低功耗Zigbee收发器镜像抑制滤波器设计

摘要

分析镜像抑制和带外衰减的要求,设计了适用于2.4 GHz 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0.18 μm 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35 dB,偏移3.5 MHz抑制超过50 dB.在1.8 V电源电压下电流为0.86 mA.%An image reject filter is designed for a 2.4 GHz Zigbee transceiver RF front-end after analyzing the requirement of image reject and out-of-band attenuation. This filter uses a 7th order Butterworth OTAC biquad structure. The complex filtering is realized through linear translation. Cross-coupled input OTA is used to expand input linear range. A PLL based on-chip frequency tuning circuit is proposed to minimize frequency variation. The circuit is implemented in a 0.18μm CMOS process. Measured results show that the bandwidth is 2.54 MHz. The image rejection ratio (IMRR) is more than 35 dB, and out-of-band attenuation is more than 50 dB at 3.5 MHz offset. The power dissipation is 0.86 mA from 1.8 V power supply.