JPH0685576A - Voice output circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In the audio output circuit, 10% distortion maximum output can be set variously without changing the power supply voltage, the circuit body or the speaker. [Structure] A voltage is applied to the + input terminal of the audio amplifier 1 from a bias source composed of the resistors 2 and 3 and the capacitor 10 via the resistor 4, and the − input terminal via the resistor 5 to the resistor 15 and variable resistor. A voltage is applied from a bias source composed of 16 and a capacitor 14, and a DC feedback voltage is applied from the output side by a resistor 6. By changing the variable resistor 16, a bias voltage difference is provided between both input terminals to bias the output midpoint voltage of the audio amplifier 1 and vary the 10% distortion maximum output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output circuit incorporated in a television receiver or the like and used for audio reproduction, and more particularly to a means for changing the maximum output of the audio output circuit. Is.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional example of a general audio amplifier in terms of circuit configuration. In the figure, 1 is an audio amplifier such as an operational amplifier, and Vcc is a power supply (or power supply voltage).

In FIG. 2, resistors 2 and 3 and a capacitor 1
0 constitutes a DC voltage source which is supplied with the DC power supply Vcc to generate a DC voltage, and applies a bias voltage to the plus side input terminal of the audio amplifier 1 via the resistor 4. A feedback resistor 6 is connected between the negative input terminal of the audio amplifier 1 and the output terminal (Va) of the audio amplifier 1, and the negative input terminal is an alternating current via a resistor 5 and a capacitor 11. Grounded. The input audio signal is applied to the plus side input terminal from the IN terminal via the capacitor 9.

The output gain with respect to the voltage between the positive and negative input terminals of the audio amplifier 1 is ideally infinite, the AC gain is determined by the ratio of the resistors 5 and 6, and the DC bias voltage is the power supply voltage. It is the midpoint voltage of resistors 2 and 3 which divides Vcc, and this appears at each terminal (plus side input terminal, output terminal (Va) point, minus side input terminal) of the audio amplifier.

In this case, the maximum output of 10% distortion (the audio output of the television receiver is specified as the maximum output when the audio output is 10%) is the power supply voltage V
Limited by cc. In a television receiver, a means for finely adjusting the power supply voltage Vcc is commonly used as an adjusting means for matching the 10% distortion maximum output with a predetermined design value.

In addition, as an example of a conventional circuit having an output level limiting function, the example shown in FIG. 1 of JP-B-62-28094 can be mentioned for reference. Assuming that the amplifier 3 shown in FIG. 1 of this publication is a voice amplifier, the circuit shown in FIG. 1 functions as a voice output circuit having an output limiting function, and the detection circuit 5 and the capacitor shown in FIG. By selecting and adjusting 6, the resistors 7 and 2, and the transistor 8, the limit value of the output level can be freely set.

[0007]

Now, in a television receiver, it is preferable to design an audio output value corresponding to the size of the housing determined by the size of the cathode ray tube. However, if such an attempt is made, This leads to a result contrary to the idea of increasing the productivity by sharing the circuit.

That is, for each model, different power supply voltage and audio output I are used in order to design an audio output value suitable for the model.
If C is used, it becomes difficult to develop a model on a common printed circuit board, and it is not possible to standardize a circuit and improve productivity.

In addition, in the model with a built-in Dolby Pro Logic, the audio output circuit has three types: front, center, and rear.
If there is a channel and each channel is used as a common power supply, even if an attempt is made to set a 10% distortion output according to the output specification of each channel, according to the speaker impedance that becomes a load (according to the conventional technique described with reference to FIG. 2), Since the maximum output of 10% distortion is determined by the power supply voltage, for example, when the front channel is 10 W and the rear channel is 5 W, the impedance of the speaker connected to the rear channel is lower than the impedance of the speaker connected to the front channel. There is no choice but to increase it.

An object of the present invention is to eliminate such disadvantages of the prior art and to output a voice corresponding to a model (size of housing) for each model without using different power supply voltage and voice output IC. An object is to provide an audio output circuit whose values can be freely designed.

[0011]

To achieve the above object, in the present invention, the maximum output voltage (10%) is maintained without changing the power supply voltage (Vcc) of the audio output circuit or the output circuit itself.
In order to freely set the distortion output voltage), the output voltage midpoint potential of an audio amplifier such as an operational amplifier is changed from the potential point of Vcc / 2 by changing the bias voltage at the input point, resulting in 10% distortion. Change the output point (maximum output).

First, the first means for that purpose is to provide a difference between the positive and negative input biases of an audio amplifier such as an operational amplifier to shift the output voltage midpoint potential.

The second means is that the input bias on the negative side of an audio amplifier such as an operational amplifier is subjected to direct current feedback from the output of the audio amplifier, and the bias voltage on the positive side is Vcc / 2.
The output voltage midpoint voltage is Vc
It is to shift from the potential point of c / 2.

[0014]

[Function] By providing the plus side input bias voltage and the minus side input bias voltage of the audio amplifier having the plus input, the minus input, and the output shown by the operational amplifier model independently, and making a difference between these voltages. That is, the positive input terminal bias voltage is applied to the positive input terminal through a resistor, and the negative input is subjected to direct current feedback from the output with a feedback resistor, and the negative input bias voltage is applied via the resistor. And the bias voltage is made different, the midpoint voltage of the audio amplifier output is Vc.
It deviates from the potential point of c / 2 (however, Vcc is a power supply voltage which is a supply source of the bias voltage).

In this state, when the sine wave signal is input as a voice signal by the capacitor cut to the plus input, 1
The output waveform (maximum output) at 0% distortion is a vertically asymmetrical waveform (one-side clipped waveform). If the difference between the bias voltages is changed, the output midpoint voltage also changes in proportion, and therefore the output (maximum output) level at 10% distortion also changes.

Further, the bias voltage for the positive side input of the audio amplifier is made variable, while the bias for the negative side input is applied only by DC feedback by the feedback resistor from the output side, and for the positive side input. If the bias voltage is changed, the midpoint voltage of the audio amplifier output also changes due to the feedback operation of the audio amplifier. Similarly to the above, in order to make the output waveform asymmetrical in the vertical direction, if the plus side input bias voltage is shifted from the potential point of Vcc / 2 which is a general operating condition, the midpoint voltage of the audio amplifier output also changes. Acts like.

[0017]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is a voice amplifier such as an operational amplifier,
Vcc is a power supply (or power supply voltage).

A voice amplifier 1 represented by an operational amplifier model has a resistor 2, resistor 3 and capacitor 1 at the + input terminal.
A bias voltage is applied by the resistor 4 from a + input bias voltage source consisting of 0, and an audio signal is input from the input terminal IN via the capacitor 9.

On the other hand, a DC feedback voltage is applied to the input terminal from the output terminal of the audio amplifier 1 (point Vb) via the feedback resistor 6, and is composed of a resistor 15, a variable resistor 16 and a capacitor 14. A bias voltage is applied from the input bias voltage source through the resistor 5.

The power supply voltage Vcc is supplied to the + input bias voltage source resistor 2, the −input bias voltage source resistor 15 and the audio amplifier 1. Output terminal of audio amplifier 1 and GN
A resistor 7 for preventing oscillation and a capacitor 13 are connected between D, and a capacitor 12 is connected from the output terminal of the audio amplifier 1.
The DC-cut output signal Vo1 is output. The resistor 8 is a resistor for direct current discharge.

In this embodiment, if the resistors 2, 3, 15 and the variable resistor 16 all have the same resistance value, all the terminals (+ input terminal, − input terminal, output terminal) of the audio amplifier 1 are Assuming that the voltage is Vcc / 2, and a sine-waveform audio signal is input from the IN terminal through the capacitor 9, FIG.
The waveform (sine waveform) indicated by the symbol Vo2 is cut and output. Note that FIG. 3 is a waveform diagram showing an audio amplifier output voltage when a sine waveform audio signal is input.

In this state, if the level of the input audio signal is increased, the upper side is limited to Vcc and the lower side is limited to GND, and a vertically clipped waveform is output. However, when the variable resistor 16 is made large and the bias voltage of the − input terminal is slightly raised from the bias voltage of the + input terminal, the DC output voltage of the audio amplifier 1 is lowered and the waveform shown by the symbol Vo1 in FIG. .

At this time, the DC output voltage of the audio amplifier 1 is
3 from the symbol Va to Vb, which is why the symbol Vo
As shown by the waveform 1, the lower waveform is clipped by being limited to GND. Therefore, the output level is limited.

The second embodiment of the present invention can also be explained with reference to FIG. As described above, FIG. 2 is a circuit diagram showing a conventional example of a general audio amplifier in terms of circuit configuration, but the present invention can be realized depending on how the operation is performed.

In FIG. 2, a + input terminal of the audio amplifier 1 is supplied with a bias voltage from a + input bias voltage source composed of a resistor 2, a resistor 3 and a capacitor 10 via a resistor 4, and a − input terminal thereof. A DC feedback voltage is applied from the output terminal (symbol Va point) of the audio amplifier 1 via the feedback resistor 6.

A resistor 5 and a capacitor 11 are connected between the input terminal and GND, the DC feedback ratio is 100%, and the AC gain is [1+ (R6 / R5)]. R5, R6
Are the resistance values of the resistors 5 and 6, respectively.

In the second embodiment, if the resistors 2 and 3 have the same resistance value, the bias voltage at the + input terminal becomes Vcc / 2, and the bias voltage at the-input terminal becomes equal to the bias voltage at the-input terminal due to the DC feedback ratio of 100%. The output terminal voltage is the same voltage (Vcc
/ 2). In this state, when an audio signal having a sine waveform is input, the waveform (sine waveform) indicated by the symbol Vo2 in FIG. 3 is capacitor-cut and output.

However, if the DC output voltage of the amplifier 1 is lowered by changing the value of the resistor 3 to a small value instead of making the resistors 2 and 3 have the same resistance value, the waveform indicated by the symbol Vo1 in FIG. As described above, the lower side waveform is limited to GND and becomes a clipped waveform. Therefore, the output level is limited by the value of the resistor 3.

[0029]

As described above, according to the present invention,
In the audio output circuit, the method to change the maximum output of 10% distortion without changing the power supply voltage and speaker impedance by changing the circuit part in common is used as the difference between the + and-input bias voltages of the audio amplifier. Can be realized by providing. Alternatively, the input bias of the audio amplifier can be realized by operating so that the DC output voltage of the audio amplifier deviates from the half of the power supply voltage.

In any case, according to the present invention, when an audio signal having a sine waveform is input, one side of the output waveform can be clipped to set the maximum output level of 10% distortion. The set value can be changed by changing the resistance value of the input side bias.

[Brief description of drawings]

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

FIG. 2 is a voice amplifier circuit diagram showing a conventional example of a voice amplifier and realizing the present invention depending on how to use it.

FIG. 3 is a waveform diagram showing an output voltage waveform when a sine-waveform audio signal is input, comparing the case of the present invention with that of a conventional one.

[Explanation of symbols]

1 ... Audio amplifier, 2-8, 15 ... Resistance, 9-14 ... Capacitor, 16 ... Variable resistance, Vo1, Vo2 ... Output terminal (or output terminal waveform), Va, Vb ... Audio amplifier output point (or audio amplifier DC) Output voltage), IN ... Audio signal input terminal, + ... Audio amplifier + input terminal, -... Audio amplifier-input terminal, Vcc ... DC power supply (or DC power supply voltage), t ...
time

Claims (3)

[Claims] 1. An audio amplifier such as an operational amplifier having a plus input side and a minus input side, wherein a bias voltage is applied to the plus input side from a power supply voltage via a first DC bias source and a first resistor. At the same time, an audio signal is input via a capacitor, an output side of the audio amplifier is connected to a negative input side via a feedback resistor, and a second DC bias source and A bias voltage is applied via the second resistor, and a voltage difference is provided between the bias voltage applied from the first DC bias source and the bias voltage applied from the second DC bias source, During operation, the midpoint voltage on the output side of the audio amplifier is deviated to a plus side or a minus side from a value of 1/2 of the power supply voltage, thereby operating the The maximum output of 10% strain as the amplifier output of the input audio signal extracted from the audio amplifier output side, not vertically symmetrical waveform, an audio output circuit, characterized in that as is one side clipped waveform. 2. The audio output circuit according to claim 1, wherein a voltage difference provided between the bias voltage applied from the first DC bias source and the bias voltage applied from the second DC bias source. Is set to set the level of the maximum output of 10% distortion as an amplified output of the input audio signal taken out from the audio amplifier output side. 3. An audio amplifier, such as an operational amplifier, having a positive input side and a negative input side, wherein a DC bias source and a first DC bias source are connected to the positive input side from the power supply voltage.
A bias voltage is applied through the resistance of
The audio signal is input via the capacitor of, the output side of the audio amplifier is connected to the negative input side via the feedback resistor, and is grounded via the second resistor and the second capacitor. In, the bias voltage applied to the plus input side is adjusted so that the midpoint voltage on the output side of the audio amplifier shifts to the plus side or minus side from the value of 1/2 of the power supply voltage. An audio output circuit characterized by being formed.