LMX25311778EVAL National Semiconductor, LMX25311778EVAL Datasheet - Page 25

• Manufacturer Part Number: LMX25311778EVAL
• Manufacturer: National Semiconductor

Specifications of LMX25311778EVAL

• Lead Free Status / Rohs Status: Not Compliant

2.4.4 DITHER -- Dithering
Dithering is useful in reducing fractional spurs, especially those that occur a a fraction of the channel spacing. The only exception
is when the fractional numerator is zero. In this case, dithering usually is not a benefit. Dithering also can sometimes increase the
PLL phase noise by a fraction of a dB. In general, if dithering is disabled, phase noise may be slightly better inside the loop bandwidth
of the system, but spurs are likely to be worse too.
2.4.5 FDM -- Fractional Denominator Mode
When this bit is set to 1, the 10 MSB bits for the fractional numerator and denominator are considered. This allows the fractional
denominator to range from 1 to 4,194,303. If this bit is set to zero, only the 12 LSB bits of the fractional numerator and denominator
are considered, and this allows a fractional denominator from 1 to 4095. When this bit is disabled, the current consumption is about
0.5 mA lower.
2.4.6 -- DIV2
When this bit is enabled, the output of the VCO is divided by 2. Enabling this bit does have some impact on harmonic content and
output power.
DITHER
DIV2
0
1
2
3
0
1
25
VCO Output Frequency
Dithering Disabled
Not Divided by 2
Dithering Mode
Strong Dithering
Weak Dithering
Divided by 2
Reserved
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