WO2012048461A1

WO2012048461A1 - Switching power amplifier for sampling and holding analog signals

Info

Publication number: WO2012048461A1
Application number: PCT/CN2010/077696
Authority: WO
Inventors: 胡章儒
Original assignee: Hu Zhangru
Priority date: 2010-10-13
Filing date: 2010-10-13
Publication date: 2012-04-19
Also published as: CN101971497A

Abstract

A switching power amplifier is disclosed. The amplifier samples and holds analog signals, and guarantees that both the front-edge and the rear-edge of the square-wave generated by a comparator are triggered by comparing with the same analog level so that the quantizing error of the analog signals, the distortion and noise of the power amplifier can be reduced.

Description

采样保持模拟信号的开关式功放Switching amplifier for sampling and maintaining analog signals

采样保持模拟信号的开关式功放Switching amplifier for sampling and maintaining analog signals

本发明描述一种开关式功放实现方案。对模拟信号进行采样保持，确保比较器产生的方波前沿和后沿都是与同一模拟电平比较而触发的，降低模拟信号的量化误差，减低开关式功放的失真和噪音。 The present invention describes a switching power amplifier implementation. The analog signal is sampled and held to ensure that the square wave leading edge and trailing edge generated by the comparator are triggered compared with the same analog level, reducing the quantization error of the analog signal and reducing the distortion and noise of the switching power amplifier.

一般地，典型的开关式功放电路结构中，是由比较器产生方波脉冲，比较器的两个输入端分别输入模拟信号和三角波信号，三角波信号的频率至少要大于模拟信号最高频率的2倍。三角波信号的幅度至少要大于模拟信号可能出现的最大幅度。我们在此假定三角波信号输入比较器的反向输入端，模拟信号输入比较器的正向输入端。那么，在三角波信号上升沿的电平大于模拟信号电平的那个瞬间比较器翻转，同时输出负向脉冲，我们设此电平为A电平。此时，三角波信号电平继续上升直到最大值，然后是下降。当三角波信号下降沿的电平小于模拟信号电平的那个瞬间，比较器翻转，同时输出正向脉冲，我们设此电平为B电平。这个过程就相当于给模拟信号取样量化，是用方波信号的占空比去表示模拟信号电平的幅度大小。这个过程是要求方波的占空比能准确地表示出模拟信号电平的幅度大小，误差是越小越好。请注意了：前文中说的'三角波信号电平继续上升直到最大值，然后是下降，'在此过程中，模拟信号电平也是变化的！也就是说A电平和B电平是不相等的！方波的前沿是由A电平触发的，后沿是由B电平触发的。如果由A到B是单向匀速变化的，那么方波信号占空比表示的是A和B的平均值，但是，实际的功放输入信号是很复杂的，其变化是无法预测的，也许A大于B，也许A小于B，也许由A到B是曲线变化的。这就会产生了量化误差，量化误差的具体表现就是失真和噪音。为了减小量化误差，就要提高方波的频率，这就会增加后级开关管的功耗。而且，靠提高方波频率来减小量化误差，其作用是有限的。只有把方波频率无限地提高，才能从理论上消除量化误差，这实际上是做不到的。也就是说，上述电路结构实际是不能从理论上消除量化误差。用锯齿波代替三角波可以减小误差，但也不能从理论上消除误差，因为理想化的锯齿波是不存在的，实际的锯齿波也是不对称三角波。一个理论上不成熟的电路结构，当然不会有好的效果。通常的商品化开关式功放，仪器测量失真很小，可实际听感不好，因为测量时用的是正弦波信号，而实际听音用的是音乐信号。正弦波信号在多数时间里是单向变化的，音乐信号在多数时间里是随机变化的。 Generally, in a typical switched power amplifier circuit structure, a square wave pulse is generated by a comparator, and two input terminals of the comparator respectively input an analog signal and a triangular wave signal, and the frequency of the triangular wave signal is at least twice greater than the highest frequency of the analog signal. . The amplitude of the triangular wave signal is at least greater than the maximum amplitude that the analog signal may appear. We assume here that the triangular wave signal is input to the inverting input of the comparator and the analog signal is input to the forward input of the comparator. Then, when the level of the rising edge of the triangular wave signal is greater than the level of the analog signal, the comparator flips and outputs the negative pulse. Let us set the level to the A level. At this time, the triangular wave signal level continues to rise until the maximum value, and then falls. When the level of the falling edge of the triangular wave signal is less than the level of the analog signal, the comparator flips and outputs a positive pulse. We set this level to B level. This process is equivalent to sampling the analog signal, using the duty cycle of the square wave signal to indicate the magnitude of the analog signal level. This process requires that the duty cycle of the square wave accurately represent the magnitude of the analog signal level, and the smaller the error, the better. Please note: the 'triangular wave signal level continues to rise until the maximum value, then the drop, 'in the process, the analog signal level is also changing! That is to say, the A level and the B level are not equal! The leading edge of the square wave is triggered by the A level, and the trailing edge is triggered by the B level. If A to B are unidirectionally variable, the square wave signal duty cycle represents the average of A and B. However, the actual power amplifier input signal is very complicated, and the change is unpredictable. Maybe A Greater than B, maybe A is less than B, and perhaps A to B is a curve change. This produces a quantization error, and the specific performance of the quantization error is distortion and noise. In order to reduce the quantization error, it is necessary to increase the frequency of the square wave, which increases the power consumption of the switching transistor of the latter stage. Moreover, the effect of reducing the quantization error by increasing the square wave frequency is limited. Only by increasing the square wave frequency infinitely can we theoretically eliminate the quantization error, which is actually impossible. That is to say, the above circuit structure actually cannot theoretically eliminate the quantization error. Replacing a triangular wave with a sawtooth wave can reduce the error, but it cannot theoretically eliminate the error because the idealized sawtooth wave does not exist, and the actual sawtooth wave is also an asymmetric triangular wave. A theoretically immature circuit structure will certainly not have a good effect. The usual commercial switch-type power amplifier, the instrument measurement distortion is very small, the actual hearing is not good, because the measurement uses a sine wave signal, and the actual listening is a music signal. The sine wave signal changes in one direction over most of the time, and the music signal changes randomly over most of the time.

采用本发明的方法，在比较器之前加上一个采样保持电路，对模拟输入信号进行采样保持，使得A电平和B电平是相等的。这样，可以大幅度地减小量化误差，降低失真。根据奈奎斯特取样定理，方波信号频率只要大于模拟信号频率两倍就能无失真地表示模拟信号。考虑到电路中其它因素，如果放大20KHZ以内的音频信号，取其5-10倍的方波频率应能有较好的效果。现在的商品化开关式功放有很多是取20KHZ音频信号的30-60倍，过高的方波频率在很大程度上抵消了开关式功放高效率的优点。 With the method of the present invention, a sample-and-hold circuit is added before the comparator to sample and hold the analog input signal such that the A level and the B level are equal. In this way, the quantization error can be greatly reduced and the distortion can be reduced. According to the Nyquist sampling theorem, the square wave signal frequency can represent the analog signal without distortion as long as it is more than twice the frequency of the analog signal. Considering other factors in the circuit, if the audio signal within 20KHZ is amplified, the square wave frequency of 5-10 times should have better effect. Many commercial switch-mode power amplifiers are 30-60 times of the 20KHZ audio signal. The excessively high square wave frequency largely offsets the high efficiency of the switch-type power amplifier.

实现本发明的方法，可以使用一般商品化的采样保持集成电路；也可以使用双向模拟开关外接电容做成。采样保持电路的开关控制信号可以用比较器输出的方波。当三角波信号上升沿的电平大于模拟信号电平的那个瞬间，比较器输出负向脉冲控制采样保持电路的双向模拟开关断开，当三角波信号下降沿的电平小于模拟信号电平的那个瞬间，比较器输出正向脉冲控制采样保持电路的双向模拟开关接通。 To implement the method of the present invention, a commercially available sample-and-hold integrated circuit can be used; or a bidirectional analog switch external capacitor can be used. The switching control signal of the sample-and-hold circuit can use the square wave output by the comparator. When the level of the rising edge of the triangular wave signal is greater than the level of the analog signal level, the comparator outputs a negative-direction pulse to control the bidirectional analog switch of the sample-and-hold circuit to be turned off, when the level of the falling edge of the triangular wave signal is less than the level of the analog signal level. The comparator output forward pulse controls the bidirectional analog switch of the sample and hold circuit to be turned on.

Claims

采样保持模拟信号的开关式功放，其特征是：在产生方波脉冲的比较器之前，加入采样保持电路，对模拟信号进行采样保持。A switching power amplifier that samples and holds an analog signal is characterized in that a sample-and-hold circuit is added before the comparator that generates the square wave pulse to sample and hold the analog signal.