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引言
本篇应用笔记概述了
MAX2538蜂窝CDMA (码分多址)混频器配合IF SAW (声表面波)滤波器匹配在183.6MHz时(7mm x 5mm封装)测试得到的性能指标。这里使用的滤波器型号为KSS的MSFC30-183-001M0。
蜂窝CDMA混频器/IF滤波器的信号通道增益、NF (噪声系数)和IIP3 (输入三阶截止点)在增益、IIP3、通增益平坦度和邻信道选择性的基础上进行了优化。本文给出了串联电路的测试性能,从这些指标可明显看出MAX2538在蜂窝CDMA应用中具有卓越的NF和IIP3。
在HGHL (高增益、高线性度)模式下获得的串联IIP3为:
(62.5dBc/2) + (-22dBm) = +9.2dBm
元件参数参见电路图,图表参见测试数据。
蜂窝CDMA混频器/IF滤波器的串联性能
MAX2538配置在蜂窝HGHL模式,电源电压(V
CC)设定在+2.80V。测量平台是一块多层PCB (印刷电路板)板,上面安装了KSS
IF CDMA滤波器。方框图如
图1所示,测得的串联性能数据参见
表1。
图1. 蜂窝模式下串联MAX2538混频器方框图
MAX2538混频器和SAW滤波器阻抗特性
SAW Filter
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KSS MSFC30-183-001M0
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MAX2338 IF Port Differential Equivalent Circuit
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12.2kΩ || 0.75pF
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MAX2338 IF External Load
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2.7kΩ
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Equivalent Differential Source Impedance presented
to SAW Filter
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2.2kΩ || 0.75pF
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Single-ended Load Impedance presented to SAW Filter
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50Ω
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SAW Filter Input Source Impedance
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788Ω || -9.8pF
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SAW Filter Output Source Impedance
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855Ω || -7.5pF
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MAX2538蜂窝混频器串联增益与IIP3测试数据
RF频率 = 880.98MHz或881.04MHz @ -22dBm单音
LO频率 = 2129.2MHz。
IF = 183.6MHz模式= HGHL (高增益、高线性度),选择IF0端口
V
DD_RX = +2.80V
表1. HGHL模式下的性能结果
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MAX2538
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IF
SAW and
Matching Loss
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Cascaded
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Gain (db)
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12.0*
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-9.0*
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+3.0
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IIP3 (dBm)
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9.2
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100
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+9.2
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NF (dB)
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8.2
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9.0
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8.5
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*在测得的串联增益为+3.0dB、混频器独立的增益为12dB的基础上估算IF滤波器接入损耗。

ΔIM
3 = -62.5dBc于IF输出端口
IIP3 = 62.5/2 + (-22dBm) = +9.2dBm
P
IN = -22dBm在881或881.2MHz单音点
P
OUT = -18.0dBm
串联增益 = +3.0dB
蜂窝CDMA混频器与IF SAW滤波器的扫频响应
MAX2538蜂窝混频器和KSS IF滤波器串联电路的响应特性:
MAX2538混频器匹配电路元件
匹配元件如下图所示:
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APP 1915:
应用笔记
1915,
AN1915,
AN 1915,
APP1915,
Appnote1915,
Appnote 1915
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