Texas Instruments LMX248 Series User manual

LMX248x Evaluation Board
User's Guide
Revised – March 2014
SNAU137

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2SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
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LMX248x
Evaluation Board Operating Instructions

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Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 3
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Table of Contents
EQUIPMENT .....................................................................................................................................................................................4
BASIC OPERATION...........................................................................................................................................................................5
LMX2485 BOARD INFORMATION....................................................................................................................................................7
RF PLL PHASE NOISE .....................................................................................................................................................................9
RF PLL FRACTIONAL SPURS .........................................................................................................................................................11
RF PLL LOCK TIME ......................................................................................................................................................................12
IF PLL LOCK TIME........................................................................................................................................................................14
IF PLL PHASE NOISE.....................................................................................................................................................................15
IF PLL SPURS................................................................................................................................................................................16
LMX2486 BOARD INFORMATION..................................................................................................................................................17
RF PLL PHASE NOISE ...................................................................................................................................................................18
RF PLL FRACTIONAL SPURS .........................................................................................................................................................20
RF PLL LOCK TIME (WITH A SPECTURM ANALYZER) ..................................................................................................................21
IF PLL PHASE NOISE.....................................................................................................................................................................22
IF PLL SPURS................................................................................................................................................................................23
IF PLL LOCK TIME........................................................................................................................................................................24
LMX2487 BOARD INFORMATION..................................................................................................................................................25
FINDING A VCO ............................................................................................................................................................................25
REPLACING THE VCO WITH A FOOTPRINT COMPATIBLE VCO......................................................................................................26
APPENDIX A: SCHEMATICS............................................................................................................................................................27
APPENDIX B: BUILD DIAGRAMS....................................................................................................................................................28
APPENDIX C: BILL OF MATERIALS ................................................................................................................................................31
APPENDIX D: QUICK START FOR EVM COMMUNICATIONS...........................................................................................................34

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Equipment
Power Supply
The Power Supply should be a low noise power supply. An Agilent 6623A Triple power supply with LC filters on the
output to reduce noise was used in creating these evaluation board instructions.
Signal Generator
The Signal Generator should be capable of frequencies and power level required for the part. A Rohde & Schwarz SML03
was used in creating these evaluation board instructions.
Phase Noise / Spectrum Analyzer
For measuring phase noise an Agilent E5052A is recommended. An Agilent E4445A PSA Spectrum Analyzer with the
Phase Noise option is also usable although the architecture of the E5052A is superior for phase noise measurements. At
frequencies less than 100 MHz the local oscillator noise of the PSA is too high and measurements will be of the local
oscillator, not the device under test.
Oscilloscope
The oscilloscope and probes should be capable of measuring the output frequencies of interest when evaluating this
board. The Agilent Infiniium DSO81204A was used in creating these evaluation board instructions.

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Basic Operation
1. Connect the signal generator output to the OSCin input of the board. For this example we use a 10 MHz sin
signal at +5dBm power level.
2. Connect a low noise 3.3 V power supply to the Vcc connector located at the top left of the board.
3. Please see Appendix D for quick start on interfacing the board. Connect PC to the uWire header.
4. Start CodeLoader4.exe.
5. Click “Select Device” “PLL-Fractional” LMX248x depending on which chip is on your board.

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6. Select USB or LPT Communication Mode on the Port Setup tab as appropriate.
7. Click “CTRL + L” to load settings into device

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LMX2485 Board Information
The LMX2485 Evaluation Board simplifies evaluation of the LMX2485 2.6 GHz/0.8 GHz PLLatinumTM dual frequency
synthesizer. The board enables all performance measurements with no additional support circuitry. The evaluation
board consists of a LMX2485 device, a RF VCO module and IF VCO & RF/IF loop filters built by discrete components.
The SMA flange mount connectors are provided for external reference input, RF and IF VCO outputs, and the power and
grounding connection. A cable assembly is bundled with the evaluation board for connecting to a PC through the parallel
printer port. By means of USB2ANY-uWire serial port emulation, the CodeLoader software included can be run on a PC
to facilitate the LMX2485 internal register programming for the evaluation and measurement.
RF LOOP FILTER
Theoretical ( NOT Measured ) Simulation
(Done with EasyPLL at http://www.ti.com/lsds/ti/wireless)
Phase Margin 48.3 deg
Pole Ratio
T3 /T1
40.2 %
Loop Bandwidth 11.3 KHz Pole Ratio
T4/T3 36.3 %
Lock Time 2400 – 2480 MHz to 1 KHz tolerance in
247 uS w/o Fastlock
Spur Gain
@ 200 KHz -45.8 dB
VCO
CPoRF
2.7 nF
47 nF
820 Ω
270 pF 180 pF
3.9 KΩ5.6 KΩ
Settings for Operation
Kφ
400 uA
Comparison
Frequency
10 MHz
Output
Frequency
2400 – 2480
MHz
PLL Supply
2.5 Volts
VCO Supply
3 Volts
Other Information
VCO Used
VARIL2450U
VCO Gain
55 MHz/Volt
VCO Input
Capacitance
22 pF

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IF LOOP FILTER
Theoretical ( NOT Measured ) Simulation ( Done with EasyPLL at www.ti.com )
Phase Margin 47.1 deg Lock Time
760 - 780 MHz
MHz to 1 KHz
tolerance in 453
uS
Loop Bandwidth 5.1 KHz Spur Gain
@ 200 KHz 22.1 dB
VCO
CPoRF
1.8 nF
10 nF
8.2 KΩ
Open Open
0 Ω0 Ω
Settings for Operation
Kφ
4 mA
Comparison
Frequency
50 kHz
Output
Frequency
760 - 780 MHz
PLL Supply
2.5 Volts
VCO Supply
3 Volts
Other Information
VCO Used
VARIL191-773U
VCO Gain
18 MHz/Volt
VCO Input
Capacitance
100 pF

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RFPLLPhaseNoise
Loop Bandwidth is about 10 kHz. Note that the phase noise gradually improves as one goes farther
from the carrier. Also note that this is done with 200 uA of current, and the true phase noise
capability of the part is not shown here because the phase noise is worse, and the VCO phase
noise could still be degrading the in-band phase noise.

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For this plot, the charge pump was increased to 1600 uA. This improves the PLL phase noise performance and
also increases the loop bandwidth so the true PLL performance can be seen. The reason that the original loop
filter was not designed for 1600 uA current was that it makes the loop filter capacitors 8X larger and also, the
lower current allows one to experiment with lower comparison frequencies like 2.5 MHz, 5 MHz, and 10 MHz.

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RFPLLFractionalSpurs
At 2400.2 MHz output frequency, the
primary fractional spur at 200 kHz is
-70.7 dBc, and the sub-fractional spur at
100 kHz is -69.5 dBc.
At 2440.2 MHz output frequency, the
primary fractional spur at 200 kHz is
-78.9 dBc, and the sub-fractional spur at
100 kHz is -72.9 dBc.
At 2480.2 MHz output frequency, the
primary fractional spur at 200 kHz is
-80.8 dBc, and the sub-fractional spur at
100 kHz is -73.4 dBc.

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RFPLLLockTime
No CSRC. RF_TOC=0
Peak time without cycle slip
reduction is 1110 uS.
Peak time without cycle slip
reduction is 1622 uS.
Positive lock time is 1220 uS
Negative Lock time is 1711 uS

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RFPLLLockTime
Cycle Slip Reduction Enabled. RF_TOC=500
Peak time with cycle slip reduction
is 222 uS.
Peak time with cycle slip reduction
is 222 uS.
Positive lock time is 345 uS
Negative Lock time is 378 uS

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IF PLL Lock Time
Peak time is 97.8 uS
Peak Time is 133.3 uS
Positive Lock time is 510 uS
Negative Lock Time is 474 uS

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IF PLLPhaseNoise

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IF PLLSpurs
Spurs at 50 kHz offset for an output frequency of
760 MHz are -97.5 dBc.
Note the cusping effect at 50 kHz. This is because
the loop bandwidth is wide relative to the
comparison frequency. This is due to the discrete
sampling action of the phase detector.
Spurs at 50 kHz offset for an output frequency of
770 MHz are -81.7 dBc.
Spurs at 50 kHz offset for an output frequency of
780 MHz are -71.7 dBc.

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LMX2486 Board Information
The LMX2486 Evaluation Board simplifies evaluation of the LMX2486 4.5 GHz/3.0 GHz PLLatinumTM dual frequency
synthesizer. The board enables all performance measurements with no additional support circuitry. The evaluation
board consists of a LMX2486 device, a RF VCO module and IF VCO & RF/IF loop filters built by discrete components.
The SMA flange mount connectors are provided for external reference input, RF and IF VCO outputs, and the power and
grounding connection. A cable assembly is bundled with the evaluation board for connecting to a PC through the parallel
printer port. By means of USB2ANY-uWire serial port emulation, the CodeLoader software included can be run on a PC
to facilitate the LMX2486 internal register programming for the evaluation and measurement.
RF Loop Filter
Phase Margin
46.5 deg
Pole Ratio T3
4.5 %
Loop Bandwidth
9.8 KHz
Pole Ratio
T4/T3
57.7 %
Theoretical Discrete
Lock Time
915 uS w/o CSR to 1
kHz
Roll-Off
@ 200 KHz
-42.7 dB
VCO
CPoRF
6.8 nF
220 nF
150 Ω
4.7 nF 15 nF
56 Ω33 Ω
Settings for Operation
Kφ
8X (760 uA)
Comparison
Frequency
20 MHz
Output
Frequency
3200 – 3300
MHz
PLL Supply
3.3 Volts from
regulator
VCO Supply
5.5 Volts
VCO Information
VCO Used
VARIL690-
KVCO
90 MHz/Volt
Input
Capacitance
22 pF
IF Loop Filter
Phase Margin 48.1 deg
Theoretical
Discrete Lock
Time
160 uS to 1 kHz
Loop Bandwidth 16.8 KHz
Spur Gain
@ 50 KHz
50.5 dB
VCO
CPoRF
680 pF
4.7 nF
4.7 KΩ
Open
0 Ω
Settings for Operation
Kφ
3.5 mA
Comparison
Frequency
200 kHz
Output
Frequency
2100 - 2200
MHz
PLL Supply
3.3 Volts from
regulator
VCO Supply
5.5 volts
VCO Information

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VCO Used
VARIL190-
KVCO
80 MHz/Volt
Input
Capacitance
120 pF
RF PLLPhase Noise
Loop Bandwidth is about 10 kHz. Note that the phase noise gradually improves as one goes farther from the
carrier. This was taken with the IF PLL powered up and IF VCO connected.

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For this plot, the charge pump was increased to 16X and the other conditions were the same.

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RF PLLFractional Spurs
At 3200.2 MHz output frequency, the primary
fractional spur at 200 kHz is
-80 dBc, and the sub-fractional spur at 100 kHz
is below the noise floor.
At 3240.2 MHz output frequency, the primary
fractional spur at 200 kHz is
– 88 dBc and the sub-fractional spur at 100
kHz is below the noise floor.
At 3200.2 MHz output frequency, the primary
fractional spur at 200 kHz is –82 dBc and the
sub-fractional spur is below the noise.