Electrical filter with adjustable RC product
US4791379A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Feb 10, 1986 |
| Grant date | Dec 13, 1988 |
| Priority date | — |
| Expiry date | Feb 10, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03H2210/043
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A continuous time electrical filter fabricated as an integrated circuit includes capacitors (CO,CN) and resistors (R1,R2). Since capacitors and resistors are difficult to integrate with accurately defined values a trimming circuit is provided which operates switches (S1-SN) to select appropriate ones of the capacitors (CN) to accurately define the cut-off frequency of the filter. The trimming circuit comprises a capacitor (TC2) which is charged through a resistor TR1 during a first period and which is discharged in incremental steps by a capacitor (TC1). The number of incremental steps is counted by a counter (11) and transferred to a register (13). The outputs (S1-SN) of the register control the switches (S1-SN). Instead of adjusting the value of the capacitors in the filter, the values of the resistors may be adjusted. If this is done a convenient procedure is to short out selected portions of the resistors. More than one capacitor or resistor may be adjusted using a single counter and register.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.