A Multiband, High-Order Notch Filter for TX Leakage Suppression in FDD Receivers

This letter presents a tunable notch filter that can be reconfigured to improve rejection while offering high power handling. The notch filter uses a series N -path filter in conjunction with an impedance-transformed shunt N -path filter to improve the transmit (TX) rejection or notch concurrent bands. A 4th-order notch provides >40-dB rejection for a single TX channel. In the dual-notch mode, the notches can be tuned to two different TX channels. Finally, a low-power single-notch mode provides >20-dB rejection with low power consumption. The filter is implemented in a 45-nm CMOS SOI process and consumes between 11.9 and 43.9 mW at 1-V supply across a tuning range from 0.45 to 0.9 GHz while providing a peak rejection >50 dB and P_{1~{\mathrm{ dB}}} as high as 15.8 dBm.