LMX2430EVAL National Semiconductor, LMX2430EVAL Datasheet - Page 8

• Manufacturer Part Number: LMX2430EVAL
• Description: EVALUATION BOARD FOR LMX2430
• Manufacturer: National Semiconductor
• Series: PLLatinum™r

Specifications of LMX2430EVAL

• Main Purpose: Timing, Frequency Synthesizer
• Utilized Ic / Part: LMX2430
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / Rohs Status: Not Compliant
• Other names: *LMX2430EVAL

LMX2430SLE EVALUATION BOARD OPERATING INSTRUCTIONS
2.5
Lock Time Measurement Using A Spectrum Analyzer
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 CodeLoader 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 LMX2430SLE 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 CodeLoader 2 Operating Instructions from National Semiconductor’s Wireless
Communications website: http://wireless.national.com/. The lock time is the time difference
between the point the frequency starts to change (T
), and the point the PLL frequency settles
1
within +/- 1 kHz range (T
), i.e. lock time = T
– T
. The single sweep feature of the spectrum
2
2
1
analyzer can be 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.
6
LMX2430SLEFPEB
February 3,2006