A 35–65GHz Quadrature-Balanced N-Path Filter with a 0.1–0.9GHz Tunable Bandwidth

In this work, we present 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 proposed filter includes transformer-based balanced quadrature hybrid couplers at the input and output, and core circuits composed of four paths. 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, which implemented in a 45-nm CMOS SOI technology, operated from 35 to 65 GHz. It achieved an insertion loss of < 8.7 dB, a return loss of < 10.3 dB, and a noise figure of < 25.7 dB. Moreover, it realized a tunable bandwidth from 0.1 to 0.9 GHz with a power consumption of 10.4–11.8mW 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.