LMX9830SMX National Semiconductor, LMX9830SMX Datasheet - Page 23

• Manufacturer Part Number: LMX9830SMX
• Manufacturer: National Semiconductor

Specifications of LMX9830SMX

• Lead Free Status / Rohs Status: Not Compliant

10.9 LOOP FILTER DESIGN
The LMX9830 has an external loop filter which must be de-
signed for best performance by the end customer. This sec-
10.9.1 Component Calculations
The following parameters are required for component value calculation of a third order passive loop filter.
Φ
F
F
KVOC
KΦ
F
T31
γ
The third order loop filter being defined has the following topology. shown in Figure 11.
Calculate the poles and zeros. Use exact method to solve for T1 using numerical methods,
Calculate the loop filter coefficients,
c
comp
OUT
Phase Margin: Phase of the open loop transfer function
Loop Bandwidth
Comparison Frequency: Phase detector frequency
VCO gain: Sensitivity of the VCO to control volts
Charge Pump gain: Magnitude of the alternating current during lock
Maximum RF output frequency
Ratio of the poles T3 to T1 in a 3rd order filter
Gamma optimization parameter
FIGURE 11. Third Order Loop Filter
23
tion therefore gives some foresight into its design. Refer also
to Loop Filter application note and National’s Webench on-
line design tool for more information.
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