针对电磁超声导波大功率激励信号的线性放大问题，研究采用多个功率场效应管线性放大并联输出电路作为功率输出级，以提高线性放大后信号输出功率的方法。采用前级场效应管线性放大电路源极驱动方式为功率输出级电路设置静态工作点，并提供瞬态交流输入信号。采用差分结构配置整个电路以抑制开关特性引起的抖动，从而实现低功耗、大瞬态输出功率的线性放大电路的设计。试验结果表明，该线性放大电路能驱动中心频率为180 kHz的电磁超声传感器，且能获得高信噪比的导波检测信号；在驱动50Ω标准负载时能输出瞬态功率可达1.8 kW的导波激励信号，且波形失真小。所提出的电磁超声导波大功率激励信号的线性放大方法能有效指导该类电路的设计。
High power linear amplifier for exciting electromagnetic acoustic transducer to generate guided waves is investigated. Linear amplification circuit with multiple power MOSFETs operating in parallel is used as the output stage of the linear amplifier in order to improve the output power of the amplified signal. The static operating point of the power output stage circuit is set up by the DC bias from the source of MOSFET driving circuit working in linear amplification mode, and the source also provides the AC input signal for the power output stage. Differential structure is used to configure the whole circuit for suppressing the jitter caused by switching characteristics, so a linear power amplifier with low power consumption and large transient output power is designed. The experiment result shows this high power linear amplifier can drive an EMAT with center frequency of 180 kHz to generate guided wave and get good SNR inspection signals. When it is used to driven 50Ω standard load, the transient output power can access 1.8 kW with very small waveform distortion. The high power linear amplification method for driving EMAT produce guided provides effective guide for the similar circuit design.
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