The MAX3874 is a compact, dual-rate clock and data recovery with limiting amplifier for OC-48 and OC-48 with FEC SONET/SDH applications. Without using an external reference clock, the fully integrated phaselocked loop (PLL) recovers a synchronous clock signal from the serial NRZ data input. The input data is then retimed by this recovered clock, providing a clean data output. An additional serial input (SLBI) is available for system-loopback diagnostic testing. Alternatively, this input can be connected to a reference clock to maintain a valid clock output in the absence of data transitions. The device also includes a loss-of-lock (LOL) output.