JP3063268B2 - Audio signal amplification 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 signal amplifying circuit in an audio reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, S / N and dynamic range have been greatly improved in a sound reproducing apparatus. The demand for listening to music has become stronger. Under such demands, as an example, a conventional audio signal amplifier circuit is configured as shown in FIG. In the figure, 21 is an input terminal to which a reproduction signal is inputted, 22 is a variable resistor for adjusting the volume,
Reference numeral 24 denotes an output terminal, and reference numeral 23 denotes an operational amplifier that is a main component of the amplifier circuit. The amplification gain is determined by a resistor or a capacitor external to the gain, and is taken out from the output terminal 24. Reference numeral 25 is a changeover switch for switching between making the frequency characteristic substantially flat and enhancing the low frequency range. A conventional audio signal reproducing circuit configured as described above will be described with reference to FIGS. FIG. 6 is a frequency characteristic diagram of the conventional audio signal reproducing circuit. The solid line indicates the frequency characteristic when the changeover switch 25 is switched upward to make it almost flat, and the low-frequency characteristic is reduced by the capacitor C21. This is because the low frequency band unnecessary for the audio signal is removed by the effect of (1). The broken line in FIG. 6 shows the frequency characteristics when the changeover switch 25 is switched down to enhance the low frequency range. The low frequency range is enhanced by the effect of the capacitor C22, and the capacitor C23 is used to improve the sound balance. The high range is also slightly enhanced by the resistor R24.

[0003]

However, the conventional audio signal amplifying circuit as described above has a first problem in that when an input signal as shown in FIG. If the headphone or speaker is made to sound at a high volume by adjusting the output 22, the output terminal 24 is clipped in the dynamic range of the power supply of the operational amplifier 23 as shown in FIG. Had a problem. This problem is remarkable when the changeover switch 25 is switched down to enhance the low frequency range.

As a second problem, when the changeover switch 25 is switched to the down position, the frequency characteristic is gradually increased in the low frequency range as shown by the broken line in FIG. There was a problem that it could be heard muffled.

[0005] In view of the above-mentioned conventional problems, the present invention provides a first method.
It is an object of the present invention to provide an audio signal amplifier circuit capable of eliminating distortion of a high-amplitude part of an amplified signal when reproducing a signal exceeding an output dynamic range of a circuit determined by a power supply voltage. It was done as. Also, as a second invention, when the low range is enhanced,
It is an object of the present invention to provide an audio signal amplifier circuit that can sharply enhance only a low frequency without increasing a middle frequency.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an audio signal amplifying circuit according to the present invention comprises a high-frequency amplifying circuit for amplifying a high-frequency component of a reproduced signal having a frequency component from a low frequency to a high frequency. A low-frequency amplifier for amplifying a low-frequency component of the reproduced signal; a limiting circuit for limiting the output of the low-frequency amplifier; and an output of the high-frequency amplifier and an output of the low-frequency amplifier. It is composed of an adder circuit.

[0007] Further, it has frequency components from low to high frequencies.
High frequency range that selectively amplifies the high frequency components of the reproduced signal
Amplifying circuit, a capacitor for removing low-frequency transmission, a low-pass filter for lowering the high-frequency amplification factor, a resistor for feeding back the output of the low-pass filter to the capacitor, and the low-pass filter Usually the low-frequency gain of the
Switching means for switching the cutoff frequency in conjunction with switching to the boosting, and the output of the high-frequency amplifier circuit.
And an addition circuit for adding the output of the low-pass filter and the output of the low-pass filter.
When augmented, the low-pass filter
In this case, the Q of the tar is increased .

[0008]

According to the present invention, the amplification of the high-frequency band by the high-frequency amplifier circuit and the amplification of the low-frequency band by the low-frequency amplifier circuit are amplified by the respective amplifier circuits. The output is limited by the limiting circuit, and is added by the addition circuit that adds the output of the high-frequency amplifier circuit and the output of the low-frequency amplifier circuit. Is not impaired, so that distortion is reduced. Also, when boosting low frequencies
Has a larger Q of the low-pass filter than normal
As a result , the low frequency band can be sharply increased, and the crossover frequency between the low frequency band amplifier circuit and the high frequency band amplifier circuit can be slightly dipped, so that the muffled feeling when the middle frequency band is enhanced does not occur.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an audio signal amplifying circuit according to the present invention.

FIG. 1 shows an embodiment of the present invention, in which 1 is an input terminal for inputting a reproduced signal of a sound reproducing apparatus, 2 is a variable resistor for adjusting the volume, and 11 is an output terminal after amplification. is there. 3 is an operational amplifier, 4 is a current control current source that outputs the same amount of current as the output current of the operational amplifier 3,
The high-frequency amplifier circuit A is composed of the capacitor C1 and the resistors R1 and R2. 5 is an operational amplifier, 6 is a current control current source that outputs the same amount of current as the output current of the operational amplifier 5, 7 is a buffer having an amplification factor of 1, and includes capacitors C3 and C4 and resistors R3, R4 and R5. Thus, the low-frequency amplifier circuit B is configured. Reference numeral 8 denotes a limiting circuit for limiting the amplitude of the low-frequency amplifier circuit B.
It is a limiter. An operational amplifier 10 is a high-frequency amplifier circuit A.
And an output voltage of the low-frequency amplifier circuit B is added to the output terminal 11 by performing a VI conversion with a resistor R7 and performing an IV conversion with a resistor R8. 9 is a changeover switch for changing the frequency characteristics, R6 is a resistor for increasing the low frequency gain, and C2 is a capacitor for increasing the high frequency gain.

The operation of the audio signal amplifying circuit configured as described above will be described below.

First, the case where the changeover switch 9 is tilted to the right will be described. The high-frequency component of the signal input to the input terminal 1 is a high-frequency amplification that constitutes a high-pass filter represented by a cutoff frequency = 1 / (2πC1 (R1 + R2)) by the operational amplifier 3 and the current control current source 4. After passing through the circuit A, the pass band gain is represented by R8 / (R1 + R2), and the low-frequency component is cutoff frequency = 1 / (2πC4 · R) by the operational amplifier 5, the current control current source 6, and the buffer 7.
5), the signal passes through the low-pass amplifier circuit B constituting the low-pass filter D, and the pass band gain is (R5 / R3) * (R
8 / R7), and the result of addition by the operational amplifier 10 for the adder circuit C is output to the output terminal 11.

This operation will be described with reference to FIG. Second
5A and 5B are explanatory diagrams of the frequency characteristics when the changeover switch 9 of the audio signal amplifier circuit of the present invention is switched to the right. FIG. 5B shows the frequency characteristics of the high-frequency amplifier circuit A, and FIG. (D) is a frequency characteristic after addition, which is a transmission frequency characteristic from the input terminal 1 to the output terminal 11, and is a low-frequency gain of the low-frequency amplifier circuit B and a high-frequency characteristic of the high-frequency amplifier circuit A. Since the gains are equal, the characteristics are almost flat. Here, the band lower than the crossover frequency is dropped because of the effect of the capacitor C3, which removes unnecessary low-frequency components as an audio signal.

Next, the case where the changeover switch 9 is tilted to the left will be described. The higher frequency part of the high frequency amplifier circuit A is C2
, The low-frequency gain of the low-frequency amplifier circuit B rises due to R6, the cut-off frequency decreases, and interferes with the cut-off frequency for removing unnecessary low-frequency waves due to C3 and R3. Peaking with Q of 0.5 or more occurs in the low frequency range.

FIG. 3 is an explanatory diagram of the frequency characteristics when the changeover switch 9 of the audio signal amplifier circuit of the present invention is switched to the left. FIG. 3B shows the frequency characteristics of the high-frequency amplifier circuit A, and FIG. (D) is a transmission frequency characteristic from the input terminal 1 to the output terminal 11, and the low frequency is enhanced by peaking with Q of 0.5 or more, The high range is slightly enhanced by the effect of C2, and a slight dip occurs near the crossover frequency.

4A and 4B are explanatory diagrams of the operation of the audio signal amplifier circuit according to the present invention. FIG. 4A shows the input signal waveform, FIG. 4B shows the output waveform of the high-frequency amplifier circuit A, and FIG. (D) is an output waveform of the output terminal 11 obtained by adding (b) and (c).

Normally, when an input signal as shown in (a) including a frequency component from a low frequency band to a high frequency band is input, the variable resistor 2 is adjusted to make a headphone or a speaker sound at a large volume. , (C), as shown by the solid line in FIG.
Is limited by the limiting circuit 8. This is remarkable when the changeover switch 9 is tilted to the left to enhance the low frequency range. However, since the limiting circuit 8 is a soft limiter, it is gently limited. Therefore, the output waveform is (d)
As shown in FIG.

As described above, according to the present embodiment, the amplification of the high frequency band by the high frequency amplifier circuit A and the amplification of the low frequency band by the low frequency amplifier circuit B are amplified in each amplifier circuit. The output of the low-frequency amplifier circuit B is limited by the limiting circuit, and is added by the addition circuit C that adds the output of the high-frequency amplifier circuit A and the output of the low-frequency amplifier circuit B. Even if it is done, the high frequency component will not be impaired thereby, and the sense of distortion will be reduced. Also,
When the low-frequency band is enhanced, peaking of Q of 0.5 or more occurs in the low-frequency band, so that the low-frequency band can be sharply enhanced, and a slight dip occurs in the crossover frequency of the low-frequency amplifier circuit B and the high-frequency amplifier circuit A. Because it can, there is no muffled feel when the midrange is enhanced.

[0019]

As described above, according to the present embodiment, the amplification of the high frequency band by the high band amplification circuit A and the low band amplification circuit B
, And the output of the low-frequency amplifier B is limited by the limiting circuit, and the addition of adding the output of the high-frequency amplifier A and the output of the low-frequency amplifier B is performed. Since the addition is performed by the circuit C, even if a low-frequency component having a large amplitude is input, the high-frequency component is not impaired by the input, thereby reducing the sense of distortion. In addition, when the low frequency is enhanced, it passes through the lower frequency than normal.
Since the Q of the filter is increased, the low frequency band can be sharply enhanced, and the crossover frequency between the low frequency amplifier circuit B and the high frequency amplifier circuit A can be slightly dipped. The feeling does not occur.

[Brief description of the drawings]

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

FIG. 2 is a frequency characteristic diagram when the changeover switch 9 of the audio signal amplifier circuit of the present invention is switched to the right.

FIG. 3 is a frequency characteristic diagram when the changeover switch 9 of the audio signal amplifier circuit of the present invention is switched to the left.

FIG. 4 is an operation waveform diagram of the audio signal amplifier circuit of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional audio signal amplifier circuit.

FIG. 6 is a frequency characteristic diagram of a conventional audio signal reproduction circuit.

FIG. 7 is an operation waveform diagram of a conventional audio signal reproduction circuit.

[Explanation of symbols]

 A: high-frequency amplifier circuit B: low-frequency amplifier circuit C: adder circuit D: low-pass filter C3: capacitor 8: limiting circuit 9: changeover switch

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-33960 (JP, A) JP-A-53-30849 (JP, A) JP-A-52-126157 (JP, A) 64508 (JP, A) JP-A-60-246111 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03G 3/20-5/28

Claims (4)

(57) [Claims] 1. A high-frequency amplifier circuit for selectively amplifying a high-frequency component of a reproduction signal having a frequency component from a low frequency band to a high frequency, and a low-frequency amplifier for selectively amplifying a low-frequency component of the reproduction signal. An audio signal amplifier comprising: an amplifier circuit; a limiting circuit for limiting an output of the low-frequency amplifier circuit; and an adding circuit for adding an output of the high-frequency amplifier circuit and an output of the low-frequency amplifier circuit. circuit. 2. The audio signal amplifying circuit according to claim 1, wherein a low-frequency characteristic can be switched by switching a low-frequency amplification factor of the low-frequency amplifier. 3. The audio signal according to claim 2, further comprising switching means for switching the frequency characteristics of the high-frequency amplifier circuit in conjunction with the switching means of the low-frequency amplifier circuit, wherein the high-frequency characteristics are also variable. Amplifier circuit. 4. It has a frequency component from a low band to a high band.
High frequency amplification that selectively amplifies the high frequency components of the playback signal
Circuit and a capacitor to eliminate low-frequency transmission,
A low-pass filter that lowers the high-frequency gain, a resistor that feeds back the output of the low-pass filter to the capacitor, and a low-frequency gain of the low- pass filter that is higher than normal.
Switching means for switching strongly and switching the cutoff frequency in conjunction with the output of the high-frequency amplifier circuit.
It comprises an addition circuit for adding the output of the low-pass filter, and the switching means enhances the low-frequency amplification factor.
Low-pass filter than normal
Wherein the Q is increased.