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

In this work, we present a $\mathrm{3 5} \mathrm{- 6 5} \mathrm{G H z}$ quadraturebalanced N-path filter with a tunable bandwidth of $0.1-0.9 \mathrm{GHz}$, 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 couplersat the input and output, and core circuits composed of four paths. The filter achieves highfrequency 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 $45-\mathrm{nm}$ CMOS SOI technology,operated from 35 to 65 GHz. It achieved an insertion loss of $\lt 8.7 \mathrm{~dB}$, a return loss of $\lt 10.3 \mathrm{~dB}$, and a noise figure of < $\mathrm{2 5. 7 ~ d B}$. Moreover, it realized a tunable bandwidth from $\mathrm{0. 1}$ to $\mathrm{0. 9}$ GHz with a power consumption of $10.4-11.8 \mathrm{~mW}$ and a chip size of $0.96 \mathrm{~mm}^{2}$. The filter achieved an $E V M$ of -41.5 dB and -32.0 dB for narrowband signals (20 Msps, 1024-QAM) and wideband (800 Msps, 64-QAM) signals, respectively.