LMX2433EVAL National Semiconductor, LMX2433EVAL Datasheet - Page 6

• Manufacturer Part Number: LMX2433EVAL
• Description: EVALUATION BOARD FOR LMX2433
• Manufacturer: National Semiconductor
• Series: PLLatinum™r

Specifications of LMX2433EVAL

• Main Purpose: Timing, Frequency Synthesizer
• Embedded: No
• Utilized Ic / Part: LMX2433
• Primary Attributes: Dual Fractional-N PLL
• Secondary Attributes: 3.6GHz, CodeLoader Graphical User Interface
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: *LMX2433EVAL

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.
The reference sidebands can be seen on a spectrum analyzer and are measured in dBc. The
CodeLoader software is used to set the desired frequency and to program the LMX2433SLE
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
LMX2433SLE device, the span can be set to 7 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.
LMX2433SLEFPEB
2.2
2.3
Loop Filter Bandwidth Measurement Using A Spectrum Analyzer
Reference Spur Measurement Using A Spectrum Analyzer
LMX2433SLE EVALUATION BOARD OPERATING INSTRUCTIONS
February 8,2006
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