Electrical filter
US4733205A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Apr 21, 1987 |
| Grant date | Mar 22, 1988 |
| Priority date | — |
| Expiry date | Apr 21, 2007 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03J3/24
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A continuous time electrical filter fabricated as an integrated circuit includes capacitors (CF,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 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 (13) control the switches (S1-SN). Alternatively the values of the filter resistors may be adjusted, a convenient procedure being to short out selected portions of the resistors. More than one capacitor or resistor may be adjusted using a single counter and register. The trimming circuit also includes a switch (TS11) which connects the parasitic capacitance (CP1, CP2) of the capacitor (TC1) and an underlying conductive layer (22) and of a dummy resistor and the underlying layer (22) in parallel with th…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.