LMX2430 datasheet(31/49 Pages) NSC

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LMX243x OSCin Sensitivity Test Setup

20053590

The block diagram above illustrates the setup required to

measure the LMX243x device’s OSCin buffer sensitivity

level. The same setup is used for the LMX2430TM Evalua-

tion Board. This setup is similar to the FinRF sensitivity setup

except that the signal generator is now connected to the

OSCin pin and both Fin pins are tied to Vcc. The 51

Ω shunt

resistor matches the OSCin input to the signal generator.

The R counter is typically set to 1000, i.e. RF_R word = 1000

or IF_R word = 1000. The reference divider output is routed

to the Ftest/LD pin by selecting the RF_R/ 2 Frequency word

(MUX[3:0] word = 14) or the IF_R/ 2 Frequency word

(MUX[3:0] word = 12) in CodeLoader. A Universal Counter is

connected to the Ftest/LD pin and is used to monitor the

output frequency of the reference divider. The expected

frequency should be the signal generator frequency divided

by twice the corresponding counter value, i.e. 2000. The

factor of two comes in because the LMX243x device has an

internal /2 circuit which is used to provide a 50% duty cycle.

In a similar way, sensitivity is typically measured over fre-

quency, supply voltage and temperature. In order to perform

the measurement, the temperature, frequency, and supply

voltage is set to a fixed value and the power level (voltage

level) of the signal at OSCin is varied. Sensitivity is reached

when the frequency error of the divided input signal is

greater than or equal to 1 Hz.

LMX2430 数据表(PDF) 31 Page - National Semiconductor (TI)