基于MAX2685的芯片简介及应用电路设计

字数:6398.页数:18

摘要
MAX2685内置低噪声放大器（LNA）与下变频混频器，构成了射频（RF）前端接收机的主要功能模块。工作频率优化于900MHz，具有低噪声系数、高增益、高线性度等特点，是蜂窝电话、无绳电话及其它无线数据通讯系统的理想选择。高增益工作模式下，电源电流为8.5mA；低增益模式下，电源电流为3.8mA。低功耗停机模式将电源电流进一步降低至0.1μA以下，可有效延长电池寿命。采用单电源供电，电压范围为+2.7V至+5.5V，适用于3节NiCd电池或一节Li+电池供电的应用。 MAX2685内部包括：LNA、LNA旁路开关、下变频混频器、本振（L0）缓冲器。LNA具有1.4dB噪声系数、15dB增益和4dBm的三阶输入交调（IP3）；混频器噪声系数为13dB，增益为6dB，输入IP3为+7dBm。LO缓冲器允许LO口提供功率仅为-8dBm的本振信号。MAX2685采用节省空间的16脚QSOP封装。 
关键字： 低噪声放大器  下变频混频器
  本地振荡缓冲器    低噪声系数放大器旁路开关

Abstract
The MAX2685’s low-noise amplifier (LNA) and down converter mixer comprise the major blocks of an RF front-end receiver. Optimized for 900MHz operation, the device’s low noise figure, high gain, and high linearity make it ideal for cellular, cordless, and wireless data applications. A low supply current of 8.5mA (high-gain mode) and 3.8mA (low-gain mode) plus a low operating supply voltage range of +2.7V to +5.5V make it suitable for use in 3-cell NiCd or 1-cell lithium-ion (Li+) battery
applications. A low-power shutdown mode further extends battery life by reducing supply current below 0.1μA. The MAX2685 includes an LNA, LNA bypass switch, down converter mixer, and local-oscillator (LO) buffer. The LNA has a low noise figure of 1.4dB, a high gain of 15dB, and an input third-order intercept point (IP3) of -4dBm. The mixer has a noise figure of 13dB, a gain of
6dB, and an input IP3 of +7dBm. In addition, an LNA bypass switch allows two levels of gain, reducing power consumption when high gain is not needed. The downconverter mixer has a single-ended RF input port and differential IF output ports. Differential operation of the IF ports offers improved even-order harmonic rejection and increased immunity to noise. An LO buffer
allows the LO port to be driven with only -8dBm of LO power. The MAX2685 is offered in a space-saving 16- pin QSOP package
Key word: low-noise amplifier    down converter mixer VCO inductor      local-oscillator (LO) buffer   LNA bypass switch

目 录

1. MAX2685芯片简介...................................................................4
2. MAX2685芯片封装与引脚功能.........................................................4
2. 1引脚封装图.......................................................................4
2. 2 表1 MAX2685芯片引脚功能.........................................................5
2. 3参数限制.........................................................................5
3. MAX2685内部结构与工作原理  .......................................................6
3．1特征.............................................................................7
3. 2功能描述.........................................................................8
3. 2. 1 低噪声放大器.................................................................8
3. 2. 2 低噪声放大器旁路开关和增益控制...............................................8
 3. 2. 3 接收混频器..................................................................8
3．2. 4 射频输入.....................................................................8
3．2. 5 本地振荡器输入...............................................................9
3．2. 6 射频输出端口................................................................10
3．2. 7 安全关机....................................................................10
4. MAX2685应用电路设计..............................................................10
4. 1 MAX2685 评估报告...............................................................10
4. 2 元件列表.......................................................................11
4. 3 特征 ..........................................................................11
4. 4 需求的测试仪器.................................................................12
4. 5 连接与安装.....................................................................12
4. 6 下变频混频器...................................................................12
4. 7 详细介绍.......................................................................13
4. 8  附图..........................................................................14
5. 总结.............................................................................17
参考文献............................................................................18