7.3.2 Carrier Detect

An internal Carrier Detector circuit is used to monitor the presence or absence of the input signal. When the input signal amplitude exceeds the carrier detector’s threshold, adaptation is activated, and CD_N is pulled low at the end of adaptation. When the input signal amplitude is below the carrier detector’s threshold, input equalization circuitry is powered down and the CD_N is pulled high to indicate absence of input signal. The LMH0324 high gain adaptive cable equalizer supports long cable reach. As a result, the carrier detector threshold is sensitive, and system designers need to pay close attention to the PCB layout to avoid excessive crosstalk from interfering with the carrier detection.

In the absence of input signal, the LMH0324 automatically goes into Power Save Mode to conserve power consumption. When valid signal is detected, the LMH0324 automatically exits the Power Save Mode and returns to the normal operating mode. An LED can be connected to CD_N through a current limiting resistor to provide visual indication of the carrier detection.