Apparatus and methods are disclosed for reducing noise leakage on the upstream
channel from a cable modem. Noise leakage from cable modems, such as from a persistently
enabled amplifier or other components in the modem, can accumulate on an upstream
channel and reduce the overall signal-to-noise ratio of signals sent to the headend.
In order to significantly reduce such noise leakage and to provide termination
of the cable plant in the modem when the modem is not transmitting data, a cable
modem arranged to improve its isolation is disclosed. The modem contains an upstream
transmitter having a control line on which the upstream transmitter can emit a
control signal. The modem also includes a switch component capable of being enabled
and disabled by the control signal on the control line. The control signal from
the upstream transmitter to the switch component enables the switch component thereby
allowing a data signal to be transmitted on an upstream channel. The switch component
includes two switches. One switch is a series switch used to enable and disable
the transmission of data. Another switch is a shunt for providing termination of
the cable plant. The cable modem also includes an amplifier for amplifying the
data signal from the upstream transmitter before being transmitted on the upstream channel.
