基于包络脉宽和相位差分调制的低功耗数字型发送前级研究

Transmitters, applied in portable wireless terminals, need good tradeoff between high efficiency and high linearity, and support multi-mode multi-band operations simultaneously. Polar modulation is a good choice among many techniques to archive such a goal. Based on favorite innovations of digitized envelope modulation, full-differential phase modulation and path delay alignment with high robustness, this project is aimed to provide a feasible system solution to low-power, low-complexity, high-efficiency, high-linearity, multi-mode and multi-band transmitters, by studying existing polar architectures and the developing trend. Phase path employs a differential delta-sigma modulated dual-path voltage-controlled oscillator, to implement the conversion from baseband-frequency digital phase to radio-frequency constant-envelope one. Digital pre-compensation technique for tuning gain curve correction ensures modulation linearity, and a quasi-continuous dual-mode calibration loop stabilizes the carrier frequency. Envelope path uses a digital pulse-width modulator to drive a power inverter followed by an LC filter, implementing the conversion from digital envelope to analog one and enabling large-current driver capability at the power supply of the switched-mode power amplifier. By match design and consideration, a simple frequency-locked loop enables reconfiguration and high accuracy features of delay cells. A simplified and zero reconfigured high-pass digital compensation filter is introduced in the envelope path to ensure time alignment, by matching the simple transfer functions between the phase and envelope paths with high robustness over process, voltage and temperature variations.

便携式无线移动终端所需的发送前级在设计上要兼顾高效率和高线性度，并支持多模多帯操作，在实现该目标的众多技术中，极座标是个不错的选择。本项目基于极座标发射机的已有架构及其发展趋势，从数字型包络调制、全差分相位调制、高鲁棒性通路延时匹配等创新点入手，致力于为低功耗、低成本、高能效、高线性、多模多带发送前级提供可行的系统方案。 相位通路采用delta-sigma差分调制双通路压控振荡器，实现基频数字相位到射频恒包络相位的搬移；引入调谐增益数字预补偿技术确保调制线性度，使用亚连续、双模式校正环路维持载波频率。包络通路利用数字型脉冲宽度调制器驱动功率级反相器及LC滤波器，实现数字包络到模拟包络的转换并为开关型功放提供大电流驱动；基于简易的锁频环，通过匹配设计，确保延时模块的可配置与精准性。在包络通路引入简易的、零点可配置的高通数字补偿滤波器，鲁棒性地匹配相位和包络通路的简单传输函数以确保延时同步。

近年来，随着各种便携式无线通信产品的应用，可植入式医疗电子设备的兴起，以及无线体域网和无线个人网的迅猛发展，人们对发射机的功耗、效率以及设计复杂度提出了很高的要求；此外，高频谱效率和高数据传输率的发展趋势促使各种工作在不同频带的非常包络数据调制方式不断涌现，为了确保好的通道抑制和低的信号失真，人们对发射机又提出了高线性度、多模多带操作的要求。.在实现这一目标的众多技术中，极坐标（将基带信号同时经过相位和包络两个通路进行调制并传递到功率放大器）是个不错的选择。本课题基于极坐标发射机的已有架构及其发展趋势，从数字型包络调制、全差分相位调制、简易的通路延时匹配等创新点入手，致力于为低功耗、低成本、高能效、高线性、多模多带发送前级提供可行的系统方案。.相位通路采用delta-sigma差分调制双通路压控振荡器（VCO），实现基频数字相位到射频恒包络相位的搬移；该VCO的调制通路采用分段偏置型的全差分LC-tank结构来确保调频线性度，其校正通路引入间歇式工作的自动载频校正（AFC）环路来维持载波频率。包络通路利用数字型脉冲宽度调制器（PWM）驱动功率级反相器及LC滤波器，实现数字包络到模拟包络的转换并为后续开关型功放提供大电流驱动；为了保证PWM核心模块-延时单元的精准性，引入单元延时自校正环路。此外，在包络通路引入简易的、零点可配置的高通数字预补偿滤波器，鲁棒性地匹配相位和包络通路的简单传输函数以确保两个通路间的延时同步。.本课题基于1.8V 180nm CMOS工艺验证了所提议的极坐标发射机架构，并详细阐述了相位调制/校正双通路、包络调制通路等关键电路的设计实现。实验数据表明，发射机的载频为1.8GHz，功耗大概为11.5mW(不考虑开关型功放)，在400kHz频偏处的相位噪声为-124.9 dBc/Hz，误差向量幅度(EVM)为4%，满足EDGE(8-PSK)信号的频谱掩摸、线性度等性能指标。