幅度校准功能的低附加相移数控衰减器

Low phase variation digital controlled attenuator with amplitude calibration function

提出了一种可用于Ka波段相控阵系统的高精度低附加相移五位数控衰减器(Digital Controlled Attenuator,DCA)。该DCA采用了嵌入式开关的T型、简化T型和Π型三种衰减结构设计基本衰减单元,实现了15.5 dB的衰减动态范围和0.5 dB的最小衰减步进。幅度校准技术被用于信号通路中,可有效降低由工艺波动引起的衰减幅度误差增大问题,增强了电路设计的鲁棒性。同时,在T型和Π型衰减结构中采用电容补偿技术提高其高频衰减性能,实现低附加相移。基于65 nm CMOS工艺,对所提出的DCA进行了优化仿真、流片与测试验证。芯片核心尺寸为500µm×150µm。测试结果表明:在25~35 GHz频带范围内,参考态插入损耗为6.54~8.6 dB,32衰减态对应的输入/输出回波损耗优于-15 dB,幅度误差RMS和相位误差RMS分别为0.12~0.26 dB和1.02°~2.07°。

This paper presents a high accuracy and low phase variation 5-bit digital controlled attenuator(DCA) for Ka-band phased-array system applications. The DCA adopts three attenuation topologies of T-type, simplified T-type and Π-type topologies with embedded switches to design the basic attenuation cells, and realizes the attenuation dynamic range of 15.5 dB and the minimum attenuation step of 0.5 dB. Amplitude calibration technology is used in signal path, which can effectively reduce the increase of attenuation amplitude error caused by process fluctuation and enhance the robustness of circuit design. At the same time, capacitance compensation technology is used in T-type and Π-type attenuation topologies to improve their high-frequency attenuation performance and achieve low phase variation. Based on 65 nm CMOS process, the proposed DCA is optimization simulated, taped out, measured and verified. The core area of the chip is 500 μm×150 μm. The measurement results show that within frequency range of 25~35 GHz, the insertion loss of reference state is 6.54~8.6 dB, the input/output return loss corresponding to 32 attenuation states is better than-15 dB, and the amplitude error RMS and phase error RMS are 0.12~0.26 dB and 1.02~2.07°, respectively.