power supply voltage Vcc and a reference voltage. This is a control current generation circuit that generates a control current Im corresponding to the voltage VB. The amplifier 1 is a differential transistor pair in which a first-stage circuit is connected to a 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 0.9 V based on the forward voltage (1 VF) of the diode and the voltage drop at the resistor (set to about 2 Vsat).
This reference voltage VB is used as the operating point voltage of the audio signal A via the resistor Rp as the non-inverting input terminal (+) of the amplifier 1.
Conveyed to. Further, the signal is 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, the inverting input terminal (-) also receives an input signal having the reference voltage VB as the operating point voltage.
As a result, the input signal received by both input terminals of the amplifier 1 is 1 VF (0.6 to 0.6 V) required as the base-emitter bias voltage even when the amplitude of the input signal is considered.
0.7V) or more. So, amplifier 1
There is no problem in the operation of.

The control current generating circuit 3 is mainly composed of an all feedback amplifier, and has a reference voltage V
The voltage of the other input signal is controlled so as to follow B. The other input signal is connected to the power supply Vcc line and the ground G.
It is given as a voltage at a connection point between resistors connected in series with the ND line. In other words, the control line 3a
Is controlled so that the voltage becomes equal to the reference voltage VB. Thereby, the resistance on the power supply Vcc side (resistance value 2 × Rf)
, A current I1 = ((Vcc−VB) / (2 × Rf)) flows, and a current I1 is supplied to a resistance (resistance value 2 × Rf) on the ground GND side.
2 = (VB / (2 × Rf)) flows. Therefore, from this connection point, these difference currents Im '= (I1-I2) =
(((Vcc / 2) -VB) / Rf) is obtained. This difference current follows the difference voltage between half 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, the resistor Rp for transmitting the reference voltage, and the feedback resistor Rf (in FIG. 1, it is shown in the drawing direction in the sign relationship). 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 affected by the control current Im, the control current Im is transmitted through the feedback resistor Rf. Flowing. The voltage level of the output signal B changes by Im × Rf, that is, ((Vcc / 2) -VB) due to the voltage drop at the resistor Rf.

Since the voltage level of the output signal B is Vm if there is no control current Im, the operating point voltage VB 'of the output signal B becomes (Vcc / 2) by adding 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 naturally takes the operating point voltage VB 'as a center. Can have sufficient amplitude (FIG. 2)
(See waveform Ba in (b)).

In addition, the discharge of the battery progresses, the value of the power supply voltage Vcc decreases, and the difference between the power supply voltage Vcc and the reference voltage VB disappears (see Vcc in FIG. 2C).
2), even when the output voltage of the amplifier 1 becomes insufficient, the output signal B which swings around the operating point voltage VB 'is not distorted in the waveform on the power supply voltage side. (See waveform Bb in FIG. 2 (c)). 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, earphones, and the like. The embodiment of the audio device with a built-in battery according to the present invention includes the above-described audio signal amplifier circuit, and the operation and effect are the same.

[0014]

As can be understood from the above description, according to the present invention, a control current having a current value corresponding to the power supply voltage is generated and applied to the input terminal on the feedback side of the amplifier. Thus, even when the power supply voltage decreases, it is possible to adjust the base current while maintaining the base potential of the first-stage transistor, which is a premise of 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 low power supply voltage as well as under a high power supply voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of an audio signal amplifying circuit of the present invention.

FIGS. 2A and 2B are explanatory diagrams thereof, wherein FIG. 2A is a graph showing a relationship between voltages, and FIGS. 2B and 2C 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)

(57) [Claims] 1. A built-in battery having an amplifier in which a base of a first-stage differential transistor pair receives an input signal and has a feedback resistor, and an audio signal amplifying circuit for outputting an output signal obtained by amplifying the received audio signal. In the audio device, a reference voltage generating circuit for generating a reference voltage having a predetermined voltage value and supplying the same as the base bias voltage; a control line whose voltage is controlled to the same voltage value as the reference voltage; substantially a first resistor for flowing a first current is connected between the power supply voltage has double the resistance line and the control line, the feedback substantially twice the resistance of resistor A second resistor having a value and connected between the control line and the ground line for flowing a second current, and controlling a difference current between the second current and the first current. Output as current And a control current generating circuit, the by the control current is applied to the base connection of the transistor towards said feedback resistor in said transistor pair is connected to the base, the input bias voltage of the amplifier An audio device with a built-in battery, comprising: an audio signal amplifying circuit in which an operating point voltage of the output signal is controlled to a voltage value substantially half of the power supply voltage while maintaining a reference voltage. 2. An audio signal amplifying circuit comprising: a base of a first-stage differential transistor pair having an amplifier having a feedback resistor for receiving an input signal and outputting an output signal obtained by amplifying the received audio signal; a reference voltage generating circuit for supplying a reference voltage as the base bias voltage generated value, the control line to which a voltage is controlled to the same voltage value with the reference voltage, substantially twice the feedback resistor A first resistor connected between a power supply voltage line having a resistance value and the control line for flowing a first current; and a control line having a resistance value substantially twice as large as the feedback resistance. And a second resistor connected between the second current and the ground line for flowing a second current, and generating a control current that outputs a difference current between the second current and the first current as a control current. A circuit; By control current is applied to the base connection of the transistor towards said feedback resistor in said transistor pair is connected to the base, the operation of the output signal while maintaining the input bias voltage of the amplifier to the reference voltage An audio signal amplifier circuit, wherein a point voltage is controlled to a voltage value substantially half of the power supply voltage.