采用直接数字频率合成器混频信号的高频功率源设计

Design of RF amplifier based on direct digital synthesizer output

提取直接数字频率合成器芯片AD9850输出的混频信号作为系统的频率源,介绍了高频功率源的结构和原理。系统的工作频率范围为(96±1)MHz,最大输出功率为10 kW。驱动级采用MOSFET晶体管功率放大模块,末级采用高频真空四极管4CW10000B。四极管采用阴地电路,工作在甲乙类。高频功率源采用压控可变衰减器进行幅度调制,为满足系统的频率和幅值稳定度要求,功率源采用带温度补偿的晶体振荡器,并让四极管工作在过压状态。在应用Ziegler-Nichols法整定控制器的PID参数时,为实现控制系统的在线自整定,系统采用了继电反馈法,由极限周期和增益得出PID参数。

As a new RF generator, the direct digital synthesizer（DDS） has been widely used. In order to reduce the high cost of the signal generator comprising a high performance DDS device, the method of picking-up a desired aliased signal DDS output is adopted in the design. A device of AD9850 is used to generate RF signal in the system, and the amplitude modulation of the system is achieved by using a voltage variable attenuator. The amplifier based on tetrode is selected to get an output power of 10kW at （96±1） MHz. Amplifier operates in a grounded cathode configuration. A short-circuited coaxial transmission line is adopted in both input circuit and output circuit. The PID-control strategy has been used in control system ,and the relay method has been used for measurement. The controller has a built-in auto-tuning function which allows the PID parameters to be determined automatically using the Ziegler-Nichols method.