Method and arrangement for filtering of signals

• US 7,447,305 B2
• Filed: 01/24/2001
• Issued: 11/04/2008
• Est. Priority Date: 01/27/2000
• Status: Expired due to Fees

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Lofmark, Bengt Gustav
• Primary Examiner(s): SINGH, RAMNANDAN P
• Application Number:
  US09/768,217
• Publication Number:
  US 20010019608A1
• Time in Patent Office: 2,841 Days
• Field of Search: 379/398, 379/349.01
• US Class Current: 379/378
• CPC Class Codes: H03H 11/24 Frequency-independent attenuators
• CPC Class Codes: H03H 7/38 Impedance-matching networks
• CPC Class Codes: H04L 25/03878 Line equalisers; line build-out devices

Abstract

A filter (45) is passive and has a complex impedance which gives good impedance matching to the complex impedance of a transmission line. Because the filter is passive, it does not need to be powered and can thus be placed in locations that lack a power supply. The filter can also function in the event of a power failure. Because the filter has an impedance which can be well matched to the complex impedance of a transmission line, problems relating to echo and side tones can be minimized.

Claims

1. A filter for filtering signals in a telecommunications system comprising a transmission line and for impedance matching to a complex impedance, wherein the filter comprises:

plural filter components;

at least one first pass band;

wherein the filter is passive;

wherein a characteristic impedance of the filter is complex so that it matches the complex impedance; and

wherein a resistance of at least one of the filter components is in series with at least one inductance of the filter components, said resistance being chosen such that said resistance in series with said at least one inductance assists in giving the filter said complex characteristic impedance.

2. A filter according to claim 1, wherein the filter includes at least one parallel combination of a first inductance in series with a first resistance and a second inductance in series with a second resistance, wherein said first inductance is large in relation to the second inductance, and wherein the first resistance is small in relation to the second resistance.

3. A filter according to claim 2, wherein the filter includes at least two circuit of which at least one circuit segment includes said parallel combination.

4. A filter according to claim 3, wherein the circuit segments are four structure-wise identical circuit segments.

5. A filter according to claim 1, wherein the filter includes at least one series combination of a first inductance in series with a first resistance and a second inductance in parallel with a second resistance, wherein the first inductance is small in relation to the second inductance, and wherein the first resistance is small in relation to the second resistance.

6. A filter according to claim 1, wherein the filter includes at least two cascade-coupled circuit segments of which at least one circuit segment includes at least said resistance that assists in giving the characteristic impedance of said filter said complex character.

7. A filter according to claim 1, wherein the resistance that assists in giving the characteristic impedance of the filter said complex character is comprised of at least one resistor.

8. A filter according to claim 1, wherein the resistance that assists in giving the characteristic impedance of the filter said complex character is comprised of at least one winding resistance of an inductor.

9. A filter according to claim 1, wherein the predetermined complex impedance is the characteristic impedance of a transmission line.

10. A filter according to claim 1, wherein the complex impedance is a European Telecommunications Standards Institute (ETSI) impedance Z_ETSI=150 nF//750 Ω

+270 Ω

.

11. A filter according to claim 1, wherein the filter includes at least one cable simulator section, which cable simulator section has a characteristic impedance that matches the complex impedance;

wherein the filter also includes at least one capacitor, wherein said capacitor assists in giving the filter at least one attenuation peak in a predetermined frequency range in coaction with said cable simulator section.

12. A filter according to claim 1, wherein the filter includes at least one cable simulator section, which cable simulator section has a characteristic impedance that matches the complex impedance;

and in that the filter includes at least one coupled coil, which coupled coil includes an inductance in the cable simulator section and assists in giving the filter at least one attenuation peak in a predetermined frequency range.

13. A filter according to claim 1, wherein the filter is a low-pass filter.

14. A filter according to claim 1, wherein the filter includes a further pass band in a predetermined frequency range, said further pass band differing from said at least first pass band.

15. A splitter filter which includes at least one filter according to claim 1.

16. A splitter filter according to claim 15, wherein said filter according to claim 1 is a low-pass filter;

and wherein the low-pass filter is connected in series to a high-pass filter.

17. A filter according to claim 1, wherein the filter is configured to match the complex impedance, and wherein the complex impedance is at least one of:

(1) impedance of the transmission line; and

(2) a standard-defined impedance.

18. A method for designing a filter intended for filtering signals in a telecommunications system and for impedance matching to a complex impedance of a transmission line, the method comprising:

providing the filter with at least one first pass band;

using only passive components in the filter;

introducing into the filter at least one resistance, said resistance being in series with at least one inductance;

choosing the resistance such that such that said resistance in series with said inductance assists in giving the filter a complex characteristic impedance that matches the complex impedance.

19. A method according to claim 18, wherein the resistance that assists in giving the filter its said complex characteristic impedance is implemented with the aid of at least one resistor.

20. A method according to claim 18, wherein the resistance which assists in giving the filter its said complex characteristic impedance is implemented with the aid of at least one winding resistance of an inductance.

21. A method according to claim 18, wherein the filter is provided with at least one parallel combination of a first inductance in series with a first resistance and a second inductance in series with a second resistance, said first inductance being large in relation to the second inductance and said first resistance being small in relation to the second resistance.

22. A method according to claim 18, wherein the filter is comprised of at least two circuit segments, of which at least one circuit segment includes said parallel combination.

23. A method according to claim 22, wherein the circuit segments are four circuit segments that are structure-wise identical.

24. A method according to claim 18, wherein the filter is provided with at least one series combination of a first inductance in series with a first resistance, and a second inductance in parallel with a second resistance, wherein the first inductance is small in relation to the second inductance, and wherein the first resistance is small in relation to the second resistance.

25. A method according to claim 18, wherein the filter is a low-pass filter.

26. A method according to claim 18, wherein the complex impedance is a European Telecommunications Standards Institute (ETSI) impedance Z_ETSI=150 nF//750 Ω

+270 Ω

.

27. A method according to claim 18, wherein the method also includes optimizing the element values of the filter components on the basis of requirements placed on the properties of said filter.

28. A method according to claim 27, wherein the method also includes an iteration procedure, in which the optimizing of said element values is repeated until the set requirements are fulfilled, and in which a circuit segment is added to and cascade-coupled with the earlier filter design with each iteration.

29. A method according to claim 28, wherein the method includes establishing a least number of circuit segments with which the set requirements can be fulfilled;

and in that a filter having said least number of circuit segments is used in the optimizing step at the beginning of the iteration procedure.

30. A method according to claim 18, wherein the filter is provided with a further pass band in a predetermined frequency range, said further pass band differing from said at least one first pass band.

31. A method of designing a splitter filter that includes a high-pass filter and a low-pass filter, wherein at least one of the filters is designed in accordance with a method according claim 18.

32. A method according to claim 31, wherein at least one of the filters designed in accordance with claim 18 is a low-pass filter;

and wherein the low-pass filter is connected to the high-pass filter in series.

33. A method according to claim 18, further comprising configuring the filter to match the complex impedance, and wherein the complex impedance is at least one of:

(1) impedance of the transmission line; and

(2) a standard-defined impedance.