Effects of non-identical resonators on BAW linearity

Nonlinear (NL) performance requirements on BAW filters and modules became increasingly stringent in the past years. Common layout strategies efficiently help to improve the overall level for H2 and IMD. However, nowadays ambitious performance targets reveal the limits of common linearization approaches on real BAW filters and modules. The prediction from electro-magnetic (EM) simulation is remarkably accurate regarding the overall level. However, usually resonators using the same layer stack and geometry are considered perfectly identical in simulation regarding their resonance frequency and spurious content, neglecting the effect of natural process variation present on a real chip. In this article, the effect of imperfect, non-identical resonators is demonstrated, focusing especially on the deteriorated NL cancellation of cascaded or antiparallel stages. An overview is given of how different variation effects manifest in the NL response and methods to analyse the measured data are presented.