Advance Data Sheet

December 1999

W3000 PLL Dual-Band Frequency Synthesizer

Lucent Technologies Inc.

21

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

Value

88 MHz/V

2.5 mA

Divider Ratio (value of midband frequency used) (N)

7850

Required Phase Margin

45°

Reference Frequency Attenuation from Additional Pole

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 k

Ω, then

C3 = 159 pF

From these initial values, the loop filter components used in the application circuit can be derived through

practical optimization.