(页数:19字数:7192)摘要：简要介绍集成中频正交解调AD8348的主要功能、内部结构、引脚排列及典型的应用电路。AD8348是一个带集成中频（IF）可变增益和基带放大器的宽带正交解调器。其工作频率是50MHZ到1000MHZ，解调带宽75MHZ，相位精确度达0.5度，振幅平衡度0.25dB，噪声系数在最大增益时为11dB. 它适用于由中频直接下正交解调成基带频率的通迅接收器,如：QAM/QPSK解调器，W-CDMA/CDMA/GSM/NADC。
关键字：正交解调 基带放大器 带宽
Abstract
It briefly introduced quadrature demodulator with an integrated intermediate frequency (IF)AD8348 with the microcontroller function, internal structure, pin array and typical apply circuit。 AD8348 is a broadband quadrature demodulator with an integrated intermediate frequency (IF) variable gain amplifier (VGA), and integrated baseband amplifiers. Operating IF frequency 50 MHz to 1000 MHz, Demodulation bandwidth 75 MHz，Phase accuracy 0.5° Amplitude balance 0.25 dB Noise figure 11 dB @ max gain。It is suitable for use in communications receivers, performing quadrature demodu-lation from IF directly to baseband frequencies..Such as QAM/QPSK demodulator W-CDMA/CDMA/GSM/NADC.
KEY WORD: quadrature demodulator baseband amplifiers bandwith
1 AD8348简介----------------------------------------------------5
1.1 AD8348特点-----------------------------------------------5
1.2 AD8348芯片简介----------------------------------------5
1.3 AD8348的电气特性--------------------------------------6
2 AD8348卦装和引脚功能-------------------------9
2.1 AD8348卦装-------------------------9
2.2 AD8348引脚功能及电路形式----------------10
3. AD8348的内部结构图和功能描述 --------12
3．1 AD8348的内部结构图------------------------------12
3．2 功能描述 ----------------------------------------------------13
3．2．1可变增益放大器（ＶＧＡ）-----------------13
3．2．2下变混频器------------------------------13
3．2．3移相器----------------------------------13
3．2．4 Ｉ／Ｑ基带放大器------------------------14
3．2．5使能------------------------------------14
3．2．6基带撤消补偿-------------------------------------------14
4. AD8348应用电路设计--------------------14
4．1 AD8348正交解调器的设计原理--------------------------14
4．1．1电源供电------------------------------------------------14
4．1．2器件使能------------------------------------------------14
4．1．3ＶＧＡ使能---------------------------------------------14
4．1．4增益控制------------------------------------------------14
4．1．5本振输入------------------------------------------------14
4．1．6中频（IF）输入---------------------------------------15
4．1．7混频输入--------------------------------15
4．1．8基带输出--------------------------------15
4．1．9基带滤波器-------------------------------------------------15
4．1．10本振产生--------------------------------------------------16
4．2整体电路原理图-----------------------------------------16
4．2．1原理图----------------------------------------------------------------16
4．2．2原理图说明----------------------------------------------------------17
4．2．3 AD8348印制板图-------------------------------------------------17
5. 总结-------------------------------------18
参考文献------------------------------------19
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