Q波段片上接收系统的关键技术研究

Q-Band is an important frequency range in radio astronomy for continuum and line observations. Since high sensitivity deep sky survey has become the main science goal for large diameter radio telescope, it's imperative to develop Q-Band multi-beam receiving system which is called Radio Camera. The project intends to research the key technologies of Q-Band system on chip receiver and first proposes the advanced development from MMIC to SOC. Main devices in a receiver such as LNA and mixer will be integrated into an entire system based on WIN 0.1um GaAs pHEMT process to realize a series of functions like low noise amplification and frequency convert for RF signals. It will largely reduce the circuit size and improve the stability and uniformity. The system will be designed with image rejection and double-balanced mixer structure to realize USB and LSB IF output, improve port isolation and signal interference. Also, the LO frequency will be reduced by using its second harmonics, which makes it possible for the IC system to get to a higher frequency. Advanced research has been completed with three LNAs, and transistors' small signal model and noise model, which ensures the project to be done properly and successfully. It's very practical and has strong scientific research value.

Q波段是开展射电天文谱线和连续谱观测的主要波段，高灵敏度深度巡天成为大口径射电望远镜的重要科学目标，被称为Radio Camera的超大规模Q波段多波束接收系统研发至关重要。本项目针对Q波段片上接收系统的关键技术开展研究，首次提出了单片微波集成电路MMIC到片上系统SOC的迈进，拟选用台湾稳懋公司0.1um GaAs pHEMT半导体工艺，将低噪声放大器、混频器等接收机前端设备进一步集成，完成对信号的低噪声放大和变频等工作，极大地减小电路尺寸，提高稳定性和一致性。本项目采用镜像抑制变频设计和双平衡式混频结构，实现双边带中频输出，提高了端口隔离度，有效改善了信号串扰问题。同时，系统对本振二次谐波的应用大大降低了本振频率，有利于电路向更高频率发展。本项目先期已进行过MMIC的预研，成功研制了三款低噪声放大器，并且对晶体管建立了小信号及噪声模型，可行性高，实用性强，有很强的科学研究价值。

天文科学观测中，射电望远镜系统灵敏度的优劣很大程度上取决于接收机的性能，为了有效提高空间分辨率，缩短积分时间，单天线焦平面阵列是射电望远镜接收系统发展的必然方向。而高度集成的片上接收系统具备重量轻，体积小，可批量生产，一致性高等优势,是用于焦平面阵列的最佳选择。.该项目使用CMOS90nm工艺和WIN150nm工艺尝试进行了多种接收系统芯片的设计，完成了WIN150nm pHEMT工艺接收系统芯片的流片并对其进行封装，搭建起常温接收测量平台，利用Labview开发出一套包含校准步骤的噪声测量系统，完成对芯片封装模块的各项性能测试，完成了片上接收系统的关键技术研究，为之后更为复杂的接收机SOC设计打下了基础。WIN150nm pHEMT工艺设计的K波段和Q波段两种接收系统芯片内部包含低噪声放大器，混频器，中频放大器，滤波和无源巴伦等结构，单颗芯片面积大小为2.5mm×1mm。实测结果显示，K波段接收系统模块实现了18~26GHz射频信号输入，DC~8GHz中频信号输出，转换增益可达到20dB左右，平均双边带转换噪声在300K左右，Q波段实现了33~45GHz射频信号输入，4~6GHz中频信号输出，转换增益在5~10dB。.该项研究将低噪声放大器，混频器和中频放大等电路集成在同一个芯片上，非常节省空间，可以批量生产，同批次芯片具有高度的一致性，极大地降低了单价。此外，该系统模块比分立系统减少了各种人工焊接和转接器件，既简化了封装的时间与成本，也保障了很好的稳定性。而从商业角度上看，市面上功能完整的片上接收系统芯片并不常见。该项研究可以更好更方便地满足天文科学观测方面对射电望远镜接收系统的需求，更好地服务于天文基础研究。