Embedded DiCAD Linear Phase Shifter for 57-65GHz Reconfigurable Direct Frequency Modulation in 90nm CMOS

論文發表人：劉怡君/ 加州大學洛杉磯分校/電機系

 

http://www.rfic2009.org/

 

現今被動和主動相移器用於直接頻率調變有非線性之相位控制及元件差異，並且對被動整合相位錯誤有高敏感度，造成錯誤向量的大小(EVM， Error Vector Magnitude)的降低。在此篇論文中，我們提出使用數位訊號控制的人工介電不同傳輸線來克服目前相移器組成之頻率調變器的問題。主要的困難點包括以下：1) 設計數位訊號控制的人工介電不同傳輸線在現今CMOS標準製程中； 2) 加入電晶體開關作為調整介電常數的控制閥；3) 使用數位訊號控制的人工介電不同傳輸線為相位器的單元物件；4) 實現四相位之相位及振幅調變器；5) 由以上設計的單元，建立可重配置調變器，避免使用數位類比轉換器、混頻器、類比濾波器、以及任何反射元件。本論文提出由數位訊號控制的人工介電不同傳輸線組成之可調變線性相移器可敏捷的轉換相位超過100度，藉由十六階的溫度計碼編碼器來控制人工介電不同傳輸線的特性。相移器和一個十六段可調變增益放大器整合在90nm CMOS製程上，整合電路提供可重配置的相位移以及直接的頻率調變在60GHz載波。相位器總共有256個狀態，相位角解析度為1.1^o，可調幅度解析度為0.0007。對於相位調變(PSK, Phase Shift Keying)以及正交振幅調變 (QAM，Quadrature Amplitude Modulation) 此相位器之靜態錯誤向量的大小為-31dB。本調變器主要面積為0.33mm²在90nm CMOS製程下。電路操作在1V供應電壓以及總共消耗 10mA電流。

 

Passive and active phase shifters for direct frequency modulation suffer from nonlinear phase control and device mismatches, and are sensitive to passive hybrid phase errors, all degrading error-vector magnitude (EVM) performance. In this paper, we employ digitally controlled artificial dielectric (DiCAD) open-stub differential transmission lines to circumvent prior phase shifter design issues for realizing a reconfigurable, direct frequency modulator. Key design challenges include: 1) design DiCAD differential transmission line structure in standard CMOS; 2) insert NMOS Pi-switch to control DiCAD permittivity; 3) create linear phase shift using DiCAD DTL; 4) realize quadrant phase and amplitude shifters using DiCAD for phase shift and amplifier impedance matching. 5) build reconfigurable modulator based on DiCAD QPAS without DAC, mixers, analog filters, quadrature LO hybrids, varactors and any reflective device.

A digitally controlled artificial dielectric (DiCAD) differential transmission line is designed to perform agile linear phase shift over 100deg with thermometer-coded 16step control. It also operates with a 16 gain-step VGA to enable re-configurable and direct-frequency modulation at 60GHz with 2562 states (1.1deg angular and 0.0007 magnitude resolutions) and -31dB static EVM for multiple PSK/QAM modulations. The modulator uses 0.33mm² core area in 90nm CMOS and consumes 10mA at 1V.