JP2709984B2 - Audio amplification circuit and audio system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit and an audio system, and more particularly, to an audio amplifier capable of driving speakers, headphones, and the like connected to audio equipment and suitable for use in an IC. It relates to a circuit and an audio system.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a reproducing circuit section of a stereo cassette tape recorder employing a conventional amplifier circuit. In order to drive two loudspeakers on the left and right because it is stereo compatible, the circuit of this example has two sets of reproduction circuits. Since these two sets of circuits are exactly the same, only one set will be described in detail, and for the other set, only the corresponding reference numerals will be given in parentheses. Note that the output stage amplifier is hereinafter referred to as a power amplifier. The reproducing circuit includes a reproducing head 6a (6b) for reading a recorded signal, and an equalizer 5a for amplifying the read signal at an amplification factor according to a frequency.
(5b) and only the AC component of the signal amplified by the equalizer 5a (5b) is converted into the power amplifier 3a (3
b) input-side coupling capacitors 4a (4
b) and a signal transmitted from the input side coupling capacitor 4a (4b) is power amplified to output the terminal 2a (2b).
And a power coupling capacitor 7a (7b) for sending only the AC component of the output from the power amplifier 3a (3b) to the load speaker 1a (1b). Load speaker 1a (1b)
Is connected to the output-side coupling capacitor 7a (7b), and the other end is connected to the output terminal 2c.
Its output terminal 2c is connected to the ground potential GND.

In an amplifier circuit for an audio signal like this example, an equalizer 5a (5b) is replaced with a graphic equalizer, a reproducing head 6a (6b) is replaced with a pickup for a compact disc, and furthermore, a signal is processed. Circuit is often used.

[0004]

However, the conventional amplifier circuit for audio needs to use a large-capacity capacitor as the output-side coupling capacitor 7a (7b), which is costly and large in size. I
There is a disadvantage that it is inferior to C conversion. Furthermore, load speaker 1
Since a (1b) is AC-coupled with reference to the ground potential GND, a circuit for eliminating the influence of noise superimposed on the power supply and a circuit for suppressing pop noise at power-on tend to be complicated. However, there is a problem that it is not preferable in terms of price and reliability. An object of the present invention is to solve such problems of the prior art,
The load speaker can be directly connected to the output terminal and driven without using an output-side coupling capacitor.
In addition, the present invention provides an audio amplifier circuit suitable for integration into an IC capable of suppressing generation of pop noise at power-on, and an audio system in which a speaker is driven by the audio amplifier circuit.

[0005]

SUMMARY OF THE INVENTION To achieve this object, an audio amplification circuit according to the present invention comprises a signal reading circuit or a signal reader or a signal input terminal, a preceding amplification circuit, and an output amplification circuit. In particular, a part of the amplifier circuit in the output stage has first and second power amplifiers to which a resistor for determining an amplification factor is connected,
Further, one end of an input-side coupling capacitor for transmitting only the AC component of the input signal from the pre-amplifier circuit is connected to the first power amplifier. In the first power amplifier, one end of the input-side coupling capacitor is connected to the non-inverting input terminal of the first power amplifier, one end of the first resistor is connected to the terminal of the reference voltage, and the other end is connected to the first terminal. One end of a second resistor is connected to a first output terminal, and the other end is connected to a first input terminal of the power amplifier.
And the output of the first power amplifier is connected to the first output terminal . In the second power amplifier, a non-inverting input terminal of the second power amplifier is connected to the reference voltage terminal, one end of a third resistor is connected to the reference voltage terminal, and the other end is connected to the second power amplifier. And one end of a fourth resistor is connected to the second output terminal, the other end is connected to the inverting input terminal of the second power amplifier, and the output of the second power amplifier is connected to the second input terminal of the second power amplifier. Connected to output terminal . Here, the first output terminal
And a second output terminal without a capacitor.
Connected to the first output stage amplifier to increase the input signal.
That the phase of the forward or reverse width is the same as that of the reference voltage amplification in the second output stage amplifier.
Each output stage amplifier operates, and the reference voltage is
Set the voltage of the output terminal 2 to a voltage other than the ground potential.
Swelling. Then , the value of the first resistor is set so that the ratio of the value of the first resistor to the value of the second resistor is substantially equal to the ratio of the value of the third resistor to the value of the fourth resistor. The value of the second resistor, the value of the third resistor, and the value of the fourth resistor are set. However, since the actual resistance value has a distribution due to the standard and the factor at the time of manufacturing, and it is difficult to exactly match the above ratio, a slight difference in the actual manufactured and manufactured circuit may cause a slight difference in the value. May appear in the above ratios. In the above case, the inverted input and the non-inverted input are relative and can be interchanged. A configuration of an audio system for achieving this object includes the audio amplifier circuit and a speaker, and first and second output terminals are connected to first and second input terminals of the speaker, respectively.

[0006]

According to the above arrangement, the first power amplifier receives only the AC component of the input signal at the non-inverting input terminal via the input side coupling capacitor, and the first power amplifier and the second resistor are connected to the first resistor. The input signal is power-amplified according to the resistance ratio and output to the first output terminal. The second power amplifier receives a reference voltage at a non-inverting input terminal, power-amplifies the reference voltage, and outputs the amplified power to a second output terminal. Therefore, the second output terminal is controlled so as to always have a constant voltage. As a result, when the potential of the first output terminal is higher than the potential of the second output terminal, the current from the first output terminal to the second output terminal is controlled, and the potential of the first output terminal becomes the second potential. When the potential is lower than the potential of the output terminal, the current from the second output terminal to the first output terminal is controlled. As described above, by operating the second output terminal at a constant voltage with the power-amplified reference potential instead of the ground potential, the speaker or the like of the load is connected to the first or the first.
It is possible to drive by directly connecting between the second output terminals, and it becomes unnecessary to provide an output-side coupling capacitor between the output terminal and a load speaker or the like. Further, the amplification factor of the first power amplifier is determined by the ratio of the value of the first resistor connected to the first power amplifier to the value of the second resistor, and the second power amplifier connected to the second power amplifier is determined. 3
The amplification ratio of the second power amplifier is determined by the ratio between the resistance value of the second power amplifier and the value of the fourth resistance.
Since the respective resistance values are set so that the power amplifier and the second power amplifier have the same value, the gain of the first power amplifier is equal to the gain of the second power amplifier. Therefore, immediately after the power is turned on, the voltages in the transient state output to the first and second output terminals become almost equal, so that no extra current flows through the load speaker or the like, and other special measures are taken. The pop sound can be suppressed without providing the. Note that the output from the first output terminal and the output from the second output terminal also cancel each other for an undesired output current due to the influence of power supply voltage fluctuations such as ripples. Sufficient control can be achieved without any special measures. Further, a characteristic part of the audio signal amplifying circuit is composed of a power amplifier and a resistor connected to the power amplifier. Since an output capacitor is not required, an IC can be easily formed.

While one set of the amplifier circuit at the output stage of the audio amplifier circuit, which is a feature of the present invention, has been described in detail, in a stereo or the like, a plurality of audio amplifier circuits coexist. , Input terminal and output terminal, power supply circuit, protection circuit, filter, equalizer, differential amplifier stage, mixer, circuit for writing, etc., independently or in conjunction with the circuit part according to the present invention, Even if present in the audio amplifier circuit of the present invention, it does not impair the features of the present invention at all. Note that the same operation is performed in an audio system.

[0008]

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram of a reproducing circuit section of a stereo cassette tape recorder employing the configuration of the audio amplifier circuit of the present invention. What differs from FIG. 2 of the conventional example is that one end of the drive terminal of the load speaker 1a (1b) is directly connected to the output terminal 2a (2b) without the output-side coupling capacitor 7a (7b). That is, the terminal 2c is connected to the output from the power amplifier 3c without being grounded to the ground potential GND. This reproducing circuit reads a recorded signal from a reproducing head 6a (6
b), an equalizer 5a (5b) for amplifying the read signal at an amplification factor according to the frequency, and a power amplifier 3a (3b) at the subsequent stage which converts only the AC component of the signal amplified by the equalizer 5a (5b). ) And a power amplifier 3a that amplifies the power of the signal transmitted from the input coupling capacitor 4a (4b) and outputs the amplified signal to the output terminal 2a (2b).
(3b), and amplify the reference voltage Vref by power and output to the output terminal 2
and a power amplifier 3c for outputting the signal to the power amplifier 3c. One end of the load speaker 1a (1b) is connected to the output terminal 2a (2b), and the other end is connected to the output terminal 2c. further,
In the power amplifier 3a (3b), one end of the input side coupling capacitor 4a (4b) is connected to the non-inverting input terminal, one end of the resistor R11 (R21) is connected to the reference voltage Vref, and the other end is the power amplifier 3a (3b). 3b) is connected to the inverting input terminal and one end of the resistor R12 (R22) is connected to the output terminal 2a.
(2b), the other end is connected to the inverting input terminal of the power amplifier 3a (3b), and the output of the power amplifier 3a (3b) is connected to the output terminal 2a (2b). In this embodiment, one end of each of the resistors RBa and RBb is connected to the reference voltage Vref, and the other end is connected to the non-inverting input terminal of the power amplifier 3a (3b), and an input bias voltage is given by the resistors. In FIG. 1, although the reference voltage Vref and the non-inverting input terminal of the power amplifier 3c are directly connected, a resistor for applying an input bias voltage may be connected between them. In the power amplifier 3c, the non-inverting input terminal of the power amplifier 3c is connected to the reference voltage Vre.
f, one end of the resistor R31 is connected to the reference voltage Vref, the other end is connected to the inverting input terminal of the power amplifier 3c, one end of the resistor R32 is connected to the output terminal 2c, and the other end is the inverting input of the power amplifier 3c. The output of the power amplifier 3c is output to the output terminal 2c. Here, the values of the respective resistors are set such that R11: R12 = R31: R32 = R21: R22.

The operation of this circuit will be described. The reproducing head 6a (6b) reads a recorded signal, and the equalizer 5a (5b) converts the signal transmitted from the reproducing head 6a (6b) at an amplification factor according to the frequency. The input side coupling capacitor 4a (4b) transmits only the AC component of the amplified signal to the subsequent power amplifier 3a (3b). The power amplifier 3a (3b) receives only the AC component of the input signal at the non-inverting input terminal via the input-side coupling capacitor 4a (4b), and outputs a resistor R11 and a resistor R12.
The power of the input signal is amplified according to the ratio of
Output to (2b). The power amplifier 2c has a reference voltage V
ref is received by the non-inverting input terminal, and the power is amplified and output to the output terminal 2c. Thus, the output terminal 2c is maintained at a constant voltage Vc obtained by amplifying the reference voltage Vref by the power amplifier 3c even in the operating state. Output terminal 2a (2b)
Is higher than the potential Vc of the output terminal 2c, the current from the output terminal 2a (2b) to the output terminal 2c is controlled,
The potential of the output terminal 2a (2b) is equal to the potential Vc of the output terminal 2c.
When it is lower, the output terminal 2c is connected to the output terminal 2a (2b).
The current to is controlled. In this way, by operating the output terminal 2c so as to maintain the power-amplified reference potential Vref instead of the ground potential, the load speaker 1a (1
b) can be directly connected between the output terminal 2a (2b) and the output terminal 2c for driving, and an output-side coupling capacitor is not required. Further, R11: R12 = R
Since the values of the respective resistors are set so that 31: R32 = R21: R22, the amplification factor of the power amplifier 3a (3b) and the amplification factor of the power amplifier 3c become substantially equal, and particularly, the power is turned on. Since the respective power amplifiers follow or operate in synchronism at the time or the like, undesired output current and pop noise at power-on due to the influence of power supply voltage fluctuations such as ripples can be suppressed. In addition, if the characteristics of the power amplifiers 3a, 3b, 3c are made uniform, the above-mentioned performance is further improved. In FIG. 1, the connection to the power supply, the connection to the ground, the connection for offset adjustment, and the like in the amplifier are omitted because they are not necessary for the description of the present invention. Further, resistors R11, R12, R31, R32, R21,
R22 and RB may be not only a single pure resistor but also a combination of a plurality of resistors, and may include a reactance component such as a capacitor. As described above, the description has been made in the case of the stereo system, but the present invention can be applied to only a monaural one-channel system.

[0010]

As described above, according to the present invention, a load speaker can be directly connected to an output terminal and driven without using an output-side coupling capacitor, and furthermore, noise superimposed on a power supply can be obtained. It is possible to suppress pop noise and noise without using a complicated circuit for maintaining performance, such as a circuit for eliminating the effect of noise and a circuit for suppressing pop noise at the time of power supply. There is an effect that an audio amplifier circuit that can reduce the entire size, reduce the cost, and improve the reliability can be realized. The same effect can be obtained even in an audio system in which a speaker is driven by such an audio amplifier circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a reproducing circuit section of a stereo cassette tape recorder according to an embodiment employing the configuration of the amplifier circuit of the present invention.

FIG. 2 is a circuit diagram of a reproduction circuit section of a stereo cassette tape recorder employing a configuration of a conventional amplifier circuit.

[Explanation of symbols]

 1a, 1b Load speakers 2a-2c Output terminals 3a-3c Differential amplifiers 4a, 4b Input-side coupling capacitors 5a, 5b Equalizers 6a, 6b Reproducing heads 7a, 7b Output-side coupling capacitors Vc Potential of output terminal 2c Vref Reference potential GND Ground potential

Claims (2)

(57) [Claims] A first input terminal for receiving an input signal; a second input terminal having a phase opposite to that of the first input terminal; receiving a reference voltage; A first output stage amplifier for amplifying an input signal and outputting the amplified signal to a first output terminal; and a third and fourth input terminals, wherein the reference voltage is supplied to a third output terminal .
And a second output stage amplifier for receiving and amplifying the received signal at an input terminal thereof and outputting the amplified signal to a second output terminal.
An amplifier circuit for controlling a current to an output terminal of the first circuit and a current from a second output terminal to a first output terminal in accordance with the input signal, wherein one end of a first resistor is connected to a terminal of the reference voltage. The other end is connected to a second input terminal, one end of a second resistor is connected to a first output terminal, the other end is connected to a second input terminal, and one end of a third resistor is connected to the reference voltage. , The other end is connected to the fourth input terminal, one end of the fourth resistor is connected to the second output terminal, the other end is connected to the fourth input terminal, the value of the first resistor The value of the first resistor and the value of the second resistor are set such that the ratio between the value of the second resistor and the value of the second resistor is equal to or substantially equal to the ratio of the value of the third resistor to the value of the fourth resistor. , The value of the third resistor, and the value of the fourth resistor are set, and the positive and negative values for the amplification of the input signal in the first output stage amplifier are set.
Phase and the reference voltage at the second output stage amplifier.
Voltage amplification is in phase with said reference voltage
Sets the voltage of the second output terminal to a voltage other than the ground potential
Between the first output terminal and the second output terminal.
An audio amplifier circuit , wherein a speaker is connected without a capacitor therebetween . A first input terminal for receiving an input signal; a second input terminal having a phase opposite to that of the first input terminal for receiving a reference voltage; A first output stage amplifier for amplifying an input signal and outputting the amplified signal to a first output terminal; and a third and fourth input terminals, wherein the reference voltage is supplied to a third output terminal .
And a second output stage amplifier for receiving and amplifying the received signal at an input terminal thereof and outputting the amplified signal to a second output terminal.
An amplifier circuit for controlling a current to an output terminal of the first circuit and a current from a second output terminal to a first output terminal in accordance with the input signal, wherein one end of a first resistor is connected to a terminal of the reference voltage. is the other end is connected to the second input terminal, the other end one end of the second resistor is connected to a first output terminal connected to the second input terminal, one end of the third resistor is a reference voltage , The other end is connected to the fourth input terminal, one end of the fourth resistor is connected to the second output terminal, the other end is connected to the fourth input terminal, the value of the first resistor The value of the first resistor and the value of the second resistor are set such that the ratio between the value of the second resistor and the value of the second resistor is equal to or substantially equal to the ratio of the value of the third resistor to the value of the fourth resistor. , The value of the third resistor, and the value of the fourth resistor are set, and the positive and negative values for the amplification of the input signal in the first output stage amplifier are set.
Phase and the reference voltage at the second output stage amplifier.
Between the first and second output terminals, and an audio amplifier circuit having the same phase with respect to the voltage amplification.
Speaker connected without a capacitor
The reference voltage is obtained by setting the voltage of the second output terminal to a voltage other than the ground potential.
An audio system that is set to voltage .