Wide-Band RF Front End for SAW-Less Receivers Employing Active Feedback and Far Out-of-Band Blocker Rejection Circuit

Elimination of the surface acoustic wave (SAW) filter from the input of a receiver can render it extremely vulnerable to various blockers and interferers. The presence of large out-of-band (OOB) blockers will result in the required linearity of the SAW-less receiver to be considerably higher than that of the conventional receivers with the input SAW filter. The ever-present undesirable signals that arise in the absence of the input SAW filter can be divided into two classes of far and near OOB blockers and interferers. Removal of these harmful signals requires two distinct approaches according to their nature. Two different methods for blocker and interferer rejection are introduced in this paper. The first method employs active feedback to reject near OOB blockers, while the second method is employed to remove far OOB blockers. Combining the two methods enables the receiver to withstand all the near and far OOB blockers. The proposed front end is fabricated in 0.18- $\mu \text{m}$ CMOS technology with the die area of 1.26 mm2. The receiver covers communication standards within 700 MHz–6-GHz bandwidth with in-band input third intercept point (IIP3) measured to be between −6 and 0.5 dBm and the effective OOB IIP3 measured to be from −5.3 dBm to as high as 35 dBm.