A baseband LPF for GSM,TD-SCDMA and WCDMA multi-mode transmitters

This paper describes a low-pass reconfigurable baseband filter for GSM,TD-SCDMA and WCDMA multi-mode transmitters.To comply with 3GPP emission mask and limit TX leakage at the RX band,the out-of -band noise performance is optimized.Due to the distortion caused by the subthreshold leakage current of the switches used in capacitor array,a capacitor bypass technique is proposed to improve the filter’s linearity.An automatic frequency tuning circuit is adopted to compensate the cut-off frequency variation.Simulation results show that the filter achieves an in-band input-referred third-order intercept point(IIP3) of 47 dBm at 1.2-V power supply and the out-of-band noise can meet TX SAW-less requirement for WCDMA & TD-SCDMA.The baseband filter incorporates -40 to 0 dB programmable gain control that is accurately variable in 0.5 dB steps.The filter’s cut-off frequency can be reconfigured for GSM/TD-SCDMAAVCDMA multi-mode transmitter.The implemented baseband filter draws 3.6 mA from a 1.2-V supply in a 0.13μm CMOS process.     

一种应用于GSM,TD-SCDMA和WCDMA多模发射机的基带低通滤波器设计

本文设计了一款应用在GSM,TD-SCDMA和WCDMA多模发射机中的可配置基带低通滤波器。为了满足3GPP发射频罩要求和限制发射机在接收频段的噪声泄露,本文对滤波器的带外噪声进行了分析和优化设计。由于开关电容阵列中开关的亚阈值泄露电流引起信号失真,本文提出了一种电容旁路技术可以降低亚阈值泄露电流从而提高电路的线性度。本文采用了一种自动频率校准电路来补偿截止频率偏差。仿真结果表明,滤波器在1.2V电源电压下可以实现47dBm的IIP3,并且滤波器的带外噪声满足TD-SCDMA和WCDMA SAW-less发射机的要求。滤波器具有-40到0dB的可变增益范围,增益步长为 0.5dB。滤波器的截至频率可配置,适用于GSM,TD-SCDMA和WCDMA多模发射机。滤波器电路在0.13μm CMOS工艺下实现,电源电压为1.2V,消耗电流3.6mA。