申論題

3.(30%) For the common-base circuit in Fig. 2, assuming the bias current to be about 1 mA, β = 100, Cμ = 0.8 pF, r_e = 25Ω, and f_T = 500 MHz:
  

(b) Use the short-circuit time-constants method to estimate the lower 3-dB frequency, f_L. (Hint: In determining the resistance seen by C₁, the effect of the 47-kΩ resistor must be taken into account.)