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分析镜像抑制和带外衰减的要求,设计了适用于2.4GHz Zigbee无线收发前端的镜像抑制滤波器。电路采用7阶巴特沃思OTA-C双二次结构,通过线性变换实现复数滤波。采用交叉耦合输入跨导器,扩大了输入线性范围。为减小滤波器频率偏差,设计了一种锁相环频率修调电路。电路利用0.18μm CMOS工艺实现。测试结果表明,复数滤波器带宽2.54MHz,镜像抑制大于35dB,偏移3.5MHz抑制超过50dB。在1.8V电源电压下电流为0.86mA。
Analyze the requirements of image rejection and out-of-band attenuation, we designed an image rejection filter for the 2.4GHz Zigbee wireless transceiver front-end. The circuit uses 7th order Butterworth OTA-C double secondary structure, through the linear transform to achieve complex filtering. The use of cross-coupled input transconductance, expanding the input linear range. In order to reduce the frequency deviation of the filter, a phase-locked loop frequency trimming circuit is designed. The circuit is implemented with a 0.18μm CMOS process. The test results show that the complex filter bandwidth of 2.54MHz, image rejection greater than 35dB, 3.5MHz offset suppressed more than 50dB. Current is 0.86mA at 1.8V supply voltage.