Capacitive Tap Weight Network Surface Acoustic Wave Transducers.

摘要

A new structure for SAW transducer tap weight control using thin film capacitors in a bridge type network has been devised. In the capacitive tap weight network (CTWN), thin film capacitors made with an SiO(x) dielectric are fabricated on each tap in the propagation path so no additional substrate area is used. The impulse response shape is controlled by the voltage attenuation on each finger. This provides a large dynamic range of tap weights without phase variation and a uniform beam width which allows the cascading of two weighted transducers without the use of a multistrip coupler. A model which accurately predicts the multitap CTWN transducer input admittance, insertion loss, thin film losses and electrical Q is presented. Design procedures for capacitive weighted bandpass filters are developed. Experimental devices with varying designs are presented which verify the CTWN model. The devices presented demonstrate tap weight control, the cascading of weighted transducers, 5 wavelength beam width transducers, tap delection techniques, general oversampling techniques and inphase-quadrature sampling. (Author)