超低中频CMOS下混频器的设计

Design of CMOS Super Low Intermediate-frequency Downmixer

低中频架构由于其镜像抑制能力强，易于集成等优点而被广泛应用于接收机的设计中。混频器作为接收机的重要模块之一，它的主要作用是完成频率转换，其性能对接收机有很大的影响。设计了一个工作于GSM850频带的超低中频CMOS混频器。为了提高转换增益和降低噪声。输入级加入了分流单元。在输出级应用共模反馈稳定输出电平。混频器工作的频带为869～894MHz，中频输出为100kHz。仿真结果显示增益为17dB，三阶交调点为9．6dB，噪声系数为17．5dB。

Because of good image- reject performance and easy to integrate the configrution of super- low- intermediate frequency is widely used in design of transceiver. As an important part of receiver, mixer is used to change the frequency. Its preformance has great effect on receiver, a super - low - intermediate frequency CMOS mixer applied in GSM is presented. A circuit to decrease the current in the input and a circuit called common - mode feedback to fix the voltage level of ouput. This mixer is applied in GSM of 869-894 MHz and with the output intermidiate frequency at 100 kHz. Its gain is 17 dB,IIP3 is 9.6 dB and noise figure is 17.5 dB.