35−65 GHz Quadrature-Balanced N-path Filter with a 0.1−0.9 GHz Tunable Bandwidth

In this paper, we propose a 35−65GHz quadrature-balanced N-path filter with a tunable bandwidth of 0.1−0.9 GHz, to realize a flexible direct digital RF modulator in terms of frequency, bandwidth, and modulation in the millimeter-wave band. The filter includes transformer-based balanced quadrature hybrid couplers at the input and output. The filter achieves high-frequency operation by driving four-phases RF signals with 50 % duty cycle clock signals. Additionally, it achieves a wide tunable bandwidth using a baseband amplifier that can control its cutoff frequency. The filter was implemented in 45-nm CMOS SOI technology. It achieved an insertion loss of < 8.7 dB. Moreover, it realized a power consumption of 10.4-11.8 mW and a chip size of 0.96 mm². The filter achieved an EVM of −41.5 dB and −32.0 dB for narrowband signals (20 Msps 1024-QAM) and wideband (800 Msps 64-QAM) signals, respectively.