VITESSE
SEMICONDUCTOR CORPORATION
ATM/SONET/SDH 622 Mb/s Transceiver Mux/Demux
with Integrated Clock Generation and Clock Recovery
Figure 6: External Integrator Capacitor
CP = 0.1
µF
CP1
CP2
Data Sheet
VSC8113
+
-
CN1
CN2
CN = 0.1
µF
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.
Page 8
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
G52154-0, Rev 4.2
3/19/99
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
