Texas Instruments LMX248 Series, User Manual

Page: 7 / 37

www.ti.com
Revised - March 2014 LMX248x Evaluation Board User’s Guide SNAU137 7
Copyright © 2014, Texas Instruments Incorporated
LMX2485 Board Information
The LMX2485 Evaluation Board simplifies evaluation of the LMX2485 2.6 GHz/0.8 GHz PLLatinum
TM
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 K Ω 5.6 K Ω
Settings for Operation
K
φ
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