LG1600KXH datasheet(5/20 Pages) AGERE

5 / 20 page

Data Sheet

June 1999

LG1600KXH Clock and Data Regenerator

Lucent Technologies Inc.

Theory of Operation (continued)

A more useful expression of the PLL characteristics is

the following*:

The jitter transfer is now directly expressed in the phys-

ical loop gain pole product,

ωb, and the loop filter time

constant,

τ. Damping ratio, ς, and natural frequency, ωn,

simply relate to these two parameters as follows:

and

* Wolaver, D.H.,

Phase-Locked Loop Circuit Design, Prentice Hall,

1991.

()

ωb 1

-----





ωb 1

-----





-------------------------------------

ςωbτ

0.5

ωn

ωn τ

⁄

For moderate damping,

ς > 2.5 (ωbτ < 0.1), the –3 dB

bandwidth of the PLL can be approximated by the loop

gain pole product:

JBW

≈ ωb = KdRxKo

while the jitter peaking can be expressed in terms of

the product of PLL bandwidth and loop filter time con-

stant:

As the last two expressions make clear, the PLL band-

width is controlled by the value of the external resistor

(see Figure 8), while the peaking depends both on the

resistor value (quadratically) and total loop filter capac-

itance.

() max 1

ωbτ

---------

≈

CKdKo

-------------------------

12-3231(F)r.3—12-3232(F)r.3

Figure 8. Jitter Bandwidth vs. External Resistor Value

100

200

250

0.0

0.2

0.6

0.8

1.0

1.2

Rx (

Ω)

0.4

150

A. LG1600KXH0622 (Cx = 0.15

µF)

°C

100

200

250

0.0

0.6

1.8

2.4

3.0

3.6

Rx (

Ω)

1.2

150

B. LG1600KXH2488 (Cx = 0)

°C

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