Hi, I have a question pertianing to the effect of capacitance of BJT amplifier circuits on the low and high frequency response of the amplifier. Why is it that the coupling and the decoupling capacitors, in effect, only affects the low frequency response of the amplifier, and why is it that the junction capacitances between any two terminals affect only the high frequency response? Because in the analysis treatment and design techniques of BJT amplifiers on the frequency response, we only consider the short-circuit time constant method of the coupling and decoupling capacitors for low frequency cutoff, ignoring its effect on the the high frequency response, and vice versa for the treatment of junction capacitances (open-circuit time constant method) on the high frequency response. But my question is why? Is there any phyiscal explanation to such estimation?