W3000 Datasheet, PDF (21/28 Pages) Agere Systems – W3000 PLL Dual-Band Frequency Synthesizer

Advance Data Sheet
December 1999
W3000 PLL Dual-Band Frequency Synthesizer
Application Information (continued)
For example, take a GSM application where a loop bandwidth of 22 kHz is required.
Other parameters specified by the system are listed below:
Parameter
VCO Gain (KVCO)
Charge Pump Current (ICP)
Divider Ratio (value of midband frequency used) (N)
Required Phase Margin
Reference Frequency Attenuation from Additional Pole
Value
88 MHz/V
2.5 mA
7850
45°
20 dB
Using the formulas above, the three time constants can be calculated as follows:
T1 = 2.63697E – 10^–6 s
T2 = 3.14484E – 10^–5 s
T3 = 2.38732E – 10^–6 s
From these values, we can derive the initial component values as follows:
R1 = 2992 Ω
C1 = 0.96 nF
C2 = 10.5 nF
If we choose R2 = 15 kΩ, then
C3 = 159 pF
From these initial values, the loop filter components used in the application circuit can be derived through
practical optimization.
Lucent Technologies Inc.
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