| Maxim MAX7057 ASK发送方案 |
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| 作者：未知 来源：Maxim 点击数：176 更新时间：2008-5-21 |
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Maxim公司的MAX7057是频率可编程的UHF(300MHz -450MHz) ASK/FSK发送器.MAX7057在功率放大器的输出级有可调的电容,从而能匹配天线或负载.发送数据的速率高达100kbps NRZ,2.7V电源时向50欧姆发送的功率为+9.2dBm,可广泛应用在RF遥控,车库门的控制,家庭自动化,汽车电子以及无线传感器.本文介绍了MAX7057的主要特性,方框图以及典型应用电路和所用的元件清单.
MAX7057:300MHz to 450MHz Frequency-Programmable ASK/FSK Transmitter
The MAX7057 frequency-programmable UHF transmitter is designed to transmit ASK/FSK data at a wide range of frequencies from 300MHz to 450MHz. The MAX7057 has internal tuning capacitors at the output of the power amplifier that are programmable for matching to an antenna or load. This allows the user to change to a new frequency and match the antenna at the new frequency simultaneously. The MAX7057 transmits at a data rate up to 100kbps nonreturn-to-zero (NRZ) (50kbps Manchester coded). Typical transmitted power into a 50 ohm load is +9.2dBm with a +2.7V supply.
The device operates from +2.1V to +3.6V and typically draws under 12.5mA of current in FSK mode (8.5mA in ASK mode) when the antenna-matching network is designed to operate over the 315MHz to 433.92MHz frequency range. For narrower operating frequency ranges, the matching network can be redesigned to improve efficiency. The standby current is less than 1μA at room temperature.
The MAX7057 reference frequency from the crystal oscillator is multiplied by a fully integrated fractional-N phase-locked loop (PLL). The multiplying factor of the PLL is set by a 16-bit number, with 4 bits for integer and 12 bits for fraction; the multiplying factor can be
anywhere between 19 and 28. The 12-bit fraction in the synthesizer sets a tuning resolution equal to the reference frequency divided by 4096; frequency deviation can be set as low as ±2kHz and as high as ±100kHz.
The fractional-N synthesizer eliminates the problems associated with oscillator-pulling FSK signal generation. The MAX7057 has a serial peripheral interface (SPI™) for selecting all the necessary settings.
The MAX7057 is available in a 16-pin SO package and is specified to operate in the -40°C to +125°C automotive temperature range.
MAX7057主要特性:
Programmable Frequency Operation with Single Crystal
Internal Variable Capacitor for Antenna Tuning with Single-Matching Network
100kbps Data Rate (NRZ)
+2.1V to +3.6V Single-Supply Operation
< 12.5mA (FSK), < 8.5mA (ASK) DC Current Drain
< 1μA Standby Current
ASK/FSK Modulation
47% Carrier Tuning Range Using One Crystal
应用:
RF Remote Controls
Garage Door Openers
Home Automation
Automotive
Wireless Sensors
Wireless Game Consoles
Wireless Computer Peripherals
Security Systems
图1.MAX7057功能方框图
图2.MAX7057典型应用电路图
表1. 典型应用电路中所用的元件清单
详情请见:
http://datasheets.maxim-ic.com/en/ds/MAX7057.pdf
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