请大家帮忙讲解一段关于PA的文字

It is positive, or in-phase, with
the fundamental, and from a frequency domain viewpoint, the action of the partially
cutoff transistor is to generate a substantial amount of second harmonic,
which reduces the dips of the fundamental sinewave and sharpens the peaks, resulting
in a lower mean level for approximately the same overall peak-to-peak amplitude.
We can note, in passing, that using the cutoff characteristic of a transistor is
not the only possible method for generating such a desirable second harmonic component.
It may be possible, for example, to tailor the frequency response of the input
matching network such that the drive voltage has some appropriate in-phase second
harmonic enhancement, assuming it is coming from another, possibly nonlinear,
amplifier driver stage.

简单翻译下， 错误的楼下指正。
从频域来看，部分截止三极管（输入）的行为是为了产生大量的二次谐波。这种行为是正向的，或者说是同相位的。
这种行为可以减少基本正弦波的凹陷，削平峰值，结果可产生接近峰峰值放大的更低的平均值。
顺便提一下，我们可以注意到用这种三极管的截止特性不仅仅是为了产生一个期望的二次谐波分量；
更可能是为了，比如说 调整输入匹配网络的频率响应  尤其是驱动电压会产生一些适当的同相的二次谐波增量
假设这些二次谐波增量是来自于其他的可能非线性放大器的驱动。
翻译的很拗口，，，

谢谢xzj1891 ，希望其他人也多帮帮忙看看。

这段文字很眼熟，来自于cripps的书，我试着大概意译一下，请后来修正，重在理解。
It is positive, or in-phase, with the fundamental, and from a frequency domain viewpoint, the action of the partially
cutoff transistor is to generate a substantial amount of second harmonic,
在频率上看，功率管在产生基波的同时，处于截至状态（如非A类）的功率管，可以产生大量的二次谐波。
which reduces the dips of the fundamental sinewave and sharpens the peaks, resulting
in a lower mean level for approximately the same overall peak-to-peak amplitude.
这将导致减少基波的导通，使其峰值更加陡峭，导致在同样的峰峰值幅度下，平均值降低。（注：个人没有觉得这句有什么意图，是说峰均比增加了，故而截至多了，线性变差?）
We can note, in passing, that using the cutoff characteristic of a transistor is
not the only possible method for generating such a desirable second harmonic component.
顺便指出，并不是只有截至特性才能产生需要二次谐波分量（这个才是作者的关键）。
It may be possible, for example, to tailor the frequency response of the input
matching network such that the drive voltage has some appropriate in-phase second
harmonic enhancement, assuming it is coming from another, possibly nonlinear,amplifier driver stage.[3721RD.com]
例如，可以裁剪输入匹配的频率响应，即输入的电压也增加近似同步的二次谐波。可以假设这个输入电压来自于前级驱动功率管输出的非线性

突然想起，这句话意味深长，应该也是C类为何比A类的饱和功率低的原因。
另外，多谢LZ给出机会，重新又学习了一下。
which reduces the dips of the fundamental sinewave and sharpens the peaks, resulting
in a lower mean level for approximately the same overall peak-to-peak amplitude.
这将导致减少基波的导通，使其峰值更加陡峭，导致在同样的峰峰值幅度下，平均值降低。

的确是Cripps的书，最近在努力看这本书，有很多不了解的地方，看得云里雾里的。