VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8061/VSC8062

2.5Gb/s 16-Bit

Multiplexer/Demultiplexer Chipset

Page 4

G52069-0, Rev 4.3

05/11/01

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VSC8061 Phase Detector Logic Diagram

The internal phase detector of the VSC8061 compares the phase difference between the internally gener-

ated divide-by-16 clock and the DCLK input. If both inputs (CLK16 and DCLK) to the phase detector are in

phase, the U and D outputs will both be low. If the rising edge of CLK16 precedes DCLK, a series of pulses

with pulse widths proportional to the phase difference will be present at the U output. Conversely, if DCLK pre-

cedes CLK16, then a series of pulses with widths proportional to the phase difference will be present at the D

output. The other output will remain low. The Phase Detector ignores phase differences for falling edges. This

circuitry is useful for implementing a Clock Multiplier Unit (CMU) function with the VSC8061. For example,

the DLCK can be the system reference clock at the parallel data rate. An external Voltage Controlled Oscillator

(VCO) at 16x the frequency of the reference clock can be used as the CLK input for the VSC8061. The phase

detector outputs (U and D) can then be used by an external integrator to generate an output that controls the

VCO. The generated 16x clock from the VCO will be phase-locked to the reference clock.

Figure 4: VSC8061 Phase Detector Logic Diagram

Figure 5: Phase Detector Input and Output Waveforms

CLK16

R

S

Q

S

R Q

U

D

DCLK

CLK16

DCLK

U

D