LMX9830SM National Semiconductor, LMX9830SM Datasheet - Page 24

• Manufacturer Part Number: LMX9830SM
• Manufacturer: National Semiconductor

Specifications of LMX9830SM

• Lead Free Status / Rohs Status: Not Compliant

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Summary:
Components can then be calculated from loop filter coefficients
Some typical values for the LMX9830 are:
Which give the following component values:
10.9.2 Phase Noise and Lock-Time Calculations
Phase noise has three sources, the VCO, crystal oscillator
and the rest of the PLL consisting of the phase detector, di-
viders, charge pump and loop filter. Assuming the VCO and
crystal are very low noise, it is possible to put down approxi-
mate equations that govern the phase noise of the PLL.
Phase noise (in-band) = PN1Hz + 20Log[N] + 10Log[F
Where PH1Hz is the PLL normalized noise floor in 1 Hz res-
olution bandwidth.
Comparison Frequency
Phase Margin
Loop bandwidth
T3 over T1 ratio
Gamma
VCO gain
Charge pump gain
Fout
C1
C2
C3
R2
R3
Symbol
T1
T2
T3
A0
A1
A2
n
N counter value
Loop Bandwidth
Loop filter pole
Loop filter zero
Loop filter zero
Total capacitance
First order loop filter coefficient
Second order loop filter coefficient
0.17
2.38
0.04
1737
7025
comp
]
Description
24
Further out from the carrier, the phase noise will be affected
by the loop filter roll-off and hence its bandwidth.
As a rule-of-thumb; ΔPhase noise = 40Log[ΔFc]
Where Fc is the relative change in loop BW expressed as a
fraction.
For example if the loop bandwidth is reduced from 100 kHz
to 50 kHz or by one half, then the change in phase noise will
be -12dB. Loop BW in reality should be selected to meet the
13
48
100
40
1.0
120
0.6
2441
20180047
20180045
nF
nF
nF
Ω
Ω
20180046
MHz
Pl rad
kHz
%
MHz per V
mA
MHz
None
rad/s
S
S
S
nF
nFs
nFs2
Units