A fully integrated Q-enhanced notch filter LNA for TX blocker suppression in FDD systems

Abstract

An LNA with integrated Q-enhanced notch filter for use in FDD transceiver systems has been demonstrated. The amplifier core is coilless, made possible by the use of capacitive shunt-series feedback to simplify matching. Additionally, a Q-enhanced notch filter is integrated which attenuates TX blockers thus making an external interstage SAW filter redundant. A prototype was produced on a 65nm CMOS process. Without filter operation it draws 16.6mA from a 1.3V supply, with filter switched on the Q-enhancement adds 2.3–4.1 mA, depending on the demanded selectivity. The filter can be disconnected from the LNA. At 100 Ω source impedance the input reflection factor S 11 does not exceed −15 dB for the chosen frequency. The tuning range of the filter is 1500–1780 MHz for RX. The LNA supplies 24.5dB gain with a noise figure of NF = 2.3 dB. For 9 dB selectivity, the gain at RX drops to 20dB and the NF increases to 4.1 dB. The point where the RX gain drops 1dB due to a TX blocker is increased from −23.3 dBm to −19.5 dBm thus showing a proof-of-concept.