LUCW3000CCN AGERE [Agere Systems], LUCW3000CCN Datasheet - Page 19

• Manufacturer Part Number: LUCW3000CCN
• Description: W3000 PLL Dual-Band Frequency Synthesizer
• Manufacturer: AGERE [Agere Systems]

Advance Data Sheet
December 1999
Application Information
A typical PLL system can be modeled as follows:
K
Z(s) = Loop filter
K
N
R
Where the open loop gain is:
Where
The circuit shown in Figure 12 uses a passive third-order loop filter for the element Z(s), defined by the network:
The purpose of the loop filter is to provide response with bandwidth sufficient not only to allow a quick lock time
but also to meet phase-noise and reference sideband requirements. Addition of a third pole formed by R2 and C3
will improve reference sideband performance with little overall impact on the loop performance. A reasonable
practical limit is that the f comparison is greater than 5 times loop bandwidth.
PD
VCO
Lucent Technologies Inc.
= Phase detector in mA/2 rad
= VCO gain in MHz/V
= Total divide ratio
= Reference divide ratio
G(s)
s = j
OPEN
=
K
PD
*
f
REF
Z
Ns
s (
* )
Kvco
CHARGE PUMP
1/R
OUTPUT
Figure 12. Third-Order Loop Filter
Figure 11. Typical PLL Model
+
C1
K
PD
W3000 PLL Dual-Band Frequency Synthesizer
R1
C2
Z(s)
1/N
R2
K
C3
VCO
s
VCO
f
VCO
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