A $Ka$ -Band Monolithic Bidirectional Up-Down Converter for High-Speed Applications

A Ka-band monolithic bidirectional distributed amplifier (BDA) with a quadrature phase-shift keying modulator/demodulator for high-speed applications is presented in this paper. A modified BDA topology is proposed to improve the isolation between the bidirectional ports. With the proposed circuit topology, the inputs and outputs of the two signal paths are switched at the same port, and the modulator/demodulator can be connected directly with the BDA to perform signal conversion. Furthermore, a cascode Darlington amplifier is employed in the gain cell of the BDA to achieve broad bandwidth. The measured small-signal gains of the BDA are 12 dB with a 3-dB bandwidth from 12 to 30 GHz for the forward and reverse paths. The integrated bidirectional up-down converter is further evaluated with the digital modulation and demodulation. For the up conversion, the measured error vector magnitude is within 9.9%. For the down conversion, the measured eye diagram is evaluated up to 2 Gb/s.