CN118826660A - A closed-loop class D amplifier with improved THD performance - Google Patents
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Abstract
本发明涉及一种提升THD性能的闭环D类功放，包括二阶积分器、均匀脉宽调制单元、功率级和反馈单元，所述二阶积分器的输入端分别与音频信号的输入端、所述反馈单元的第一端连接，所述二阶积分器的输出端与所述均匀脉宽调制单元的输入端连接，所述均匀脉宽调制单元的输出端与所述功率级的输入端连接，所述功率级的输出端分别与所述反馈单元的第二端、负载扬声器连接，所述均匀脉宽调制单元包括开关电容滤波器，以及与所述开关电容滤波器连接的第一比较器和第二比较器。本发明滤除原有二阶积分器输出的残余高频谐波成分，滤除开关纹波，从而实现均匀脉宽调制工作，提升闭环D类功放的THD性能。并且，本发明实现结构简单，不需要使用额外的电感单元。
The present invention relates to a closed-loop class D power amplifier for improving THD performance, comprising a second-order integrator, a uniform pulse width modulation unit, a power stage and a feedback unit, wherein the input end of the second-order integrator is respectively connected to the input end of the audio signal and the first end of the feedback unit, the output end of the second-order integrator is connected to the input end of the uniform pulse width modulation unit, the output end of the uniform pulse width modulation unit is connected to the input end of the power stage, the output end of the power stage is respectively connected to the second end of the feedback unit and a load speaker, and the uniform pulse width modulation unit comprises a switched capacitor filter, and a first comparator and a second comparator connected to the switched capacitor filter. The present invention filters out the residual high-frequency harmonic components output by the original second-order integrator and filters out the switching ripple, thereby realizing uniform pulse width modulation operation and improving the THD performance of the closed-loop class D power amplifier. In addition, the present invention has a simple structure and does not require the use of an additional inductor unit.
Description
技术领域Technical Field
本发明涉及音频功放技术领域，特别涉及D类音频功放技术领域，更具体地涉及一种提升THD性能的闭环D类功放。The present invention relates to the technical field of audio power amplifiers, in particular to the technical field of class D audio power amplifiers, and more specifically to a closed-loop class D power amplifier with improved THD performance.
背景技术Background Art
D类功放主要使用了脉宽调制技术(PWM)，其工作在开关模式时功率管总是处于导通或者截止的状态，转换效率在理想情况下可以达到100％，实际应用效率也可达到70％以上，因此应用越来越广泛。但是其总谐波失真(THD)会由于输出级开关导通电阻的非线性、开关的死区时间以及器件引入的噪声等因素而变差。因此，提升D类功放THD的研究对提高音频系统的性能十分重要。Class D amplifiers mainly use pulse width modulation technology (PWM). When working in switching mode, the power tube is always in the on or off state. The conversion efficiency can reach 100% under ideal conditions, and the actual application efficiency can reach more than 70%. Therefore, its application is becoming more and more extensive. However, its total harmonic distortion (THD) will deteriorate due to factors such as the nonlinearity of the on-resistance of the output stage switch, the dead time of the switch, and the noise introduced by the device. Therefore, research on improving the THD of Class D amplifiers is very important to improve the performance of audio systems.
对于传统的开环D类功放来说，是将输入的音频信号直接送到比较器的输入端与三角波进行比较得到PWM波形，再利用PWM波形驱动输出级。开环方式具有合适的特性，但是存在很多非理想因素，例如开关导通电阻的非线性以及其对电源的噪声抑制性较差，会导致输出波形存在很大的失真，因此通常需要在输出端加一个二阶LC低通滤波器来滤除输出信号的高频方波，同时也增加了电路的体积和成本。For traditional open-loop Class D amplifiers, the input audio signal is directly sent to the input of the comparator to compare with the triangle wave to obtain a PWM waveform, and then the PWM waveform is used to drive the output stage. The open-loop method has suitable characteristics, but there are many non-ideal factors, such as the nonlinearity of the switch on-resistance and its poor noise suppression of the power supply, which will cause a large distortion of the output waveform. Therefore, it is usually necessary to add a second-order LC low-pass filter at the output end to filter out the high-frequency square wave of the output signal, which also increases the size and cost of the circuit.
现在大多数D类功放采用闭环设计方式，输出级不采用LC滤波器，而是利用负反馈来提高对电源和衬底噪声的抑制能力，使输出级的失真重新引入电路中进行处理从而提升功放的THD性能。现有的闭环D类功放大多使用两级放大器来实现音频带内较高的增益，同时它也衰减了更高频的信号。THD的定义为：Most Class D amplifiers now use a closed-loop design. The output stage does not use an LC filter, but uses negative feedback to improve the suppression of power supply and substrate noise, so that the distortion of the output stage is reintroduced into the circuit for processing, thereby improving the THD performance of the amplifier. Existing closed-loop Class D amplifiers mostly use two-stage amplifiers to achieve higher gain within the audio band, and at the same time it also attenuates higher-frequency signals. THD is defined as:
其中，VOUT,f表示D类功放在频率为f时的基波输出，VOUT,2f、VOUT,3f和VOUT,4f分别表示在频率为2f、3f和4f时的谐波输出成分。Wherein, V OUT,f represents the fundamental output of the class D power amplifier at frequency f, and V OUT,2f , V OUT,3f and V OUT,4f represent the harmonic output components at frequencies 2f, 3f and 4f respectively.
带有负反馈的闭环D类功放THD可近似被线性化估计为：The THD of a closed-loop class D amplifier with negative feedback can be approximately linearized and estimated as:
其中，THDop为开环D类功放的THD，G和H分别为D类功放的开关增益及反馈系数。Wherein, THD op is the THD of the open-loop class-D power amplifier, and G and H are the switching gain and feedback coefficient of the class-D power amplifier, respectively.
由公式(2)可得，当环路增益越大时，THDcl越小，相应闭环D类功放THD性能越好。但在进行PWM调制工作时，由于环路负反馈本身存在非线性因素，二阶积分器的输出仍存在高频谐波成分，因此带有谐波的信号与三角波进行比较时，会在在脉宽调制中引入相位误差和占空比误差，最终在通路中引入开关纹波，使得闭环D类功放在高频率时由于存在谐波导致输出信号存在失真，因此其THD性能不如其对应的线性功放模型。From formula (2), it can be seen that when the loop gain is larger, the THD cl is smaller, and the THD performance of the corresponding closed-loop class D power amplifier is better. However, when performing PWM modulation, due to the nonlinear factors of the loop negative feedback itself, the output of the second-order integrator still has high-frequency harmonic components. Therefore, when the signal with harmonics is compared with the triangle wave, phase error and duty cycle error will be introduced in the pulse width modulation, and finally switching ripple will be introduced in the path, so that the closed-loop class D power amplifier has distorted output signals due to the presence of harmonics at high frequencies, so its THD performance is not as good as its corresponding linear power amplifier model.
发明内容Summary of the invention
本发明提供一种提升THD性能的闭环D类功放，以解决现有闭环D类功放由于负反馈引入的高频谐波而造成信号失真的问题。The present invention provides a closed-loop class D power amplifier with improved THD performance, so as to solve the problem of signal distortion caused by high-frequency harmonics introduced by negative feedback in the existing closed-loop class D power amplifier.
本发明提供的一种提升THD性能的闭环D类功放，包括二阶积分器、均匀脉宽调制单元、功率级和反馈单元，所述二阶积分器的输入端分别与音频信号的输入端、所述反馈单元的第一端连接，所述二阶积分器的输出端与所述均匀脉宽调制单元的输入端连接，所述均匀脉宽调制单元的输出端与所述功率级的输入端连接，所述功率级的输出端分别与所述反馈单元的第二端、负载扬声器连接，所述均匀脉宽调制单元包括开关电容滤波器，以及与所述开关电容滤波器连接的第一比较器和第二比较器。The present invention provides a closed-loop class D power amplifier for improving THD performance, comprising a second-order integrator, a uniform pulse width modulation unit, a power stage and a feedback unit, wherein the input end of the second-order integrator is respectively connected to the input end of an audio signal and the first end of the feedback unit, the output end of the second-order integrator is connected to the input end of the uniform pulse width modulation unit, the output end of the uniform pulse width modulation unit is connected to the input end of the power stage, the output end of the power stage is respectively connected to the second end of the feedback unit and a load speaker, and the uniform pulse width modulation unit comprises a switched capacitor filter, and a first comparator and a second comparator connected to the switched capacitor filter.
进一步地，所述开关电容滤波器的输入端与所述二阶积分器的输出端连接，所述开关电容滤波器的第一输出端与所述第一比较器的正相输入端连接，所述开关电容滤波器的第二输出端与所述第二比较器的正相输入端连接，所述第一比较器的反相输入端分别与所述第二比较器的反相输入端、三角波信号连接。Furthermore, the input end of the switched capacitor filter is connected to the output end of the second-order integrator, the first output end of the switched capacitor filter is connected to the non-inverting input end of the first comparator, the second output end of the switched capacitor filter is connected to the non-inverting input end of the second comparator, and the inverting input end of the first comparator is respectively connected to the inverting input end of the second comparator and the triangular wave signal.
进一步地，所述均匀脉宽调制单元设置为：来自所述二阶积分器的预放大信号经过所述开关电容滤波器后，所述开关电容滤波器输出均匀的音频放大信号，所述均匀的音频放大信号传输至所述第一比较器和所述第二比较器的正相输入端，与所述三角波信号进行比较，得到滤除纹波之后的开关信号。Furthermore, the uniform pulse width modulation unit is configured as follows: after the pre-amplified signal from the second-order integrator passes through the switched capacitor filter, the switched capacitor filter outputs a uniform audio amplified signal, and the uniform audio amplified signal is transmitted to the positive phase input terminal of the first comparator and the second comparator, and compared with the triangular wave signal to obtain a switching signal after the ripple is filtered out.
进一步地，所述开关电容滤波器包括两个相同的开关电容模块。Furthermore, the switched capacitor filter includes two identical switched capacitor modules.
进一步地，所述开关电容模块包括第一开关、第二开关、第三开关、第四开关、第一电容和第二电容，所述第一开关的第一端与所述第三开关的第一端连接，所述第一开关的第二端分别与所述第二开关的第一端、所述第一电容的第一端连接，所述第三开关的第二端分别与所述第四开关的第一端、所述第二电容的第一端连接，所述第一电容的第二端和所述第二电容的第二端均接地，所述第二开关的第二端与所述第四开关的第二端连接。Further, the switch capacitor module includes a first switch, a second switch, a third switch, a fourth switch, a first capacitor and a second capacitor, the first end of the first switch is connected to the first end of the third switch, the second end of the first switch is respectively connected to the first end of the second switch and the first end of the first capacitor, the second end of the third switch is respectively connected to the first end of the fourth switch and the first end of the second capacitor, the second end of the first capacitor and the second end of the second capacitor are both grounded, and the second end of the second switch is connected to the second end of the fourth switch.
进一步地，所述开关电容滤波器设置为：所述第一开关和所述第四开关由占空比为1/2的脉冲信号控制，所述第二开关和所述第三开关由脉冲信号的反相信号控制。Furthermore, the switch capacitor filter is configured as follows: the first switch and the fourth switch are connected by a pulse signal with a duty cycle of 1/2. The second switch and the third switch are controlled by a pulse signal The inverted signal control.
进一步地，所述开关电容滤波器还设置为：所述第一开关和所述第四开关在一个采样周期中的前半周期导通，所述第二开关和所述第三开关在一次采样周期中的后半周期导通。Furthermore, the switched capacitor filter is further configured such that: the first switch and the fourth switch are turned on in the first half of a sampling cycle, and the second switch and the third switch are turned on in the second half of a sampling cycle.
进一步地，所述第一开关、所述第二开关、所述第三开关和所述第四开关采用互补型开关。Furthermore, the first switch, the second switch, the third switch and the fourth switch are complementary switches.
本发明在现有闭环D类功放的脉宽调制工作基础上增加开关电容滤波器，根据开关电容的采样保持原理，滤除原有二阶积分器输出的残余高频谐波成分，滤除开关纹波，从而实现均匀脉宽调制工作，提升闭环D类功放的THD性能。并且，本发明实现结构简单，不需要使用额外的电感单元。The present invention adds a switched capacitor filter on the basis of the pulse width modulation work of the existing closed-loop class D power amplifier, and according to the sampling and holding principle of the switched capacitor, filters out the residual high-frequency harmonic components output by the original second-order integrator, and filters out the switching ripple, thereby achieving uniform pulse width modulation work and improving the THD performance of the closed-loop class D power amplifier. In addition, the present invention has a simple implementation structure and does not require the use of an additional inductor unit.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1是按照本发明的提升THD性能的闭环D类功放的结构示意图。FIG. 1 is a schematic structural diagram of a closed-loop class-D power amplifier for improving THD performance according to the present invention.
图2是图1中开关电容滤波器的结构及对应的采样时钟示意图。FIG. 2 is a schematic diagram of the structure of the switched capacitor filter in FIG. 1 and the corresponding sampling clock.
图3(a)是根据零阶保持器原理的开关电容滤波器的采样原理图，图3(b)是图3(a)对应的幅频特性曲线。FIG3( a ) is a sampling principle diagram of a switched capacitor filter based on the zero-order holder principle, and FIG3( b ) is an amplitude-frequency characteristic curve corresponding to FIG3( a ).
图4是按照本发明的闭环D类功放与现有闭环D类功放的输出结果对比图。FIG. 4 is a diagram comparing the output results of the closed-loop class D power amplifier according to the present invention and the existing closed-loop class D power amplifier.
具体实施方式DETAILED DESCRIPTION
下面结合附图，给出本发明的较佳实施例，并予以详细描述。The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.
本发明提供的提升THD性能的闭环D类功放，增加开关电容滤波器，根据开关电容的采样原理滤除在PWM调制工作中引入的可能的开关纹波，进一步提升D类功放的THD性能。The closed-loop class D power amplifier with improved THD performance provided by the present invention adds a switched capacitor filter, and filters out possible switching ripples introduced in PWM modulation work according to the sampling principle of the switched capacitor, thereby further improving the THD performance of the class D power amplifier.
如图1所示，本发明提供的提升THD性能的闭环D类功放，包括二阶积分器1、均匀脉宽调制单元2、功率级3和反馈单元4。其中，二阶积分器1的输入端分别与音频信号的输入端、反馈单元4的第一端连接，二阶积分器1的输出端与均匀脉宽调制单元2的输入端连接，均匀脉宽调制单元2的输出端与功率级3的输入端连接，功率级3的输出端分别与反馈单元4的第二端、负载扬声器5连接。As shown in Fig. 1, the closed-loop class D power amplifier for improving THD performance provided by the present invention comprises a second-order integrator 1, a uniform pulse width modulation unit 2, a power stage 3 and a feedback unit 4. The input end of the second-order integrator 1 is respectively connected to the input end of the audio signal and the first end of the feedback unit 4, the output end of the second-order integrator 1 is connected to the input end of the uniform pulse width modulation unit 2, the output end of the uniform pulse width modulation unit 2 is connected to the input end of the power stage 3, and the output end of the power stage 3 is respectively connected to the second end of the feedback unit 4 and the load speaker 5.
均匀脉宽调制单元2包括开关电容滤波器21，以及与开关电容滤波器21连接的第一比较器22和第二比较器23。具体地，开关电容滤波器21的输入端与二阶积分器1的输出端连接，开关电容滤波器21的第一输出端与第一比较器22的正相输入端连接，开关电容滤波器21的第二输出端与第二比较器23的正相输入端连接，第一比较器22的反相输入端分别与第二比较器23的反相输入端、外接三角波信号连接。需要说明的是，三角波信号由系统其它基础模块振荡器产生。The uniform pulse width modulation unit 2 includes a switched capacitor filter 21, and a first comparator 22 and a second comparator 23 connected to the switched capacitor filter 21. Specifically, the input end of the switched capacitor filter 21 is connected to the output end of the second-order integrator 1, the first output end of the switched capacitor filter 21 is connected to the positive phase input end of the first comparator 22, the second output end of the switched capacitor filter 21 is connected to the positive phase input end of the second comparator 23, and the inverting input end of the first comparator 22 is respectively connected to the inverting input end of the second comparator 23 and the external triangular wave signal. It should be noted that the triangular wave signal is generated by the oscillator of other basic modules of the system.
本发明的均匀脉宽调制单元的工作原理为：输入信号Vin与反馈单元4经过叠加运算后传输至二阶积分器1，二阶积分器1输出带有纹波的输入信号的预放大信号V1，预放大信号V1经过开关电容滤波器21，根据开关电容滤波器的采样保持原理，线性化过滤高频谐波成分，得到更为均匀的音频放大信号V2，然后将音频放大信号V2传输至第一比较器22和第二比较器23的正相输入端，与三角波信号Vosc进行比较，得到滤除纹波之后的开关信号，即均匀脉宽调制单元2输出脉宽调制信号传输至功率级3。功率级3用于为均匀脉宽调制单元2输出的脉宽调制信号设置死区时间和脉冲的高电平转换，得到控制负载扬声器5的开关脉冲信号。The working principle of the uniform pulse width modulation unit of the present invention is as follows: the input signal Vin and the feedback unit 4 are transmitted to the second-order integrator 1 after superposition operation, and the second-order integrator 1 outputs the pre-amplified signal V1 of the input signal with ripples, and the pre-amplified signal V1 passes through the switch capacitor filter 21, and according to the sampling and holding principle of the switch capacitor filter, the high-frequency harmonic components are linearly filtered to obtain a more uniform audio amplified signal V2, and then the audio amplified signal V2 is transmitted to the positive phase input end of the first comparator 22 and the second comparator 23, and compared with the triangular wave signal Vosc to obtain a switching signal after the ripple is filtered out, that is, the uniform pulse width modulation unit 2 outputs the pulse width modulation signal and transmits it to the power stage 3. The power stage 3 is used to set the dead time and the high-level conversion of the pulse for the pulse width modulation signal output by the uniform pulse width modulation unit 2, and obtain the switching pulse signal for controlling the load speaker 5.
上述开关电容滤波器21包括两个具有相同结构和工作原理的开关电容模块，分别对应闭环D类功放的两个差分信号通路。以单边通路的开关电容模块为例，如图2所示，其包括第一开关S1、第二开关S2、第三开关S3、第四开关S4、第一电容C1和第二电容C2。具体地，第一开关S1的第一端与第三开关S3的第一端连接，并作为开关电容滤波器21的输入端接收上述预放大信号V1；第一开关S1的第二端分别与第二开关S2的第一端、第一电容C1的第一端连接，第三开关S3的第二端分别与第四开关S4的第一端、第二电容C2的第一端连接，第一电容C1的第二端和第二电容C2的第二端均接地；第二开关S2的第二端与第四开关S4的第二端连接，并作为开关电容滤波器21的输出端输出上述音频放大信号V2。The above-mentioned switched capacitor filter 21 includes two switched capacitor modules with the same structure and working principle, which correspond to the two differential signal paths of the closed-loop class D power amplifier. Taking the switched capacitor module of the unilateral path as an example, as shown in Figure 2, it includes a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a first capacitor C1 and a second capacitor C2. Specifically, the first end of the first switch S1 is connected to the first end of the third switch S3, and receives the above-mentioned pre-amplified signal V1 as the input end of the switched capacitor filter 21; the second end of the first switch S1 is respectively connected to the first end of the second switch S2 and the first end of the first capacitor C1, the second end of the third switch S3 is respectively connected to the first end of the fourth switch S4 and the first end of the second capacitor C2, and the second end of the first capacitor C1 and the second end of the second capacitor C2 are both grounded; the second end of the second switch S2 is connected to the second end of the fourth switch S4, and outputs the above-mentioned audio amplified signal V2 as the output end of the switched capacitor filter 21.
开关电容滤波器21的工作原理为：四个采样开关的通断由系统中振荡器输出的脉冲信号控制，具体来说，第一开关S1和第四开关S4由占空比为1/2的脉冲信号控制，脉冲信号的频率与PWM调制的三角波信号的频率相同，第二开关S2和第三开关S3则由脉冲信号的反相信号控制。根据采样保持原理，第一开关S1和第四开关S4在一个采样周期中的前半周期导通，第二开关S2和第三开关S3在一次采样周期中的后半周期导通，即在一个采样周期内对输入信号采样两次，最小化由于采样造成的延时，滤除二阶积分器输出信号的残余高频谐波成分。且为了最小化采样开关的电荷注入和最小化从脉宽调制三角波的时钟反馈，实际电路应用中，上述四个开关均采用互补型开关。The working principle of the switched capacitor filter 21 is as follows: the on and off of the four sampling switches are controlled by the pulse signal output by the oscillator in the system. Specifically, the first switch S1 and the fourth switch S4 are controlled by the pulse signal with a duty cycle of 1/2. Control, pulse signal The frequency of the triangular wave signal is the same as that of the PWM modulated signal. The second switch S2 and the third switch S3 are controlled by the pulse signal The inverted signal Control. According to the sampling and holding principle, the first switch S1 and the fourth switch S4 are turned on in the first half of a sampling cycle, and the second switch S2 and the third switch S3 are turned on in the second half of a sampling cycle, that is, the input signal is sampled twice in one sampling cycle, minimizing the delay caused by sampling and filtering out the residual high-frequency harmonic components of the output signal of the second-order integrator. In order to minimize the charge injection of the sampling switch and minimize the clock feedback from the pulse width modulated triangle wave, in actual circuit applications, the above four switches are all complementary switches.
在传统闭环D类功放结构中，二阶积分器输出的音频放大信号存在残余高频成分，会引起和三角波信号及输入信号的混叠，从而引入不必要的开关纹波。为克服现有闭环D类功放存在的开关纹波导致信号保真度较差的缺点，本发明在现有闭环D类功放中增加开关电容滤波器单元，利用开关电容的零阶保持器原理，采用恒值外推规律，即将前一采样时刻nT的采样值x(n)不增不减地保持到下一个采样时刻(n+1)T，n为正整数。零阶保持器是一种线性时不变系统，其输入和输出之间的关系可以用差分方程表示：y(n+1)＝x(n)。In the traditional closed-loop Class D amplifier structure, the audio amplified signal output by the second-order integrator has residual high-frequency components, which will cause aliasing with the triangular wave signal and the input signal, thereby introducing unnecessary switching ripple. In order to overcome the disadvantage of poor signal fidelity caused by the switching ripple in the existing closed-loop Class D amplifier, the present invention adds a switched capacitor filter unit to the existing closed-loop Class D amplifier, utilizes the zero-order holder principle of the switched capacitor, and adopts the constant value extrapolation law, that is, the sampling value x(n) at the previous sampling time nT is maintained without increase or decrease to the next sampling time (n+1)T, where n is a positive integer. The zero-order holder is a linear time-invariant system, and the relationship between its input and output can be expressed by a differential equation: y(n+1)=x(n).
图3(a)为根据零阶保持器原理的开关电容滤波器的采样原理图，图3(b)为对应的幅频特性曲线。采样开关的目的为线性化过滤高频谐波，同时减少对音频性能的影响，零阶保持器主要用于将输入信号的幅度保持不变，直到下一个采样周期。图3(a)中横坐标t为时间，纵坐标e(t)为输出采样信号，T为开关电容的采样周期，x(t)和y(t)分别为开关电容滤波器的输入和输出。从图中可以看出，在下一个开关周期到来之前，采样电压保持不变。因此利用此原理，在现有的闭环D类功放结构中新增开关电容滤波器，可实现滤除高频谐波的效果。Figure 3(a) is a sampling principle diagram of a switched capacitor filter based on the zero-order holder principle, and Figure 3(b) is the corresponding amplitude-frequency characteristic curve. The purpose of the sampling switch is to linearly filter high-frequency harmonics while reducing the impact on audio performance. The zero-order holder is mainly used to keep the amplitude of the input signal constant until the next sampling cycle. In Figure 3(a), the horizontal axis t is time, the vertical axis e(t) is the output sampling signal, T is the sampling period of the switched capacitor, and x(t) and y(t) are the input and output of the switched capacitor filter, respectively. It can be seen from the figure that the sampling voltage remains unchanged before the next switching cycle arrives. Therefore, by using this principle, adding a switched capacitor filter to the existing closed-loop Class D power amplifier structure can achieve the effect of filtering out high-frequency harmonics.
由公式y(n+1)＝x(n)和图3(a)的采样原理图可知，开关电容在采样保持工作后的输出信号是阶梯波，且含有高次谐波，其传递函数可表示为：From the formula y(n+1)=x(n) and the sampling principle diagram of FIG3(a), it can be seen that the output signal of the switch capacitor after the sampling and holding operation is a step wave and contains high-order harmonics. Its transfer function can be expressed as:
其中，s为频域变量，T为采样周期。 Among them, s is the frequency domain variable and T is the sampling period.
图3(b)的幅频特性曲线中的ωs为开关电容的采样角频率，纵坐标为开关电容的幅频特性，根据该特性曲线可以看出，开关电容的零阶保持器原理在高频段内的增益较小，因此将其应用于闭环D类功放的环路中，可以滤出二阶积分器输出的高频谐波。In the amplitude-frequency characteristic curve of FIG3(b), ωs is the sampling angular frequency of the switched capacitor, and the ordinate is the amplitude-frequency characteristic of the switched capacitor. According to the characteristic curve, it can be seen that the zero-order holder principle of the switched capacitor has a small gain in the high-frequency band. Therefore, applying it to the loop of a closed-loop class-D power amplifier can filter out the high-frequency harmonics output by the second-order integrator.
以差分功放的单边工作为例，图4为本发明的新型环路滤波闭环D类功放与现有闭环D类功放的输出结果对比图。图中Vin为闭环D类功放的模拟输入信号，V1’为现有D类功放的二阶积分器单元的输出，从图中可以看出，由于电路存在某些非线性因素导致V1’存在较多纹波，将该信号经过PWM调制后，会在D类功放的输出产生不必要的谐波，造成信号失真。V2’为本发明的闭环D类功放中的开关电容滤波器的输出，与现有结构相比，开关滤波器经过每个采样周期内对其输入信号的幅度保持，滤除了V1’原有的高频谐波，因此输出更为均匀的近似正弦波。将V2’与系统产生的三角波进行PWM调制，减少了高频谐波在PWM调制引起的相位误差或占空比误差，实现均匀脉宽调制，提升了D类功放的THD性能。Taking the unilateral operation of the differential power amplifier as an example, FIG4 is a comparison diagram of the output results of the new loop-filtered closed-loop class D power amplifier of the present invention and the existing closed-loop class D power amplifier. In the figure, Vin is the analog input signal of the closed-loop class D power amplifier, and V1' is the output of the second-order integrator unit of the existing class D power amplifier. It can be seen from the figure that due to certain nonlinear factors in the circuit, V1' has more ripples. After the signal is PWM modulated, unnecessary harmonics will be generated at the output of the class D power amplifier, causing signal distortion. V2' is the output of the switched capacitor filter in the closed-loop class D power amplifier of the present invention. Compared with the existing structure, the switching filter maintains the amplitude of its input signal during each sampling cycle, filters out the original high-frequency harmonics of V1', and thus outputs a more uniform approximate sine wave. V2' is PWM modulated with the triangle wave generated by the system, which reduces the phase error or duty cycle error caused by high-frequency harmonics in PWM modulation, achieves uniform pulse width modulation, and improves the THD performance of the class D power amplifier.
本发明提出的提升闭环D类功放THD性能的新型环路滤波器设计，该滤波器设计除现有结构外新增开关电容滤波器，基于脉宽调工作原理，利用开关电容的零阶保持器的特性，滤除现有电路中出现的高频谐波成分，从而实现均匀脉宽调制，进而滤除了环路中的开关纹波，减小输出信号的THD，降低信号的失真度。The present invention proposes a novel loop filter design for improving the THD performance of a closed-loop class-D power amplifier. In addition to the existing structure, the filter design adds a switched capacitor filter. Based on the pulse width modulation working principle, the characteristics of the zero-order holder of the switched capacitor are utilized to filter out high-frequency harmonic components appearing in the existing circuit, thereby achieving uniform pulse width modulation, thereby filtering out the switching ripple in the loop, reducing the THD of the output signal, and reducing the distortion of the signal.
以上所述的，仅为本发明的较佳实施例，并非用以限定本发明的范围，本发明的上述实施例还可以做出各种变化。即凡是依据本发明申请的权利要求书及说明书内容所作的简单、等效变化与修饰，皆落入本发明专利的权利要求保护范围。本发明未详尽描述的均为常规技术内容。The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.
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