Datasheet

Dirty Input
Clock
Dist.
PLL
LMK04000
(Clock Jitter Cleaner)
Clean
Reference
Clock
Ultra-Clean
Local Oscillator
LMX2541
(RF Synthesizer)
PLL
LMX2541SQ2060E, LMX2541SQ2380E
LMX2541SQ2690E, LMX2541SQ3030E
LMX2541SQ3320E, LMX2541SQ3740E
SNOSB31I –JULY 2009–REVISED FEBRUARY 2013 www.ti.com
System Diagram
LMX2541 Frequency Coverage
2060E 2380E 2690E 3030E 3320E 3740E
VCO
_DIV
Start Stop Start Stop Start Stop Start Stop Start Stop Start Stop
1 1990.0 2240.0 2200.0 2530.0 2490.0 2865.0 2810.0 3230.0 3130.0 3600.0 3480.0 4000.0
2 995.0 1120.0 1100.0 1265.0 1245.0 1432.5 1405.0 1615.0 1565.0 1800.0 1740.0 2000.0
3 663.3 746.7 733.3 843.3 830.0 955.0 936.7 1076.7 1043.3 1200.0 1160.0 1333.3
4 497.5 560.0 550.0 632.5 622.5 716.3 702.5 807.5 782.5 900.0 870.0 1000.0
5 398.0 448.0 440.0 506.0 498.0 573.0 562.0 646.0 626.0 720.0 696.0 800.0
6 331.7 373.3 366.7 421.7 415.0 477.5 468.3 538.3 521.7 600.0 580.0 666.7
7 284.3 320.0 314.3 361.4 355.7 409.3 401.4 461.4 447.1 514.3 497.1 571.4
8 248.8 280.0 275.0 316.3 311.3 358.1 351.3 403.8 391.3 450.0 435.0 500.0
… … … … … … … … … … … … …
63 31.6 35.6 34.9 40.2 39.5 45.5 44.6 51.3 49.7 57.1 55.2 63.5
All devices have continuous frequency coverage below a divide value of 8 (7 for most devices) down to their
minimum frequency achievable with divide by 63. The numbers in bold show the upper end of this minimum
continuous frequency range. For instance, the LMX2541SQ3740E option offers continuous frequency coverage
from 55.2 MHz to 571.4 MHz and LMX2541SQ2060E offers continuous frequency coverage from 31.6 MHz to
280 MHz. If using the part in External VCO mode, all parts have roughly the same performance and any option
will do.
Determining the Best Frequency Option of the LMX2541 to Use
When there are multiple devices that can satisfy the frequency requirement, performance characteristics can
sometimes be used to make a decision. Consider the following example of where an output frequency of 1200 to
1250 MHz is desired with a channel spacing of 100 kHz. From the frequency table, the LMX2541SQ2380E could
be used with a divide value of 2, or the LMX2541SQ3740E option could be used with a divide value of 3. This
raises the question: Which one has better performance? The following table is helpful in comparing the
performance.
Performance What Makes it
Why
Characteristic Better
Fractional spurs at the VCO are independent of VCO frequency, but when the VCO frequency is
divided down by a factor of VCO_DIV, the fractional spurs improve by a factor of 20·log(VCO_DIV).
Fractional Spurs Also, the fractional channel spacing can be made wider at the VCO, which makes the fractional spurs
Larger Value
and farther from the carrier.
of VCO_DIV
Fraction Noise The fractional noise of the modulator is divided down in a similar way as fractional spurs. In
applications where this is dominant, this larger division can have an impact. Consult the applications
section for more information on the fractional phase noise.
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Product Folder Links: LMX2541SQ2060E LMX2541SQ2380E LMX2541SQ2690E LMX2541SQ3030E
LMX2541SQ3320E LMX2541SQ3740E