电表计量芯片中sigma-delta ADC的系统级分析

提出一种基于sigma-delta 模拟数字转换器（ADC）设计的解决方案.该方案主要包括提高sigma-delta ADC 中比较器的反馈电压精确度和sigma-delta ADC 的转换精确度来提高电能计量的精确度.实际应用中,电能计量芯片包括2 路以上的sigma-delta ADC 转换通道,一部分通路用于实现固定幅度的电压模数转换,因而电压数字量的SQNR 为一定值,另外的通路则实现用户用电产生电流的模数转换,因而电流数字量的SQNR 随用户用电量而变,通过将电压数字量与电流数字量相乘,即得到用户所用电量及相应的有效值.经验证,当反馈电压存在x%的偏差时,会使电能计量和有效值计量分别产生2x%和x%的偏差.当电流通道SQNR（信号至量化噪声比）低于30 dB 时,会使电能计量产生0.5%的误差,电流通道有效值计量误差大于0.4%.

Analysis of sigma-delta ADC in digital power metering applications

The design of the power metering system is described. Both theoretical analysis and simulations are made to examine the influence of the sigma-delta Analog to Digital Converter(ADC) on this system. It points out that the reference voltage in sigma-delta ADC is a key factor in power metering system. As an offset of x% in sigma-delta ADC, reference voltage results in a 2x% bias in power measurement and x% in RMS(Root Mean Square) measurement. In addition, the resolution of sigma-delta ADC also affects the performance of the system. This is especially true in current RMS calculation channel because this channel adopts the current input, whose SQNR(Signal-to-Quantization-Noise Ratio) is low when the current is small.