JP7425646B2 - limiter circuit - Google Patents

Description

Embodiments disclosed in this specification and the like relate to a limiter circuit.

In general, audio power amplifier ICs are generally equipped with an output voltage limiter that suppresses excessive output voltage to protect the speaker, and an output current limiter that suppresses excessive output current to protect the IC itself.

Patent No. 3562141

Since conventional current limiters do not use an attenuator, the audio signal when the current limiter operates has a clipped waveform, resulting in noticeable deterioration of audio characteristics. Furthermore, in order to improve audio characteristics during current limiter operation, there is a technique that uses a voltage limiter with an attenuator. However, when using a conventional voltage limiter, there are problems such as a sacrifice in output power and difficulty in obtaining a stable limit value.

One of the problems that the embodiments disclosed in this specification etc. are intended to solve is that the overcurrent limiter is not affected by the overcurrent limiter, regardless of the load impedance or the time constant of the output LC filter. Another object of the present invention is to provide a limiter circuit that enables playback without excessively deteriorating sound quality.

The limiter circuit according to the embodiment of the present invention includes an attenuator circuit that attenuates the voltage supplied to the power amplifier circuit, and a first output current based on the output current when the output current of the power amplifier circuit reaches a reference current value. an attenuator control circuit that generates a reference voltage value of a first absolute value circuit that outputs a first absolute value of voltage; a first comparator that compares the first absolute value of voltage with a second reference voltage value; a second absolute value circuit that outputs a second absolute voltage value based on the first reference voltage value; and a second absolute value circuit that latches the second absolute voltage value in response to the output signal of the first comparator, and a first voltage latch circuit that outputs the attenuator; and a second comparator that compares the second absolute voltage value with the first reference voltage value from the first voltage latch circuit; The circuit is characterized in that the circuit attenuates the voltage supplied to the power amplifier circuit in response to the output signal of the second comparator .

According to the present invention, it is possible to provide a limiter circuit that enables reproduction without excessively deteriorating sound quality even during overcurrent limiter operation, regardless of the load impedance or the time constant of the output LC filter.

FIG. 1 is a diagram showing the configuration of a power amplifier circuit having a limiter circuit according to a first embodiment. FIG. 2 is a diagram for explaining the operation of the limiter circuit when connected to a heavy load. FIG. 3 is a diagram for explaining a power amplifier circuit having a limiter circuit according to a comparative example. FIG. 4 is a diagram showing an example of a current limiter circuit included in the power amplifier circuit shown in FIG. 3. FIG. 5 is a diagram for explaining the operation of the limiter circuit according to the comparative example when a heavy load is connected. FIG. 6 is a diagram showing the configuration of a power amplifier circuit having a limiter circuit according to the second embodiment. FIG. 7 is a diagram for explaining the operation of the limiter circuit 7 when a light load is connected.

Hereinafter, embodiments of the limiter circuit will be described in detail with reference to the drawings. In the following embodiments, parts with the same reference numerals perform similar operations, and redundant explanations will be omitted as appropriate.

(First embodiment)
FIG. 1 is a diagram showing the configuration of a power amplifier circuit D1 having a limiter circuit 1 according to the first embodiment. As shown in FIG. 1, the power amplifier circuit D1 receives an input signal from the input voltage source 2 via the input node 3. The power amplifier circuit D1 amplifies the input signal and outputs it to the filter 4. The signal output from the power amplifier circuit D1 is output to a speaker 6 as a load via a filter 4 such as an LC filter and an output node 5.

The power amplifier circuit D1 includes a limiter circuit 1 and a first power amplifier circuit 20. The limiter circuit 1 includes an attenuator circuit 10, a current detection circuit 21, and an attenuator control circuit 30. Hereinafter, the configurations of the attenuator circuit 10, the first power amplifier circuit 20, the current detection circuit 21, and the attenuator control circuit 30 will be explained in detail.

The attenuator circuit 10 attenuates the voltage supplied to the first power amplifier circuit 20. The attenuator circuit 10 includes a first resistor 101, a first node 102, and a first voltage control circuit 103. The first voltage control circuit 103 controls the resistance value of the voltage control resistor based on the voltage and attenuates the input voltage signal. The first voltage control circuit 103 outputs the attenuated input voltage signal to the first node 102 and operates so that the first node 102 does not become higher than a predetermined reference potential.

The first power amplifier circuit 20 is a power amplifier that amplifies an input signal and outputs it to the filter 4.

The current detection circuit 21 detects the output current of the first power amplifier circuit 20. The current detection circuit 21 is, for example, a current mirror circuit that receives part of the output current of the first power amplifier circuit 20 as input. The current detection circuit 21 outputs the detected output current to the attenuator control circuit 30.

The attenuator control circuit 30 generates a first reference voltage value based on the output current when the output current of the first power amplifier circuit 20 reaches the reference current value, and controls the attenuator based on the first reference voltage value. The circuit 10 is controlled. The attenuator control circuit 30 includes a first absolute value circuit 301, a first reference voltage source 303, a second node 305, a first comparator 306, a third node 307, a second absolute value circuit 310, and a fourth , a voltage latch circuit 313, a second comparator 315, a fifth node 317, a capacitor 319, and a sixth node 320.

The first absolute value circuit 301 performs IV conversion on the current detected by the current detection circuit 21 and outputs the current as a first voltage absolute value to one input terminal of the first comparator 306 via the second node 305. Output to.

The first reference voltage source 303 supplies the reference voltage V1 (an example of the second reference voltage value) to the other input terminal of the first comparator 306.

The first comparator 306 outputs a high level signal when the first voltage absolute value output from the first absolute value circuit 301 becomes larger than the reference voltage V1. The high level signal output from the first comparator 306 is output to the voltage latch circuit 313 via the third node 307.

Note that the reference voltage V1 supplied from the first reference voltage source 303 is the output current limit value that the output current of the first power amplifier circuit 20 (i.e., the output current detected by the current detection circuit 21) targets. The third node 307 is set to a high level (a high level signal is output from the first comparator 306) when the second comparator reaches the third node 307.

The second absolute value circuit 310 transmits a second absolute value of voltage based on the voltage supplied to the first power amplifier circuit 20 to one input terminal of the second comparator 315 via a fourth node 311. supply

The voltage latch circuit 313 latches the second voltage absolute value output by the second absolute value circuit 310 in response to the output signal of the first comparator 306. The voltage latch circuit 313 supplies the latched second voltage absolute value to the other input terminal of the second comparator 315 via the fifth node 317 as the first reference voltage value.

The second comparator 315 compares the second absolute voltage value from the second absolute value circuit 310 and the first reference voltage value from the voltage latch circuit 313 . The second comparator 315 outputs a high level signal when the second voltage absolute value from the second absolute value circuit 310 becomes larger than the first reference voltage value from the voltage latch circuit 313. The high level signal output from the second comparator 315 is subjected to phase control by the capacitor 319 and output to the first voltage control circuit 103 of the attenuator circuit 10 via the sixth node 320.

The first voltage control circuit 103 controls the resistance value of the voltage control resistor in response to the high level signal output from the second comparator 315, thereby attenuating the input voltage signal. That is, when the second absolute value of the voltage output from the second absolute value circuit 310 is larger than the first reference voltage value output from the voltage latch circuit 313, the control signal from the second comparator 315 1 voltage control circuit 103. The first voltage control circuit 103 attenuates the input voltage signal and outputs it to the first node 102, so that the second voltage absolute value output from the second absolute value circuit 310 is output from the voltage latch circuit 313. Control is performed so that the output voltage does not exceed the first reference voltage value.

The first reference voltage value output from the voltage latch circuit 313 is the second reference voltage value latched by the voltage latch circuit 313 at the timing when the output current of the first power amplifier circuit 20 reaches the target output current limit value. is the absolute voltage value of Therefore, since it is an instantaneous value based on the output current of the first power amplifier circuit 20, it is not easily influenced by the time constant.

Next, the operation of the limiter circuit according to the first embodiment will be explained.

FIG. 2 is a diagram for explaining the operation of the limiter circuit 1 when connected to a heavy load 6 (eg, low resistance such as 2Ω). That is, FIG. 2A shows the voltage waveform at the input node 3 (input voltage waveform) and the voltage waveform at the output node 5 (output voltage waveform) with solid lines and broken lines, respectively. FIG. 2(b) shows the current waveform of the output current Iout of the first power amplifier circuit 20. FIG. 2(c) shows the reference voltage V1 (second reference voltage value) of the first reference voltage source 303 and the voltage waveform (waveform of the first voltage absolute value) at the second node 305. There is. FIG. 2D shows the voltage waveform at the fifth node 317 (first reference voltage) and the voltage waveform at the fourth node 311 (waveform of the second voltage absolute value). FIG. 2E shows the voltage waveform at the sixth node 320 (the output waveform of the second comparator 315).

As shown in FIG. 2(b), assume that the output current of the first power amplifier circuit 20 reaches the output current limit value IL at time t1. In this case, as shown in FIG. 2(d), the voltage at the sixth node 320 increases due to the output signal from the second comparator 315 at time t1. The first voltage control circuit 103 operates in response to the output signal from the second comparator 315 to attenuate the input voltage.

In conjunction with the operation of the first voltage control circuit 103, the output voltage waveform becomes a waveform attenuated compared to the input voltage waveform after time t1, as shown in FIG. 2(a). In conjunction with the attenuation of the output voltage waveform, the first absolute value of the voltage output by the first absolute value circuit 301 is lower than the reference voltage V1 of the first reference voltage source 303, as shown in FIG. It gets lower. Furthermore, in conjunction with the change in the first voltage absolute value, after time t1, the second voltage absolute value output by the second absolute value circuit 310 is the second voltage latched by the voltage latch circuit 313. lower than the absolute value.

The above series of operations is executed each time the output current of the first power amplifier circuit 20 reaches the output current limit value IL at time t1.

FIG. 3 is a diagram for explaining a power amplifier circuit D3 having a limiter circuit 8 according to a comparative example. FIG. 4 is a diagram showing an example of the current limiter circuit 9 included in the power amplifier circuit D3 shown in FIG.

Further, FIG. 5 is a diagram for explaining the operation of the limiter circuit 8 when a heavy load 6 (for example, a low resistance such as 2Ω) is connected. That is, FIG. 5A shows the voltage waveform at the input node 3 (input voltage waveform) and the voltage waveform at the output node 5 (output voltage waveform) with a solid line and a broken line, respectively. FIG. 5(b) shows the current waveform of the output current of the second power amplifier circuit 22. FIG. 5C shows the reference voltage V3 of the third reference voltage source 803 and the voltage waveform at the node 805. FIG. 5(d) shows the voltage waveform at node 811.

As shown in FIG. 3, the voltage supplied to the second power amplification circuit 22 is input by the third absolute value circuit 801 to one terminal of the comparator 807 as a voltage absolute value. Further, the reference voltage V3 of the third reference voltage source 803 is input to the other terminal of the comparator 807. When the third voltage absolute value from the third absolute value circuit 801 is larger than the reference voltage V3, the comparator 807 controls the first voltage control circuit 103 as shown in FIG. 5(d). A signal is output to node 811. The first voltage control circuit 103 attenuates the input voltage signal and outputs it to the first node 102, thereby increasing the voltage output from the third absolute value circuit 801 as shown in FIG. 5(c). Control is performed so that the absolute value (voltage at node 805) does not become larger than reference voltage V3.

When using the limiter circuit 8 according to such a comparative example, the reference voltage as the threshold of the voltage limiter is set based on the current flowing through the heaviest load expected in use (for example, in the case of low resistance such as 2Ω). Set V3. However, when such a setting is made, if a load lighter than the load based on the setting (for example, a high resistance such as 16Ω) is connected to the power amplifier circuit D3, the voltage is controlled more than necessary and the output is Power is sacrificed.

Further, the current limiter circuit 9 shown in FIG. 4 is provided, for example, in a power amplifier circuit, and includes an input circuit 901, an output transistor 902, a base control transistor 903, an output current sense resistor 904, and an output node 905. In response to a control signal supplied via input circuit 901, output transistor 902 operates and output current flows. When the output current flows and the voltage generated at the output current sense resistor 904 reaches, for example, 0.7 V or more, the base control transistor 903 controls the base-emitter voltage of the output transistor 902, thereby limiting the output current. .

Since the current limiter circuit 9 does not use the attenuator circuit 10, the audio signal during the current limiter operation has a clipped waveform as shown in FIGS. 5(a) and 5(b), and the audio characteristics are significantly deteriorated.

For example, in the limiter circuit 8 shown in FIG. 3, the node monitored in the third absolute value circuit 801 is configured to monitor the output current or a signal obtained by IV conversion of the output current instead of the output voltage (using an attenuator). A current limiter configuration (current limiter configuration) is also envisioned. However, the output current waveform is affected by the load impedance and the time constant of the output LC filter. Therefore, it is extremely difficult to realize a circuit that can obtain a stable limit value due to the difference between the transient response of the limiter and the transient response of the output current.

In contrast, the limiter circuit according to the embodiment includes an attenuator circuit 10 and an attenuator control circuit 30. The attenuator circuit 10 attenuates the voltage supplied to the first power amplifier circuit 20. The attenuator control circuit 30 generates a first reference voltage value based on the output current when the output current of the first power amplifier circuit 20 reaches the reference current value, and generates a first reference voltage value based on the first reference voltage value. Controls the attenuator circuit 10.

More specifically, the attenuator control circuit 30 includes a first absolute value circuit 301, a first comparator 306, a second absolute value circuit 310, a voltage latch circuit 313, and a second comparator 315. The first absolute value circuit 301 converts the output current of the first power amplifier circuit 20 into a voltage and outputs a first voltage absolute value. The first comparator 306 compares the first absolute voltage value and the second reference voltage value. The second absolute value circuit 310 outputs a second absolute voltage value based on the voltage supplied to the power amplifier circuit. The voltage latch circuit 313 latches the second absolute voltage value in response to the output signal of the first comparator 306 and outputs the first reference voltage value. The second comparator 315 compares the second absolute voltage value and the first reference voltage value from the voltage latch circuit 313. The attenuator circuit 10 responds to the output signal of the second comparator 315 to attenuate the voltage supplied to the first power amplifier circuit 20 .

Therefore, the output current of the first power amplifier circuit 20 reaching the output current limit value IL is used as a trigger, and the first reference voltage value is set based on the output current of the first power amplifier circuit 20 at the time of current detection. is generated, and the attenuator circuit 10 can be controlled based on this. More specifically, the attenuator control circuit 30 compares a first voltage absolute value obtained by converting the output current of the first power amplifier circuit 20 into a voltage with a second reference voltage value, and The voltage supplied to the power amplifier circuit that is latched at the timing when the absolute voltage value exceeds the second reference voltage value can be set as the first reference voltage value.

The attenuator circuit 10 controls the first power amplifier circuit based on the first reference voltage value (output voltage limit value) generated at the timing when the output current at the time of current detection exceeds the reference value (output current limit value). The voltage supplied to 20 can be attenuated, and the output current can be stably controlled. In other words, since there is no need to directly monitor the output current or a signal obtained by IV conversion of the output current, the output current limiter operates stably even if a speaker or filter with an impedance having a complicated time constant is connected. Furthermore, since the path from the input of the amplifier circuit to the load is the same as that of the voltage limiter, audio deterioration during limiter operation can be minimized.

As a result, regardless of the load impedance or the time constant of the output LC filter, reproduction is possible without excessively deteriorating the sound quality even when the overcurrent limiter is operating.

(Second embodiment)
Next, the limiter circuit 7 according to the second embodiment will be explained.

FIG. 6 is a diagram showing the configuration of a power amplifier circuit D2 having a limiter circuit 7 according to the second embodiment. As shown in FIG. 6, the power amplifier circuit D2 includes a limiter circuit 7 and a first power amplifier circuit 20. The limiter circuit 7 includes an attenuator circuit 10, a current detection circuit 21, and an attenuator control circuit 30. Hereinafter, a different configuration from the attenuator control circuit 30 described in the first embodiment will be described.

The attenuator control circuit 30 includes a first absolute value circuit 301, a first reference voltage source 303, a second node 305, a first comparator 306, a third node 307, a fourth node 311, a second absolute value circuit It includes a value circuit 310, a second reference voltage source 312, a voltage latch circuit 313, an analog switch 314, a second comparator 315, a seventh node 318, a capacitor 319, and a sixth node 320.

The first comparator 306 outputs a high level signal when the first voltage absolute value output from the first absolute value circuit 301 becomes larger than the reference voltage V1. The high level signal output from the first comparator 306 is output to the voltage latch circuit 313 and analog switch 314 via the third node 307.

The second reference voltage source 312 supplies the reference voltage V2 (an example of the third reference voltage value) to the other input terminal of the second comparator 315 via the seventh node 318.

The voltage latch circuit 313 latches the second voltage absolute value output by the second absolute value circuit 310 in response to the output signal of the first comparator 306. The voltage latch circuit 313 outputs the latched second voltage absolute value to the other input terminal of the second comparator 315 via the seventh node 318 as the first reference voltage value.

Analog switch 314 controls the connection of seventh node 318 in response to the output signal of first comparator 306 . Specifically, analog switch 314 connects seventh node 318 and voltage latch circuit 313 in response to a high level signal from first comparator 306 . Further, the analog switch 314 connects the seventh node 318 and the second reference voltage source 312 when the first comparator 306 does not output a high level signal. For example, when the load 6 is light and the output current of the first power amplifier circuit 20 does not reach the target output current limit value, the analog switch 314 causes the seventh node 318 to connect to the second reference voltage source 312. Connected.

Here, by setting the reference voltage V2 (third reference voltage value) to a target output voltage limit value, control equivalent to that of a normal voltage limiter can be realized.

The second comparator 315 compares the second absolute voltage value from the second absolute value circuit 310 and the first reference voltage value from the voltage latch circuit 313 . The second comparator 315 outputs a high level signal when the second voltage absolute value from the second absolute value circuit 310 becomes larger than the first reference voltage value from the voltage latch circuit 313. The high level signal output from the second comparator 315 is subjected to phase control by the capacitor 319 and output to the first voltage control circuit 103 of the attenuator circuit 10 via the sixth node 320.

Further, the second comparator 315 compares the second voltage absolute value from the second absolute value circuit 310 and the reference voltage V2 from the second reference voltage source 312. The second comparator 315 outputs a high level signal when the second voltage absolute value from the second absolute value circuit 310 becomes larger than the reference voltage V2 from the second reference voltage source 312. The high level signal output from the second comparator 315 is subjected to phase control by the capacitor 319 and output to the first voltage control circuit 103 of the attenuator circuit 10 via the sixth node 320.

The first voltage control circuit 103 controls the resistance value of the voltage control resistor in response to the high level signal output from the second comparator 315, and attenuates the input voltage signal.

That is, when the second voltage absolute value outputted from the second absolute value circuit 310 is larger than the first reference voltage value outputted from the voltage latch circuit 313, the first voltage control circuit 103 controls the second voltage control circuit 103 to The first voltage control circuit 103 is controlled by the control signal from the comparator 315. Furthermore, when the second voltage absolute value output from the second absolute value circuit 310 is larger than the reference voltage V2 from the second reference voltage source 312, the first voltage control circuit 103 controls the second comparator. The first voltage control circuit 103 is controlled by a control signal from 315.

FIG. 7 is a diagram for explaining the operation of the limiter circuit 7 when a light load 6 (for example, a high resistance such as 16Ω) is connected. That is, in FIG. 7A, the voltage waveform at input node 3 (input voltage waveform) and the voltage waveform at output node 5 (output voltage waveform) are shown by solid lines and broken lines, respectively. FIG. 7(b) shows the current waveform of the output current Iout of the first power amplifier circuit 20. FIG. 7C shows the reference voltage V1 (second reference voltage value) of the first reference voltage source 303 and the voltage waveform (waveform of the first voltage absolute value) at the second node 305. There is. FIG. 7(d) shows the voltage waveform at the seventh node 318 (latched second voltage absolute value or reference voltage V2) and the voltage waveform at the fourth node 311 (waveform of the second voltage absolute value). It shows. FIG. 7E shows the voltage waveform at the sixth node 320 (the output waveform of the second comparator 315).

As shown in FIG. 7(b), the output current of the first power amplifier circuit 20 has not reached the output current limit value IL at time t1. Therefore, as shown in FIG. 7C, the voltage at the second node 305 does not reach the reference voltage V1 (second reference voltage value) of the first reference voltage source 303.

On the other hand, as shown in FIG. 7(d), when the voltage at the fourth node 311 becomes larger than the voltage at the seventh node 318, the second comparator 315 at time t1 as shown in FIG. 7(e). The voltage at the sixth node 320 increases due to the output signal from the . The first voltage control circuit 103 operates in response to the output signal from the second comparator 315 to attenuate the input voltage.

In conjunction with the operation of the first voltage control circuit 103, the output voltage waveform becomes a waveform attenuated compared to the input voltage waveform after time t1, as shown in FIG. 7(a).

The series of operations described above is executed each time the voltage input to the first power amplifier circuit 20 reaches the reference voltage V2 (third reference voltage value) from the second reference voltage source 312. Further, when a heavy load 6 is connected, the limiter circuit 7 can perform the same operation as the limiter circuit 1 described in the first embodiment.

As described above, in the limiter circuit 7 according to the present embodiment, when the first voltage absolute value is smaller than the first reference voltage value (for example, when the light load 6 is (when connected to circuit D2), the second absolute voltage value and the third reference voltage value V3 are compared. Further, when the first voltage absolute value is larger than the first reference voltage value (for example, when the heavy load 6 is connected to the power amplifier circuit D2), the second comparator 315 controls the second comparator 315 to The voltage absolute value and the first reference voltage value from the first voltage latch circuit are compared. Therefore, according to the limiter circuit 7 according to the present embodiment, reproduction is possible without excessively deteriorating sound quality even during overcurrent limiter operation, regardless of the load impedance or the time constant of the output LC filter.

Although the embodiments of the present invention have been described above, the above embodiments are presented as examples and are not intended to limit the scope of the invention. The novel embodiment described above can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments are included within the scope and gist of the invention, and are included within the scope of the invention described in the claims and its equivalents.

1, 7 Limiter circuit 3 Input node 4 Filter 5 Output node 6 Load (speaker)
10 Attenuator circuit 20 First power amplifier circuit 30 Attenuator control circuit 101 First resistor 102 First node 103 First voltage control circuit 301 First absolute value circuit 303 First reference voltage source 305 Second node 306 first comparator 307 third node 310 second absolute value circuit 311 fourth node 313 voltage latch circuit 315 second comparator 317 fifth node 318 seventh node 319 capacitor 320 sixth node D1, D2 power amplifier circuit

Claims (2)

an attenuator circuit that attenuates the voltage supplied to the power amplifier circuit;
Attenuator control that generates a first reference voltage value based on the output current when the output current of the power amplifier circuit reaches a reference current value, and controls the attenuator circuit based on the first reference voltage value. comprising a circuit ;
The attenuator control circuit includes:
a first absolute value circuit that converts the output current of the power amplifier circuit into a voltage and outputs a first voltage absolute value;
a first comparator that compares the first voltage absolute value and a second reference voltage value;
a second absolute value circuit that outputs a second voltage absolute value based on the voltage supplied to the power amplifier circuit;
a first voltage latch circuit that latches the second voltage absolute value and outputs the first reference voltage value in response to the output signal of the first comparator;
a second comparator that compares the second voltage absolute value and the first reference voltage value from the first voltage latch circuit;
The attenuator circuit attenuates the voltage supplied to the power amplifier circuit in response to the output signal of the second comparator.
limiter circuit. When the first voltage absolute value is smaller than the second reference voltage value, the second comparator compares the second voltage absolute value and a third reference voltage value, and If the voltage absolute value of is larger than the second reference voltage value, comparing the second voltage absolute value and the first reference voltage value from the first voltage latch circuit;
The limiter circuit according to claim 1 .

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