A Circuit Technique for Enhancing Gain of Complementary Input Operational Amplifier with High Power Efficiency


IEICE TRANSACTIONS on Electronics   Vol.E98-C   No.4   pp.315-321
Publication Date: 2015/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.315
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design---Architecture, Circuit, Device and Design Methodology)
Op-Amp,  CMOS,  Complementary Input,  Gain Enhancement,  

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Negative feedback technique employing high DC gain operational amplifier (op-amp) is one of the most important techniques in analog circuit design. However, high DC gain op-amp is difficult to realize in scaled technology due to a decrease of intrinsic gain. In this paper, high DC gain op-amp using common-gate topology with high power efficiency is proposed. To achieve high DC gain, large output impedance is required but input transistors' drain conductance decreases output impedance of conventional topology such as folded cascode topology with complementary input. This is because bias current of the output side transistors is not separated from the bias current of the input transistors. On the other hand, proposed circuit can suppress a degradation of output impedance by inserting common-gate topology between input and output side. This architecture separates bias current of the input transistors from that of the output side, and hence the effect of the drain conductance of input transistors is reduced. As the result, proposed circuit can increase DC gain about 10 dB compared with the folded cascode topology with complementary input in 65 nm CMOS process. Moreover, power consumption can be reduced because input NMOS and PMOS share bias current. According to the simulation results, for the same power consumption, in the proposed circuit gain-bandwidth product (GBW) is improved by approximately 30% and noise is also reduced in comparison to the conventional topology.