Two-stage small-signal amplifier with Darlington and Sziklai pairs

A New circuit model of two-stage small-signal amplifier using Darlington and Sziklai pairs is proposed for the first time. Proposed circuit is obtained by cascading a small-signal Darlington pair amplifier with that of Sziklai pair based small-signal amplifier with minor modifications. Proposed amplifier essentially uses two additional biasing resistances in its design. It crops considerably high voltage and current gain (345.523 and 464.357 respectively) with audible range bandwidth of 43.363 KHz for AC input signals swinging in 10-30mV range at 1KHz or lower frequency. Proposed circuit-architecture successfully removes the poor response problem of conventional Darlington pair amplifiers at higher frequencies and narrow bandwidth problem of recently announced (by authors) circuits of small-signal Sziklai pair amplifier. Variations in voltage gain with frequency and various biasing components like biasing resistances, DC supply voltage and coupling capacitors are discussed in length. Temperature sensitivity of performance parameters, THD and small-signal AC equivalent circuit analysis of the proposed circuit are elaborately studied. Proposed design can be implemented in cascadable gain blocks for receivers, 715Hz-44KHz frequency range power sources and in the circuits where reproduction of signal with simultaneously high voltage and current gain is the prime requirement.