Texas Instruments LMX248 Series, LMX2485, LMX2487, LMX2486 User Manual
LMX248x Evaluatio n Boa rd
User's Guide
Revised – March 2014
SNAU137
LMX248x
Evaluation Board Operating I nstructions
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2 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
Copyright © 2014, Texas Instruments Incorporated
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Table of Contents
EQUIPMENT ..................................................................................................................................................................................... 4
BASIC OPERATION ........................................................................................................................................................................... 5
LMX2485 BOARD INFORMATION .................................................................................................................................................... 7
PLL PHASE NOISE ..................................................................................................................................................................... 9
RF
PLL FRACTIONAL SPURS ......................................................................................................................................................... 11
RF
PLL LOCK TIME ...................................................................................................................................................................... 12
RF
PLL LOCK TIME ........................................................................................................................................................................ 14
IF
PLL PHASE NOISE ..................................................................................................................................................................... 15
IF
PLL SPURS ................................................................................................................................................................................ 16
IF
LMX2486
PLL PHASE NOISE ................................................................................................................................................................... 18
RF
PLL FRACTIONAL SPURS ......................................................................................................................................................... 20
RF
PLL LOCK TIME (WITH A SPECTURM ANALYZER) .................................................................................................................. 21
RF
PLL PHASE NOISE ..................................................................................................................................................................... 22
IF
PLL SPURS ................................................................................................................................................................................ 23
IF
PLL LOCK TIME ........................................................................................................................................................................ 24
IF
LMX2487
INDING A VCO ............................................................................................................................................................................ 25
F
EPLACING THE VCO W IT H A FOOTPRINT COMPATIBLE VCO ...................................................................................................... 26
R
APPENDIX A: SCHEMATICS ............................................................................................................................................................ 27
PPENDIX B: BUILD DIAGRAMS .................................................................................................................................................... 28
A
PPENDIX C: BIL L OF MATERIALS ................................................................................................................................................ 31
A
PPENDIX D: QUICK START FOR EVM COMMUNICATIONS ........................................................................................................... 34
A
BOARD INFORMATION .................................................................................................................................................. 17
BOARD INFORMATION .................................................................................................................................................. 25
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 3
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Equipment
Power Supply
The Power Supp ly should be a low noise power s upply. 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 E505 2A is recommended. An Agilent E4445A PSA Spectr um 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 to o high and measurements will be of the loc al
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.
4 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
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Basic Operation
1. Connect the signal generator output to the OSCin input of the board. For this ex ample 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.
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 5
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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
6 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
Copyright © 2014, Texas Instruments Incorporated
RF LOOP FILTER
Theoretical ( NOT Measured ) Simulation
(Done with EasyPLL at http://www.ti.com/lsds/ti/wireless)
Pole Ratio
T3 /T1
VCO
CPoRF
2.7 nF
47 nF
820 Ω
270 pF
180 pF
3.9 KΩ 5.6 KΩ
Kφ
400 uA
Comparison
Frequency
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
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LMX2485 Board Information
TM
The LMX2485 Evaluation Board simplifies evaluat ion of the LMX2485 2.6 GHz/0.8 GHz PLLatinum
synthesizer. The board enables a ll performance measurements with no additional support circuitry. The evaluation
board consists of a LMX 2485 device, a RF VCO module and IF VCO & RF/IF loop fi lters built by discrete c omponents.
The SMA flange mount c onnector s are pr ovided f or ex ternal r ef erenc e inp ut, RF an d I F VCO outpu ts , and t he power and
grounding connection. A cable ass embly is bundled with the evaluation boar d f or c onnec ting to a PC throu gh t he parall el
printer port. By means of USB2ANY-uWire seria l port e mulation, the CodeLoader sof tware inclu ded c an be ru n o n a PC
to facilitate the LMX2485 internal register programming for the evaluation and measurement.
dual frequency
Phase Margin 48.3 deg
Loop Bandwidth 11.3 KHz
2400 – 2480 MHz to 1
Lock Time
KHz tolerance in
247 uS w/o Fastlock
Pole Ratio
Spur Gain
@ 200 KHz
40.2 %
T4/T3
36.3 %
-45.8 dB
Settings for Operation
10 MHz
22 pF
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 7
Copyright © 2014, Texas Instruments Incorporated
IF LOOP FILTER
Theoretical ( NOT Measured ) Simulation ( Done with EasyPLL at www.ti.com )
760 - 780 MHz
uS
VCO
CPoRF
1.8 nF
10 nF
8.2 KΩ
Open
Open
0 Ω 0 Ω
Settings for Operation
Kφ
4 mA
Comparison
Frequency
Output
Frequency
PLL Supply
2.5 Volts
VCO Supply
3 Volts
Other Information
VCO Used
VARIL191-773U
VCO Gain
18 MHz/Volt
VCO Input
Capacitance
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Phase Margin 47.1 deg Lock Time
MHz to 1 KHz
tolerance in 453
Loop Bandwidth 5.1 KHz
Spur Gain
@ 200 KHz
22.1 dB
50 kHz
760 - 780 MHz
100 pF
8 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
Copyright © 2014, Texas Instruments Incorporated
Loop Bandwidth is about 10 kHz. Note that the phase noise gradually improves as one goes farther
noise could still be degrading the in-band phase noise.
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RF PLL Phase Noise
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 bec ause the phase noise is worse, and the VCO phase
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 9
Copyright © 2014, Texas Instruments Incorporated
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For this plot, the charge pump was increased to 1600 uA. This improves the PLL phase noise performance and
lower current allows one to experiment with lower comparison frequencies like 2.5 MHz, 5 MHz, and 10 MHz.
also increases the loop bandwidth so the tr ue P LL performance can be seen. The reason that the origina l loop
filter was not designed for 1600 uA cur rent was that it makes the loop filter capacitors 8X larger and als o, the
10 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
Copyright © 2014, Texas Instruments Incorporated
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RF PLL Fractional Spurs
At 2400.2 MHz output frequency, the primary fr actional 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 f requency, the primary fr actional 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 f requency, the primary fr actional spur at 200 kHz is
-80.8 dBc, and the sub-fractional spur at 100 kHz is -73.4 dBc.
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 11
Copyright © 2014, Texas Instruments Incorporated
RF PLL Loc k Time
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Peak time withou t cycle slip
reduction is 1110 uS.
Peak time withou t cycle slip
reduction is 1622 uS.
No CSRC. RF_TOC=0
Positive lock time is 1220 uS
Negative Lo ck time i s 171 1 uS
12 SNAU137 LMX248x Evaluation Board User’s Guide Revised - March 2014
Copyright © 2014, Texas Instruments Incorporated
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