作者：陈佳佳 （常州铁道高等职业技术学校，江苏 常州 213011）
摘 要：【目的】N通道滤波器由于时钟采样特性，能够使不需要的奇次和偶次谐波经上采样后出现在输出端，影响有用信号的传输。偶次谐波可通过差分结构解决，而奇次谐波正面临重大挑战。【方法】笔者在TSMC 40 nm工艺、1.1 V供电电压下设 计了一款基于时钟相位差原理的抑制3k次谐波差分6通道滤波器。该滤波器由单端转双端的差分6通道滤波器、两个跨导放大器和片外变压器构成，差分6通道滤波器用于抑制偶次和3k次谐波，跨导放大器用于提高增益，片外变压器用于阻抗匹配以提高Q值。【结果】Cadence Spectre RF仿真结果显示，中心频率fs可调范围为200 MHz~1.1 GHz，3次谐波抑制高达42 dB， 带外抑制达到32 dB，电压增益为10 dB，带内线性度IIP3大于8 dBm，噪声系数NF小于6 dB。【结论】相比于近期类似工作， 该滤波器谐波抑制性能有显著提升，整体性能也较好，可应用于多模多频接收机前端，有着良好的应用前景。
A Differential N-Path Filter for Suppressing 3k Harmonic Based on Phase Difference Principle
Author: Chen Jiajia
(Changzhou Railway Higher Vocational and Technical School, Jiangsu Changzhou 213011)
Abstract: [Objective] Due to the clock sampling characteristics, N-path filters can cause unwanted odd and even harmonics to appear at the output after upsampling, affecting the transmission of useful signals. Even harmonics can be solved through differential structures, while odd harmonics are facing significant challenges. [Method] The author designed a 3k harmonic suppression differential 6-path filter based on the principle of clock phase difference under the TSMC 40 nm process and 1.1 V supply voltage. This filter consists of a single ended to double ended differential 6-path filter, two transconductance amplifiers, and an off chip transformer. The differential 6-path filter is used to suppress even and 3k harmonics, the transconductance amplifier is used to increase gain, and the off chip transformer is used for impedance matching to improve Q value. [Result] Cadence Spectre RF simulation results show that the adjustable range of center frequency fs is 200 MHz~1.1 GHz, with 3rd harmonic suppression up to 42 dB, out of band suppression up to 32 dB, voltage gain of 10 dB, in band linearity IIP3 greater than 8 dBm, and noise coefficient NF less than 6 dB. [Conclusion] Compared with similar recent work, the harmonic suppression performance of this filter has significantly improved, and the overall performance is also good. It can be applied to the front-end of multimode and multi frequency receivers, and has good application prospects.
Keywords: N-path filter; harmonic suppression; differential structure; transconductance amplifier