Surface wave device with capacitance
US5821834A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 8, 1997 |
| Grant date | Oct 13, 1998 |
| Priority date | — |
| Expiry date | May 8, 2017 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03H9/0057
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A surface wave device filter comprises two 2-pole waveguide coupled double mode resonators (WCRs) electrically connected together in cascade. To permit narrowing of the filter passband for improved out-of-band rejection, e.g. for use of the filter as an intermediate frequency channel filter in a wireless communications system, while maintaining good matching for low ripple in the passband, a shunt capacitance is connected in parallel with the static capacitances of the two WCRs. The shunt capacitance is constituted by interdigital fingers provided on the same piezoelectric substrate as one or both of the WCRs, perpendicularly to the WCR fingers to avoid surface wave interference, conveniently in space otherwise used by rails of the WCRs, optionally with oppositely phased fingers to cancel surface waves generated by these fingers. A capacitance can be similarly provided on the same substrate as any other type of surface wave device.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.