JPS6110304A - Distortion preventing circuit - Google Patents

Abstract

PURPOSE:To prevent distortion of an output of an amplifier without so much reduction in the decrease in the feeling of maximum sound volume even at an excess of input by suppressing a low frequency component among amplifier inputs in response to an output of distortion detection of an amplifier. CONSTITUTION:An input signal IN is fed to an amplifier 12 via a tone control circuit 20 controlling the frequency characteristic. An input/output signal of the amplifier 12 is fed to input terminals 2, 1 of the distortion detector 21 and outputted from an output terminal 3 as a distortion detection signal. The distortion detection signal is used as a low sound frequency control signal of the tone control circuit 20 to suppress the low frequency component of the input signal IN. The more or less of deterioration in sound quality is caused, but the amplitude decrease of the frequency component sensing to ears is prevented and the distortion is prevented without reducing the feeling of sound volume.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a distortion prevention circuit at the time of excessive input in audio power amplifiers, etc. The present invention relates to a distortion prevention circuit in the case of excessive input in audio power amplifiers, etc. It is something to do.

[Conventional technology]

As shown in FIG. 6, the speaker 11 is connected to the power amplifier 12.
In an audio system driven by a power amplifier 12
In some cases, a distortion reduction circuit 13 is provided so that the output OUT is not distorted even when an excessive input is applied. The distortion reduction circuit 13 shown in this example includes a level detector 14 that detects the level of the output OUT of the amplifier 12, and uses the detection output as a control input to appropriately attenuate the audio signal λKIN supplied to the amplifier 12. This is an AGC circuit consisting of an electronic attenuator 15. Therefore, even if the external input IN is excessive, the amplifier 1
Since it can be attenuated before inputting to 2,
No distortion occurs in the output OUT.

[Problem that the invention seeks to solve]

However, such an AGO function has the disadvantage that when the maximum output of the power amplifier 12 is small, the sense of volume is reduced and the sound is not audibly impressive.

[Means for solving problems]

The present invention aims to improve the above-mentioned drawbacks by not performing the gain reduction operation uniformly to prevent distortion, but selectively performing it on parts that have a large energy distribution but have a low contribution to the sense of loudness. That is. For this reason, the present invention provides a distortion detector for detecting distortion of an amplifier or an operation level detector for predicting the occurrence of distortion, and a method for suppressing the bass part of the amplifier input based on the output of the detector. The present invention is characterized in that it includes a frequency characteristic control circuit.

[Effect]

The spectrum of an audio signal usually has large amplitude components distributed in the bass region. Furthermore, the auditory sense of volume for a signal with a constant amplitude decreases in the bass range. Therefore, if a gain reduction operation is performed selectively on the bass range to prevent distortion, it will cause some deterioration in sound quality, but it will prevent the amplitude of other frequency components that are more perceptible to the ear from decreasing, reducing the perceived volume. Distortion can be prevented without causing damage. The frequency characteristic control circuit may be a tone control circuit or a loudness control circuit having a bass boost function, and in a system equipped with these, they can be used together.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which 20 is an electronic tone control circuit and 21 is a distortion detector.

The tone control circuit 20 is divided into a low tone circuit and a high tone circuit, and in this example, the low tone circuit is used for distortion reduction operation. The distortion detector 21 has two input terminals 1.2, which input the output and input of the amplifier 12, compare waveforms, and detect the occurrence of distortion from the difference. 3 is a control output terminal.

FIG. 2 is a detailed diagram of the distortion detector 21, where CMP is a voltage comparator. The voltage to input terminal 1 of this comparator CMP (output 0UT of amplifier 12) is divided by the gain of amplifier 12 by variable resistor VR, and the voltage at input terminal 2 (amplifier I2 input).

In this way, if the input to amplifier 12 (assumed to be a common-mode amplifier) becomes excessive and distortion occurs, the input from terminal 1 will no longer increase, but the input from terminal 2 will increase. The device CMP produces an output. Capacitor C
1 and C2 and diodes DI and D2 constitute a voltage doubler detection circuit, the output of which becomes a control signal from terminal 3. By inputting this control signal to the bass section of the electronic tone control circuit 20 and controlling its electronic volume circuit (WJ not shown), distortion can be prevented by restricting only the bass section of the input IN.

FIG. 3 shows a level detector 22 that predicts the occurrence of distortion as another example of a circuit that can be used in place of the distortion detector 21. In this case, terminal 2 is an empty terminal, and the output OUT of amplifier 12 is input to terminal 1. The amplified output OUT input from terminal 1 is voltage-divided by a variable resistor VR, and then passed through a bump amplifier BUF to a voltage doubler detection circuit (C+, Ct, D
I, D2). In this case, an output is always generated from the voltage doubler detection circuit, but only when the voltage exceeds the Zener voltage of the Zener diode ZD, current flows through the resistor R, and a control voltage is generated at the terminal 3. Therefore, if the Zener voltage described above is set according to the output level at which distortion begins to occur in the amplifier 12, distortion detection similar to that of the distortion detector 21 can be performed.

FIG. 4 shows another embodiment of the invention. In this example, the distortion output halo bass filter (LPF) 23 (!Ni-level detector 22
The treble distortion detection section uses a bypass filter (
) (PF) 24 and a level detector 22H. The output of the bass level detector 22L is used to control the bass section of the tone control circuit 20 as in FIG. On the other hand, the output of the treble level detector 22H is used to control the amount of attenuation of the electronic attenuator 25 connected between the tone control circuit 20 and the power amplifier 12. In this case, the suppression of the bass region by the tone control circuit 20 and the suppression of the entire range by the electronic attenuator 25 are performed in a mixed manner, so when both act simultaneously, the circuit in FIG. 6 and the circuit in FIG. characteristics can be obtained. Furthermore, if the bass part of the input IN is low and the middle and treble parts are excessively input, the electronic attenuator 25 will suppress the entire range even if the bass distortion detection does not operate, so the minimum operation (6th (as shown in the figure) is guaranteed. In addition, Lehe/L
'& Output device 22 Tone control circuit 20 with output of L
If you control the treble range at the same time (without suppressing only the middle range), you can achieve balanced distortion prevention.

FIG. 5 shows a different embodiment of the invention. In both the examples of FIG. 1 and FIG. 4, the electronic tone control circuit 20 is used exclusively for distortion prevention, but in the example of FIG. 5, it is also used for manual control. That is, TCL, TC, are the manual control inputs for tone control, and TCL is the bass control signal, T
C, is a treble control signal. 26 is an adder that adds the control output of the distortion detector 21 and the external bass control signal TCL to provide a bass control input to the tone control circuit 20. Treble control human power TCH is direct tone control circuit 2
0 treble section to control its electronic porium section (not shown).

〔Effect of the invention〕

As described above, according to the present invention, since distortion is prevented by lowering the bass part of the amplifier input where the sense of volume is low, even when an excessive input is applied, the amplifier can be operated without significantly reducing the sense of maximum volume. Output distortion can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a distortion detector, FIG. 3 is a circuit diagram showing a specific example of a level detection circuit, and FIGS. This figure is a block diagram showing another embodiment of the present invention, and FIG. 6 is a block diagram showing an example of a conventional distortion reduction circuit. In the figure, 12 is an amplifier, 20 is an electronic tone control circuit, 21 is a distortion detector, 22 is a level detector, 23 is a low-pass filter, 24 is a bypass filter, 25 is an electronic attenuator, and 26 is an adder. Applicant Fujitsu Ten Ltd. Representative Patent Attorney Minoru Aoyagi Figure 1 Figure 2 Figure 3 Figure 41!1 Figure 5 Figure 6

Claims (2)

[Claims] (1) A distortion detector for detecting distortion of the amplifier or an operation level detector for predicting the occurrence of distortion, and frequency characteristic control for suppressing the bass part of the amplifier input based on the output of the detector. A distortion prevention circuit comprising a circuit. (2) The distortion prevention circuit according to claim 1, wherein the frequency characteristic control circuit shares an electronic tone control circuit for adjusting sound quality.