Method and apparatus for adjusting an active filter
First Claim
1. A method for adjusting an active filter, comprising:
- providing an adjustable capacitor for determining a frequency response of said filter;
determining a measure of the frequency response and receiving a nominal frequency response;
selecting an adjustment parameter from a plurality of adjustment parameters stored in a memory arrangement based on the measure of the frequency response and the nominal frequency response; and
adjusting the adjustable capacitor on the basis of the selected adjustment parameter,wherein selecting from the memory arrangement uses an addressable table memory whose address has a word length comprising at least two digits, and at least one digit in the address word length is filled with a digital value derived from the determined measure of the frequency response, and at least one digit in the address word length is filled with a digital value which describes the nominal frequency response.
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Accused Products
Abstract
An adjustable filter, particularly for use as an antialiasing filter in digital telecommunications networks, includes adjustable capacitors which determine frequency response for the purpose of accurate alignment with a particular cut-off frequency. The active filter includes, in line with the invention, a control device with a measuring device for ascertaining the actual cut-off frequency of the filter. On the basis of the ascertained actual cut-off frequency of the filter and the information about the nominal cut-off frequency which is to be set, an adjustment parameter for the adjustable capacitor is selected from a memory arrangement. This adjustment parameter is used to adjust the adjustable capacitor such that the desired nominal cut-off frequency is obtained and, at the same time, the alignment is performed to achieve the nominal cut-off frequency with sufficient accuracy.
19 Citations
19 Claims
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1. A method for adjusting an active filter, comprising:
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providing an adjustable capacitor for determining a frequency response of said filter; determining a measure of the frequency response and receiving a nominal frequency response; selecting an adjustment parameter from a plurality of adjustment parameters stored in a memory arrangement based on the measure of the frequency response and the nominal frequency response; and adjusting the adjustable capacitor on the basis of the selected adjustment parameter, wherein selecting from the memory arrangement uses an addressable table memory whose address has a word length comprising at least two digits, and at least one digit in the address word length is filled with a digital value derived from the determined measure of the frequency response, and at least one digit in the address word length is filled with a digital value which describes the nominal frequency response. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit arrangement for filtering an electrical signal, comprising:
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an active filter including at least one adjustable capacitor that determines frequency response; a circuit to determine a measure of the frequency response of the active filter; a memory arrangement which is adapted to store a plurality of adjustment parameters for adjusting the at least one adjustable capacitor, wherein the memory arrangement includes a table memory for storing digital values in binary form as adjustment parameters; and a control device which is adapted to select a stored adjustment parameter depending on said determined measure of the frequency response and on a nominal frequency response fed to the circuit arrangement and to adjust the at least one adjustable capacitor on the basis of the selected adjustment parameter, wherein the table memory includes an address word length having at least two digits, and the circuit arrangement fills at least one digit in the address word length with a digital value derived from the determined measure of the frequency response and fills at least one digit in the address word length with a digital value which describes the nominal frequency response. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification