WO2018133565A1

WO2018133565A1 - Gain control device

Info

Publication number: WO2018133565A1
Application number: PCT/CN2017/114585
Authority: WO
Inventors: 林其亮; 吴顺达
Original assignee: 深圳市中移联半导体科技有限公司
Priority date: 2017-01-20
Filing date: 2017-12-05
Publication date: 2018-07-26
Also published as: CN106656085B; CN106656085A

Abstract

The invention provides a gain control device comprising a pre-amplifier circuit, a voltage control circuit, a modulation circuit, an amplitude detection circuit, a zero-crossing circuit, a clip protection and amplitude detection circuit, and a gain control circuit. The pre-amplifier circuit, the voltage control circuit, and the modulation circuit are sequentially connected to each other. The voltage control circuit is connected to the gain control circuit via the amplitude detection circuit and the zero-crossing circuit, respectively. The modulation circuit is connected to the gain control circuit via the clip protection and amplitude detection circuit. The gain control device provided in the invention is utilized to provide favorable audio quality while providing protection for a speaker effectively, preventing the speaker from being damaged as a result of exceeding maximum power.

Description

Gain control device

Technical field

The present invention relates to the field of electronic circuit technologies, and in particular, to a gain control device.

Background technique

The audio amplifier is a power amplifier that amplifies the audio signal to drive the speaker for sound amplification. In the audio processing process, in order to enhance the effect of music playback and increase the loudness of music playback, it is usually necessary to perform automatic gain control on the input audio signal to adjust the signal amplitude of the input audio signal, attenuate the large value signal, and amplify the small amplitude. The value signal ensures the smoothness of the signal amplitude. Most current audio power amplifiers have automatic gain control (AGC). AGC is an automatic control method that automatically adjusts the gain of the amplifier circuit with the signal strength. The function of the AGC automatic gain control circuit is to automatically keep the amplitude of the output signal within a small range when the input signal amplitude varies greatly. An automatic control circuit.

The gain control method in the prior art can maintain the output power at a set power threshold when detecting that the output power of the amplifier is greater than a predetermined power threshold. However, the existing gain control method is easy to cause distortion when controlling the gain, affecting the audio playback effect; and when detecting that the output signal of the amplifier is greater than a predetermined preset threshold, although the output signal can be automatically reduced, the signal output value in the process is already Exceeding the maximum power value of the speaker can easily cause damage to the speaker.

A patent control file with the publication number CN104485909A provides a gain control method And the device uses multiple sets of AGC control circuits to judge the output of the amplifier, and performs different time gain control for different output sizes, which can improve the playing effect of the music file and enhance the user experience. However, when the output exceeds the first preset threshold (such as the maximum power of the speaker), the gain will drop rapidly, but the signal output has already exceeded the maximum power value of the speaker, or the speaker is damaged. At the same time, since the D-type audio amplifier judges whether the output is cut off from the integrator output judgment, and judges that the different output power is judged from the output of the first-stage adjustable gain amplifier, the positions determined by the two mechanisms are different, so it is not suitable. Used on Class D audio amplifiers.

The patent document disclosed in CN104767498A provides a gain control method and apparatus that uses zero-crossing detection to avoid adjusting the gain of the amplifier at the peak of the output signal, thereby improving the music playback effect. However, when there are multiple sets of AGC control circuits, it is not possible to choose whether or not zero-crossing detection is required to change the gain. If there is a low-frequency music signal input, when the output signal exceeds the maximum power limit of the speaker, the gain must be reduced quickly and in time. If the gain must be changed after the zero-crossing detection, the speaker may be damaged. In addition, the second detection circuit of the zero-crossing detection circuit uses the high threshold and the low threshold level to determine the output signal, that is, the output signal does not send the zero-cross detection signal at the lowest point, so the change of the gain will still result. A certain noise, affecting the playback effect.

Summary of the invention

In view of the above problems, the purpose of the present invention is to design a gain control device that can maintain good sound quality while effectively protecting the speaker and preventing the speaker from being damaged beyond the maximum power.

The specific technical solution of the present invention is as follows:

A gain control device comprising a pre-stage gain amplifier, a voltage control circuit, a modulation circuit, an amplitude detection circuit, a zero-crossing detection circuit, an anti-cracking amplitude detection circuit and a gain control circuit, the pre-stage gain amplifier and the voltage control circuit And the modulation circuit is sequentially connected, the voltage control circuit is respectively connected to the gain control circuit by the amplitude detection circuit and the zero-cross detection circuit, and the modulation circuit is connected to the gain control by the anti-cutting amplitude detection circuit Circuit; among them,

The voltage control circuit is configured to detect and control an output signal of the pre-stage gain amplifier;

The amplitude detecting circuit is configured to receive an output signal of the voltage control circuit and compare it with a preset threshold, and output a corresponding gain signal;

The zero-crossing detection circuit is configured to determine whether an output signal of the voltage control circuit crosses a zero point, and output a corresponding gain signal to the gain control circuit at a zero-crossing point;

The anti-cutting amplitude detecting circuit is configured to detect whether an output signal of the modulation circuit is topped, and output a corresponding gain signal to the gain control circuit when a topping occurs;

The gain control circuit is configured to determine, according to the gain signals output by the amplitude detecting circuit, the zero-crossing detecting circuit and the anti-cutting amplitude detecting circuit, whether gain control is required, and when the gain control is required, the pre-stage gain amplifier The gain is controlled.

Specifically, the gain control device of the present invention is applicable to a class D audio amplifier.

Specifically, the amplitude detecting circuit of the present invention includes N amplitude detecting circuits, N≥1.

Specifically, the gain control circuit of the present invention further includes: receiving the frame separately The gain signal output by the degree detection circuit, the zero-crossing detection circuit, and the anti-cutting amplitude detection circuit, and whether or not the zero-crossing point is required is the gain control.

Specifically, the voltage control circuit of the present invention includes: a first comparator, a first control switch, a second comparator, and a second control switch;

The input end of the first comparator is respectively connected to the output signal of the pre-stage gain amplifier and the first reference voltage, and the output end of the first comparator is connected to the first control switch;

The input end of the second comparator is respectively connected to the output signal of the pre-stage gain amplifier and the second reference voltage, and the output end of the second comparator is connected to the second control switch.

Specifically, the zero-crossing detection circuit of the present invention includes: a third comparator, a first delay circuit, a second delay circuit, and an exclusive OR gate, wherein the input ends of the third comparator are respectively connected to the output of the voltage control circuit a signal, the output of the third comparator is connected to the first delay circuit through the non-gate, and the other is directly connected to the second delay circuit, and the outputs of the first delay circuit and the second delay circuit are respectively connected to the XOR gate Two inputs.

The gain control device provided by the present invention has the following advantages compared with the prior art:

(1) The speaker can be effectively protected by the voltage control circuit to prevent the speaker from being damaged beyond the maximum power;

(2) The proposed multi-group AGC gain control function, combined with zero-crossing detection and anti-cutting detection, can completely judge the output signal to further judge how the gain changes, and can effectively protect the speaker while maintaining good performance. Sound quality

(3) The zero-crossing detection circuit can change the gain at the minimum signal, avoiding the noise when the gain changes, and can maintain good sound quality.

DRAWINGS

The embodiments of the present invention are further described below with reference to the accompanying drawings, wherein:

Figure 1 is a circuit diagram of the present invention;

Figure 2 is a circuit diagram of Embodiment 1 of the present invention;

Figure 3 is a diagram showing the relationship between the signal and the gain of the amplifier of the present invention;

Figure 4 is a circuit diagram of a voltage control circuit of the present invention;

Figure 5 is a circuit diagram of the amplitude detecting circuit of the present invention;

6 is a schematic diagram of input and output of the amplitude detecting circuit of the present invention;

Figure 7 is a circuit diagram of the zero-crossing detecting circuit of the present invention;

Figure 8 is a schematic diagram showing the input and output of the zero-crossing detection circuit of the present invention.

detailed description

The invention will be further described in detail below with reference to the drawings and specific embodiments.

The invention provides a gain control device, please refer to FIG. 1 , which includes a pre-stage gain amplifier, a voltage control circuit, a modulation circuit, an amplitude detection circuit, a zero-crossing detection circuit, an anti-cutting amplitude detection circuit and a gain control circuit. The pre-stage gain amplifier, the voltage control circuit and the modulation circuit are sequentially connected, and the voltage control circuit is respectively connected to the gain control circuit through the amplitude detection circuit and the zero-cross detection circuit, and the modulation circuit passes the anti-cutting A top amplitude detecting circuit is coupled to the gain control circuit. among them,

The voltage control circuit is configured to detect and control an output of the pre-stage gain amplifier signal;

The gain control device provided by the invention can effectively protect the speaker and prevent the speaker from being damaged. In the first stage preamplifier amplifier output, plus the voltage control circuit, the set voltage control point is the maximum power P _MAX of the load speaker. When the output voltage of the amplifier exceeds the maximum power of the speaker, it is limited by the voltage control circuit to the maximum voltage point, and the voltage is not exceeded. At the same time, the amplitude detection circuit detects the output of the voltage control circuit and outputs a signal of the gain reduction to the gain control. The circuit quickly reduces the gain.

Specifically, the gain control circuit of the present invention further comprises: respectively receiving the gain signals output by the amplitude detecting circuit, the zero-crossing detecting circuit and the anti-cutting amplitude detecting circuit, and determining whether a zero-crossing point is required to perform gain control. The zero-crossing detection of the present invention determines whether it is necessary to reduce the gain when the signal crosses zero via the gain control circuit. If the output signal has exceeded P _MAX or the voltage output signal is topped, there is no need to wait for a zero crossing signal, and the gain control circuit will immediately reduce the gain as quickly as possible. Especially when the input is a low frequency signal, if you want to wait for the zero-crossing signal to reduce the gain, the speaker will be in a high voltage condition for a long time, which is easy to cause damage. And if the output is cut-off distortion, and the gain is not quickly lowered, the sound quality is impaired. The invention makes the detection point closer to zero, avoids changing the gain at a position where the signal is high, and causes noise.

Specifically, the gain control device of the present invention is applicable to a class D audio amplifier, and the modulation circuit uses a class D modulation circuit. Please refer to FIG. 2 for a circuit diagram of the first embodiment.

The amplitude detecting circuit can have many groups, and the amplitude detecting circuit includes N amplitude detecting circuits, N≥1. The speed of the gain reduction can be adjusted according to the power limit range of the speaker to increase the dynamic range of the sound.

Please refer to FIG. 3 for the relationship between the amplifier signal and the gain. In this embodiment, three amplitude detection circuits are provided, which are maximum power P _MAX , buffer power P _MED , and rated power P _RMS . Speaker power must not exceed P _MAX or it will be damaged. The speaker power can be operated for a long time under P _RMS , and between P _MAX and P _RMS can be properly adjusted to allow the sound to stay in this power range for a short time, which can increase the dynamic range of the sound. That this added power P _MED determination, P _MED is approximately 1.2 times the P _RMS, power is P _RMS buffer, a plurality set of power control determines the time, allowing richer loudness.

Referring to area A in Figure 3, when the sound suddenly becomes larger and exceeds P _MAX , the voltage control circuit limits the output voltage to the control voltage point, preventing the speaker from being damaged, and the gain control circuit controls the gain to drop rapidly (eg 0.16ms/dB), lowering the signal below P _MAX . Or other cases, when the amplifier power supply voltage is low, the output is subject to clipping distortion when it is not yet connected to P _MAX . At this time, the gain control circuit also controls the gain to drop rapidly (such as 0.16ms/dB) to make the sound signal No distortion, avoiding unpleasant sounds.

Referring to area B in Figure 3, when the output is between P _MAX and P _MED , the gain will drop at a medium speed (such as 0.64ms/dB), allowing a brief high volume output. In area C of Figure 3, when the output is between P _MED and P _RMS , the control gain is slowly reduced (eg 21ms/dB) to allow for a brief high volume output. In area D in Figure 3, the gain is maintained when the output is between P _RMS and P _HYS . In the area E, F, and G in Figure 3, when the input signal becomes smaller, the gain will be maintained for 10ms first, and the gain will be slowly restored (such as 41ms/dB) until the initial value of the gain is restored, or the output is between P _RMS and P. _HYS will stop.

Specifically, please refer to FIG. 4 , which is a circuit diagram of a voltage control circuit. The voltage control circuit in this embodiment includes a first comparator OP_H, a first control switch MP_H, a second comparator OP_L, and a second control switch MP_L. An input end of the first comparator is respectively connected to an output signal of the pre-stage gain amplifier and a first reference voltage, and an output end of the first comparator is connected to the first control switch; and an input end of the second comparator is respectively connected to the pre-stage An output signal of the gain amplifier and a second reference voltage, and an output of the second comparator is connected to the second control switch.

The purpose of the voltage control circuit is to prevent the speaker from being damaged by preventing the output power from exceeding the maximum power P _{MAX of the} speaker. The working principle is to detect the relationship between the output signals VOP and VON of the pre-stage gain amplifier and the reference voltages Vref_H and Vref_L. When the VOP or VON exceeds the upper limit Vref_H or lower than the lower limit Vref_L, the comparator OP_H or OP_L circuit is respectively controlled to control. The first control switch MP_H or the second control switch MP_L is switched to limit the signal output by the gain amplifier to a voltage limiting VOP and VON.

Specifically, please refer to FIG. 5 is a circuit diagram of the amplitude detecting circuit. Comparing the output signals VOP and VON of the voltage control circuit with Vref _RMS and Vref _HYS respectively, the ATT _RMS and RLS _RMS signals can be obtained, and then sent to the gain control circuit for gain. control.

Please refer to FIG. 6 , which is a schematic diagram of the input and output of the amplitude detecting circuit. When the ATT _RMS is high, the gain control circuit is ready to reduce the gain, and when the RLS _RMS is high, the gain control circuit is ready to increase the gain. The difference between Vref _RMS and Vref _HYS must exceed the gain reduction of 1 bit, otherwise there will be a problem that the gain jumps up and down. The purpose of the delay circuit is to prevent the circuit from being disturbed and causing malfunction. The delay time can be several microseconds. Other different magnitude decisions can be made with the same amplitude detection circuit architecture.

The anti-shaving amplitude detection circuit is similar to the amplitude detection circuit. Referring to Figure 5, the reference voltage is the upper limit of the triangular wave. The PWM generator in the D-type modulator compares the VOP1 and VON1 output from the integrator with the triangular wave to obtain a PWM signal. When the output signal has a clipping condition, that is, when the duty of OUTP and OUTN reaches 100% or 0%, the output signals of the integrator (VOP1 and VON1) will exceed the amplitude range of the triangular wave, so by judging whether the integrator output is Exceeding the upper limit of the triangle wave can detect whether the amplifier output has been topped. When topping occurs, the amplifier will quickly reduce the gain and avoid the distortion of the sound.

Specifically, please refer to FIG. 7 is a circuit diagram of the zero-crossing detection circuit. The zero-crossing detection circuit includes: a third comparator, a first delay circuit, a second delay circuit, and an exclusive OR gate, wherein an input end of the third comparator is respectively connected to an output signal of the voltage control circuit, and a third comparison The output end of the device is connected to the first delay circuit through a non-gate, and the other circuit is directly connected to the second delay circuit. The outputs of the first delay circuit and the second delay circuit are respectively connected to the two input ends of the XOR gate. Comparing the output signal of the voltage control circuit with a third comparator The VOP and VON signals are processed by a delay circuit and an exclusive OR gate to obtain a pulse signal whose width is determined by the delay circuit.

Please refer to Figure 8 for the input and output of the zero-crossing detection circuit. When the input signal suddenly stops, VOP and VON will not be able to cross, and the comparator will not be able to change. At this time, the pulse detection circuit will detect whether there is no pulse signal sent over a period of time. If the pulse signal of the last time has exceeded 50ms and no next pulse wave has been sent, the pulse wave detection circuit will forcibly send a pulse signal, so that the gain control circuit can smoothly control the gain. The pulse wave sent by this root is sent without input signal, so the gain change will be when the signal is the smallest, so changing the gain at this time will not produce noise.

Specifically, the gain control circuit respectively receives signals from the amplitude detecting circuit, the anti-cutting amplitude detecting circuit and the zero detecting circuit, determines whether it is necessary to reduce the gain or restore the gain, and at what speed the gain is reduced, and whether the zero crossing is required Gain, etc., to control the gain of the preamplifier.

The specific embodiments of the invention described above are not intended to limit the scope of the invention. Any other various changes and modifications made in accordance with the technical idea of the present invention are intended to be included within the scope of the appended claims.

Claims

A gain control device, comprising: a pre-stage gain amplifier, a voltage control circuit, a modulation circuit, an amplitude detecting circuit, a zero-crossing detecting circuit, an anti-cutting amplitude detecting circuit and a gain control circuit, the pre-stage gain amplifier The voltage control circuit and the modulation circuit are sequentially connected, and the voltage control circuit is respectively connected to the gain control circuit through the amplitude detection circuit and the zero-cross detection circuit, and the modulation circuit is connected by the anti-cutting amplitude detection circuit. The gain control circuit; wherein

The voltage control circuit is configured to detect and control an output signal of the pre-stage gain amplifier;

The amplitude detecting circuit is configured to receive an output signal of the voltage control circuit and compare it with a preset threshold, and output a corresponding gain signal;

The zero-crossing detection circuit is configured to determine whether an output signal of the voltage control circuit crosses a zero point, and output a corresponding gain signal to the gain control circuit at a zero-crossing point;

The anti-cutting amplitude detecting circuit is configured to detect whether an output signal of the modulation circuit is topped, and output a corresponding gain signal to the gain control circuit when a topping occurs;

The gain control circuit is configured to determine, according to the gain signals output by the amplitude detecting circuit, the zero-crossing detecting circuit and the anti-cutting amplitude detecting circuit, whether gain control is required, and when the gain control is required, the pre-stage gain amplifier The gain is controlled.
The gain control apparatus according to claim 1, wherein said gain control means is applied to a class D audio amplifier.
The gain control apparatus according to claim 1, wherein said amplitude detecting circuit comprises N amplitude detecting circuits, N ?
The gain control device according to claim 1, wherein the gain control circuit further comprises: respectively receiving gain signals output by the amplitude detecting circuit, the zero-crossing detecting circuit, and the anti-cutting amplitude detecting circuit, and determining whether Gain control is required when zero crossing is required.
The gain control device according to claim 1, wherein the voltage control circuit comprises: a first comparator, a first control switch, a second comparator, and a second control switch;

The input end of the first comparator is respectively connected to the output signal of the pre-stage gain amplifier and the first reference voltage, and the output end of the first comparator is connected to the first control switch;

The input end of the second comparator is respectively connected to the output signal of the pre-stage gain amplifier and the second reference voltage, and the output end of the second comparator is connected to the second control switch.
The gain control apparatus according to claim 1, wherein said zero-crossing detecting circuit comprises: a third comparator, a first delay circuit, a second delay circuit, and an exclusive OR gate, the input of said third comparator The terminals respectively connect the output signals of the voltage control circuit, the output of the third comparator is connected to the first delay circuit through the non-gate, and the other is directly connected to the second delay circuit, the first delay circuit and the second delay circuit The output ends are respectively connected to the two input ends of the XOR gate.