Cable modem tuner

Details Cable modem tuner Cable modem tuner

1998-06-24

2001-01-02

Faile, Andrew I. (Department: 2711)

Television

Two-way video and voice communication

User positioning

C348S014160, C348S014160, C348S731000, C455S311000, C455S318000, C455S177100, C455S200100

Utility Patent

active

06169569

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to cable modems and, more particularly, to a cable modem tuner which includes a front end decoupler stage which enables the tuner to employ a single conversion architecture within a cable modem coupled to a CATV network.
BACKGROUND OF THE INVENTION
A tuner is a device which amplifies a radio frequency (or “RF”) signal received by an antenna or via cable and converts the received RF signal into a fixed intermediate frequency (or “IF”) signal. Tuners are used in a variety of applications. For example, television sets are often equipped with tuners for selecting specific broadcast channels from VHF (54 to 88 and 174 to 216 MHz) and UHF (470 to 860 MHz) frequency bands. Similarly, cable boxes are equipped with a tuner to select between as many as 121 cable channels which are received in a single frequency band which extends between 54 and 860 MHz.
Two types of tuners presently in use are respectively known as “single conversion” and “double conversion” tuners. In a single conversion tuner, an RF signal for a selected channel is converted into an IF signal. Double conversion tuners, on the other hand, convert the RF signal for a selected channel into a first intermediate signal and then convert the first intermediate signal into the IF signal. While more expensive than the single conversion tuner, the ability of the double conversion tuner to handle larger amounts of signal and to prevent return signals from passing back onto the cable has resulted in the widespread use of double conversion tuners in cable boxes.
In recent years, it has been proposed that the infrastructure of the CATV network may be used to provide PC users with access to the internet and other high speed data networks. A cable modem is a device which allows high speed data accesses to the internet via the CATV network at speeds 1,000 times faster than that of a telephone modem. Other services which may be available via a cable modem include access to CD-ROM and streaming video servers. It is expected that the implementation of a high-speed data network to the home will require the establishment of various standards for home systems which will be used to access the network. One such standard which is already in use is known as the multimedia cable network standard (or “MCNS”). In order to comply with the MCNS limitation on the return signals passing back onto the cable, existing cable modem tuners employ a double conversion architecture. If, however, it were possible to construct a cable modem tuner which complied with MCNS standards while employing a single conversion architecture, considerable cost savings could be achieved. It is, therefore, the object of this invention to provide such a cable modem tuner.
SUMMARY OF THE INVENTION
In various embodiments thereof, the present invention is of a tuner for a cable modem and a cable modem which incorporates the tuner. The tuner includes a front end decoupler stage and a single conversion tuner. The front end decoupler stage passes RF signals received at an input thereof to an input of the single conversion tuner coupled to an output of the front end decoupler circuit. The single conversion tuner selects, from the plurality of RF signals received thereby, an RF signal to be converted into an IF signal for output therefrom while rejecting the remainder of the plurality of RF signals. The front end decoupler stage also acts to isolate the single conversion tuner from the input thereof, thereby preventing the rejected ones of the plurality of RF signals, as well as return signals originating within the single conversion turner, from passing back through the front end decoupler stage.
In one aspect of this embodiment of the invention, the front end decoupler stage prevents the rejected ones of the plurality of RF signals and the return signals originated by the single conversion turner from being transmitted to devices which reside on a cable coupled to the input of the front end decoupler stage. In another aspect thereof, the plurality of RF signals are contained in a band which extends from about 54 MHz to about 860 MHz.
In still another aspect thereof, the tuner includes a front end duplex filter stage for coupling the tuner to a network, a computer system and the front end decoupler stage. Signals received from the network are directed by the front end duplex filter stage to the front end decoupler stage while signals received from the computer system are directed by the front end duplex filter stage to the network. Alternately, the tuner may instead include a first, input/output (“I/O”), port, a second, input, port and a third, output, port. RF signals from a CATV cable pass to the front end decoupler stage via a downstream signal path which extends from the CATV cable, through the I/O port, the output port and on to the input of the front end decoupler stage while signals generated by a computer pass to the network via an upstream signal path which extends from the computer system, through the input port, the I/O port and on to the CATV cable.
In a still further aspect of this alternate configuration, the tuner also includes a first filter positioned between a node which joins the upstream and downstream paths and the input to the front end decoupler circuit and a second filter positioned between the node and the input port. The first filter prevents signals generated by the computer system from passing to the front end decoupler circuit while the second filter prevents RF signals received from the CATV cable from passing to the input port. Preferably, the first filter may be a high bandpass filter having a pass band which extends from about 54 MHz to about 860 MHz while the second filter is a low bandpass filter having a pass band which extends from about 5 MHz to about 42 MHz.
In still other aspects thereof, the front end decoupler circuit may include either a broadband filter for passing the plurality of RF signals, each at a discrete frequency within a frequency range or the broadband filter in combination with an automatic gain control (“AGC”) circuit.


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