Apparatus and method for freezing the states of a receiver during silent line state operation of a network device

Abstract

A method for maintaining the states of a receiver during the silent line state of a network device operating in a low power link suspend mode is presented. Accordingly, a method of freezing the states of the equalizer and keeping the receiver clock locked to a frequency that is approximately equal to that of the input data while providing for rapid adjustment to the phase and thus recovery of the input data is presented. During Silent Line State (SLS), the receiver states are frozen using methods that avoid parasitic decay. Also, the receive clock phase lock loop is locked onto the local transmit clock since the local transmit clock has a frequency approximating the incoming data frequency. During the SLS, the transmitter of the remote network device may have been turned off to conserve power therefore the receiver has no way of immediately knowing the phase of an incoming data. Thus, in order to prevent loss of data, the receiver loops of the receiving network device are trained to the frequency of the transmitting remote network device using periodic Link Suspend packets. Thus, in most cases, only the phase of the incoming signal need be acquired when data arrives. The phase may be quickly acquired using loop bandwidth shift methods whereby the receive clock phase lock loop bandwidth is increased to a value that aids rapid acquisition of the input clock and then, after acquisition, the bandwidth is shifted to a low value to enhance noise rejection during tracking.