Coupled Resonator Filters: Wide-band modeling, frequency versus pseudo-time characterizations

Radiofrequency transmission circuits are going towards integration of all functions including filters. In this domain, acoustic filters using Surface Acoustic Waves (SAW) or Bulk Acoustic Waves (BAW) are being studied increasingly and in particular advanced structures such as Coupled Resonator Filter (CRF). A wide band modeling of the complete CRF filter is proposed. This model is compared to simulation and the limitation of RF pads necessary for characterization is highlighted. Adding to the simulation the measurement of single RF pads validates this assumption. Another problem is the industrial test of all filters after fabrication. Usually, frequency domain characterizations are performed. Nevertheless, this method is time consuming, needs expensive equipment and is not suitable for industrial testing. A new method of filter characterization is proposed using a digitally modulated signal where the carrier frequency is chosen close to the central frequency of the filter. Then, at the filter output, Error Vector Magnitude (EVM) is analyzed. This EVM gives us information on the filter behavior and presents good agreements with simulations. In fine, these results are compared to S-parameters to validate the new proposed method.