LMX2434EVAL National Semiconductor, LMX2434EVAL Datasheet - Page 8

• 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

2.5
The principle behind this is to use the spectrum analyzer as an FM demodulator to detect the
frequency change over time when the PLL is switching between two frequencies. This method is
called the Zero-Span mode. The idea is to convert the FM of the signal to amplitude variations
and then measure these variations over time. The center frequency of the spectrum analyzer is
first set to the final (settling) frequency. The frequency span and resolution bandwidth are both
set to 10 kHz, and the video bandwidth is set to 100 kHz. The scale is set to 2 dB per division and
the step size is set to 1 kHz per division. A filter response is displayed. The spectrum analyzer is
tuned off the center frequency so that the slope of the tunable filter is used as an FM to AM
converter. The linear section (slope) of the filter is at 5 kHz from the center frequency. The slope
is approximately 1 dB/ 1 kHz. The frequency span is finally set to 0 Hz. A sweep time of 30 msec
is used.
A x1 probe is used to connect the MICROWIRE to the external trigger on the rear panel of the
spectrum analyzer. Using the Code Loader software, port address ‘C1’ is selected for the
TRIGGER programming pin. The TRIGGER is then set to HIGH. Using the Burst Mode menu of
the software, a macro is created to program the LMX2434SLE device to switch between the
maximum and minimum frequency alternately over time. It is necessary to include a sufficient
delay, such as 10000000, after each programming command. Refer to the Burst Mode Tab
section in the
Communications website: wireless.national.com. The lock time is the time difference between the
point the frequency starts to change (T
range (T
used to capture the trace. (+/- 1 kHz tolerance corresponds to +/- 1 dB from the settling
frequency).
Due to a maximum frequency range specification of 2.5GHz, the modulation domain analyzer
cannot be used for the RF lock time measurement. Do to component tolerances, the maximum of
some Vail 690-4700T VCOs used will not reach 4760 MHz with a tuning voltage of 2.0V and/or
used will not reach 4625 MHz with a tuning voltage of 0.5V. The 2.0V is 0.5V below the 2.5V
supply rail and 0.5V is above the ground rail, which is the delta specification in the datasheet.
Also, Figure 4.1.6 and 4.1.7 shows lock times to and from 4625 and 4760 MHz. On instances
where VCO does not reach these frequencies, use 4645 and/or 4740 MHz frequency. Other than
the frequency the waveform should be the same as shown in Figures 4.1.6 and 4.1.7.
LMX2434SLEFPEB
Lock Time Measurement Using A Spectrum Analyzer
2
), i.e. lock time = T
Code Loader Operating Instructions
LMX2434SLE EVALUATION BOARD OPERATING INSTRUCTIONS
2
– T
1
. The single sweep feature of the spectrum analyzer can be
1
), and the point the PLL frequency settles within +/- 1 kHz
May 12, 2006
from National Semiconductor’s Wireless
6