Cascade low-pass filter to improve xDSL band attenuation for POTS splitter
First Claim
1. A low-pass filter, comprising:
- a first differential mode inductor in series with a second differential mode inductor and a third differential mode inductor;
first and second resistors in parallel with the first differential mode inductor;
first and second capacitors in parallel with the second differential mode inductor;
third and fourth capacitors in parallel with the third differential mode inductor;
a first shunt leg interposed between the first and second differential mode inductors and coupled across the first and second differential mode inductors;
a second shunt leg interposed between the second and third differential mode inductors and coupled across the second and third differential mode inductors; and
a third shunt leg coupled across the third differential mode inductor.
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Abstract
Cascade low-pass filters are useful in attenuating the xDSL band in a POTS splitter. The design of the low-pass filter is a sixth-order filter having two stages. A first stage includes a fourth-order filter, preferably with a stop-band frequency of approximately 48 kHz. A second stage includes a second-order filter in cascade with the fourth-order filter. For this filter, the stop-band frequency is preferably approximately 29 kHz. The inductance value of the second stage is relatively small in comparison to the inductance values of the first stage. In this manner, improvements in xDSL band attenuation are facilitated with little or no eroding of the voice band performance such as insertion loss, pass-band attenuation and return loss.
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Citations
40 Claims
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1. A low-pass filter, comprising:
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a first differential mode inductor in series with a second differential mode inductor and a third differential mode inductor;
first and second resistors in parallel with the first differential mode inductor;
first and second capacitors in parallel with the second differential mode inductor;
third and fourth capacitors in parallel with the third differential mode inductor;
a first shunt leg interposed between the first and second differential mode inductors and coupled across the first and second differential mode inductors;
a second shunt leg interposed between the second and third differential mode inductors and coupled across the second and third differential mode inductors; and
a third shunt leg coupled across the third differential mode inductor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A low-pass filter, comprising:
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a first differential mode inductor in series with a second differential mode inductor, wherein the first differential mode inductor has an inductance value of approximately 21 mH and wherein the second differential mode inductor has an inductance value of approximately 10 mH;
a third differential mode inductor in series with the second differential mode inductor, wherein the third differential mode inductor has an inductance value of approximately 2.8 mH;
first and second resistors in parallel with the first differential mode inductor, wherein the first and second resistors each have a resistance value of approximately 2.37 kΩ
;
first and second capacitors in parallel with the second differential mode inductor, wherein the first and second capacitors each have a capacitance value of approximately 0.0022 μ
F;
third and fourth capacitors in parallel with the third differential mode inductor, wherein the third and fourth capacitors each have a capacitance value of approximately 0.022 μ
F;
a first shunt leg interposed between the first and second differential mode inductors and coupled across a first and second winding of the first differential mode inductor, wherein the first shunt leg comprises a fifth capacitor having a capacitance value of approximately 0.022 μ
F and a third resistor coupled in series with the fifth capacitor and having a resistance value of approximately 51.1 Ω
;
a second shunt leg interposed between the second and third differential mode inductors and coupled across a first and second winding of the second differential mode inductor, wherein the second shunt leg comprises a sixth capacitor having a capacitance value of approximately 0.036 μ
F; and
a third shunt leg coupled across a first and second winding of the third differential mode inductor, wherein the third shunt leg comprises a seventh capacitor having a capacitance value of approximately 0.010 μ
F;
wherein the third differential mode inductor is interposed between the second shunt leg and the third shunt leg.
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20. A low-pass filter, comprising:
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a fourth-order first stage comprising;
a first differential mode inductor in series with a second differential mode inductor;
first and second resistors in parallel with the first differential mode inductor, wherein the first and second resistors each have approximately the same resistance value;
first and second capacitors in parallel with the second differential mode inductor, wherein the first and second capacitors each have approximately the same capacitance value;
a first shunt leg interposed between the first and second differential mode inductors and coupled across a first and second winding of the first differential mode inductor; and
a second shunt leg interposed between the second and third differential mode inductors and coupled across a first and second winding of the second differential mode inductor;
a second-order second stage in cascade with the first stage, the second stage comprising;
a third differential mode inductor having an inductance value of less than half of an inductance value of the first differential mode inductor or an inductance value of the second differential mode inductor;
third and fourth capacitors in parallel with the third differential mode inductor, wherein the third and fourth capacitors each have approximately the same capacitance value; and
a third shunt leg coupled across a first and second winding of the third differential mode inductor;
wherein the third differential mode inductor is interposed between the second shunt leg and the third shunt leg. - View Dependent Claims (21)
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22. A low-pass filter, consisting essentially of:
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a first differential mode inductor in series with a second differential mode inductor and a third differential mode inductor;
a first resistor in parallel with a first winding of the first differential mode inductor;
a second resistor in parallel with a second winding of the first differential mode inductor;
a first capacitor in parallel with a first winding of the second differential mode inductor;
a second capacitor in parallel with a second winding of the second differential mode inductor;
a third capacitor in parallel with a first winding of the third differential mode inductor;
a fourth capacitor in parallel with a second winding of the third differential mode inductor;
a first shunt leg comprising a first end coupled between the first windings of the first and second differential mode inductors and a second end coupled between the second windings of the first and second differential mode inductors;
a second shunt leg comprising a first end coupled between the first windings of the second and third differential mode inductors and a second end coupled between the second windings of the second and third differential mode inductors; and
a third shunt leg comprising a first end coupled to the first winding of the third differential mode inductor and a second end coupled to the second winding of the third differential mode inductor;
wherein the third differential mode inductor is coupled between the second and third shunt legs. - View Dependent Claims (23)
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24. A POTS splitter, comprising:
a low-pass filter for coupling between an xDSL out port and a POTS port, wherein the low-pass filter comprises;
first, second and third differential mode inductors in series between the POTS port and the xDSL out port;
first and second resistors in parallel with the first differential mode inductor;
first and second capacitors in parallel with the second differential mode inductor;
third and fourth capacitors in parallel with the third differential mode inductor;
a first shunt leg interposed between the first and second differential mode inductors and coupled across the first and second differential mode inductors;
a second shunt leg interposed between the second and third differential mode inductors and coupled across the second and third differential mode inductors; and
a third shunt leg coupled across the third differential mode inductor. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A POTS splitter, comprising:
a low-pass filter for coupling between an xDSL out port and a POTS port, wherein the low-pass filter comprises;
a first differential mode inductor having a first winding and a second winding, wherein the first winding corresponds to a tip line and the second winding corresponds to a ring line;
a second differential mode inductor in series with the first differential mode inductor and having a first winding and a second winding, wherein the first winding corresponds to the tip line and the second winding corresponds to the ring line;
a third differential mode inductor in series with the first and second differential mode inductors and having a first winding and a second winding, wherein the first winding corresponds to the tip line and the second winding corresponds to the ring line;
a first resistance in parallel with the first winding of the first differential mode inductor;
a second resistance in parallel with the second winding of the first differential mode inductor;
a first capacitance in parallel with the first winding of the second differential mode inductor;
a second capacitance in parallel with the second winding of the second differential mode inductor;
a third capacitance in parallel with the first winding of the third differential mode inductor;
a fourth capacitance in parallel with the second winding of the third differential mode inductor;
a fifth capacitance in series with a third resistance coupled between the tip line and the ring line;
a sixth capacitance coupled between the tip line and the ring line; and
a seventh capacitance coupled between the tip line and the ring line;
wherein the fifth capacitance and the third resistance are interposed between the first and second differential mode inductors;
wherein the sixth capacitance is interposed between the second and third differential mode inductors; and
wherein the third differential mode inductor in interposed between the sixth and seventh capacitances. - View Dependent Claims (35, 36)
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37. A remote-side xDSL modem, comprising:
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a low-pass filter for coupling between an xDSL out port and a POTS port, wherein the low-pass filter consists essentially of;
a first differential mode inductor in series with a second differential mode inductor and a third differential mode inductor;
a first resistor in parallel with a first winding of the first differential mode inductor, wherein the first winding of the first differential mode inductor corresponds to a tip line of the xDSL out port;
a second resistor in parallel with a second winding of the first differential mode inductor, wherein the second winding of the first differential mode inductor corresponds to a ring line of the xDSL out port;
a first capacitor in parallel with a first winding of the second differential mode inductor, wherein the first winding of the second differential mode inductor corresponds to the tip line of the xDSL out port;
a second capacitor in parallel with a second winding of the second differential mode inductor, wherein the second winding of the second differential mode inductor corresponds to the ring line of the xDSL out port;
a third capacitor in parallel with a first winding of the third differential mode inductor, wherein the first winding of the third differential mode inductor corresponds to the tip line of the xDSL out port;
a fourth capacitor in parallel with a second winding of the third differential mode inductor, wherein the second winding of the third differential mode inductor corresponds to the ring line of the xDSL out port;
a first shunt leg comprising a first end coupled between the first windings of the first and second differential mode inductors and a second end coupled between the second windings of the first and second differential mode inductors;
a second shunt leg comprising a first end coupled between the first windings of the second and third differential mode inductors and a second end coupled between the second windings of the second and third differential mode inductors; and
a third shunt leg comprising a first end coupled to the first winding of the third differential mode inductor and a second end coupled to the second winding of the third differential mode inductor;
wherein the third differential mode inductor is coupled between the second and third shunt legs. - View Dependent Claims (38, 39, 40)
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Specification