US 5,963,112 AGranted

Cascaded higher order filter with low sensitivity to component values and a method for designing the same

AssigneeGlobespan Technologies, Inc.

InventorGeorge S. Moschytz

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Abstract

The present invention provides a higher order filter with low sensitivity to component values and to a method of designing the same. The higher order filter is constructed of second and/or third order filter circuits which have been desensitized with respect to component values and gain by impedance tapering the filter circuits. The filter circuits are impedance tapered by successively scaling the resistors and/or capacitors from left to right to minimize loading on the first filter section and to maximize the quality factor of the passive pole. The impedance of the filter sections is increased from left to right by increasing the resistor values and/or by decreasing the capacitor values from left to right. Once the lower order filter circuits have been designed, they are cascaded to provide a higher order filter with low sensitivity to component values and gain.

Claims19

Dependent claims

A cascaded filter with low sensitivity to component values and gain, said filter comprising:

a first resistor-capacitor section comprising a first resistor having a first terminal and a second terminal and a first capacitor having a first terminal and a second terminal, said first resistor having a value R.sub.1, said first capacitor having a value C.sub.1, wherein the first terminal of said first capacitor is electrically coupled to said second terminal of said first resistor;
a second resistor-capacitor section electrically coupled to said first resistor capacitor section, said second resistor-capacitor section comprising a second resistor having a first terminal and a second terminal and a second capacitor having a first terminal and a second terminal, said second resistor having a value R.sub.2, said second capacitor having a value C.sub.2, wherein the first terminal of said second capacitor is electrically coupled to said second terminal of said second resistor;
a third resistor-capacitor section electrically coupled to said second resistor-capacitor section, said third resistor-capacitor section comprising a third resistor having a first terminal and a second terminal and a third capacitor having a first terminal and a second terminal, said third resistor having a value R.sub.3, where R.sub.3 =(R.sub.2 .times.r.sub.1), where r.sub.1 is greater than 1, said third capacitor having a value C.sub.3 wherein the first terminal of said third capacitor is electrically coupled to the second terminal of said third resistor;
and
a fourth resistor-capacitor section electrically coupled to said third resistor-capacitor section, said fourth resistor-capacitor section comprising a fourth resistor having a first terminal and a second terminal and a fourth capacitor comprising a first terminal and a second terminal, said fourth resistor having a value R.sub.4, said fourth capacitor having a value C.sub.4, wherein the first terminal of said fourth capacitor is electrically coupled to said first terminal of said fourth resistor, wherein the value C.sub.2 =C.sub.1 .rho., wherein .rho. is greater than 1, and wherein C.sub.4 =C.sub.3 /.rho..sub.2, wherein .rho..sub.2 is greater than 1.

2 more elements

A cascaded filter with low sensitivity to component values and gain, said filter comprising:

a first resistor-capacitor section comprising a first resistor having a first terminal and a second terminal and a first capacitor having a first terminal and a second terminal, said first resistor having a value R.sub.1, said first capacitor having a value C.sub.1, wherein the first terminal of said first capacitor is electrically coupled to said second terminal of said first resistor;
a second resistor-capacitor section electrically coupled to said first resistor capacitor section, said second resistor-capacitor section comprising a second resistor having a first terminal and a second terminal and a second capacitor having a first terminal and a second terminal, said second resistor having a value R.sub.2, said second capacitor having a value C.sub.2, wherein the first terminal of said second capacitor is electrically coupled to said second terminal of said second resistor;
a third resistor-capacitor section electrically coupled to said second resistor-capacitor section, said third resistor-capacitor section comprising a third resistor having a first terminal and a second terminal and a third capacitor having a first terminal and a second terminal, said third resistor having a value R.sub.3, where R.sub.3 =R.sub.2 .times.r.sub.1 and where r.sub.1 is greater than 1, said third capacitor having a value C.sub.3, wherein the first terminal of said third capacitor is electrically coupled to the second terminal of said third resistor;
and
a fourth resistor-capacitor section electrically coupled to said third resistor-capacitor section, said fourth resistor-capacitor section comprising a fourth resistor having a first terminal and a second terminal and a fourth capacitor comprising a first terminal and a second terminal, said fourth resistor having a value R.sub.4, said fourth capacitor having a value C.sub.4, wherein the first terminal of said fourth capacitor is electrically coupled to said first terminal of said fourth resistor, wherein R.sub.2 =R.sub.1 .times.r, wherein r is greater than 1, and wherein R.sub.4 =R.sub.3 .times.r.sub.2 wherein r.sub.2 is greater than 1.

2 more elements

Dependencies are inferred from the claim text.