Abstract: The authors present a thorough analysis of the 1/f noise, linearity and conversion gain of a CMOS active double-balanced Gilbert mixer circuit. This mixer, adopting PMOSFETs as loads, is used for direct conversion receiver operating in the 2.4-GHz ISM band. To lower the 1/f noise of this mixer, the parasitic vertical NPN (V-NPN) BJT is used as switch, and the low noise shunt circuits paralleled with the PMOSFETs are adopted as loads. A high performance operational amplifier is also applied with the PMOSFETs, which not only provides a suitable DC bias voltage for the desired signals in the zero intermediate frequency (IF) band to avoid the saturation of the following stage, but also produces enough high conversion gain for the mixer. Meanwhile, the capacitor cross-coupled (CCC) circuits applied in the input transconductance (G_m) stage allow further increasing the conversion gain. Besides, to enhance the linearity of the mixer, the common gate (CG) amplifiers as transconductance (G_m) input stage devices are adopted. The mixer is fabricated with the TSMC 0.18-μm 1-Poly 6-Metal RF CMOS process. The resulting mixer achieves 17.78 dB conversion gain, 13.24 dB NF and 4.45 dBm IIP3 with 3 mA current consumption under a 1.5 V power supply.

Key words: direct conversion receiver, RF front-end, active double-balanced Gilbert mixer, low noise shunt circuit, 1/f noise, common gate amplifier, capacitor cross-coupled

摘要： 对带有源负载的CMOS双平衡Gilbert有源混频器的1/f噪声、线性度与转换增益进行深入分析。这款采用PMOSFETs做负载的混频器工作于2.4 GHz频段。为降低混频器的1/f噪声, 利用双阱工艺中的寄生垂直NPN晶体管作为开关, 同时在PMOSFETs处并联最低噪声的分流电路作为负载。运用在PMOSFETs处的高性能运算放大器, 不仅为零中频输出提供了合适的直流偏置电压, 以避免下级电路的饱和, 并能够为混频器提供足够高的转换增益。同时, 在输入跨导(G_m)级电路中采用电容交叉耦合电路能够将转换增益进一步提高。为了增加混频器的线性度, 采用共栅放大器作为输入跨导级电路。这款混频器采用TSMC 0.18m 1-Poly 6-Metal RF CMOS工艺, 在1.5 V电源电压、3 mA的电流消耗下获得了17.78 dB的转换增益、13.24 dB的噪声因子和4.45 dBm输入三阶交调点的高性能。

关键词: 直接下转换接收机, RF前端, 有源双平衡Gilbert混频器, 低噪声分流电路, 1/f噪声, 共栅放大器, 电容交叉耦合