Multiple output allpass switched capacitor filters
US4716388A · kind A · utility
Inventor
Key dates
| Filing date | Dec 24, 1984 |
| Grant date | Dec 29, 1987 |
| Priority date | — |
| Expiry date | Dec 24, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03H19/002
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
This invention comprises two separate topologies for implementing a second order allpass function filter which is vital for equalization of the phase of other arbitrary response magnitude shaping filters. While the allpass response itself does not affect the frequency spectrum of the signal, these topologies have available outputs that have either bandpass or bandstop characteristics. Thus, two types of useful frequency characteristics formed by the filters that have exactly the same resonant frequency and Q (or Quality factor). Using the well known general two amplifier topology to implement a monolithic switched allpass filter with a high Q leads to very high capacitance ratios and hence excessive silicon area in manufacture. Both the topologies described here reduce the required silicon area by either reducing the required capacitance ratios or making the sensitivity to the smallest capacitor extremely small allowing it to violate otherwise necessary area-to-perimeter matching of the capacitor geometries. Reducing the overall silicon area reduces the overall cost of producing the filters and allows more functionality to be integrated on a single silicon chip.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.