Abstract—New circuit model of a two-stage small-signal Sziklai pair amplifier is proposed for the first time. The proposed amplifier circuit, which is obtained by cascading a small-signal Sziklai pair amplifier (Stage-1) with triple-transistor based compound Sziklai amplifier (Stage-2), is analyzed on the qualitative scale. Performance of the proposed amplifier is compared with that of Stage-1 and Stage-2 amplifier circuits to provide a wide spectrum to the qualitative studies. Proposed amplifier uses three additional biasing resistances in its circuit configuration and crops high voltage gain (237.50), high current gain (339.98) with wider bandwidth (2MHz) in 1-15mV range of AC input at 1 KHz. The proposed circuit successfully removes the poor response problem of conventional Darlington pair amplifiers at higher frequencies and narrow bandwidth problem of recently developed (by authors) circuit of small-signal Sziklai pair amplifier. Variation in voltage gain as a function of frequency and different biasing resistances, bandwidth and harmonic distortion of the amplifier is also pursued. The proposed amplifier may be useful for those applications where high voltage and current gain would be the prime requirement of amplification in a wider frequency range, spanned approximately from 200Hz to 2.5MHz. Index Terms—Small signal amplifiers, Sziklai amplifiers, complimentary Darlington pair amplifiers. I. INTRODUCTION Single or multi-stage RC coupled Darlington pair amplifiers are popularly used to amplify small signals in the range of milli-volts [1]-[7]. These amplifiers are usually known for high β value but suffer from the problem of poor response at higher frequencies [3]-[6]. Researches and available literatures have widely explored the usefulness of Darlington pair amplifiers [1]-[7] but least efforts are made to configure a small-signal amplifier using Sziklai pair [8], [9], which is often compared with Darlington‟s unit due to almost identical value of β. Sziklai pair [8], named after its inventor George Sziklai, is a composite unit of two bipolar transistors of opposite polarities (one NPN and other PNP transistor) and sometimes known as „Complimentary Darlington pair‟. Polarity of Sziklai pair unit is always determined by the driver transistor [8], [9]. The current gain factor (β) of Sziklai pair is slightly less than Darlington pair topology, because it has a small amount of in-built negative feedback which reduces the current gain [9]. However Sziklai pairs hold better linearity than Manuscript received October 5, 2012; revised January 10, 2013. The authors are with the Department of Physics and Electronics of Dr. Ram Manohar Lohia Avadh University, Faizabad - 224001, U.P., India (e-mail: sachida_shukla@yahoo.co.in; susmrita @rediffmail.com). Darlington pairs when used in linear circuits. Another major advantage of Sziklai pair over Darlington pair is that its base turn-on voltage is only half of the Darlington's turn-on voltage [8], [9]. II. EXPERIMENTAL CIRCUITS Present paper crops a comparative study of small-signal Sziklai pair amplifier (Fig. 1), Compound Sziklai amplifier (Fig. 2) and a two stage proposed amplifier (Fig. 3), obtained by cascading circuits of Fig. 1 and Fig. 2 with minor modifications [10], [11]. Fig. 1. Sziklai pair amplifier Circuit of Sziklai pair amplifier [10] of Fig. 1 accommodates a PNP (Q2N2907A with β=231.7) driver-transistor Q1 and an NPN (Q2N2222 with β=255.9) follower-transistor Q2 in its paired unit. In addition, an extra biasing resistance R D between collector of transistor Q1 and ground is introduced and emitter of PNP transistor Q1 is directly connected with the DC supply voltage. On the other hand, Compound Sziklai amplifier [11] of Fig. 2 is obtained by adding an extra PNP transistor Q3 and biasing resistance R D2 in the circuit of Fig. 1. Joint-unit of transistors Q1 (PNP) and Q2 (NPN) in circuit of Fig. 2 constitute PNP Sziklai pair while Q2 (NPN) and Q3 (PNP) jointly form Darlington pair like configuration. However, the proposed two-stage Sziklai pair based small-signal amplifier, as depicted in Fig. 3, is obtained by cascading circuits of Fig. 1 and Fig. 2 with minor modifications. In this circuit (Fig. 3), emitter of the transistor Q1 of first stage Sziklai pair amplifier is connected to the collector of the transistor Q2 (at node-7 in Fig. 3) whereas in its original circuit it was directly connected to the V CC (at node-4 in Fig. 1). The second stage of the proposed two-stage amplifier (Fig. 3) carries triple transistor based compound Sziklai amplifier after removal of biasing resistance R 1 from the original circuit (Fig. 2). Development and Qualitative Analysis of a New Circuit Model of Two-Stage Small-Signal Sziklai Pair Amplifier SachchidaNand Shukla and Susmrita Srivastava International Journal of Computer Theory and Engineering, Vol. 5, No. 4, August 2013 668 DOI: 10.7763/IJCTE.2013.V5.772