This document discusses voltage series feedback amplifiers. It defines voltage series feedback as a voltage amplifier topology where voltage is sampled at the output and mixed at the input. The key properties are: - The voltage gain (Av) is VO/VI and the feedback factor (β) is Vf/Vo. - Input resistance (Rif) increases compared to the open loop input resistance (Ri), where Rif = Ri(1 + βAv). - Output resistance (Rof) decreases compared to the open loop output resistance (Ro), where Rof = Ro/(1 + βAv).