Integrated filter circuit with variable frequency characteristics
US4667120A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 10, 1985 |
| Grant date | May 19, 1987 |
| Priority date | — |
| Expiry date | Apr 10, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03H11/1291
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A filter integrated circuit having a reference level generator circuit for attenuating its input signal and generating a reference level signal, a pseudofilter circuit including resistors and a variable capacitor as filter elements, and an error amplifier unit for comparing the level of the output signal of the reference level generator circuit with the level of the output signal of the pseudofilter circuit and for generating an automatic adjustment control signal in accordance with the level difference between the output signals. The automatic adjustment control signal is supplied to the pseudofilter circuit to change the capacitance value of the variable capacitor in the pseudofilter circuit so that the output signal level of the pseudofilter circuit may become equal to the level of the reference signal. The automatic adjustment control signal is also supplied to at least one filter circuit to change the capacitance of a variable capacitor included therein. As a result, the deviation in the filter characteristics caused by deviations in the resistance of a resistor and in the capacitance of the capacitor is corrected.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.