real part of the small-signal short-circuit input impedance, common-emitter [h_ie(real); Re(h_ie)]

The in‑phase (real) component of the small-signal ac rms base-emitter voltage divided by the ac rms base current with the collector-emitter voltage held constant.

NOTE The fact that the collector-emitter voltage is held constant implies that the collector terminal is open-circuited.

References