高频管和低频管由于构造不同,他们的频率特性参数相差很大。我们知道,晶体管在低频段都具有一定的放大系数β,而且在频率较低的一个频段内,放大系数β是不随工作频率的改变而改变的,但随着晶体管工作频率的不断提高,晶体管的放大系数就会随之下降,呈现图1所示的曲线(晶体管放大系数β随频率f的变化曲线)。当β随频率下降到等于1时(曲线中 Due to the different structure of the high-frequency tube and low-frequency tube, their frequency characteristics of parameters vary greatly. We know that the transistor in the low frequency band has a certain amplification factor β, and in a lower frequency band, the amplification factor β does not change with the operating frequency change, but with the continuous improvement of the transistor operating frequency, the transistor The amplification factor will be decreased, showing the curve shown in Figure 1 (transistor amplification factor β with the frequency f curve). When β decreases with frequency to equal 1 (in the curve