Reflection and Amplification of Acoustic Surface Waves by Interdigital Transducers with Active Circuit Loading

It has been shown that when the reactance at the electrical port of an interdigital surface-wave transducer is tuned out, near-perfect reflection of acoustic surface waves can be obtained at either acoustic port. An inverted common-collector (ICC) transistor circuit can be used to accomplish this tuning and simultaneously generate a negative resistance that can be used to provide reflection and transmission gain for the surface waves. Some theoretical and experimental results for such a situation in the case of surface waves propagating in the Z direction on Y-cut LiNbO₃ are presented. In particular, electrically controlled variable (digital) time delay has been demonstrated using this technique.