| Summary: | 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 1.02～2.07o, respectively.
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