Active filter
US4779056A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 4, 1987 |
| Grant date | Oct 18, 1988 |
| Priority date | — |
| Expiry date | Dec 4, 2007 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03H11/126
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A filter comprises an amplifier circuit arrangement having a signal input (1) and a signal output (8) and a coupling (36) between a point (37) on a signal path (39) to the signal input and a point (38) on a signal path from the signal output. The amplifier circuit arrangement comprises an inverting amplifier (6) to the input (5) of which the signal input (1) is connected via a series impedance (7), e.g. a resistor. A feedback impedance (9), e.g. a capacitor, connects the amplifier output (8) to its input so that this input constitutes a virtual ground. The phase relationship between the input and output signals of such an arrangement changes from inverting to non-inverting at frequencies at which the gain of the amplifier drops to below unity because of forward feed through the feedback impedance (9), thereby upsetting the phase relationship between the signals passing through the arrangement and those passing through the coupling. Accordingly, a further impedance (10), e.g. a capacitance, is provided between the common point ( 11) of the series and feedback impedances and ground. At frequencies at which the amplifier gain is high, this further impedance has virtually no effect bec…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.