82V3002APVG datasheet(13/30 Pages) RENESAS

13 / 30 page

FUNCTIONAL DESCRIPTION

October 15, 2008

IDT82V3002A

WAN PLL WITH DUAL REFERENCE INPUT

Figure - 5 TIE Control Circuit Diagram

The TIE Control Block will work under the control of the Step

Generation circuit when it is enabled manually or automatically (by the

TIE_en pin or TIE auto-enable logic generated by the State Control

Circuit).

The selected reference signal is compared with the feedback signal

(current output feedback from the Frequency Select Circuit) by the

Measure Circuit. The phase difference between the input reference and

the feedback signal is sent to the Storage Circuit for TIE correction. The

Trigger Circuit generates a virtual reference with the phase corrected to

the same position as the previous reference according to the value

stored in the Storage Circuit. With this TIE correction mechanism, the

reference is switched without generating a step change in phase.

Figure - 6 shows the phase transient that would result if a reference

switch is performed with the TIE Control Block enabled.

Figure - 6 Reference Switch with TIE Control Block Enabled

The phase difference in the Storage Circuit can be cleared by

applying a logic low pulse to the TCLR pin. The reset pulse should be at

least 300 ns.

When the IDT82V3002A primarily enters Holdover Mode for short

time periods and then turns back to Normal Mode, the TIE Control

Circuit should not be enabled. This will prevent undesired accumulated

phase change between the input and output.

If the TIE Control Block is disabled manually or automatically during

the reference switching, the phase of the output signal will align with that

of the new reference. The phase slope is limited to 5 ns per 125 µs.

Figure - 7 shows the phase transient resulting from a reference switch

with the TIE Control Block disabled.

Step Generation

TIE_en

Select

Circuit

Fref0

Fref1

IN_sel

Measure

Circuit

Storage

Circuit

Trigger

Circuit

Feedback

signal

TCLR

Fref

Virtual

Reference

Signal

Input Clock

Fref0

Time = 0.00 s

Time = 0.25 s

Time = 0.50 s

Time = 0.75 s

Time = 1.0 s

Time = 1.25 s

Time = 1.50 s

Time = 1.75 s

Output Clock

Fref1

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