Abstract

Using the pulse-width modulation (PWM) is a very convenient and efficient way to generate the approximation of the AC, in the simplest case sinewaves in the embedded test & measurement solutions. Partly, because the on-chip PWM modulator is available in most of the microcontroller and DSP chips. In the current paper improved (compared with conventional PWM) implementation of the binary waveforms is proposed. The idea is based first on the conversion of the desired AC (e.g., sinewave) to quantize in the amplitude domain waveform, to be further converted to the binary pulses with a duty cycle, corresponding to each quantization level. Such an approach is described and analyzed, with several examples of the implementation and application for impedance measurement solutions. The results show the significant improvements of the approximated binary signals both in the frequency and time domain, by optional simple low- or bandpass filtering of the binary signal, over classical PWM, while still preserving simplicity (e.g., number of needed binary signal segments) of the generated waveforms (e.g., compared with delta-sigma bitstreams). The beneficial usage of the proposed approach for the impedance measurement applications is described, as well as to generate excitation waveforms, as well as to be used as reference waveforms for synchronous demodulation of the response signal. It is shown, that for the frequency range of 10 to 70 kHz total harmonic distortion below 2.5% can be achieved by the proposed improved PWM solution.

中文翻译：

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改进的基于 PWM 的正弦波生成：阻抗测量示例

摘要

使用脉宽调制 (PWM) 是生成交流电近似值的一种非常方便且有效的方法，在最简单的情况下是嵌入式测试和测量解决方案中的正弦波。部分原因是大多数微控制器和 DSP 芯片都配备了片上 PWM 调制器。在当前的论文中，提出了二进制波形的改进（与传统 PWM 相比）实现。该想法首先基于将所需的AC（例如正弦波）转换为幅度域波形中的量化，然后进一步转换为具有与每个量化级别相对应的占空比的二进制脉冲。通过阻抗测量解决方案的实施和应用的几个示例来描述和分析这种方法。结果表明，通过对二进制信号进行可选的简单低通或带通滤波，近似二进制信号在频域和时域方面均比传统 PWM 有了显着改进，同时仍然保持简单性（例如，所需二进制信号段的数量）生成的波形（例如，与 delta-sigma 比特流相比）。描述了所提出的方法对于阻抗测量应用的有益用途，以及生成激励波形以及用作响应信号同步解调的参考波形。结果表明，对于 10 至 70 kHz 的频率范围，通过所提出的改进 PWM 解决方案可以实现低于 2.5% 的总谐波失真。