LMX2434EVAL National Semiconductor, LMX2434EVAL Datasheet - Page 6

• 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

2.2
The loop bandwidth is the bandwidth of the closed loop PLL system. It is, by definition, the
frequency that makes the forward loop gain equal to zero. The spectrum analyzer span is set to
view the characteristic rising, peaking, and falling of the phase noise. To measure the loop
bandwidth is rather complex. It is simpler to measure the 0 dB bandwidth. Although, not exactly
the same, the 0 dB bandwidth is a sufficient estimate of the loop filter bandwidth. The 0 dB
bandwidth is defined as the frequency where the phase noise falls back to the level of the close-in
value after rising to its peak value. The value measured is typically greater than the true loop
filter bandwidth. For this evaluation, the 0 dB bandwidth is measured.
2.3
The reference sidebands can be seen on a spectrum analyzer and are measured in dBc. The
Code Loader software is used to set the desired frequency and to program the LMX2434SLE
device. Refer to Appendix E for more details. The spectrum analyzer is set to the desired center
frequency and the span is set to allow the reference sidebands to be viewed. For the
LMX2434SLE device, the span can be set to 6 MHz during the RF or IF VCO measurements
because their loop filter designs are based on a 2.5 MHz reference frequency. The spurious
output is the difference between the level of the VCO output frequency tone and the level of the
spur at an offset equal to the carrier frequency +/- the reference frequency. For a more accurate
account of the device’s spurious performance, the reference spurs across the VCO’s frequency
band should be determined. The worst-case spur is typically defined as the PLL’s spur
performance.
LMX2434SLEFPEB
Loop Filter Bandwidth Measurement Using A Spectrum Analyzer
Reference Spur Measurement Using A Spectrum Analyzer
LMX2434SLE EVALUATION BOARD OPERATING INSTRUCTIONS
May 12, 2006
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