Loop Filter Calculation Examples; Loop Filter For Vcxo Pll - Renesas 8V19N49 Series Manual

8V19N49x Hardware Design Guide
The Rs, Cs, and Cp can be the actual value used in the 2
rd
determine the 3 order loop filter R3 and C3.
1. Pick an R3 value. Suggest R3 ~ 1.5xRs
Where,
γ is ratio between the 1
2. The Timing Commander software tool is provided to calculate the loop filter component values. To use the
spread sheet, user can enters the follow parameters:
fc, Fpd, fvco, α and β
The software tool will provide the component values, Rs, Cs, and Cp as result. The tool will also calculate
maximum phase margin for verification.
rd
The 3 order loop filter, R3 and C3, are also calculated using the actual 2
3.3

Loop Filter Calculation Examples

3.3.1

Loop Filter for VCXO PLL

3.3.1.1 Second Order Loop Filter for the VCXO PLL
This section provides calculation examples for the VCXO PLL loop filter value. The 8V19N490 VCXO phase lock
loop block diagram is displayed in
the reference CLK input frequency = 30.72MHz and a VCXO with output frequency of 122.88MHz is used.
R31UH0005EU0100 Rev.1.0
Jun 3, 2021
Charge Pump Driv er
Rs
Cs
Figure 7. Typical 3
st
pole frequency and the 2
nd
Figure 8. A 2 order loop filter for VCXO is shown in
Figure 8. 8V19N490 VCXO PLL Block Diagram
VCO Control Input
R3
Cp C3
Loop Filter Return
rd
Order Loop Filter
nd
order loop filter. The following equation helps
nd
pole frequency. Suggest γ greater than 3.
nd
order loop filter components values.
Figure 9. In this example,
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