Class-D power amplifier with magnetic bead nonlinear suppression and operation method of class-D power amplifier

Abstract

The invention provides a class-D power amplifier with magnetic bead nonlinear suppression and an operation method thereof, and relates to the technical field of power amplifier circuits, the class-D power amplifier comprises a two-stage integrator circuit, an RC feedback compensation network, a PWM wave generation circuit and a drive circuit; wherein the two-stage integrator circuit comprises an outer ring integrator and an inner ring integrator, and the outer ring integrator is used for suppressing nonlinearity of magnetic beads; the outer ring integrator and the inner ring integrator jointly suppress power level nonlinearity, and the output swing of the outer ring integrator is reduced by adopting a resistor feedforward mode; the RC feedback compensation network compensates the phase shift introduced by the magnetic beads and limits the bandwidth by adjusting an inner-loop closed-loop transmission function; the PWM wave generating circuit quantizes an output signal of the inner ring integrator into square waves with different pulse widths; and the driving circuit processes the square wave signal output by the PWM wave generating circuit and then drives the high-power tube. According to the invention, the nonlinearity of the magnetic beads can be suppressed, so that the linearity of signals actually received by the loudspeaker is optimized, and the fidelity of the whole audio link is improved.

Description

Technical Field

[0001] This invention relates to the field of power amplifier circuit technology, specifically to a Class D power amplifier with nonlinear suppression via a ferrite bead and its operating method. Background Technology

[0002] Reference Figure 1 As shown, a conventional Class D power amplifier circuit in the prior art includes three parts: a two-stage integrator, a PWM wave generation circuit, and a drive circuit. The two-stage integrator circuit is used for loop filtering, suppressing the PWM switching signal and amplifying the audio signal; the PWM wave generation circuit is used to generate a triangular wave signal, modulating the signal within the audio range into a high-frequency square wave signal with a different duty cycle; the drive circuit is used to drive a low-impedance speaker load.

[0003] In the two-stage integrator circuit, RF, C1, and Opa1 constitute the first-stage integrator, R2, C2, and Opa2 constitute the second-stage integrator, and CR is a feedforward capacitor that forms a zero point to cancel the phase shift of one of the poles of the two-stage integrator. The two-stage integrator together suppress high-frequency signals near the switching frequency, while providing high loop gain for audio band signals and suppressing power stage nonlinearity.

[0004] The PWM wave generation circuit consists of a triangular wave generator circuit and a comparator circuit. The triangular wave generator circuit generates a triangular wave of a certain frequency, which is used as one end of the comparator input and compared with the output signal of the second-stage integrator. The amplitude of the triangular wave is converted into square waves with different duty cycles, which are used to generate the switching signal for driving the power stage.

[0005] The drive circuit consists of a drive control circuit, a pre-drive circuit, and a power stage circuit (switching power transistor). Its input is a square wave signal output from the PWM wave generation circuit. After the square wave signal is processed by the digital state machine of the drive control module, it is sent to the pre-drive stage to drive the high-power transistor, and finally outputs a switching signal to drive the speaker load.

[0006] Figure 1 The power amplifier circuit shown can only suppress the nonlinearity of the output power stage. The ferrite beads located on the audio signal link after the power stage, which are used to reduce EMI interference from the power amplifier to other modules, will introduce new nonlinearity.

[0007] In the prior art, such as the invention patent with publication number CN102832893B, a Class D power amplifier is disclosed, including an amplification module, which includes an integrator; the Class D power amplifier also includes a filtering module, which is connected to the P input terminal and the N input terminal of the integrator respectively. An externally input digital signal is input to the filtering module for analog filtering, and the filtering module outputs a first analog signal and a second analog signal that are out of phase. The first analog signal and the second analog signal are correspondingly input to the integrator from the P input terminal and the N input terminal of the integrator for power amplitude integration.

[0008] In summary, there are no existing circuits to suppress and optimize the nonlinearity introduced by ferrite beads. Therefore, how to suppress the nonlinearity of ferrite beads to optimize the linearity of the signal actually received by the speaker and improve the fidelity of the entire audio link has become a problem that needs to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a Class D power amplifier with nonlinear suppression via ferrite beads and its operation method.

[0010] According to the present invention, a Class D power amplifier with nonlinear suppression via a ferrite bead and its operating method are provided as follows:

[0011] In one aspect, a Class D power amplifier with nonlinear suppression by a ferrite bead is provided, comprising: a two-stage integrator circuit, an RC feedback compensation network, a PWM wave generation circuit, and a drive circuit.

[0012] The output of the two-stage integrator circuit is connected to the input of the PWM wave generation circuit, and is used to filter and adjust the gain of the input audio signal before transmitting it to the PWM wave generation circuit.

[0013] The output terminal of the PWM wave generation circuit is connected to the input terminal of the drive circuit, and is used to convert the signal output by the two-stage integrator circuit into a high-frequency square wave signal and transmit it to the drive circuit.

[0014] The output of the drive circuit is filtered by a ferrite bead and a capacitor and then used to connect to the speaker load. The drive circuit and the two-stage integrator circuit form a closed-loop feedback through an RC feedback compensation network.

[0015] The two-stage integrator circuit includes an outer-loop integrator and an inner-loop integrator. The outer-loop integrator is used to suppress the nonlinearity of the ferrite bead. The outer-loop and inner-loop integrators jointly suppress the nonlinearity of the power stage, and a resistor feedforward method is used to reduce the output swing of the outer-loop integrator. The RC feedback compensation network compensates for the phase shift introduced by the ferrite bead and limits the bandwidth by adjusting the inner-loop closed-loop transfer function. The PWM wave generation circuit quantizes the output signal of the inner-loop integrator into square waves with different pulse widths. The driving circuit processes the square wave signal output by the PWM wave generation circuit and drives the high-power transistor.

[0016] Preferably, in the two-stage integrator circuit, the outer loop integrator includes a resistor Rf, a resistor RI, a capacitor C1, and an operational amplifier Opa1; one end of the resistor Rf is connected to the output signal, and the other end is connected to the inverting input terminal of the operational amplifier Opa1; the capacitor C1 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier Opa1; one end of the resistor RI is connected to the inverting input terminal of the operational amplifier Opa1, and the other end is connected to the output terminal of the DAC.

[0017] The inner loop integrator includes resistors R2 and R3, capacitors C2 and CR, and operational amplifier Opa2; the output of the power amplifier is connected to the inverting input of operational amplifier Opa2 through resistor R3, capacitor C2 is connected in parallel between the inverting input and output of operational amplifier Opa2, one end of resistor R2 is connected to the output of operational amplifier Opa1, and the other end is connected to the inverting input of operational amplifier Opa2, and feedforward capacitor CR is connected in parallel with R2;

[0018] The resistor feedforward is achieved through a resistor Rfront, with one end of the resistor Rfront connected to the input signal and the other end connected to the input terminal of the operational amplifier Opa2.

[0019] Preferably, the RC feedback compensation network includes resistor R3, resistor R2, capacitor C2, capacitor CR, operational amplifier Opa2, and driving circuit, wherein:

[0020] The resistor R3, capacitor C2, and operational amplifier Opa2 form the main path of the inner loop integrator. The resistor R2 and capacitor C are connected in parallel to the inverting input terminal of operational amplifier Opa2, and together with Opa2 and C2, they form zero-point compensation. C2 is connected in parallel between the inverting input terminal and the output terminal of Opa2.

[0021] The output of the drive circuit is connected to the inverting input of the operational amplifier Opa2 through a feedback path, so that the inner loop closed-loop transfer function exhibits the characteristic of zero-first and pole-second, compensating for the phase shift introduced by the ferrite bead and limiting the outer loop bandwidth.

[0022] Preferably, the PWM wave generating circuit includes a triangular wave generating circuit and a comparator. The output terminal of the triangular wave generating circuit is connected to the non-inverting input terminal of the comparator, the output terminal of the operational amplifier Opa2 in the inner loop integrator is connected to the inverting input terminal of the comparator, and the output terminal of the comparator is connected to the input terminal of the drive circuit.

[0023] The triangular wave generating circuit generates a triangular wave at a fixed frequency. The comparator compares the triangular wave with the signal output by the operational amplifier Opa2 and outputs square wave signals with different duty cycles.

[0024] Preferably, the driving circuit includes a driving control module, a pre-driving stage, a high-power transistor, a ferrite bead, and a filter capacitor; in the PWM wave generation circuit, the output terminal of the comparator is connected to the input terminal of the driving control module, the output terminal of the driving control module is connected to the input terminal of the pre-driving stage, the output terminal of the pre-driving stage is connected to the gate of the high-power transistor, the source of the NMOS high-power transistor is grounded, the source of the PMOS high-power transistor is connected to the power supply, and the drains of both are connected to the speaker load. The output terminal of the high-power transistor is connected to the inverting input terminal of the operational amplifier Opa2 in the two-stage integrator circuit through a feedback path. In addition, the output signal of the high-power transistor is filtered by the ferrite bead and capacitor and then connected to the inverting input terminal of Opa1 through the resistor Rf.

[0025] Secondly, a method for operating a Class D power amplifier with nonlinear suppression via a ferrite bead is provided, the method comprising:

[0026] Two-stage integration processing steps: The input audio signal is processed by the two-stage integrator circuit. The outer loop integrator suppresses the nonlinearity of the ferrite bead. The outer loop integrator and the inner loop integrator work together to suppress the nonlinearity of the power stage. At the same time, the output swing of the outer loop integrator is reduced by resistor feedforward.

[0027] Feedback compensation steps: Using an RC feedback compensation network, the RC passive network is combined with an active operational amplifier to make the closed-loop transfer function of the inner loop compensate for the phase shift introduced by the insertion of the ferrite bead into the outer loop, while limiting the bandwidth to reduce the high-frequency carrier aliasing back tone band.

[0028] PWM modulation steps: The PWM wave generation circuit compares the output signal of the inner loop integrator with the triangular wave, quantizes it into square waves of different pulse widths, and outputs them to the drive circuit.

[0029] Drive output steps: The drive circuit receives a square wave signal, which is processed by the digital state machine of the drive control module and then drives the high-power transistor through the pre-drive stage. The output signal of the high-power transistor is filtered by a ferrite bead and a capacitor before driving the speaker load.

[0030] Preferably, in the two-stage integration processing step, the nonlinear signal V introduced by the magnetic bead... N The process of (s) being passed to the output satisfies the formula:

[0031]

[0032] Among them, H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) This is the output signal.

[0033] Preferably, in the two-stage integration processing step, the total harmonic distortion (THD) of the output signal satisfies the formula:

[0034]

[0035] Among them, V N (s) represents the nonlinear signal introduced by the magnetic bead; H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) The output signal is n; n is the order of the harmonics, and the nonlinear signal is represented by the various harmonics of the input signal; H o (s) represents the gain of the signal from input to output, i.e.

[0036] Preferably, in the feedback compensation step, the RC feedback compensation network ensures that the inner loop closed-loop transfer function satisfies the formula:

[0037]

[0038] Among them, G pwm The output power transistor supply voltage PVDD is divided by the peak-to-peak value of the triangular wave voltage Vpp; V1 and V p These are the output signals of Opa1 and the high-power transistor in the power stage, respectively (these two points are also the input and output of the inner loop); s is the complex frequency domain variable in the Laplace transform; R2 and R3 are resistors R2 and R3, respectively; C R C1 and C2 are capacitors CR and C2, respectively.

[0039] Preferably, in the PWM modulation step, the triangular wave is generated by the triangular wave generating circuit of the PWM wave generating circuit, and its frequency is a fixed switching frequency. It is compared with the output signal of the inner loop integrator through a comparator to generate a square wave signal.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention integrates a ferrite bead into the loop and employs a feedback principle. It uses loop gain to suppress the nonlinearity of the ferrite bead and compensates for the phase shift introduced by the ferrite bead to meet the loop stability requirements. Specifically, it provides more than 20dB of loop suppression for the nonlinearity introduced by the ferrite bead within the audio band, improving the linearity of the signal received by the speaker and the audio quality. At the same time, it is compatible with ferrite beads with different peak impedances, ensuring that the loop is always in a stable state.

[0042] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1 A schematic diagram of an existing Class D power amplifier circuit without nonlinear suppression using ferrite beads;

[0045] Figure 2 This is a schematic diagram of the circuit structure of the Class D power amplifier with nonlinear suppression function of magnetic beads according to the present invention;

[0046] Figure 3 This is a schematic diagram illustrating the principle of the circuit in this invention for suppressing nonlinearity of the magnetic bead.

[0047] Figure 4 This is a schematic diagram illustrating the principle of frequency compensation in the circuit of the present invention. Detailed Implementation

[0048] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0049] This invention provides a Class D power amplifier with nonlinear suppression via a ferrite bead, as described above. Figure 2As shown, the circuit includes a two-stage integrator circuit, an RC feedback compensation network, a PWM wave generation circuit, and a drive circuit. The input audio signal sequentially passes through the two-stage integrator for filtering and gain adjustment, is modulated by the PWM wave generation circuit, amplified by the drive circuit, and then filtered by a ferrite bead and capacitor before finally outputting a signal to drive the speaker load. The two-stage integrator and RC feedback compensation network are crucial for suppressing nonlinearity and ensuring loop stability. The overall design incorporates the ferrite bead into the feedback loop, utilizing the loop gain to suppress the nonlinearity introduced by the ferrite bead, while simultaneously suppressing power stage nonlinearity.

[0050] The circuit connection method for Class D power amplifiers is as follows: Figure 2 As shown, the output of the two-stage integrator circuit is connected to the input of the PWM wave generation circuit, used to filter and adjust the gain of the input audio signal before transmitting it to the PWM wave generation circuit. The output of the PWM wave generation circuit is connected to the input of the driver circuit, used to convert the signal output from the two-stage integrator circuit into a high-frequency square wave signal and transmit it to the driver circuit. The output of the driver circuit is filtered by a ferrite bead and then connected to the speaker load. A closed-loop feedback is formed between the driver circuit and the two-stage integrator circuit through an RC feedback compensation network.

[0051] The two-stage integrator circuit includes an outer-loop integrator and an inner-loop integrator. Its core functions are to perform loop filtering on the signal, amplify the audio signal, suppress high-frequency interference, and specifically suppress nonlinearity. The outer-loop integrator is used to suppress the nonlinearity of the ferrite bead; the outer-loop and inner-loop integrators jointly suppress the nonlinearity of the power stage, and a resistor feedforward method is used to reduce the output swing of the outer-loop integrator; the RC feedback compensation network compensates for the phase shift introduced by the ferrite bead and limits the bandwidth by adjusting the inner-loop closed-loop transfer function; the PWM wave generation circuit quantizes the output signal of the inner-loop integrator into square waves of different pulse widths; the drive circuit processes the square wave signal output by the PWM wave generation circuit and drives the high-power transistor.

[0052] Specifically, in the two-stage integrator circuit, the outer loop integrator includes a resistor Rf, a resistor RI, a capacitor C1, and an operational amplifier Opa1; one end of the resistor Rf is connected to the input signal, and the other end is connected to the inverting input terminal of the operational amplifier Opa1; the capacitor C1 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier Opa1; one end of the resistor RI is connected to the inverting input terminal of the operational amplifier Opa1, and the other end is connected to the DAC output terminal.

[0053] The inner-loop integrator includes resistors R2 and R3, capacitors C2 and CR, and operational amplifier Opa2. The output terminal of the power stage is connected to the inverting input terminal of operational amplifier Opa2 through resistor R3. Capacitor C2 is connected in parallel between the inverting input terminal and the output terminal of operational amplifier Opa2. One end of resistor R2 is connected to the output terminal of operational amplifier Opa1, and the other end is connected to the inverting input terminal of operational amplifier Opa2. Feedforward capacitor CR is connected in parallel with R2.

[0054] Resistive feedforward is achieved through resistor Rfront, with one end of Rfront connected to the input signal and the other end connected to the input of op-amp Opa2.

[0055] The working process of the two-stage integrator circuit: The input audio signal and the feedback signal first enter the outer loop integrator. The outer loop integrator uses the high loop gain in the audio segment to specifically suppress the nonlinearity introduced by the ferrite bead (the ferrite bead will produce nonlinear distortion due to its own characteristics, and the outer loop integrator suppresses this distortion through feedback adjustment).

[0056] The output signal of the outer loop integrator is transmitted to the inner loop integrator. The inner loop integrator and the outer loop integrator work together: together they provide high loop gain for the audio band signal and suppress the nonlinearity of the power stage (switching power transistor) (the switching action of the power stage will produce distortion, which can be suppressed by the high gain loop); at the same time, they suppress the high frequency components of the PWM switching signal (high frequency interference near the switching frequency) through filtering.

[0057] Resistor feedforward design (through a specific resistor path): Reduces the output swing of the outer loop integrator and avoids op-amp Opa1 output saturation (preventing op-amp performance degradation due to excessive swing).

[0058] Specifically, the RC feedback compensation network includes resistors R3 and R2, capacitors C2 and CR, operational amplifier Opa2, and a driver circuit. Its main functions are to compensate for phase shift, limit bandwidth, ensure loop stability, and reduce high-frequency interference. Specifically, resistors R3 and C2, along with operational amplifier Opa2, form the main path of the inner-loop integrator. Resistor R2 and capacitor CR are connected in parallel to the inverting input of operational amplifier Opa2, working together with C2 and Opa2 to form zero-point compensation. The output of the driver circuit is connected to the inverting input of operational amplifier Opa2 through the feedback path, causing the inner-loop closed-loop transfer function to exhibit a "zero-first, pole-second" characteristic, compensating for the phase shift introduced by the ferrite bead and limiting the outer-loop bandwidth.

[0059] The working process of the RC feedback compensation network: After the ferrite bead is included in the loop of the outer loop integrator, it will introduce an additional phase shift (different ferrite beads have different pole positions; low pole ferrite beads will reduce the outer loop phase margin, and high pole ferrite beads will expand the bandwidth, resulting in high frequency interference).

[0060] The closed-loop transfer function formed by the inner-loop integrator and the RC network exhibits a "zero-first, pole-later" characteristic: in the low-frequency band, the phase shift introduced by the zero-point compensation ferrite bead is increased (to improve the phase margin and ensure loop stability); in the high-frequency band, the signal amplitude is rapidly attenuated through the pole (to limit the gain-bandwidth product of the outer loop), preventing the high-frequency carrier (the high-frequency signal generated by PWM modulation) from re-aliasing back into the audio band (to prevent high-frequency interference from affecting audio quality).

[0061] This design is compatible with ferrite beads of different peak impedances. Regardless of the pole height introduced by the ferrite bead, it can be adapted through the inner loop characteristics to ensure stability.

[0062] Specifically, the PWM wave generation circuit modulates the audio signal into a high-frequency square wave (switching signal), including a triangular wave generation circuit and a comparator. The output of the triangular wave generation circuit is connected to the non-inverting input of the comparator, the output of the operational amplifier Opa2 in the inner loop integrator is connected to the inverting input of the comparator, and the output of the comparator is connected to the input of the drive circuit.

[0063] The triangular wave generator circuit produces a triangular wave of a fixed frequency. The comparator compares the triangular wave with the signal output by the op-amp Opa2 and outputs square wave signals with different duty cycles.

[0064] The working process of the PWM wave generation circuit: The triangular wave generation circuit generates a triangular wave of fixed frequency (as a carrier wave) and inputs it to one end of the comparator;

[0065] The audio signal (already filtered and gain adjusted) output from the inner loop integrator is input to the other end of the comparator;

[0066] The comparator compares the audio signal with a triangular wave and converts the amplitude information of the audio signal into a high-frequency square wave with different duty cycles (the larger the amplitude of the audio signal, the higher the duty cycle of the square wave). This square wave is used as a switching control signal to drive the power stage and is transmitted to the drive circuit.

[0067] Specifically, the drive circuit amplifies the PWM square wave signal to drive the low-impedance speaker load. It includes a drive control module, a pre-drive stage, a high-power transistor, a ferrite bead, and a filter capacitor. The output of the comparator in the PWM wave generation circuit is connected to the input of the drive control module, the output of the drive control module is connected to the input of the pre-drive stage, the output of the pre-drive stage is connected to the gate of the high-power transistor, the source of the Nmos power transistor is grounded, the source of the Pmos power transistor is connected to the power supply, and the drains of both are connected to the speaker load. The output of the high-power transistor is connected to the inverting input of the operational amplifier Opa2 in the two-stage integrator circuit through a feedback path. In addition, the output signal is connected to the inverting input of Opa1 after passing through the ferrite bead and the filter capacitor and then through Rf.

[0068] The driving circuit works by receiving the square wave signal output from the PWM wave generation circuit.

[0069] The square wave signal is first processed by the digital state machine of the drive control module (to optimize signal timing, prevent power transistor malfunction, and prevent power supply and ground connection, etc.).

[0070] The processed signal is passed to the pre-drive stage, where the signal is initially amplified before driving the high-power switching transistor (power stage).

[0071] The power stage switching transistor performs high-speed switching action according to the duty cycle of the square wave signal, and finally outputs an amplified switching signal, which drives the speaker load (the speaker produces sound by vibration) after being filtered by a ferrite bead and a capacitor.

[0072] This invention also provides a method for operating a Class D power amplifier with nonlinear suppression via a ferrite bead, the method specifically including:

[0073] Two-stage integration processing steps: The input audio signal and the feedback signal are processed by the two-stage integrator circuit. The outer loop integrator suppresses the nonlinearity of the ferrite bead. The outer loop integrator and the inner loop integrator work together to suppress the nonlinearity of the power stage. At the same time, the output swing of the outer loop integrator is reduced by the resistor feedforward method.

[0074] In this two-stage integration process, the nonlinear signal V introduced by the magnetic bead N The process of (s) being passed to the output satisfies the formula:

[0075]

[0076] Among them, H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) This is the output signal.

[0077] The total harmonic distortion (THD) of the output signal satisfies the following formula:

[0078]

[0079] Among them, V N (s) represents the nonlinear signal introduced by the magnetic bead; n is the order of the harmonics, and the nonlinear signal is represented by the various harmonics of the input signal; H O (s) represents the gain of the signal from input to output, i.e.

[0080] Feedback compensation steps: Using an RC feedback compensation network, the RC passive network is used in conjunction with an active operational amplifier to make the closed-loop transfer function of the inner loop compensate for the phase shift introduced by the insertion of the ferrite bead into the outer loop, while limiting the bandwidth to reduce the high-frequency carrier aliasing back tone band.

[0081] In the feedback compensation step, the RC feedback compensation network ensures that the inner loop closed-loop transfer function satisfies the formula:

[0082]

[0083] Among them, G pwm The output power transistor's supply voltage PVDD is divided by the peak-to-peak value of the triangular wave voltage Vpp; V1, V pThese are the output signals of Opa1 and the high-power transistor in the power stage, respectively; s is the complex frequency domain variable in the Laplace transform; R2 and R3 are resistors R2 and R3, respectively; C R C1 and C2 are capacitors CR and C2, respectively.

[0084] PWM modulation steps: The PWM wave generation circuit compares the output signal of the inner loop integrator with the triangular wave, quantizes it into square waves of different pulse widths, and outputs them to the drive circuit. The triangular wave is generated by the triangular wave generator circuit of the PWM wave generation circuit, and its frequency is a fixed switching frequency. It is compared with the output signal of the inner loop integrator through a comparator to generate a square wave signal.

[0085] Drive output steps: The drive circuit receives a square wave signal, which is processed by the digital state machine of the drive control module and then drives a high-power transistor through the pre-drive stage. The high-power transistor outputs a switching signal, which is then filtered by a ferrite bead and a capacitor to drive the speaker load.

[0086] The present invention will now be described in more detail.

[0087] This invention provides a Class D power amplifier with ferrite bead nonlinearity suppression. The ferrite bead is integrated into the loop and a feedback principle is used to suppress the nonlinearity of the ferrite bead by utilizing the loop gain. At the same time, the phase shift introduced by the ferrite bead is compensated to meet the loop stability requirements. This achieves the suppression of ferrite bead nonlinearity, thereby optimizing the linearity of the signal actually received by the speaker and improving the fidelity of the entire audio link.

[0088] Reference Figure 2 As shown, the Class D power amplifier consists of four parts: a two-stage integrator circuit, an RC feedback compensation network, a PWM wave generation circuit, and a drive circuit.

[0089] Two-stage integrators are used as loop filters to suppress PWM switching signals and amplify audio signals. The outer-loop integrator suppresses ferrite bead nonlinearity, and the outer-loop and inner-loop integrators together suppress power stage nonlinearity. At the same time, a resistor feedforward method is used to reduce the output swing of the outer-loop integrator.

[0090] RC feedback compensation networks are used to adjust the positions of loop zeros and poles to meet loop stability requirements. In an RC feedback compensation network, an RC passive network, in conjunction with an active operational amplifier, enables the closed-loop transfer function of the inner loop to compensate for the phase shift introduced by the insertion of a ferrite bead into the outer loop. This ensures loop stability while limiting bandwidth and reducing high-frequency carrier realiasing back into the audio band.

[0091] The PWM wave generation circuit generates a triangular wave signal, modulating the signal within the audio range into a high-frequency square wave signal with different duty cycles. The output signal of the inner loop integrator is quantized into square waves of different pulse widths, and the results are provided to the drive circuit.

[0092] The driver circuit is used to drive a low-impedance speaker load. Its input is a square wave signal output from the PWM module. This square wave signal is processed by the digital state machine of the driver control module and then sent to the pre-driver stage to drive the high-power transistor.

[0093] Figure 2 In the two-stage integrator circuit shown, Rf, RI, C1, and Opa1 constitute the outer loop integrator, which is used for loop filtering to suppress switching signals and provide high loop gain for audio signals. The output signal of this integrator is transmitted to the input of the inner loop. Rfront is used to reduce the output swing of the first-stage integrator and prevent Opa1 output saturation.

[0094] R3, C2, R2, CR, and Opa2 constitute the inner-loop integrator, which is also used for loop filtering to suppress switching signals and provides high loop gain for audio signals. The output of this integrator is transmitted to the PWM wave generation circuit. The outer-loop integrator suppresses the nonlinearity of the ferrite bead, and the outer-loop and inner-loop integrators together suppress the nonlinearity of the power stage.

[0095] Figure 2 In the RC feedback compensation network shown, the inner loop, composed of R3, C2, R2, CR, Opa2, and the driver circuit, has a closed-loop transfer function that, from the perspective of the outer loop, first has zeros and then poles. This serves to compensate for phase and limit bandwidth. The specific principle is as follows: Figure 4 As shown.

[0096] Figure 2 The PWM generation circuit shown consists of a triangular wave generator circuit and a comparator circuit. The triangular wave generator circuit generates a triangular wave with a certain switching frequency, which is used as one end of the comparator input and compared with the output signal of the inner loop integrator. The amplitude of the triangular wave is converted into square waves with different duty cycles, which are used to generate the switching signal for driving the power stage.

[0097] Reference Figure 3 The diagram shows the principle of a Class D power amplifier circuit with ferrite bead nonlinearity suppression function. As shown in formula (1), the nonlinearity introduced by the ferrite bead will pass through the loop gain H at the output. C The suppression of G(s) and G(s) ultimately results in the closed-loop THD as shown in Equation (2).

[0098]

[0099] Among them, H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) For output signal; V N(s) represents the nonlinear signal introduced by the magnetic bead; n is the order of the harmonics, and the nonlinear signal is represented by the various harmonics of the input signal; H O (s) represents the gain of the signal from input to output, i.e.

[0100] Reference Figure 4 As shown, the frequency compensation principle of a Class D power amplifier circuit with ferrite bead nonlinearity suppression is as follows. This schematic diagram only shows half of the fully differential circuit. Ferrites of different strengths introduce poles at different positions in the loop. If the poles introduced by the ferrite beads are relatively low, it will affect the phase margin of the outer loop. If the introduced pole frequency is very high, it will expand the bandwidth. To accommodate ferrite beads of different strengths, the closed-loop transfer function of the inner loop (the inner loop as seen from the outer loop) needs to exhibit a zero-first, pole-later characteristic. This allows for phase compensation at low frequencies and rapid amplitude decay at high frequencies to limit the outer loop gain-bandwidth product (GBW), suppressing harmonics near fck (the switching frequency of PWM modulation in the power amplifier) ​​and preventing them from re-aliasing into the audio range. Figure 4 The inner loop circuit shown has exactly this closed-loop transfer characteristic. Its closed-loop transfer function from V1 to Vp is shown in equation (3).

[0101]

[0102] Among them, G pwm The output power transistor's supply voltage PVDD is divided by the peak-to-peak value of the triangular wave voltage Vpp; V1, V p These are the output signals of Opa1 and the high-power transistor in the power stage, respectively (these two points are also the input and output of the inner loop); s is the complex frequency domain variable in the Laplace transform; R2 and R3 are resistors R2 and R3, respectively; C R C1 and C2 are capacitors CR and C2, respectively.

[0103] This invention provides a Class D power amplifier with nonlinear suppression via a ferrite bead and its operation method. The ferrite bead is integrated into the feedback loop of the Class D power amplifier. By using the feedback principle, the loop gain is used to suppress the nonlinearity introduced by the ferrite bead. Compared with the original method where the nonlinearity of the ferrite bead is directly superimposed on the signal received by the speaker, this effectively reduces signal distortion, optimizes the linearity of the signal actually received by the speaker, and improves the fidelity of the entire audio link.

[0104] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0105] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A Class D power amplifier with nonlinear suppression via a ferrite bead, characterized in that, include: Two-stage integrator circuit, RC feedback compensation network, PWM wave generation circuit and drive circuit; The output of the two-stage integrator circuit is connected to the input of the PWM wave generation circuit, and is used to filter and adjust the gain of the input audio signal before transmitting it to the PWM wave generation circuit. The output terminal of the PWM wave generation circuit is connected to the input terminal of the drive circuit, and is used to convert the signal output by the two-stage integrator circuit into a high-frequency square wave signal and transmit it to the drive circuit. The output of the drive circuit is filtered by a ferrite bead and a capacitor and then used to connect to the speaker load. The drive circuit and the two-stage integrator circuit form a closed-loop feedback through an RC feedback compensation network. The two-stage integrator circuit includes an outer-loop integrator and an inner-loop integrator. The outer-loop integrator is used to suppress the nonlinearity of the ferrite bead. The outer-loop and inner-loop integrators jointly suppress the nonlinearity of the power stage, and a resistor feedforward method is used to reduce the output swing of the outer-loop integrator. The RC feedback compensation network compensates for the phase shift introduced by the ferrite bead and limits the bandwidth by adjusting the inner-loop closed-loop transfer function. The PWM wave generation circuit quantizes the output signal of the inner-loop integrator into square waves with different pulse widths. The driving circuit processes the square wave signal output by the PWM wave generation circuit and drives the high-power transistor.

2. The Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 1, characterized in that, In the two-stage integrator circuit, the outer loop integrator includes a resistor Rf, a resistor RI, a capacitor C1, and an operational amplifier Opa1; one end of the resistor Rf is connected to the output signal, and the other end is connected to the inverting input terminal of the operational amplifier Opa1; the capacitor C1 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier Opa1; one end of the resistor RI is connected to the inverting input terminal of the operational amplifier Opa1, and the other end is connected to the output terminal of the DAC. The inner loop integrator includes resistors R2 and R3, capacitors C2 and CR, and operational amplifier Opa2. The output terminal of operational amplifier Opa1 is connected to the inverting input terminal of operational amplifier Opa2 through resistor R2. Capacitor C2 is connected in parallel between the inverting input terminal and the output terminal of operational amplifier Opa2. One end of resistor R3 is connected to the output terminal of the power amplifier, and the other end is connected to the inverting input terminal of operational amplifier Opa2. One end of feedforward capacitor CR is connected to the output terminal of operational amplifier Opa1, and the other end is connected to the input terminal of operational amplifier Opa2. The resistor feedforward is achieved through a resistor Rfront, with one end of the resistor Rfront connected to the input signal and the other end connected to the input terminal of the operational amplifier Opa2.

3. The Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 1, characterized in that, The RC feedback compensation network includes resistor R3, resistor R2, capacitor C2, capacitor CR, operational amplifier Opa2, and driving circuit, wherein: The resistor R3, capacitor C2, and operational amplifier Opa2 form the main path of the inner loop integrator. The resistor R2 and capacitor CR are connected in parallel to the inverting input terminal of operational amplifier Opa2, and together with C2 and Opa2, they form zero-point compensation. The output of the drive circuit is connected to the inverting input of the operational amplifier Opa2 through a feedback path, so that the inner loop closed-loop transfer function exhibits the characteristic of zero-first and pole-second, compensating for the phase shift introduced by the ferrite bead and limiting the outer loop bandwidth.

4. The Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 1, characterized in that, The PWM wave generation circuit includes a triangular wave generation circuit and a comparator. The output terminal of the triangular wave generation circuit is connected to the non-inverting input terminal of the comparator. The output terminal of the operational amplifier Opa2 in the inner loop integrator is connected to the inverting input terminal of the comparator. The output terminal of the comparator is connected to the input terminal of the drive circuit. The triangular wave generating circuit generates a triangular wave at a fixed frequency. The comparator compares the triangular wave with the signal output by the operational amplifier Opa2 and outputs square wave signals with different duty cycles.

5. The Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 1, characterized in that, The driving circuit includes a driving control module, a pre-driving stage, a high-power transistor, a ferrite bead, and a filter capacitor. In the PWM wave generation circuit, the output of the comparator is connected to the input of the driving control module, the output of the driving control module is connected to the input of the pre-driving stage, the output of the pre-driving stage is connected to the gate of the high-power transistor, the source of the NMOS power transistor is grounded, the source of the PMOS power transistor is connected to the power supply, and the drains of both are connected to the speaker load. The output of the high-power transistor is connected to the inverting input of the operational amplifier Opa2 in the two-stage integrator circuit through a feedback path. The output signal is connected to the inverting input of Opa1 through the ferrite bead and the filter capacitor.

6. A method for operating a Class D power amplifier with nonlinear suppression via a ferrite bead, characterized in that, include: Two-stage integration processing steps: The input audio signal is processed by the two-stage integrator circuit. The outer loop integrator suppresses the nonlinearity of the ferrite bead. The outer loop integrator and the inner loop integrator work together to suppress the nonlinearity of the power stage. At the same time, the output swing of the outer loop integrator is reduced by resistor feedforward. Feedback compensation steps: Using an RC feedback compensation network, the RC passive network is combined with an active operational amplifier to make the closed-loop transfer function of the inner loop compensate for the phase shift introduced by the insertion of the ferrite bead into the outer loop, while limiting the bandwidth to reduce the high-frequency carrier aliasing back tone band. PWM modulation steps: The PWM wave generation circuit compares the output signal of the inner loop integrator with the triangular wave, quantizes it into square waves of different pulse widths, and outputs them to the drive circuit. Drive output steps: The drive circuit receives a square wave signal, which is processed by the digital state machine of the drive control module and then drives the high-power transistor through the pre-drive stage. The output signal of the high-power transistor is filtered by a ferrite bead and a capacitor before driving the speaker load.

7. The operating method of the Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 6, characterized in that, In the two-stage integration process, the nonlinear signal V introduced by the magnetic bead N The process of (s) being passed to the output satisfies the formula: Among them, H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) This is the output signal.

8. The operating method of the Class D power amplifier with nonlinear suppression using ferrite beads according to claim 7, characterized in that, In the two-stage integration processing step, the total harmonic distortion (THD) of the output signal satisfies the formula: Among them, V N (s) represents the nonlinear signal introduced by the magnetic bead; H C (s) represents the forward gain from input to output; G(s) represents the transfer function of the feedback circuit; V IN (s) is the input signal; V OUT(s) The output signal is n; n is the order of the harmonics, and the nonlinear signal is represented by the various harmonics of the input signal; H O (s) represents the gain of the signal from input to output, i.e.

9. The operating method of the Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 6, characterized in that, In the feedback compensation step, the RC feedback compensation network ensures that the inner loop closed-loop transfer function satisfies the formula: Among them, G pwm The output power transistor's supply voltage PVDD is divided by the peak-to-peak value of the triangular wave voltage Vpp; V1, V p These are the output signals of Opa1 and the high-power transistor in the power stage, respectively; s is the complex frequency domain variable in the Laplace transform; R2 and R3 are resistors R2 and R3, respectively; C R C1 and C2 are capacitors CR and C2, respectively.

10. The method for operating a Class D power amplifier with nonlinear suppression using a ferrite bead according to claim 6, characterized in that, In the PWM modulation step, the triangular wave is generated by the triangular wave generation circuit of the PWM wave generation circuit. Its frequency is a fixed switching frequency. After being compared with the output signal of the inner loop integrator by a comparator, a square wave signal is generated.

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