Figure P10.45 shows a diode-connected transistor with the bias circuit omitted. Utilizing the BJT high-frequency, hybrid-π model with rx = 0 and ro =∞, derive an expression for Zi(s) as a function of re and Cπ . Find the frequency at which the impedance has a phase angle of 45° for the case in which the BJT has fT= 400 MHz and the bias current is relatively high. What is the frequency when the bias current is reduced so that Cπ ? Cμ? Assume α = 1.
