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摩尔定律已经逼近物理极限,未来的发展趋势是将延续摩尔定律和超越摩尔定律结合起来,实现更高级的系统——微系统[1-4]。
微系统是一种利用微纳加工技术在微纳尺度上制备而成的电子系统。它涵盖了微电子、光电子、MEMS等多种电子元器件,同时涉及架构、软件以及算法等多种要素,具有体积小、高度集成等特点[5-8]。
本文设计了一种新型三维集成射频模拟数字一体化微系统,变频部分采用直接变频架构,从方案和实现两方面详细介绍了微系统的架构、设计、工艺和验证,重点介绍了一种全新的散热方案。
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一个典型的直接变频发射机架构如图1所示,其中
$ I({{t}}) $ 和$ Q({{t}}) $ 是两路正交基带信号,$ \cos (\omega t) $ 和$ \sin (\omega t) $ 是两路正交的载波信号,$ S({{t}}) $ 为输出信号:$$ S({{t}}) = I({{t}}) \cos ({\omega _{\rm{c}}}t) - Q({{t}}) \sin ({\omega _{\rm{c}}}t) $$ (1) 理想的直接变频发射机输出是一个单边带信号,不存在边带泄露和载波泄露问题。实际的集成电路具有离散性和非线性特征,导致直接变频发射机不是理想状态,输入的I/Q信号存在幅相不平衡、直流失调等问题,因此输出信号也存在幅相不平衡,所以传统的直接变频发射机存在边带泄露和载波泄露等问题。
为了便于分析问题,将基带信号和载波信号表示成带误差变量的形式:
$$ \begin{split} &\qquad\quad S({{t}}) = I({{t}}) \cos ({\omega _{\rm{c}}}t) - Q({{t}}) \sin ({\omega _{\rm{c}}}t) =\\ & [{A_{1i}} \cos ({\omega _{\rm{f}}}t + {\phi _i}) + {B_i}] \times [{A_{2i}} (\cos ({\omega _{\rm{c}}}t) + {\theta _i}) + {C_i}] -\\ & [{A_{1q}} \sin ({\omega _{\rm{f}}}t + {\phi _q}) + {B_q}] \times [{A_{2q}} (\sin {\omega _{\rm{c}}}t + {\theta _q}) + {C_q}] \end{split} $$ (2) 整理后得到:
$$ S({{t}}) = {S_{{\rm{usb}}}}({{t}}) + {S_{{\rm{dsb}}}}({{t}}) + {S_{{\rm{cl}}}}({{t}}) + {S_{{\rm{bl}}}}({{t}}) + {S_{{\rm{dc}}}}({{t}}) $$ (3) $$ \begin{split} {S_{{\rm{usb}}}}({{t}}) =& \dfrac{1}{2}{A_{1i}}{A_{2i}}\cos [({\omega _{\rm{f}}} + {\omega _{\rm{c}}})t + ({\phi _i} + {\theta _i})] +\\& \dfrac{1}{2}{A_{1q}}{A_{2q}}\cos [({\omega _{\rm{f}}} + {\omega _{\rm{c}}})t + ({\phi _q} + {\theta _q})] \end{split} $$ (4) $$ \begin{split} {S_{{\rm{dsb}}}}({{t}}) =& \dfrac{1}{2}{A_{1i}}{A_{2i}}\cos [({\omega _{\rm{c}}} - {\omega _{\rm{f}}})t + ({\theta _i} - {\phi _i})] - \\& \dfrac{1}{2}{A_{1q}}{A_{2q}}\cos [({\omega _{\rm{c}}} - {\omega _{\rm{f}}})t + ({\theta _q} - {\phi _q})] \end{split} $$ (5) $$ {S_{{\rm{cl}}}}({{t}}) = {B_i}{A_{2i}}\cos ({\omega _{\rm{c}}}t + {\theta _i}) - {B_q}{A_{2q}}\sin ({\omega _{\rm{c}}}t + {\theta _q}) $$ (6) $$ {S_{{\rm{bl}}}}({{t}}) = {C_i}{A_{1i}}\cos ({\omega _{\rm{f}}}t + {\phi _i}) - {C_q}{A_{1q}}\sin ({\omega _{\rm{f}}}t + {\phi _q}) $$ (7) $$ {S_{{\rm{dc}}}}({{t}}) = {B_i}{C_i} - {B_q}{C_q} $$ (8) 式中,
${S_{{\rm{usb}}}}({{t}})$ 是有用的上边带信号;${S_{{\rm{dsb}}}}({{t}})$ 是干扰的下边带信号;${S_{{\rm{cl}}}}({{t}})$ 是干扰的载波泄露信号;${S_{{\rm{bl}}}}({{t}})$ 是干扰的基带泄露信号;${S_{{\rm{dc}}}}({{t}})$ 是干扰的直流偏移信号。由式(5)可知,边带镜像来源于I/Q信号和载波信号的幅相不平衡;由式(6)可知,载波泄露来源于I/Q信号的直流失调和载波信号的幅相不平衡;由式(7)可知,基带泄露来源于载波信号的直流失调和I/Q信号的幅相不平衡;由式(8)可知,直流偏移来源于载波信号和I/Q信号的直流失调。
传统的直接变频架构中,存在式(3)所包含的基带泄露、直流泄露、载波泄露和边带镜像,恶化了误差矢量幅度(error vector magnitude, EVM)和相邻信道功率比(adjacent channel power ratio, ACPR)。
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直接变频架构收发器已经存在很多年,但I/Q平衡、镜像抑制、LO泄漏和直流失调等问题限制了其应用。ADI公司首先采用智能硅片设计和高级校准算法,克服了上述缺点[9]。直接变频收发器不但会在初始化时自动跟踪并校正这些误差,还能随着时间、温度、电源和流程自动跟踪和校正。设计中可以存在影响信号路径的因素,但智能硅片设计将这些影响降到最低,误差通过正交误差校正(orthogonal error correction, QEC)算法消除。
在直接变频收发器上,QEC算法在片内ARM处理器中执行。它实时监测内部信号路径、射频输出、输入信号和外部系统环境的信息,智能预测信号路径,而不是做出本能的被动式反应。该算法性能出色,以数字方式辅助模拟信号路径发挥最佳性能。
New Three-Dimensional Integrated RF-Analog-Digital Microsystem
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摘要: 设计了一种新型三维集成射频模拟数字一体化微系统。传统的射频前端尺寸为250 mm×120 mm,经过微系统集成后尺寸仅为37 mm×37 mm,面积减小了95%。该微系统基于一体化陶瓷三维封装架构,集成多种裸芯片和无源器件,实现内部信号的电气互连;采用一种全新的散热方案,定制开发了一种高导热复合热沉盖板,热导率从15 W/(m·K)提升至150 W/(m·K)以上。在FC裸芯片和盖板之间填充导热硅胶,形成了一条新的散热途径,达到高效散热的效果。Abstract: Recent years, microsystem has become one of the hot issues in electronic information field. This paper introduces a new three-dimensional integrated radio frequency (RF)-analog-digital microsystem. The architecture, process and verification of the microsystem are described in detail from the aspects of scheme and implementation. The traditional RF frontend is 250 mm × 120 mm size, while the microsystem is only 37 mm × 37 mm size, reducing its area by 95%. Based on the integrated ceramic three-dimensional package architecture, the microsystem integrates a variety of bare chips and passive devices to realize the electrical interconnection of internal signals. A new heat dissipation scheme is adopted to customize and develop a high thermal conductivity composite heat sink cover plate. The thermal conductivity is increased from 15 W/(m·K) to 150 W/(m·K) above. The thermal conductive silica gel is filled between the FC bare chip and the cover plate to form a new heat dissipation route and achieve efficient heat dissipation.
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Key words:
- integration /
- microsystem /
- RF analog digital /
- three-dimensional integration
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