LMX2434EVAL National Semiconductor, LMX2434EVAL Datasheet - Page 4

• Manufacturer Part Number: LMX2434EVAL
• Description: EVALUATION BOARD FOR LMX2434
• Manufacturer: National Semiconductor
• Series: PLLatinum™r

Specifications of LMX2434EVAL

• Main Purpose: Timing, Frequency Synthesizer
• Utilized Ic / Part: LMX2434
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / Rohs Status: Not Compliant
• Other names: *LMX2434EVAL

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3.0 Optimizing Sensitivity at 2.0
GHz
Now suppose the requirement is to optimize the perfor-
mance at 2.0 GHz for an LO to be used in a particular US
TBQM handset application. Figure 2 now shows that the
FinRF input impedance lies on the lower half of the Smith
Chart. From the LMX243x UTCSP FinRF Input Impedance
Table, ZFinRF = 14.32 - j38.66Ω at 2.0 GHz.
To move closer to 50Ω and to an ideal match, a 4.7 nH series
inductor is placed between the VCO output and the FinRF
input of the PLL as shown in Figure 9. The impedance is then
illustrated in Figure 10.
FIGURE 10. LMX243x UTCSP FinRF Input Impedance
FIGURE 9. 4.7 nH Series Match at 2.0 GHz
with 4.7 nH Series Match
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Figure 11 shows that an approximate 2.0 dB improvement in
sensitivity is achieved at 2.0 GHz with the addition of the 4.7
nH series inductor. Figure 11 also shows that the sensitivity
gets much worse at frequencies other than 2.0 GHz. Simi-
larly, this evaluation is performed under typical conditions,
with Vcc = 2.50V and T
Summary
The results shown in this note reflect conditions using a PCB
with optimized grounding around 5.0 GHz. Most PCB de-
signs may not be well grounded at 5.0 GHz and therefore
may not achieve the sensitivity shown in the graphs above.
However, this paper demonstrates that a single element
match offers a seemingly good solution for today’s stringent
PCB space and cost reduction requirements with an en-
hancement in sensitivity performance over a non-matched
solution.
FIGURE 11. LMX243x UTCSP FinRF Input Sensitivity
Improvement at 2.0 GHz
A
= 25˚C.
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