Telephonic communications – Line equalization or impedance matching
Reexamination Certificate
1998-03-16
2001-11-06
Chan, Wing F. (Department: 2643)
Telephonic communications
Line equalization or impedance matching
C379S394000
Reexamination Certificate
active
06314180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems and, more specifically, to a system and method for providing a termination of a subscriber loop connection that is dependent on a frequency of signals transmitted across the subscriber loop connection.
BACKGROUND OF THE INVENTION
Many current communications systems transmit data across a subscriber loop communication line, referred to here in as a “subscriber line.” The subscriber line is typically coupled to a communications network and to data communication equipment (DCE) at a customer's premises. For example, in the plain old telephone system (POTS), a subscriber line transfers data between a central office (CO) located within a public switched telephone network (PSTN) and a DCE, such as a modem or telephone, located at a customer's premises.
The PSTN is capable of supporting multiple types of communication signals. For example, the PSTN is designed to communicate voice signals associated with POTS communications, and the PSTN is also capable of data communication between data terminal equipment, such as computers, via the use of modems. T
1
(1.544 Mbps) and Subrate Digital Service are other examples of data communication over the PSTN. Voice signals are typically communicated within a frequency band of 0 to 4 kilo-Hertz (KHz) while the frequency band of data signals vary with the type of data communication equipment utilized. However, data signals are frequently transmitted at frequency ranges much higher than the frequency band of voice signals. For example, data signals may be transmitted within a frequency range of 16 KHz to 80 KHz.
As known in the art, each end of the subscriber line should be terminated with a suitable impedance in order to enable communication of signals across the subscriber line. The amount of suitable impedance depends on the type of transmission medium and frequency band of the communication established on the subscriber line. For example, in voice signals associated with POTS communication, a relatively high termination impedance is desired while a relatively low termination impedance is desired for the communication of high frequency data signals. A typical termination impedance for POTS communication is between 600 and 900 Ohms, whereas a typical termination impedance for data communications within the 16 to 80 Klz band is approximately 135 Ohms.
Conventional communications networks usually terminate each end of the subscriber line with a single communications device. Therefore, the network utilizes conventional POTS splitters and POTS switches to route voice signals to POTS communications devices and to route data signals to data communications devices which support higher frequency ranges. Consequently, each communications device terminates its connection with a predetermined impedance suitable for the type and frequency band of communication supported by the communications device.
However, in order to increase the efficiency of data communication, it is desirable for each communications device to be capable of supporting either voice signals associated with POTS communication or of supporting data signals which communicate at higher frequencies. Accordingly, it is desirable for the communications device to adjust its termination impedance to correspond with the frequency band of the signals being communicated.
Thus, a heretofore unaddressed need exists in the industry for providing a system and method of varying an impedance of a communications device as a function of a frequency of the signals being communicated so that signals of different frequencies can be supported by the communications device.
SUMMARY OF THE INVENTION
The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. The present invention provides a system and method for varying an impedance of a communications device as a function of a frequency of signals received by the communications device.
The present invention utilizes a current source and a feedback mechanism. The feedback mechanism receives signals from a transmission line and attenuates the signals when the signals have frequencies within a predefined frequency range. The feedback mechanism then transmits the signals as feedback signals to a current source which responds to the feedback signals in order to drive the transmission connection and thereby simulate a termination impedance of a communications device.
In accordance with another feature of the present invention, the predefined frequency range is defined by frequencies between 0 KHz and 4 KHz. Therefore, the termination impedance simulated by the frequency dependent synthetic termination system is relatively high for communications within the 0 KHz to 4 KHz frequency band and is relatively low for communications within the 16 KHz to 80 KHz frequency band.
The present invention can also be viewed as providing a method for varying an impedance value of a communications device as a function of a frequency of a signal received from a transmission line. Briefly described, the method can be broadly conceptualized by the following steps: receiving a signal from a transmission line, attenuating the signal when a frequency of the signal is within a predefined frequency range, transmitting the signal to a current source, and driving the transmission line with the current source based on the signal transmitted to the current source.
The present invention has many advantages, a few of which are delineated hereafter, as mere examples.
An advantage of the present invention is that the apparent termination of a communications device can be varied as a function of the frequency of signals received by the communications device.
Another advantage of the present invention is that a communications device can be designed to support the communication of signals of various frequencies. Therefore, the communications device can be designed to support both the communication of voice signals within a 0 K.Hz to 4 KHz frequency band and the communication of data signals within a 16 KHz to 80 KHz frequency band, for example.
Another advantage of the present invention is that both data and voice signals of various frequencies can be communicated through a communications network without the use of plain old telephone system (POTS) splitters since the same communications device can support both data and voices signals of various frequencies.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings in the detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention, as is defined by the claims.
REFERENCES:
patent: 5121080 (1992-06-01), Scott, III et al.
patent: 5504811 (1996-04-01), Kiko et al.
patent: 5585763 (1996-12-01), Navabi et al.
patent: 5747893 (1998-05-01), Bennett et al.
patent: 5999619 (1999-12-01), Bingel
Chan Wing F.
Paradyne Corporation
Thomas Kayden Horstemeyer & Risley, L.L.P.
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