Spring 2014 IAB & Research Review
March 5 - 6
High Rejection True RF Channel-Select Filter
The introduction of 39nm capacitive actuation gaps, voltage-controlled frequency tuning, and a stress relieving coupled array design has enabled a 0.09% bandwidth 223.4-MHz channel-select filter with only 2.7dB of in-band insertion loss and 50dB of out-of-channel interferer rejection, marking 25dB improvement over previous generation capacitive-gap transduced filters. It also comes in tandem with a 20dB shape factor of 2.7 realized by a hierarchical mechanical circuit design utilizing 206 micromechanical circuit elements, all contained in an area footprint (sans bond pads) of only 600um×420um. The key to such low insertion loss for this tiny percent bandwidth is Q’s >8,800 supplied by capacitive-gap transduced polysilicon disk resonators employing for the first time gaps small enough to generate coupling strengths on the order of (Cx/Co) ~0.1%, which is a 10× improvement over previous efforts. This filter is the first demonstrated that truly offers low insertion loss and high rejection channel-selection for ultra-low power communication front-ends targeted for autonomous sensor networks.