JPH1032444A - amplifier - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce heat generation for continuous large output, and to secure maximum output by soft amplitude limiting characteristics against instantaneous excessive amplitude, to reduce the size. Provided is an amplifier capable of obtaining a high dynamic output without a sense of distortion. SOLUTION: A main amplifier 1, an input amplitude limiting circuit 2 provided at an input portion of the main amplifier 1, and operational amplifiers Q3 and Q3 'for applying a limit level setting voltage to the input amplitude limiting circuit 2 are provided. A pair of comparison circuits 3, 3 '
An output level detection circuit 4 for obtaining a comparison control voltage having a time delay based on the output of the main amplifier 1 and applying the control voltage to the comparison circuit 3, and a comparison control circuit having no time delay based on the output of the main amplifier 1. It comprises a pair of output level detection circuits 5, 5 'for obtaining a control voltage and applying the control voltage to the comparison circuits 3, 3'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier for handling a signal having a large dynamic range, such as an audio system, a loudspeaker, an electronic musical instrument, and the like. And a voice power amplifier having an amplitude limiting function.

[0002]

2. Description of the Related Art Generally, as is well known, an abnormal sound is generated from a speaker if an amplifier clips at a large amplitude of a signal. This is because the waveform is distorted by the signal clipping,
This is because high-level high-order harmonic components are mixed in the reproduced sound as distortion. Conventionally, in order to prevent such a phenomenon, a limiter circuit is inserted in the input section of the amplifier to suppress the amplitude of the input signal when the amplitude is large so as not to clip. Such a conventional amplifier for audio having an amplitude limiting function uses an amplitude limiting circuit with a time delay, and therefore does not operate for an instantaneous large output, but for a continuous large output. By performing the restriction operation,
The dynamic output keeps the maximum output determined by the power supply voltage of the amplifier, keeps the continuous output low by the amplitude limiting circuit, and keeps the heat generated by the continuous large output low. As a result, audio amplifiers having high dynamic output despite their small size have been put to practical use.

[0003]

FIG. 3 shows a time characteristic of an amplitude limiting level in which the conventional amplifier performing the excessive amplitude limiting operation described above uses the amplitude limiting action as a reference for the same purpose as the embodiment. In the case of a continuous high-output signal that lasts longer than the delay time T1 until the amplitude limiting circuit starts operating, finally, according to the amplitude limiting characteristic of the conventional example represented by a two-dot chain line in FIG. Although the amplitude is limited to the low amplitude limit level Le, which has the effect of preventing the thermal runaway of the amplifier together with the amplitude distortion, the amplitude limitation is not applied to any instantaneous excessive input included within the delay time T1, so A clip level Lc continuously determined by a dotted line and determined by the power supply voltage.
Causes a voltage clip. This clip generally has a hard clipping characteristic as if it were modulated by a square wave, and as described above, it has a very unpleasant distortion feeling because the waveform is distorted, and furthermore, the power supply modulation which is modulated by the ripple of the power supply Is generated, which is weighted by the clipping distortion, and has a problem to be solved in that the reproduced sound quality is greatly impaired.

In order to solve the above-mentioned conventional problems, the present invention detects the output signal level when a signal clip occurs in the main amplifier and detects a time delay with respect to a continuous excessive amplitude. And an amplitude limiting level that is close to the clipping level Lc due to the power supply voltage without a time delay for an instantaneous excessive amplitude.
By using the amplitude limiting operation that is not hard at Lm, the unpleasant feeling of distortion is removed while securing a high dynamic output despite being small, and at the same time, the heat generation is suppressed to a large continuous output. It is an object of the present invention to provide an amplifier capable of performing the following.

[0005]

The amplifier according to the present invention for achieving the above object will be described with reference to the symbols used in the description of the embodiments. An amplifier having an amplitude limiting function that operates with a time delay and an amplitude limiting function that also operates without a time delay with respect to a large amplitude input signal.
An input amplitude limiting circuit 2 at an input of the main amplifier 1 for limiting the amplitude of an input signal; and an operational amplifier Q for applying a limit level setting voltage to the input amplitude limiting circuit 2
A set of positive and negative comparators 3 and 3 'comprising Q3' and an output level detecting circuit 4 for obtaining a comparison control voltage having a time delay based on the output of the main amplifier 1 and applying the control voltage to the comparator 3;
And a set of positive and negative output level detection circuits 5, 5 'for obtaining a comparison control voltage having no time delay based on the output of the main amplifier 1 and applying the control voltage to the comparison circuits 3, 3'. It has a characteristic configuration.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In implementing an amplifier having such a configuration, an example will be described with reference to FIG. 1 showing a basic configuration of a circuit. An input amplitude limiting circuit provided at an input section of a main amplifier 1 will be described. 2, diodes D1 and D2 are connected in opposite directions to each other in accordance with the polarity of the signal. The diodes D1 and D2 are reverse-biased at a voltage corresponding to the amplitude limiting level. When the voltage of the input signal of the main amplifier 1 is lower than the reverse bias voltage applied to the diodes D1 and D2, the input signal is amplitude-limited. Without being input to the main amplifier 1. The reverse bias voltages applied to the diodes D1 and D2 are the comparison control voltages Va, Vb and Vb 'obtained from the output voltage of the main amplifier 1 by the output level detection circuits 4, 5, 5', and the power supply. The reference voltage obtained by dividing the voltage is compared with the transistors Q1, Q2 and the comparison circuits 3, 3 '.
Are obtained by comparison and amplification by the operational amplifiers Q3 and Q3 'included in.

In order to supply the respective reverse bias voltages to the diodes D1 and D2, the diodes D1 and D2 on the positive side are supplied.
Is connected to a comparison circuit 3 centered on an operational amplifier Q3, and a diode D2 on the negative side is connected to a comparison circuit 3 'centered on an operational amplifier Q3'. Usually, such operational amplifiers are often composed of two circuits, and therefore, the operational amplifier Q3 is used as an operational amplifier Q3 (1 /
2), the operational amplifier Q3 'may be expressed as an operational amplifier Q3 (2/2). In the comparison circuit 3 on the positive side, the comparison control voltages Va and Vb are applied to the opposite polarity inputs of the operational amplifier Q3,
The power supply voltage + BV is divided and applied to the positive input by resistors R10 and R11 as a reference for comparison. The output terminal of the operational amplifier Q3 is connected via a resistor R2 to a diode D1 on the positive side of the input amplitude limiting circuit 2 and a resistor R13
Is connected to the opposite polarity input terminal of the operational amplifier Q3 'of the comparison circuit 3' on the negative side.

The operational amplifier Q3 'of the comparison circuit 3' on the negative side
The output from the operational amplifier Q3 on the positive electrode side is applied as a comparison voltage to the reverse polarity input of each of the above, and each comparison control voltage Vb 'obtained by the output level detection circuit 5'.
Are applied simultaneously. Also, the positive input terminal is grounded,
The structure is such that only an output whose polarity is inverted is obtained. The output terminal of the operational amplifier Q3 is connected to a negative diode D2 of the input amplitude control circuit 2 via a resistor R3.

The aforementioned output level detection circuits 4, 5, 5 '
The output level detecting circuit 4 is a circuit for obtaining a comparison control voltage Va for operating an amplitude limiting circuit that operates with a time delay. The output level detecting circuit 4 includes a diode D4 connected to the output of the main amplifier 1 for rectifying the output voltage. It comprises a voltage dividing resistor R7, a voltage dividing resistor R8 and a capacitor C1, and the terminal of the capacitor C1 is connected via a resistor R9 to an operational amplifier Q3 forming a comparison circuit.
Is connected to the reverse polarity input terminal. When the output voltage of the main amplifier 1 is rectified to charge the capacitor C1 through the resistor R7, a circuit having a time constant is formed by the combined impedance of the resistor R7 and the resistor R8 and the capacitor C1.
The voltage of the capacitor C1, that is, the comparison control voltage Va rises with a time delay corresponding to the time constant.

The output level detecting circuit 5 is a positive-side circuit for obtaining a comparison control voltage Vb for operating an amplitude limiting circuit having no time delay, and is connected to the output of the main amplifier 1.
A voltage dividing resistor R4 and a voltage dividing resistor VR1 capable of changing a set level.
, A diode D3 connected to the voltage dividing output section in a direction to obtain a positive voltage, and a transistor Q1 for comparing the rectified voltage of the diode D3 with the power supply voltage + BV. The collector of the transistor Q1 is connected to the resistor R6. Connected to the opposite polarity input terminal of the operational amplifier Q3. When the voltage of the divided output section becomes higher than the sum of the power supply voltage + BV, the forward voltage of the diode D3, and the VBE of the transistor Q1, the transistor Q1 is turned on, and the comparison control voltage Va is used as the comparison control voltage Vb. And applied to the opposite polarity input terminal of the operational amplifier Q3.

The output level detecting circuit 5 'is a negative side circuit for obtaining a comparison control voltage Vb for operating an amplitude limiting circuit having no time delay, and is connected to the output of the main amplifier 1.
A voltage dividing resistor R14 and a voltage dividing resistor VR2 that can change the set level
A diode D5 connected to the voltage dividing output section in a direction to obtain a positive polarity voltage, and a transistor Q2 for comparing the rectified voltage of the diode D5 with the power supply voltage -BV. The collector of the transistor Q2 has a resistor R16. Is connected to the opposite polarity input terminal of the operational amplifier Q3 '. When the voltage of the divided output section is equal to the power supply voltage -BV and the diode D5
Becomes higher than the sum of the forward voltage of the transistor Q2 and VBE of the transistor Q2, the transistor Q2 conducts, and is added to the output of the operational amplifier Q3 as a control voltage Vb 'for comparison and applied to the reverse polarity input terminal of the operational amplifier Q3'. Is done.

The operation of the output level detecting circuit 4 having a time constant according to the embodiment of the present invention will be described. First, the output of the main amplifier 1 is rectified by the diode D4 and passed through the dividing circuit of the resistors R7 and R8. The capacitor C1 is charged. This voltage is used to connect the power supply voltage + BV to the resistor R10,
The voltage is compared by the voltage divided by R11, amplified by the operational amplifier Q3, and applied to the diode D1 through the resistor R2. On the other hand, the output of the operational amplifier Q3 is applied to the opposite polarity input terminal of the operational amplifier Q3 'through the resistor R13, and the output whose polarity is inverted is applied to the diode D2 through the resistor R3. While the input of the main amplifier 1 is sufficiently small, in other words, while the output is not clipped, the output of the operational amplifier Q3 is positive and the output of the operational amplifier Q3 'is negative. As a result, the diodes D1 and D2 are reverse-biased, and the input voltage is applied to the input of the main amplifier 1 without being subjected to the amplitude limitation.

When a continuous large-amplitude signal is input, the voltage of the capacitor C1 increases, the output of the operational amplifier Q3 decreases, and the output of the operational amplifier Q3 'increases. Diode D
1, the reverse bias voltage of D2 becomes low, the diodes D1 and D2 conduct at the peak of the input of the main amplifier 1, and the amplitude is limited. For a large instantaneous input, this circuit does not operate because of a delay due to a time constant determined by the combined impedance of the resistors R7 and R8 and the capacitor C1, and therefore acts as an amplitude limiting circuit with a time delay. FIG. 3 shows the amplitude limiting characteristics after time T1 at which the output level detection circuit 4 of the present invention starts operating in a solid line graph. Since the amplitude limiting characteristic of this portion is similar to that of the conventional example together with the amplitude limiting level Le, the two graphs are close to each other.

For an instantaneous large input, the output level detection circuit 5 mainly operates on the plus side, and a voltage obtained by dividing the output of the main amplifier 1 by a resistor R7 and a semi-fixed resistor VR1;
The power supply voltage + BV is compared by the transistor Q1,
The divided voltage is the power supply voltage + BV and the diode D
When the voltage becomes higher than the sum of the forward voltage of 3 and VBE of transistor Q1, transistor Q1 conducts. as a result,
The collector current of the transistor Q1 is added to the comparison control voltage Va as a comparison control voltage Vb through a resistor R6 and applied to the opposite polarity input terminal of the operational amplifier Q3, so that the output voltage of the operational amplifier Q3 decreases and the diode D1 Is conducted, and the amplitude limiting circuit operates without a time delay. The reverse bias voltage when the diode D1 conducts, that is, the output voltage of the operational amplifier Q3, is adjusted by adjusting the semi-fixed resistor VR1 so that the output of the main amplifier 1 becomes the amplitude limit level Lm immediately before being clipped by the power supply voltage. Is set. In FIG. 3 described above, the amplitude limiting characteristic by the output level detection circuit 5 is indicated by a dotted line. Further, in order to prevent the state in which the amplitude is limited from becoming similar to a hard clip due to the limit of the power supply voltage, the output level detection circuit 5 is provided with a soft amplitude limiting characteristic as shown by a dashed line in FIG. Such a circuit may be used.

On the negative side, the output level detection circuit 5 'operates mainly, and the voltage obtained by dividing the output of the main amplifier 1 by the resistor R14 and the semi-fixed resistor VR2 is compared with the power supply voltage -BV by the transistor Q2. When the divided voltage becomes higher than the sum of the power supply voltage -BV, the forward voltage of the diode D5, and the VBE of the transistor Q2, the transistor Q2 conducts. As a result, the collector current of the transistor Q2 passes through the resistor R16 and the control voltage VB 'for comparison.
Is added to the inverted output of the control voltage Va for comparison by the operational amplifier Q3 and applied to the opposite polarity input terminal of the operational amplifier Q3 ', so that the output voltage of the operational amplifier Q3' is reduced.
The diode D2 conducts, and the amplitude limiting circuit operates without a time delay. Even in this case, the reverse bias voltage when the diode D2 conducts, that is, the output voltage of the operational amplifier Q3 'is semi-fixed so that the output of the main amplifier 1 becomes the amplitude limit level LM immediately before being clipped by the power supply voltage. It is set by adjusting the resistance VR2. The amplitude limiting characteristic is the same as that of the output level detection circuit 5 shown in FIG.

As apparent from the above description of the operation, the output level detecting circuit 4 and the operational amplifier Q3 act as a time-delayed amplitude limiting circuit for a continuous large-amplitude signal, and the level of the output signal is reduced. To minimize the generation of heat due to continuous large output while preventing the occurrence of clipping distortion, and for an instantaneous excessive input, set the maximum operation level to the amplitude limit level Lm immediately before the clip level Lc by the power supply. With this setting, clipping distortion due to hard clipping and modulation distortion due to an unpleasant power supply voltage can be prevented while keeping the instantaneous dynamic power large, and an amplifier with an incomparably excellent audibility can be obtained.

[0017]

FIG. 1 is an explanatory diagram showing the most basic circuit configuration, and FIG. 2 is a specific circuit diagram of the first embodiment based on FIG.

FIG. 2 shows a circuit configuration of the first embodiment, which is the same as the basic circuit example shown in FIG. 1 used for explaining the operation of the circuit of the embodiment. Have been identified. All used circuit elements use components that are usually used in general equipment. The power supply voltage is set to ± 12 V, and the maximum output of the main amplifier 1 is 50
W, continuous output is 25W. The reverse bias voltage of the diodes D1 and D2 of the input amplitude limiting circuit 2 at the time of no signal or small amplitude is set to about 10V.

The time constant of the integration circuit, which is determined by the combined impedance of the resistors R7 and R8 and the capacitor C1 of the output level detection circuit 4, is required to be large enough so as not to impair the dynamic range of the reproduced signal. It is set to about 2.5 seconds in consideration of the duration of the input.

The state of the amplitude limiting operation based on the operation of the output level detecting circuits 5 and 5 'is shown by a dotted line in FIG. In order to operate, and to prevent modulation distortion due to the ripple of the power supply, the clipping level Lc by the power supply is about -1 dB.

Although the embodiments and modifications which are considered to be representative of the present invention have been described above, the present invention is not limited to the structure of an output level detection circuit, an input amplitude limiting circuit and the like. The present invention is not limited to only the structure described above, but can be implemented with the above-mentioned constituent features of the present invention, achieving the object of the present invention, and appropriately modifying within the range having the following effects. It is.

[0022]

The amplifier according to the present invention has an amplitude limiting function that operates with a time lag with respect to a continuous large amplitude input signal. , While suppressing the heat generation due to the continuous large output, it is possible to obtain a small-sized audio amplifier having a high dynamic output.

Since it also has an amplitude limiting function that operates without a time delay, for an instantaneous excessive input,
By setting the operation level immediately before the amplifier's clip level, an amplifier that does not cause modulation distortion or hard clip distortion due to power supply ripple that is harsh even at excessive input while maintaining large instantaneous dynamic power is realized. can do.

As is clear from the above, the amplifier of the present invention has an extremely useful effect as an audio amplifier, which is capable of obtaining a natural tone reproduction with a powerful and high dynamic range and without clipping. It was obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a circuit showing a basic configuration of an amplifier according to the present invention.

FIG. 2 is a circuit diagram of a first embodiment of the present invention.

FIG. 3 shows the time of the amplifier, the embodiment and the conventional example of the present invention.
It is an amplitude limitation characteristic figure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main amplifier 2 Input amplitude limiting circuit 3, 3 'comparison circuit 4 Output level detection circuit 5, 5' Output level detection circuit

Claims (1)

[Claims] An amplifier having an amplitude limiting function that operates with a time delay with respect to a large amplitude input signal and an amplitude limiting function that also operates without a time delay with respect to a large amplitude input signal, A main amplifier (1), an input amplitude limiting circuit (2) at the input section of the main amplifier (1) for limiting the amplitude of an input signal, and a limit level setting voltage applied to the input amplitude limiting circuit (2) 1 including the operational amplifiers Q3 and Q3 '
A set of comparison circuits (3), (3 ') and a comparison control voltage having a time delay based on the output of the main amplifier (1) are obtained.
(3) an output level detection circuit (4) applied to the main amplifier
A pair of positive and negative output level detection circuits (5) and (5 ') for obtaining a comparison control voltage having no time delay based on the output of (1) and applying the same to the comparison circuits (3) and (3') An amplifier comprising: