一种可降低开关电源电磁干扰的扩频时钟电路  

A Spread Spectrum Clock Generator for EMI Reduction of Switch Mode Power Converter

作　　者：钟超超 宋奎鑫 孔瀛 康磊 梁庭[1] ZHONG Chaochao;SONG Kuixin;KONG Ying;KANG Lei;LIANG Ting(Key Laboratory of Micro/Nano Devices and Systems,Ministry of Education,North University of China,Taiyuan,030051,CHN;Aerospace Science and Technology Corporation,Beijing Microelectronics Technology Institute,Beijing,100029,CHN)

机构地区：[1]中北大学微纳器件与系统教育部重点实验室,太原030051 [2]中国航天科技集团公司北京微电子技术研究所,北京100029

出　　处：《固体电子学研究与进展》2024年第3期239-244,共6页Research & Progress of SSE

摘　　要：介绍了一种基于0.18μm BCD工艺实现的可用于降低开关电源转换器电磁干扰(Electromagnetic inter⁃ference,EMI)的扩频时钟电路,电路中的双相张弛振荡器可在1.8~4.0 MHz工作,采用了一个三输入比较器配合时序电路实现了振荡器的正常启动。为避免传统三角波调制方法产生人耳可闻噪声、导致输出噪声较大等缺点,采用了伪随机调制方法,首先通过7位线性移位反馈寄存器生成伪随机码,再使用电流舵数模转换器将伪随机码转换为电流,最终伪随机变化的电流控制振荡器频率以伪随机的方式变化。本文提出的扩频时钟电路应用在一款降压DC-DC转换器芯片中并进行了流片,测试结果表明扩频后功率谱基波峰值幅度下降10 dB,二次谐波峰值幅度下降17 dB,功率谱中没有明显的调制频率分量,可有效降低DC-DC转换器的EMI。A spread spectrum clock circuit based on a 0.18μm BCD process that can be used to reduce the electromagnetic interference(EMI)of switching power converter was presented.The dualphase relaxation oscillator in the circuit could operate at 1.8-4.0 MHz,and a three-input comparator was used to realize the oscillator in conjunction with a timing circuit for startup.In order to avoid the disadvantages of traditional triangular wave modulation methods,such as audible noise to human ears and large output noise,a pseudo-random modulation method was adopted.Firstly,a pseudo-random code was generated by a 7-bit linear shift feedback register.Then,a current steering digital-to-analog converter was used to convert the pseudo-random code into current.Finally,the pseudo-randomly varying current controled the frequency of the oscillator to vary in a pseudo-random manner.The spread spectrum clock circuit proposed in this work had been applied in a step-down DC-DC converter chip and taped out.The measured results show that the peak amplitude of fundamental and second har⁃monic reduce 10 dB and 17 dB,respectively.There is no obvious modulation frequency component in the power spectrum with spread spectrum enabled.The EMI of the DC-DC converter is effectively reduced.

关 键 词：扩频 低电磁干扰 伪随机 张弛振荡器 

分 类 号：TN432[电子电信—微电子学与固体电子学]