LMX2471SLEX National Semiconductor, LMX2471SLEX Datasheet - Page 17

• Manufacturer Part Number: LMX2471SLEX
• Description: IC PLL LP 3.6GHZ/1.7GHZ 24-CSP
• Manufacturer: National Semiconductor
• Type: PLL Frequency Synthesizer, Delta Sigmar

Specifications of LMX2471SLEX

• Pll: Yes with Bypass
• Input: CMOS
• Output: CMOS
• Number Of Circuits: 1
• Ratio - Input:output: 3:3
• Differential - Input:output: Yes/No
• Frequency - Max: 3.6GHz
• Divider/multiplier: Yes/Yes
• Voltage - Supply: 2.25 V ~ 2.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-Laminate UTCSP
• Frequency-max: 3.6GHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LMX2471SLEXTR

Bench Test Setups
INPUT IMPEDANCE MEASUREMENT PROCEDURE
The above block diagram shows the test procedure measur-
ing the input impedance for the LMX2471. This applies to the
FinRF, FinIF, and OSCin pins and is measured in a 50 ohm
environment. The basic test procedure is to calibrate the
network analyzer, ensure that the part is powered up, and
then measure the input impedance. The network analyzer
can be calibrated by using either calibration standards or by
soldering resistors directly to the evaluation board. An open
can be implemented by putting no resistor, a short can be
implemented by using a 0 ohm resistor, and a load can be
implemented by using two 100 ohm resistors in parallel.
Note that no DC blocking capacitor is used for this test
procedure. This is done with the PLL removed from the PCB.
This requires the use of a clamp down fixture that may not
always be generally available. If no clamp down fixture is
available, then this procedure can be done by calibrating up
to the point where the DC blocking capacitor usually is, and
then adding a 0 ohm resistor back for the actual measure-
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17
ment. Once that the network analyzer is calibrated, it is
necessary to ensure that the PLL is powered up. This can be
done by toggling the power down bits (RF_PD and IF_PD)
and observing that the current consumption indeed in-
creases when the bit is disabled. Sometimes it may be
necessary to apply a signal to the OSCin pin in order to
program the part. If this is necessary, disconnect the signal
once it is established that the part is powered up. It is useful
to know the input impedance of the PLL for the purposes of
debugging RF problems and designing matching networks.
Another use of knowing this parameter is make the trace
width on the PCB such that the input impedance of this trace
matches the real part of the input impedance of the PLL
frequency of operation. In general, it is good practice to keep
trace lengths short and make designs that are relatively
resistant to variations in the input impedance of the PLL.
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