Input Resistance

From the input, the EF amp and the CE amp look identical. (This is actually an approximation, which we will examine later in the course.) Thus the input resistance of the EF amp and CE amp are considered the same and given by R_in = R_B||R_TB where R_TB is the resistance looking into the base:

$$R_{TB}=r_{\pi} + \beta R_E$$ (53)

Since the input resistance contains this multiplicative $\beta$factor, it is usually fairly large which is usually desirable for a voltage amp.