This invention relates generally to receivers and specifically to a method, apparatus and system for receiving a plurality of signals having different frequency bandwidths.
Typical communication systems involve transmitting and receiving signals that have an approximately fixed frequency bandwidth. However, some systems allow for signals having different bandwidths. For example, one such system is being proposed by the Multimedia Cable Network System (MCNS) consortium for data over cable television communication in the Data Over Cable Service Interface Specification (DOCSIS). The specification proposes a standard for data communication that will allow for signals transmitted in the upstream direction (from the subscriber to the head-end office) to have one of five different bandwidths. Therefore, the receivers at the head-end will be required to have the ability to receive signals that may have any one of the five frequency bandwidths.
Typical receivers contain a first mixer that shifts the incoming signal to an intermediate frequency (IF) before the signal is filtered through an IF filter. The IF filter is typically chosen to have a frequency pass band that is slightly wider than the incoming signal. Therefore, in systems that allow transmitted signals to have one of a variety of frequency bandwidths, the IF filter will not be able to effectively filter a signal with a bandwidth that is substantially narrower than the bandwidth of the IF filter.
One attempt at solving this problem includes using multiple IF filters having different frequency bandwidths and switching the appropriate IF filter into the receiver circuitry in order to receive a particular signal. However, this attempt is expensive and requires additional circuitry. In addition, this attempt is inefficient since it requires a finite time to switch from receiving a signal having one bandwidth to a signal having a different bandwidth.
Therefore, there exists a need for a method, apparatus, and system for efficiently and inexpensively receiving a plurality of signals having different frequency bandwidths.