VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8113

ATM/SONET/SDH 622 Mb/s Transceiver Mux/Demux

with Integrated Clock Generation and Clock Recovery

Page 8

© VITESSE SEMICONDUCTOR CORPORATION

G52154-0, Rev 4.2

741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896

3/19/99

Figure 6: External Integrator Capacitor

Clock Recovery

The fully monolithic Clock Recovery Unit (CRU) consists of a Phase Detector, a Frequency Detector, a

Loop Filter and a Voltage Controlled Oscillator (VCO). The phase detector compares the phase information of

the incoming data with the recovered clock. The frequency detector compares the frequency component of the

data input with the recovered clock to provide the pull in energy during lock acquisition. The LoopFilter inte-

grates the phase information from the phase and frequency detectors and provides the control voltage to the

VCO.

The CRU provides a lock detect function. If the frequencies of the serial data stream and the CRU’s recov-

ered clock are different, a data bit in the serial data stream will occasionally be dropped. If the Frequency Detec-

tor does not detect this condition in a moving 1.5

µs window, the CRULOCKDET output is asserted to signal

that the CRU is frequency locked to the serial data stream. This output is forced low if it detects that a data bit is

dropped or if the recovered clock frequency drifts more than 5% from the CMU’s output frequency.

+

-

CP1

CP2

CN1

CN2

CP = 0.1

µF

CN = 0.1

µF