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Eliminate the Influence of SMPS Ripple Noise for WiFi Receiver with LMS Algorithms
ZHANG Yan,BU Gang,WANG Mingming
Electronic Science and Technology    2019, 32 (1): 11-15.   DOI: 10.16180/j.cnki.issn1007-7820.2019.01.003
Abstract   (413 HTML6 PDF(pc) (1610KB)(36)  

Aim

ing at the problem of ripple when the switching mode power supply was applied to the RF front-end analog circuit, a scheme of eliminating ripple in the digital baseband by using adaptive filtering was proposed. WiFi transceiver system based on IEEE802.11b wireless communication protocol was established by using simulink, and LMS adaptive filter was utilized in digital baseband to suppress the ripple. Simulation results showed that the signal quality could be significantly improved by the adaptive filter. When the ripple amplitude was within 150 mV, the received signal could meet the protocol requirements. Based on these results, an adaptive filter was designed, including both front end and layout. The power consumption analysis showed that the final adaptive filter consumed only 1.35 mW at 33 MHz clock frequency and 1.98 V supply voltage, validating the possibility of using switching mode power supplies for WIFI receivers to achieve significant power savings.


Figure 2. Diagram of baseband signal generation
Extracts from the Article
基带信号产生框图如图2所示,随机信号产生之后经过直接序列扩频、DQPSK(Differential Quadrature Phase Shift Keyin)调制、升余弦成型滤波转换为适合传输的波形。最后经过射频发射电路直接上变频并加噪声衰减为-85 dBm的信号。
使用Verilog实现自适应滤波器系统,取输入信号(signal_in)为1 MHz、2 MHz、3 MHz、4 MHz、5 MHz的混合信号,参考输入信号(ref_input,ref_input1)频率为2 MHz,仿真结果如图7所示。从图中可以看出,在LMS算法收敛之前时,输出信号和输入信号“signal”相差不大,而在LMS算法收敛之后,可以观察到输出信号中的2 MHz分量被大量滤除。
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