TI公司的LMX2571是低功耗宽带PLLatinum™ RF频率合成器,集成了Delta-Sigma分数N PLL,多核压控振荡器(VCO),可编输出分压器和两个输出缓冲器.VCO核频率高达5.376MHz,连续输出频率10 MHz 到1344 MHz,主要用在双向无线电,陆基雷达,点对点微波通信,SDR,矢量信号分析仪,无线通信测试仪,无线中继器,TETRA基站等.本文介绍了LMX2571主要特性,框图,几种典型应用电路,以及LMX2571EVM评估板(EVM)主要特性,电路图,材料清单和PCB设计图.

The LMX2571 is a low-power, high-performance, wideband PLLatinum™ RF synthesizer that integrates a delta-sigma fractional N PLL, multiple core voltage-controlled oscillator (VCO), programmable output dividers and two output buffers. The VCO cores work up to 5.376 GHz resulting in continuous output frequency range of 10 MHz to 1344 MHz.

This synthesizer can also be used with an external VCO. To that end, a dedicated 5-V charge pump and an output divider are available for this configuration.A unique programmable multiplier is also incorporated to help improve spurs, allowing the system to use every channel even if it falls on an integer boundary.

The output has an integrated SPDT switch that can be used as a transmit/receive switch in FDD radio application. Both outputs can also be turned on to provide 2 outputs at the same time.

The LMX2571 supports direct digital FSK modulation through programming or pins. Discrete level FSK, pulse shaping FSK, and analog FM modulation are supported.

A new FastLock technique can be used allowing the user to step from one frequency to the next in less then 1.5 ms even when an external VCO is used with a narrow band loop filter.

LMX2571主要特性:

Any Frequency from 10 MHz to 1344 MHz
Low Phase Noise and Spurs
–123 dBc/Hz at 12.5 kHz Offset @ 480 MHz
–145 dBc/Hz at 1 MHz Offset @ 480 MHz
Normalized PLL Noise Floor of –231 dBc/Hz
Spurious Better Than –75 dBc/Hz
New FastLock to Reduce Lock Time
A Novel Technique to Remove Integer Boundary Spurs
Integrated 5-V Charge Pump and Output Dividerfor External VCO Operation
2-, 4- and 8-level or Arbitrary Level Direct Digital FSK Modulation
One TX/RX Output or Two Fanout Outputs
Crystal, XO or Differential Reference Clock Input
Low Current Consumption
39-mA Typical Synthesizer Mode (Int. VCO)
9-mA Typical PLL Mode (Ext. VCO)
24-Bit Fractional-N Delta Sigma Modulator

LMX2571主要应用:

2-Way Radio
Land Defense: Radar
Military: Radar/Electronic Warfare
Point-to-Point Microwave Backhaul
Software Defined Radio (SDR)
Vector Signal Analyzer
Wireless Communications Tester
Endoscope
Military and Avionics Imaging
Oscilloscope
Signal & Waveform Generator
TETRA Base Station
Vector Signal Generator
Wireless Repeater

图1.LMX2571框图

图2.LMX2571应用框图

图3.LMX2571合成器双工模式应用电路图

图4.LMX2571PLL双工模式应用电路图

图5.LMX2571合成器/PLL双工模式应用电路图

LMX2571EVM评估板(EVM)

The Texas Instruments LMX2571EVM evaluation module (EVM) helps designers evaluate the operationand performance of the LMX2571 Wideband Frequency Synthesizer. The EVM contains one FrequencySynthesizer.

The LMX2571EVM is an evaluation board for the LMX2571 which is a frequency synthesizer with low noise, high performance integrated VCO. The VCO core is a low noise 5GHz VCO, after the output channel divider, the divided down frequencies are 10MHz to 1400MHz.

The internal VCO is bypassable, allowing the use of external VCO. A separated 5V charge pump is dedicated for external VCO, eliminating the need for an op-amp to support 5V VCO. Output of the external VCO can also route through another output channel divider.

LMX2571EVM can be programmed via (1) SPI programming, (2) I2S programming and (3) PIN mode. PIN mode supports up to 8-level FSK modulation. The board can be powered with a 5V external supply.

LMX2571EVM评估板(EVM)主要特性:

External VCO option
Output channel divider supports 10MHz to 1400MHz operations
Direct digital FSK modulation
One TX/RX output or two fanout outputs
Crystal, XO or differential reference clock input

图6.LMX2571EVM评估板(EVM)外形图

图7.LMX2571EVM评估板(EVM)电路图
LMX2571EVM评估板(EVM)材料清单:



图8.LMX2571EVM评估板(EVM)PCB元件装配图(顶层)

图9.LMX2571EVM评估板(EVM)PCB设计图(顶层)

图10.LMX2571EVM评估板(EVM)PCB设计图(地层)

图11.LMX2571EVM评估板(EVM)PCB设计图(电源层)

图12.LMX2571EVM评估板(EVM)PCB设计图(底层)
详情请见:
http://www.ti.com/lit/ds/snas654/snas654.pdf
和http://www.ti.com/lit/ug/snau176a/snau176a.pdf

snas654.pdf
snau176a.pdf