The present invention generally relates to improved telecommunications systems and in particular to an improved digital/POTS telecommunications system. Still more particularly, the present invention relates to an improved digital/POTS splitter design.
The basic functions and requirements for POTS Splitter are well defined in TIE1.4/98-007R5, Annex E, which is hereby incorporated by reference. The POTS splitter is used to split “Plain Old Telephone System” (POTS) voiceband signals from Asymmetric Digital Subscriber Line (ADSL) signals traveling over the same telephone line.
In conventional systems, the POTS splitter is designed as a LC low-pass filter. With regard to ADSL signals, a low-pass filter provides protection from the high-frequency transients and impedance effects that occur during POTS operation, e.g., ringing transients, ring trip transients, and off-hook transients and impedance changes. With regard to POTS voice band service, the low-pass filter provides protection from ADSL signals which may impact through non-linear or other effects remote devices, e.g., handset, fax, voice band modem, etc., and central office operation.
TIE1.4/98-007R5, Annex E specifies acceptable ranges for insertion loss in the voice band, return loss in the voice band, and attenuation distortion in the ADSL band, among other requirements. These requirements make the common POTS splitter design, which incorporates a differential pair of conventional LC low-pass filter circuits, less than ideal for this purpose. Because the inductor used in a conventional LC low-pass filter circuit is frequency independent in the voice range, it is very hard to meet each of the requirements above at same time. It would therefore be desirable to provide an improved low-pass filter circuit for a POTS splitter which optimizes the TIE1.4 requirements.
The POTS splitter design of the preferred embodiment incorporates a low-pass filter which improves the voice-band loss characteristics without sacrificing performance with regard to the voice-band insertion loss or the ADSL-band attenuation distortion. This is accomplished by replacing the inductor of the conventional POTS splitter low-pass circuit with a parallel-connected inductor and resistor.
With reference now to the figures, and in particular with reference to
This invention is used to get lower inductive impedance at high frequency (3 KHz–4 KHz), so a better return loss is obtained without interfering with other performance characteristics.
The imaginary part if the impedance is (Equation 2):
As the frequency goes high,
goes high, and the inductance of this device,
goes low due to the addition of the resistor.
R1=R2=R/2
L1=L2=L/4
where L1 and L2 are the inductance of each transformer winding. Of course, this is merely exemplary; according to different requirements for the central office and remote end POTS splitters, the value of R and L may change in different designs.
For purposes of this discussion, the conventional circuit comprised by L1 and C2 in
It will then be clear that, in
In normal operation, a combined voice-band and ADSL signal is received by the splitter circuits at inputs L1T and L1R of
According to the preferred embodiment, the values of the components of
Also according to the preferred embodiment, the values of the components of
Of course, while the component values of the preferred embodiment are shown above, those of skill in the art will recognize that these values can be varied according to specific system requirements. In particular, in
Further, the position of the frequency-sensitive inductive device within the POTS splitter will vary the overall performance characteristics of the splitter. For example, in
The preferred embodiment, by incorporating this frequency-sensitive inductive device, will simultaneously minimize the magnitude of ripple in the high frequency band (3 K–4 KHz) and maximize the return loss at high frequency band (3 K–4 KHz), without negatively affecting, to any substantial degree, the attenuation distortion of the ADSL band.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
5848150 | Bingel | Dec 1998 | A |
6137880 | Bella | Oct 2000 | A |
6567519 | Ham | May 2003 | B1 |