Silicon Laboratories Inc.

Gerard Pepenella

Bruno Werner Garlepp

Philip David Steiner

Multiple integrated circuits (ICs) are connected via growth inputs, into a network configuration, e.g. a ring network or a mesh network, to form a communications switch. Each IC includes additional growth inputs beyond those needed to form the switch. These growth inputs can be used to add additional functionality, e.g. protection or transmultiplexing, to the switch.

Distributed switch architecture including a growth input/output bus structure

A first phase-locked loop circuit that includes a crystal oscillator, receives a reference clock signal and supplies a first phase-locked loop output signal based on the reference clock during normal operational mode and a stored value in holdover mode. A second phase-locked loop circuit receives the first phase-locked loop output signal and utilizes the first phase-locked loop output signal when generating an output clock in holdover mode. The second phase-locked loop utilizes the first phase-locked loop output signal during operation in the holdover mode to generate the output clock and utilizes the reference clock during normal operational mode to generate the output clock. Alternatively, the second phase-locked loop utilizes the first phase-locked loop output signal both during operation in the holdover mode and during normal operational mode to generate the output clock. The first phased-lock loop circuit may include a low pass filter coupled to the loop filter, which supplies a low pass filtered signal to the crystal oscillator in holdover mode. The first phased-lock loop circuit may include a low pass filter and a delay circuit coupled to the loop filter, which supply a delayed and low pass filtered signal to the crystal oscillator in holdover mode.

Method and apparatus for generating a clock signal in holdover mode

A loss of signal condition is evaluated for an input data stream according to a signal strength threshold level. The signal strength threshold level is determined according to a supplied loss of signal (LOS) threshold level. Two hysteresis modes are used to ensure the hysteresis at low LOS threshold levels is sufficient. The first mode uses hysteresis for the signal strength threshold level that is proportional to the LOS threshold level when the LOS threshold level is above a predetermined level. The second mode employs fixed hysteresis for the signal strength threshold level when the LOS threshold level is below the predetermined level. The hysteresis provides a signal strength threshold level that has a greater magnitude on deassertion of a loss of signal indication than on assertion of the loss of signal indication.

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Manorville, NY, United States of America

Gerard Pepenella