A SiGe-BiCMOS Wideband Active Bidirectional Digital Step Attenuator With Bandwidth Tuning and Equalization

A 6-bit active digital step attenuator (DSA), which simultaneously achieves wide bandwidth, flat gain characteristics, and bidirectional operation, is proposed for wideband phased-array antennas. In addition, it supports bandwidth tuning and equalization function to reduce complexity and physical size of systems. The proposed circuit utilizes an active double-pole double-throw switch, which provides positive gain with four-way switching and bidirectional operation. In addition, the simplified switched T-type topologies are applied to improve the insertion loss and save on chip area for low-attenuation states (0.5, 1, and 2 dB). Implemented in a 130-nm SiGe-BiCMOS technology platform, the proposed active DSA provides the advantages of seamless integration with digital control blocks and wide operational bandwidth due to its low parasitic capacitance. The active DSA exhibits flat in-band gain of >7 dB and the input/output return losses <9 dB from 2 to 20 GHz, which covers S-, C-, X-, and Ku-bands. In addition, it shows the root-mean-square amplitude and phase errors of <0.3 dB and <3.4°, respectively. The measured output 1-dB compression point is −3.6 dBm with a dc power consumption of 75 mW. The chip area of the active DSA is $1.43\times 1.23$ mm2, including pads.

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