【作者】 岳彬；

【导师】 刘平；

【作者基本信息】 郑州大学 ， 物理电子学， 2011， 硕士

【摘要】 振荡器伴随着科技的发展,已经广泛的应用于各类电子产品中,它的发展也逐渐呈现出多元化的趋势,其中大功率、高频化的振荡器是其发展的一个重要方向,这种振荡器能够产生功率较大的射频能量,用于等离子体源的激发、热处理装置以及大功率发射机等众多领域。振荡器实现将直流能量转化为交流能量的功能主要是由射频功率放大电路完成的,放大电路也随之呈现出大功率、高频化、高效率的发展趋势,这对其核心的功率器件提出了更高的要求,本课题选用功率MOSFET作为功率器件,它广泛应用于中、高频范围,在频率超过MHz的领域范围内其它器件无法替代。本论文主要的任务是设计一个具有幅度稳定功能的功率MOSFET射频振荡器,要实现振荡器输出幅度稳定,通常采用负反馈控制的方法,将振荡器输出的幅度转变为与之相对应的控制信号,通过反馈控制来实现振荡器输出幅度的稳定。然而,负反馈电路虽然能够改良振荡电路的性能,但是它也可能产生自激振荡,该振荡可能会使输出幅度比没有加负反馈电路前更加不稳定,使振荡器输出类似于调幅波的波形,无法达到稳幅的目的,面对这个问题,就要求对整个振荡电路做稳定性的分析,找出调整电路的方法,避免反馈环路产生自激振荡,从而达到稳幅的目的。本文主要从三个方面进行了电路的分析和设计。首先,设计了一个输出功率为100W,频率为13.56MHz的射频功率振荡器,通过对静态工作点的设置,使振荡电路由起振时的AB类工作状态转变到稳定振荡时的C类工作状态；其次,采用自动增益控制(AGC)电路,通过将检测出的振荡器输出幅度转化为与之相对应的控制量,通过控制功率MOSFET的栅源电压来使射频功率振荡器输出的幅度稳定；第三,通过对整个设计电路的传递函数分析,采用劳斯判据来判断电路是否稳定,根据判断结果,采用调节反馈电路中三极管发射极电阻阻值的方法,避免AGC环路产生自激振荡,使整个电路工作在稳定的状态,从而达到了稳定振荡器输出幅度的目的。更多还原

【Abstract】 With the development of science and technology, oscillator has been widely used in various electronic products. And the development of oscillator is presenting the diversified trends, among which oscillator with high-power and high frequency is an important development direction. This kind of oscillator can produce higher RF energy that can be used in many fields, like exciting of plasma source, heat treatment device, high-powered transmitter and etc. Oscillator’s function to transit DC to AC energy form is realized by RF power amplifier circuit, which is also presenting high power, high frequency and high efficiency trend, which put forward higher request to the core power device. This paper take the power MOSFET as the power device, which is widely used in medium and high frequency range and can not be replaced by other devices in the frequency range over the MHz frequency.The main task of this thesis is to design a RF power MOSFET oscillator which has the stable amplitude function. To realize the stability of oscillator output amplitude, the method of negative feedback is usually adopted, which changes oscillator’s output amplitude into the corresponding control signal, and realizes the stability of output amplitude by feedback controlling. Though, the negative feedback circuit can improve the performance of the oscillating circuit, it can emerge the phenomenon of self-excited oscillation which could make the output of amplitude more unstable than the circuit without negative feedback, make the oscillator amplitude wave output similar to the waveform of modulation wave, and cannot reach the purpose of steady amplitude output. Confronted with this problem, the whole system of oscillating circuit should be analyzed for stability, finding out the method of adjusting circuit to reach the purpose of steady amplitude output.The circuit is mainly analyzed and designed from three aspects in this article. Firstly, a high-power oscillator with frequency 13.56MHz and output power 100W is designed. Through setting the stable working position, the working state of the oscillator is transited from class-AB at starting-oscillating moment to class-C at stable oscillating moment. Secondly, using an automatic gain control circuit, through transiting the output amplitude of the oscillator into the corresponding controlling parameter, controlling the gate-source voltage of the power MOSFET, it can make the output amplitude of RF power oscillator stable. Thirdly, by analyzing of the whole designed circuit’s transfer function and adopting Royce criterion, it can judge that whether the circuit is stable or not. According to the judgment, by adjusting transistor emitter resistance’s value in feedback circuit, self-excited oscillation can be avoided in AGC loop, which makes the whole circuit work in stable state, and further realizes the purpose of stable amplitude output of the oscillator.更多还原