Two-Stage Highly Selective Receiver Front End Based on Impedance Transformation Filtering

In order to achieve blocker rejection comparable to surface acoustic wave (SAW) filters, we propose a two-stage tunable receiver front-end architecture based on impedance frequency transformation and low-noise transconductance amplifier (LNTA) circuits. The filter rejection is captured by a linear periodically varying model that includes band limitation by the LNTA output impedance and the related parasitic capacitances of the impedance transformation circuit. The effect of thermal noise folding on the circuit noise figure, as well as clock phase mismatch on filter gain are also discussed. As a proof of concept, a chip design of a tunable radio-frequency front end using 65-nm CMOS technology is presented. In measurements the circuit achieves blocker rejection competitive to SAW filters with noise figure 3.2-5.2 dB, out of band IIP3 > +17 dBm and blocker P_{1 dB} > +5 dBm over frequency range of 0.5-3 GHz.