A dc detection circuit and method for class d audio power amplifier

Abstract

The application discloses a DC detection circuit and method for a CLASSD audio power amplifier. A duty cycle difference detection module detects the duty cycle difference of a signal in a CLASSD loop, and outputs a high-level signal to a logic processing module when the duty cycle difference exceeds a limit, and is used for starting an audio signal modulation module. The audio signal modulation module is connected with a signal and realizes direct-current energy accumulation, and outputs a high-level signal to the logic processing module when a set threshold voltage VT is reached. A dynamic self-adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal, and outputs a high-level DC_DETECT signal when the logic processing module simultaneously detects the high-level signal, so as to trigger a direct-current protection action and realize chip shutdown. The DC fault problem is solved, the output audio load is protected, and the user experience is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit design, and particularly relates to a DC detection circuit and method for a CLASSD audio power amplifier. BACKGROUND

[0002] The CLASSD audio power amplifier is applied to the scenes of vehicle-mounted sound, intelligent sound box, TWS earphone and the like. The Class D power amplifier drives a loudspeaker through PWM modulation, and if a direct current voltage appears at an output end (for example, the duty cycle is unbalanced due to chip damage), the loudspeaker coil will be overheated and burned out, and the audio system will be permanently damaged. Therefore, the DC detection circuit of the CLASSD audio power amplifier is suitable for a direct current (DC) fault detection and protection system of the Class D power amplifier chip. The DC detection scheme needs to be balanced between reliability (avoiding false triggering) and response speed (fast protection), especially in a complex environment (for example, vehicle-mounted temperature change and plug-in interference).

[0003] The traditional technical scheme has three defects: 1) the response time of the circuit is in a fixed response time form due to the existing circuit structure design, and cannot quickly respond to a DC fault. The circuit cannot respond to a sudden DC fault (for example, a transient short circuit of a chip) and must wait until the time set by a timer is completed; 2) the risk of false judgment is high: a continuous low-frequency signal (for example, 20Hz music) can cause a temporary overrun of a duty cycle difference value, and false triggering of protection; a power plug-in surge, radio frequency noise and the like can cause false triggering of DC detection; 3) the fixed threshold value has no environmental adaptability: the fixed threshold value and fixed delay time cannot adapt to temperature / load changes; the traditional scheme adopts a fixed duty cycle difference threshold value (for example, ±14%), but in actual application, the impedance of a loudspeaker changes with temperature / frequency (for example, the impedance of a vehicle-mounted sound drops sharply when starting at low temperature), and the fixed threshold value can cause: low-temperature leakage (when the load impedance decreases, the same DC offset is more harmful to the loudspeaker); false reporting at high temperature, for example, the same duty cycle offset actually outputs a lower voltage when the internal resistance of a chip increases at high temperature.

[0004] Corresponding technical problems to be solved in the field include: 1) how to shorten the response time and improve the adaptability to complex environments while retaining the reliability of the timing confirmation mechanism; 2) how to distinguish between transient interference and real DC faults, and avoid the system from entering an unnecessary protection waiting period and affecting user experience; 3) how to dynamically adapt to the load and temperature changes of the CLASS D system, and avoid high-temperature leakage and low-temperature false reporting. SUMMARY

[0005] The present application aims to provide a DC detection circuit for a CLASSD audio power amplifier, solve the problem of DC faults, protect the output audio load, and improve user experience.

[0006] To realize the above technical purposes, the application provides a DC detection circuit for a CLASSD audio power amplifier, which comprises a duty cycle difference detection module, an audio signal modulation module, a dynamic adaptive threshold adjustment module and a logic processing module; the duty cycle difference detection module detects the duty cycle difference of PWMN signal and PWMP signal in the CLASSD loop, and outputs a high level DETECT1 signal to the logic processing module when the duty cycle difference exceeds the limit, while the audio signal modulation module is started; the audio signal modulation module is connected with OUTP signal and OUTN signal and realizes direct current energy accumulation, and outputs a high level DETECT2 signal to the logic processing module when the set threshold voltage VT is reached; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal; when the logic processing module detects the high level DETECT1 signal and the high level DETECT2 signal at the same time, a high level DC_DETECT signal is outputted, triggering the direct current protection action, and the chip is shut down.

[0007] The application provides a DC detection circuit for a CLASSD audio power amplifier, which introduces multi-dimensional decision-making and dynamic adaptive design, solves the DC fault problem, protects the output audio load and improves user experience.

[0008] As a further improvement, the audio signal modulation module is composed of a demodulator, an integrator and a comparator, the demodulator and the integrator realize the process of direct current energy accumulation, and the audio signal modulation module outputs the high level DETECT2 signal when the output voltage of the integrator exceeds the threshold voltage VT; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the comparator in the audio signal modulation module by detecting a temperature signal TEMP, and lowers the threshold voltage VT when the temperature rises, and raises the threshold voltage VT when the temperature falls, and the dynamic adaptive threshold adjustment module also outputs a gain control signal Gain_control to the audio signal modulation module.

[0009] As a further improvement, it comprises: a first stage circuit STAGE1 as a demodulator to restore the sinusoidal audio signal in a single channel into a direct current VP voltage and a direct current VN voltage; a second stage circuit STAGE2 as an input gating module to be controlled by the high level DETECT1 signal and output a signal VM voltage with higher voltage from the direct current VP voltage and the direct current VN voltage; a third stage circuit STAGE3 as an integral comparison module to use the signal VM voltage as an input signal to form an integral voltage VX by integration and select to output the high level DETECT2 signal after comparison with the threshold voltage VT; a fourth stage circuit STAGE4 as the duty cycle difference detection module; a fifth stage circuit STAGE5 as a temperature sampling module to obtain an amplified temperature sampling signal VC voltage; a sixth stage circuit STAGE6 as a threshold voltage adjustment module, the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through a voltage follower; the relationship between the threshold voltage VT and temperature T is: wherein: VT0 is a reference threshold, is a negative temperature coefficient, and T0 is a reference temperature.

[0010] As a further improvement, the demodulator comprises first and second resistors R1, R2 connected to first and second buffers BUFFER1, BUFFER2 respectively, and first and second capacitors C1, C2 with one end grounded and the other end connected to the first and second buffers BUFFER1, BUFFER2 respectively, the generated VLP signal and VLN signal are amplified as input signals to the demodulator through the first and second resistors R1, R2 to restore the sinusoidal audio signal in a single channel into a direct current VP voltage and a direct current VN voltage.

[0011] As a further improvement, the input gating module comprises a first comparator COMP1, an inverter INV and a multiplexer MUX connected in sequence, the signals of the direct current VP voltage and the direct current VN voltage are compared by the first comparator COMP1 to output a S1 signal and a S1_N signal with opposite phase formed by the inverter INV; the S1 signal and the S1_N signal control the multiplexer MUX to output the signal VM voltage with higher voltage from the direct current VP voltage and the direct current VN voltage to be used for integration of the third stage circuit STAGE3; the high level DETECT1 signal is used as a clock of the multiplexer MUX, when the high level of the high level DETECT1 signal is detected, the multiplexer MUX is allowed to start working.

[0012] As a further improvement, the integral comparison module is composed of third and fourth resistors R3, R4, third capacitor C3, first operational amplifier Avl and second comparator COMP2; the third and fourth resistors R3, R4, third capacitor C3 and the first operational amplifier Avl form an integrator, the input signal is the signal VM voltage, and the output signal is the integral voltage VX; the transfer function between the integral voltage VX and the signal VM voltage is: , and the second comparator COMP2 compares when the integral voltage VX rises to be greater than the threshold voltage VT, the high level DETECT2 signal is output, and the response time Tresponse of the third stage circuit STAGE3 is: Tresponse = (VT x R3 x C3) / VDC, wherein: VDC is the DC component of the audio signal, and the integral time constant .

[0013] As a further improvement, the duty cycle difference detection module is composed of two buffers, an OR gate and a D flip-flop; the input signal is the duty cycle alternately changed PWM P and PWM N, and the output signal is the high level DETECT1 signal; the PWM P and the PWM N pass through the respective buffers and the OR gate, combine the two signals with the same high level pulse width, and output the signal VA; when the duty cycle of the signal VA exceeds the duty cycle of the clock reference signal CLK_ref as the first threshold voltage comparison signal, the D flip-flop outputs the high level DETECT1 signal as the input signal of the logic processing module, and also acts as the clock of the multiplexer MUX in the audio signal modulation module.

[0014] As a further improvement, the temperature sampling module is composed of zero temperature coefficient current source IPTAT, transistor Q1 and second operational amplifier Av2; the input signal is the ambient temperature, the current with zero temperature coefficient flows through the emitter junction BE of the transistor to generate a sampling voltage with negative temperature coefficient, the sampling voltage is amplified by the second operational amplifier Av2 to obtain the amplified temperature sampling signal VC voltage as the output signal; the threshold voltage adjustment module is composed of voltage follower Av3, automatic gain control module and OSC module; the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through the voltage follower; the OSC module is an RC oscillator, and the clock reference signal CLK_ref in the form of square wave is output by charging and discharging the capacitor in the RC oscillator, and the temperature sampling signal VC voltage adjusts the duty cycle of the clock reference signal CLK_ref by changing the charging and discharging current of the capacitor.

[0015] As a further improvement, when the temperature increases, the temperature sampling signal VC voltage decreases, the threshold voltage VT voltage decreases, the duty cycle of the clock reference signal CLK_ref becomes smaller, and the temperature sampling signal VC voltage calculation formula is: Wherein: G is the gain of the second operational amplifier Av2, and VBE is the emitter junction voltage of the triode Q1.

[0016] As a further improvement, in the D flip-flop, the duty cycle of the clock reference signal CLK_ref is set to 57% and serves as a first reference threshold and is adjusted with temperature variation, the zero-temperature-coefficient current source IPTAT is set to 100 mu A, the emitter junction voltage VBE of the triode Q1 at 25 DEG C is 0.7 V, and its temperature coefficient is , the second operational amplifier Av2 is configured to have a gain G of 5, and outputs the temperature sampling signal VC voltage , and the temperature coefficient of the temperature sampling signal VC voltage is .

[0017] As a further improvement, the reference threshold VT0 is 0.7 V at 25 DEG C, and at 85 DEG C, the threshold voltage VT automatically decreases to about 0.57 V; at -40 DEG C, the threshold voltage VT increases to 0.85 V.

[0018] Correspondingly, the application also provides a DC detection method for a CLASSD audio power amplifier, which first adopts the DC detection circuit for a CLASSD audio power amplifier provided by the application; when the duty cycle difference detection module detects that the duty cycle difference in the CLASSD loop is out of limit, a high-level DETECT1 signal is output to the logic processing module, and is used to start the audio signal modulation module; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal, the audio signal modulation module that has been started realizes direct-current energy accumulation and outputs a high-level DETECT2 signal to the logic processing module when reaching a set threshold voltage VT; the logic processing module outputs a high-level DC_DETECT signal, triggers a direct-current protection action, and the chip is shut down.

[0019] The technical scheme of the DC detection circuit and method for a CLASSD audio power amplifier provided by the application mainly solves the problems of shortening the response time and improving the adaptability to complex environments under the premise of retaining the reliability of the timing confirmation mechanism, distinguishing transient interference from real DC faults, avoiding the system from entering unnecessary protection waiting periods and affecting user experience, and dynamically adapting to the load and temperature changes of the CLASS D system to avoid high-temperature missed detection and low-temperature false reporting. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The implementation schematic diagram of the DC detection circuit of the application in the CLASSD loop control;

[0021] Figure 2 The circuit principle schematic diagram of the audio signal modulation module and the duty cycle difference detection module of the application;

[0022] Figure 3 The circuit principle schematic diagram of the dynamic adaptive threshold voltage adjustment module of the application;

[0023] Figure 4 The working waveform diagram of Figure 2 The working waveform diagram of

[0024] Figure 5 The working waveform diagram of the threshold voltage adjustment module of the application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0026] As shown in Figure 1 and Figure 3 The application provides a DC detection circuit for a CLASSD audio power amplifier, which comprises a duty cycle difference detection module, an audio signal modulation module, a dynamic adaptive threshold adjustment module, and a logic processing module. The duty cycle difference detection module detects the duty cycle difference between PWMN signals and PWMP signals in a CLASSD loop, and outputs a high-level DETECT1 signal to the logic processing module when the duty cycle difference exceeds a limit, while starting the audio signal modulation module. The audio signal modulation module connects OUTP signals and OUTN signals and realizes direct-current energy accumulation, and outputs a high-level DETECT2 signal to the logic processing module when a set threshold voltage VT is reached. The dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal. When the logic processing module simultaneously detects the high-level DETECT1 signal and the high-level DETECT2 signal, a high-level DC_DETECT signal is output, triggering a direct-current protection action, and the chip is shut down.

[0027] The application provides a DC detection circuit for a CLASSD audio power amplifier, which introduces multi-dimensional decision-making and dynamic adaptive design, solves the DC fault problem, protects the output audio load, and improves user experience.

[0028] As a further improvement, the audio signal modulation module is composed of a demodulator, an integrator and a comparator, the demodulator and the integrator implement the process of direct current energy accumulation, the audio signal modulation module outputs the high level DETECT2 signal when the output voltage of the integrator exceeds the threshold voltage VT; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the comparator in the audio signal modulation module by detecting the temperature signal TEMP, lowers the threshold voltage VT when the temperature rises, and raises the threshold voltage VT when the temperature falls, and the dynamic adaptive threshold adjustment module also outputs a gain control signal Gain_control to the audio signal modulation module.

[0029] As a further improvement, it includes: a first stage circuit STAGE1 as a demodulator to restore the sinusoidal audio signal in a single channel to direct current VP voltage and direct current VN voltage; a second stage circuit STAGE2 as an input gating module to control and output the signal VM voltage with higher voltage from the direct current VP voltage and the direct current VN voltage by the high level DETECT1 signal; a third stage circuit STAGE3 as an integral comparison module to use the signal VM voltage as an input signal to form an integral voltage VX by integration and select to output the high level DETECT2 signal after comparison with the threshold voltage VT; a fourth stage circuit STAGE4 as a duty cycle difference detection module; a fifth stage circuit STAGE5 as a temperature sampling module to obtain an amplified temperature sampling signal VC voltage; a sixth stage circuit STAGE6 as a threshold voltage adjustment module, the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through a voltage follower; the relationship between the threshold voltage VT and the temperature T is: wherein: VT0 is the reference threshold, is the negative temperature coefficient, and T0 is the reference temperature.

[0030] As a further improvement, the demodulator includes first and second resistors R1, R2 connected to first and second buffers BUFFER1, BUFFER2 respectively, first and second capacitors C1, C2 with one end grounded and the other end connected to the first and second buffers BUFFER1, BUFFER2 respectively, and the generated VLP signal and VLN signal as input signals are input to the demodulator through the first and second resistors R1, R2 respectively, to restore the sinusoidal audio signal in a single channel to direct current VP voltage and direct current VN voltage.

[0031] As a further improvement, the input gating module comprises a first comparator COMP1, an inverter INV and a multiplexer MUX connected in sequence, the signals of the direct current VP voltage and the direct current VN voltage are compared by the first comparator COMP1, and the S1 signal and the S1_N signal with opposite phase formed by the inverter INV are output; the S1 signal and the S1_N signal control the multiplexer MUX to output the signal VM voltage with higher voltage between the direct current VP voltage and the direct current VN voltage for the integration of the third stage circuit STAGE3; the high level DETECT1 signal is used as the clock of the multiplexer MUX, and when the high level of the high level DETECT1 signal is detected, the multiplexer MUX is allowed to start working.

[0032] As a further improvement, the integration comparison module is composed of a third resistor R3, a fourth resistor R4, a third capacitor C3, a first operational amplifier Av1 and a second comparator COMP2; the third resistor R3, the fourth resistor R4, the third capacitor C3 and the first operational amplifier Av1 constitute an integrator, the input signal is the signal VM voltage, and the output signal is the integration voltage VX; the transfer function between the integration voltage VX and the signal VM voltage is: The integration voltage VX is compared by the second comparator COMP2, and when the integration voltage VX rises to be greater than the threshold voltage VT, the high level DETECT2 signal is output, and the response time Tresponse of the third stage circuit STAGE3 is: Tresponse=(VT×R3×C3) / VDC, wherein: VDC is the DC component of the audio signal, and the integration time constant .

[0033] As a further improvement, the duty cycle difference detection module is composed of two buffers, an OR gate and a D flip-flop; the input signals are the PWMP and the PWMN with alternating duty cycles, and the output signal is the high level DETECT1 signal; the PWMP and the PWMN pass through the respective buffers and the OR gate, combine the pulse widths of the two signals with high level, and output the signal VA; when the duty cycle of the signal VA exceeds the duty cycle of the clock reference signal CLK_ref as the first threshold voltage comparison signal, the D flip-flop outputs the high level DETECT1 signal as the input signal of the logic processing module, and also acts as the clock of the multiplexer MUX in the audio signal modulation module.

[0034] As a further improvement, the temperature sampling module is composed of a zero-temperature-coefficient current source IPTAT, a transistor Q1 and a second operational amplifier Av2; the input signal is the ambient temperature, and a sampling voltage with a negative temperature coefficient is generated by the current with a zero-temperature coefficient flowing through the emitter junction BE of the transistor, the sampling voltage is amplified by the second operational amplifier Av2 to obtain the amplified temperature sampling signal VC voltage as the output signal; the threshold voltage adjustment module is composed of a voltage follower Av3, an automatic gain control module and an OSC module; the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through the voltage follower; the OSC module is an RC oscillator, and the clock reference signal CLK_ref in the form of a square wave is output by charging and discharging the capacitor in the RC oscillator, and the temperature sampling signal VC voltage adjusts the duty cycle of the clock reference signal CLK_ref by changing the charging and discharging current of the capacitor, thereby realizing the function of adjusting the threshold duty cycle with temperature change.

[0035] As a further improvement, when the temperature rises, the temperature sampling signal VC voltage decreases, the threshold voltage VT voltage decreases, and the duty cycle of the clock reference signal CLK_ref becomes smaller, and the temperature sampling signal VC voltage calculation formula is: wherein: G is the gain of the second operational amplifier Av2, and VBE is the emitter junction voltage of the transistor Q1.

[0036] As a further improvement, in the D flip-flop, the duty cycle of the clock reference signal CLK_ref is set to 57% and serves as a first reference threshold and is adjusted with temperature change, the zero-temperature-coefficient current source IPTAT is set to 100 μA, the emitter junction voltage VBE of the transistor Q1 at 25℃ is 0.7 V, and the temperature coefficient thereof is , the second operational amplifier Av2 is configured to have a gain G of 5, and outputs the temperature sampling signal VC voltage , and the temperature coefficient of the temperature sampling signal VC voltage is , which provides sufficient sensitivity for subsequent threshold adjustment.

[0037] As a further improvement, the reference threshold VT0 is 0.7 V at 25℃, and at 85℃, the threshold voltage VT automatically decreases to about 0.57 V; at -40℃, the threshold voltage VT increases to 0.85 V, thereby realizing the protection characteristics of being more sensitive at high temperature and more resistant to interference at low temperature.

[0038] Correspondingly, the application also provides a DC detection method for a CLASSD audio power amplifier, which first adopts a DC detection circuit for a CLASSD audio power amplifier provided by the application; when a duty cycle difference value detection module detects that a duty cycle difference value in a CLASSD loop is out of limit, a high-level DETECT1 signal is output to a logic processing module, which is used to start an audio signal modulation module; a dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal; the audio signal modulation module that has been started realizes direct current energy accumulation and outputs a high-level DETECT2 signal to the logic processing module when reaching a set threshold voltage VT; the logic processing module outputs a high-level DC_DETECT signal to trigger a direct current protection action, and the chip is shut down.

[0039] The technical scheme of the DC detection circuit and method for the CLASSD audio power amplifier provided by the application mainly solves the problems of shortening the response time and improving the adaptability to complex environments under the premise of retaining the reliability of the timing confirmation mechanism; distinguishing transient interference from real DC faults to avoid the system from entering unnecessary protection waiting periods and affecting user experience; and dynamically adapting to the load and temperature changes of the CLASS D system to avoid high-temperature missed detection and low-temperature false reporting.

[0040] In the preferred embodiment shown in Figure 1 The application provides an implementation mode of the DC detection circuit in the CLASSD loop control, which realizes the design of the application by introducing multi-dimensional judgment and dynamic adaptation, and realizes two-level logic detection function, dynamic adjustment function and fault prediction function.

[0041] The overall DC detection circuit mainly includes a duty cycle difference value detection module, an audio signal modulation module, a dynamic adaptive threshold adjustment module and a logic processing module. The duty cycle difference value detection module detects the duty cycle difference value of the PWMN and PWMP signals in the CLASSD loop, and outputs a high level when the duty cycle difference value is out of limit (such as ±14) to start the audio signal modulation module. The audio signal modulation module mainly consists of a demodulator, an integrator and a comparator. When the audio signal modulation module receives the high level output by the duty cycle difference value detection module, it starts to work, realizes the process of direct current energy accumulation through the internal demodulator and integrator, and outputs a high level when the output voltage of the integrator exceeds the set threshold voltage. The dynamic adaptive threshold adjustment module adjusts the threshold voltage of the comparator by detecting the temperature signal. The resistivity of the semiconductor material (such as the voice coil wire) decreases with the increase of temperature, and the speaker resistance decreases with the increase of temperature. The same DC offset is more harmful to the speaker, so the threshold voltage is reduced to protect the speaker, and the threshold voltage is raised when the temperature decreases.

[0042] Figure 2 The patent application is about the specific embodiment of the audio signal modulation module and the duty cycle difference detection module. PWMP, PWMN, VLP, VLN, CLK_ref, VT are input signals. DETECT1 and DETECT2 are output signals. VLP and VLN are known amplified sinusoidal voltage signals of audio signals and are input signals of the circuit of the application. In the D flip-flop, the duty cycle of the clock reference signal CLK_ref is set to 57% and is the first reference threshold and is adjusted with temperature variation, and VT and Gain_control are output signals of the dynamic adaptive threshold adjustment module.

[0043] STAGE1 is a demodulator composed of resistor R1, capacitor C1 and buffer. VLP and VLN restore the sinusoidal audio signal in a single channel to a direct current voltage through this module.

[0044] STAGE2 is an input gating module composed of comparator COMP, inverter and multiplexer. Two signals S1 and S1_N are output by comparing VP and VN. S1 and S1_N are opposite in phase, and control the multiplexer to output the signal VM with higher voltage in VP and VN, which is used for integration in STAGE3. DETECT1 is the output signal of STAGE4, which is used as the clock of MUX in this module. When the high level of DETECT1 is detected, the multiplexer is allowed to start working.

[0045] STAGE3 is an integral comparison module composed of resistors R3, R4, capacitor C3, operational amplifier Av and comparator COMP. Resistors R3, R4, capacitor C3 and operational amplifier Av constitute an integrator, and the input signal is VM, and the output signal is VX. The transfer function between VX and VM is

[0046] ,

[0047] When the integral voltage VX rises to be greater than the voltage VT, the comparator COMP outputs a high level signal DETECT2. The response time of the STAGE3 module is .

[0048] VDC is the DC component of the audio signal. In order to achieve fast protection (<100μs) in the event of a sudden DC fault, while avoiding the false triggering of the low frequency component (such as 20Hz) of the audio, the integration time constant is designed to be 1ms. Accordingly, when a serious fault of VDC>500mV is detected, the response time Tresponse<50μs.

[0049] STAGE4 is duty cycle difference detection module, which is composed of two buffers, an OR gate and a D flip-flop; the input signal is the duty cycle alternating PWM P and PWMN, and the output signal is DCTECT1; PWM P and PWMN pass through the buffer and OR gate, combine the two signals with high level pulse width and output signal VA; when the duty cycle of VA signal exceeds the duty cycle of CLK_ref, the D flip-flop outputs a high level signal DCTECT1; DCTECT1 is both the input signal of the logic processing module and the clock of the MUX in the audio signal modulation module.

[0050] Figure 3 For the specific embodiments of the dynamic adaptive threshold voltage adjustment module in this application.

[0051] STAGE5 is temperature sampling module, which is composed of zero temperature coefficient current source, transistor and operational amplifier; the input signal is the ambient temperature, and the output signal is VC; the zero temperature coefficient current flows through the BE junction of the transistor to generate a negative temperature coefficient sampling voltage, and the sampling voltage is amplified by the operational amplifier to obtain the amplified temperature sampling signal VC; the zero temperature coefficient current source IPTAT is set to 100 μA. The VBE of transistor Q1 at 25℃ is about 0.7V, and its temperature coefficient is about . The operational amplifier is configured as a same-phase amplifier with a gain G=5, so the output voltage . Finally, the temperature coefficient of VC is about , which provides sufficient sensitivity for subsequent threshold adjustment.

[0052] STAGE6 is threshold voltage adjustment module, which is composed of voltage follower, automatic gain control module and OSC module; the VC voltage outputs the same-phase and driving-capable VT signal through the voltage follower; the OSC module is a conventional RC oscillator, which outputs the CLK_ref in the form of square wave by charging and discharging the capacitor, and the VC voltage adjusts the duty cycle of CLK_ref by changing the charging and discharging current of the capacitor, thereby realizing the function of adjusting the duty cycle threshold with temperature change; when the temperature rises, the VC voltage decreases, the VT voltage decreases, and the duty cycle of CLK_ref becomes smaller; the specific working waveform can be seen in Figure 5 .

[0053] The relationship between the output voltage VT of the temperature compensation module and the temperature T is designed as

[0054] ,

[0055] wherein VT0=0.7V is the reference threshold at 25℃, It is a negative temperature coefficient. Therefore, at 85℃, VT automatically reduces to about 0.57V; at -40℃, VT increases to about 0.85V, so that the protection characteristic is more sensitive at high temperature and more resistant to interference at low temperature.

[0056] Figure 4 It is Figure 2 The specific waveform of the module. Figure 4 VDD in the module is a power supply voltage generated by an internal reference voltage source and a starting circuit, and has voltage stability and certain driving capacity; when the audio input signal (VLP / VLN) does not contain a direct current component (VDC), both are swung up and down with VDD / 2 as the reference. Once VDC is introduced into the signal, the common-mode level of VLP and VLN will be offset, and becomes VDD / 2 + VDC and VDD / 2 - VDC respectively. This common-mode drift will directly cause the duty cycle difference of the differential PWM signal (PWMP and PWMN) to increase significantly.

[0057] As Figure 4 Before t1, neither the DC voltage nor the audio signal enters the audio system, and the system works at a duty cycle of 50%; after t1, the DC voltage and the audio signal enter the audio system, and the system starts to work; at t2, the duty cycle difference detection module detects that the maximum duty cycle of PWMP is greater than that of CLK_ref, and outputs a high-level DETECT1 signal; at the same time, the high-level DETECT1 is the clock of the MUX, the MUX starts to work, and outputs the larger value VM of the common-mode voltage (VP and VN are the common-mode voltages of VLP and VLN respectively) of the sinusoidal wave signal VLP and VLN in the output channel; VM passes through the integrator to output the voltage VX, and the VX voltage gradually accumulates the DC voltage over time; at t3, when the VX voltage is greater than VT, a high-level DCTECT2 signal is output; △t is the response time of the module, which is related to the DC voltage, the integral gain and the comparator threshold.

[0058] When the logic processing module simultaneously detects the DCTECT1 signal and the DCTECT2 signal, a high-level DC_DETECT signal is output, triggering the DC protection action, and the chip is shut down.

[0059] Compared with the prior art, the technical scheme has the beneficial effects as follows:

[0060] 1. The application breaks through the technical prejudice of relying only on a single criterion in the time domain, and innovatively fuses and cooperatively judges the physical information in the digital domain (amplitude), the analog domain (energy slope) and the environmental domain (temperature); this is not a simple function superposition, but fundamentally solves the contradiction between'reliability' and'speed' through a new 'and' logic architecture; such a multi-dimensional information fusion idea is unprecedented in the field.

[0061] 2、The traditional technology only relies on the duty cycle difference detection method, and the transient interference or low frequency continuous audio signal is easy to cause the DC protection signal to be triggered, and the application provides a DC detection circuit for a CLASSD audio power amplifier, which solves the problem of high false trigger rate in the DC protection circuit by adopting duty cycle difference detection verification and audio signal modulation double path verification.

[0062] 3、The traditional technical solution often needs to be triggered by timing, and the application accelerates the judgment through the integral path, and the direct current energy accumulation speed can reflect the severity of the direct current fault, avoids invalid waiting, and solves the problem of fixed response speed of the DC protection circuit.

[0063] 4、The technical scheme of the application adjusts the threshold value by sampling the temperature signal, and dynamically adjusts the duty cycle difference threshold value and the integral voltage threshold value, and the linkage environmental parameter optimizes the response speed and safety of the DC protection signal under high and low temperature.

[0064] 5、The application achieves the technical effect that the skilled person in the art has been pursuing for a long time but has not been able to achieve at the same time: while greatly improving the response speed (from hundreds of milliseconds to microseconds), not only the reliability is not sacrificed, but also the false trigger rate is further significantly reduced. This 'fast and accurate' effect proves that the technical scheme of the application is not obvious, but has outstanding substantial features, and is particularly suitable for complex environments and high reliability requirements, such as vehicle audio (wide temperature range, large vibration), high-end intelligent sound box (high power, low distortion requirement).

[0065] The application provides a DC detection circuit for a CLASSD audio power amplifier, which introduces multi-dimensional judgment and dynamic self-adaption design through specific technical scheme, circuit working principle and connection mode of the whole circuit, solves the DC fault problem, protects the output audio load, and improves the user experience.

[0066] It should be understood that the scope to be protected by the application is not limited to the non-limiting embodiments, and it should be understood that the non-limiting embodiments are only described as examples. The substantial protection scope required by the application is more embodied in the scope provided by the independent claims, and its dependent claims.

Claims

1. A DC detection circuit for a CLASS-D audio power amplifier, characterized by: The duty cycle difference detection module, the audio signal modulation module, the dynamic adaptive threshold adjustment module, and the logic processing module are included. The duty cycle difference detection module detects the duty cycle difference between the PWMN signal and the PWMP signal in the CLASSD loop, and outputs a high level DETECT1 signal to the logic processing module when the duty cycle difference exceeds a limit, while starting the audio signal modulation module. The audio signal modulation module connects the OUTP signal and the OUTN signal and realizes direct current energy accumulation, and outputs a high level DETECT2 signal to the logic processing module when a set threshold voltage VT is reached. The dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting a temperature signal, and outputs a high level DC_DETECT signal to trigger a direct current protection action and shut down the chip when the logic processing module detects the high level DETECT1 signal and the high level DETECT2 signal at the same time. The audio signal modulation module is composed of a demodulator, an integrator, and a comparator, the demodulator and the integrator realize the process of direct current energy accumulation, and the audio signal modulation module outputs the high level DETECT2 signal when the output voltage of the integrator exceeds the threshold voltage VT, the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the comparator in the audio signal modulation module by detecting a temperature signal TEMP, and lowers the threshold voltage VT when the temperature rises, and raises the threshold voltage VT when the temperature falls, and the dynamic adaptive threshold adjustment module also outputs a gain control signal Gain_control to the audio signal modulation module.

2. The DC detection circuit for CLASS D audio power amplifier according to claim 1, characterized in that: It includes: The first stage circuit STAGE1 as a demodulator restores the single-channel sinusoidal audio signal to direct current VP voltage and direct current VN voltage; The second stage circuit STAGE2 as an input gating module is controlled by the high level DETECT1 signal and outputs the signal VM voltage with higher voltage among the direct current VP voltage and the direct current VN voltage, the third stage circuit STAGE3 as an integral comparison module uses the signal VM voltage as an input signal to form an integral voltage VX and selects the high level DETECT2 signal after comparison with the threshold voltage VT, and the fourth stage circuit STAGE4 as the duty cycle difference detection module; The fifth stage circuit STAGE5 as a temperature sampling module obtains an amplified temperature sampling signal VC voltage; The sixth stage circuit STAGE6 as a threshold voltage adjustment module, the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through a voltage follower; The threshold voltage VT and the temperature T relationship is: , wherein: VT0 is a reference threshold value, is the negative temperature coefficient and T0 is the reference temperature.

3. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 2, characterized in that: The demodulator comprises first and second resistors R1, R2 connected to first and second buffers BUFFER1, BUFFER2 respectively, and first and second capacitors C1, C2 having one end grounded and the other end connected to the first and second buffers BUFFER1, BUFFER2 respectively, and the generated VLP signal and VLN signal are amplified as input signals and input into the demodulator through the first and second resistors R1, R2, so as to restore the sinusoidal audio signal in a single channel into direct current VP voltage and direct current VN voltage.

4. The DC detection circuit for a CLASS-D audio power amplifier of claim 3, wherein: The input gating module comprises a first comparator COMP1, an inverter INV and a multiplexer MUX connected in sequence, the first comparator COMP1 compares the signals of the direct current VP voltage and the direct current VN voltage, and outputs an S1 signal and an S1_N signal opposite in phase to the S1 signal through the inverter INV; The S1 signal and the S1_N signal control the multiplexer MUX to output the signal VM voltage with higher voltage between the direct current VP voltage and the direct current VN voltage, for integration of the third stage circuit STAGE3; The high level DETECT1 signal is used as a clock of the multiplexer MUX, and when the high level of the high level DETECT1 signal is detected, the multiplexer MUX is allowed to start working.

5. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 4, characterized in that: The integral comparison module is composed of a third resistor R3, a fourth resistor R4, a third capacitor C3, a first operational amplifier Avl and a second comparator COMP2; the third resistor R3, the fourth resistor R4, the third capacitor C3 and the first operational amplifier Avl constitute an integrator, an input signal is the signal VM voltage, and an output signal is the integral voltage VX; a transfer function between the integral voltage VX and the signal VM voltage is: , The high level DETECT2 signal is output through the second comparator COMP2 when the integration voltage VX rises to be greater than the threshold voltage VT, and the response time Tresponse of the third stage circuit STAGE3 is Tresponse=(VT×R3×C3) / VDC, where: VDC is the DC component of the audio signal, the integration time constant .

6. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 5, characterized in that: The duty cycle difference detection module is composed of two buffers, an OR gate and a D flip-flop; the input signals are the PWMP and the PWMN with alternating duty cycles, and the output signal is the high level DETECT1 signal; the PWMP and the PWMN pass through the respective buffers and the OR gate, combine the two signals with high level pulse width together and output a signal VA; when the duty cycle of the signal VA exceeds the duty cycle of the clock reference signal CLK_ref as the first threshold voltage comparison signal, the D flip-flop outputs the high level DETECT1 signal as the input signal of the logic processing module, and also acts as the clock of the multiplexer MUX in the audio signal modulation module.

7. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 6, characterized in that: The temperature sampling module is composed of a zero temperature coefficient current source IPTAT, a transistor Q1 and a second operational amplifier Av2; the input signal is the ambient temperature, a current with zero temperature coefficient flows through the emitter junction BE of the transistor to generate a sampling voltage with negative temperature coefficient, the sampling voltage is amplified by the second operational amplifier Av2 to obtain the amplified temperature sampling signal VC voltage as the output signal; the threshold voltage adjustment module is composed of a voltage follower Av3, an automatic gain control module and an OSC module; the temperature sampling signal VC voltage outputs the threshold voltage VT signal with the same phase and driving capability through the voltage follower; the OSC module is an RC oscillator, which outputs the clock reference signal CLK_ref in the form of square wave by charging and discharging the capacitor in the RC oscillator, and the temperature sampling signal VC voltage adjusts the duty cycle of the clock reference signal CLK_ref by changing the charging and discharging current of the capacitor.

8. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 7, characterized in that: When the temperature rises, the temperature sampling signal VC voltage decreases, the threshold voltage VT voltage decreases, the duty cycle of the clock reference signal CLK_ref becomes smaller, and the temperature sampling signal VC voltage calculation formula is: Wherein: G is the gain of the second operational amplifier Av2, VBE is the emitter junction voltage of the triode Q1.

9. A DC detection circuit for a CLASS-D audio power amplifier as claimed in claim 8, characterized in that: In the D flip-flop, the duty cycle of the clock reference signal CLK_ref is set to 57% and as a first reference threshold and adjusted with temperature variation, the zero temperature coefficient current source IPTAT is set to 100μA, the emitter junction voltage VBE of the transistor Q1 at 25℃ is 0.7V, and its temperature coefficient is , the second operational amplifier Av2 is configured as a gain G of 5, and outputs the temperature sampling signal VC voltage , and the temperature coefficient of the temperature sampling signal VC voltage is .

10. The DC detection circuit for a CLASS-D audio power amplifier of claim 9, wherein: The reference threshold VT0 is 0.7V at 25℃, and the threshold voltage VT automatically decreases to about 0.57V at 85℃; the threshold voltage VT increases to 0.85V at -40℃.

11. A DC detection method for a CLASS D audio power amplifier, comprising: First, a DC detection circuit for a CLASSD audio power amplifier according to any one of claims 1 to 10 is used; when the duty cycle difference detection module detects that the duty cycle difference in the CLASSD loop is out of limit, a high level DETECT1 signal is output to the logic processing module, which is used to start the audio signal modulation module; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the audio signal modulation module by detecting the temperature signal; the started audio signal modulation module realizes direct current energy accumulation and outputs a high level DETECT2 signal to the logic processing module when the set threshold voltage VT is reached; the logic processing module outputs a high level DC_DETECT signal to trigger the direct current protection action and shut down the chip; the audio signal modulation module is composed of a demodulator, an integrator and a comparator, the demodulator and the integrator realize the process of direct current energy accumulation, and the audio signal modulation module outputs the high level DETECT2 signal when the output voltage of the integrator exceeds the threshold voltage VT; the dynamic adaptive threshold adjustment module adjusts the threshold voltage VT of the comparator in the audio signal modulation module by detecting the temperature signal TEMP, and lowers the threshold voltage VT when the temperature rises and raises the threshold voltage VT when the temperature falls; the dynamic adaptive threshold adjustment module also outputs a gain control signal Gain_control to the audio signal modulation module.

Images