LMX2541SQE2060E/NOPB National Semiconductor, LMX2541SQE2060E/NOPB Datasheet - Page 31

• Manufacturer Part Number: LMX2541SQE2060E/NOPB
• Description: IC PLL FREQ SYNTH W/VCO 36LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Clock/Frequency Synthesizer (RF)r

Specifications of LMX2541SQE2060E/NOPB

• Pll: Yes
• Input: Clock
• Output: Clock
• Number Of Circuits: 1
• Ratio - Input:output: 2:2
• Differential - Input:output: No/No
• Frequency - Max: 2.24GHz
• Divider/multiplier: Yes/No
• Voltage - Supply: 3.15 V ~ 3.45 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-LLP
• Frequency-max: 2.24GHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMX2541SQE2060ETR

INPUT AND OUTPUT IMPEDANCE TEST SETUP
A network analyzer can be used to measure the input
impedance of the OSCin and ExtVCOin pin as well as the
output impedance of the RFout pin. The general technique is
to connect the desired pin with no DC blocking capacitor to a
network analyzer and measure the impedance directly. The
part needs to be programmed to ensure that it is in a known
state. There are some special considerations that should be
taken for different measurements of the three different
impedances.
OSCin Input Impedance Measurement
For this pin, the provided calibration standards are typically
good enough for a decent measurement. A single-ended
measurement at the OSCin or OSCin* pins can be made For
a differential measurement, this needs to be treated by the
instrument as a two port network.
ExtVCOin Input Impedance Measurement
Because this pin goes higher in frequency, it is often difficult
get a good measurement at higher frequencies because of
the effects of the board and SMA connector. One technique
31
that can be used is instead of using the provided calibration
standards that come with the equipment, solder resistors di-
rectly to the board in order to calibrate out the effects of the
board as well. A 0 ohm resistor functions as a short, no re-
sistor functions as an open, and two parallel 100 ohm resis-
tors serve as a load. These should be soldered as close to
the part as possible. Once this calibration is done, the mea-
surement can be done as normal.
RFout Output Impedance Measurement
Although output and input impedance are not the same thing,
they can be measured in a similar way. Because this pin is a
higher frequency, it is better to use the same method for cal-
ibration as used for the ExtVCOin pin. The other consideration
for the RFout pin is that there are many different settings that
impact this input impedance. When in bypass mode
(VCO_DIV=1), the VCOGAIN and OUTTERM words can
change the impedance. When in divided mode (VCO_DIV>1),
the DIVGAIN and OUTTERM words can impact the
impedance.
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