Rail-to-rail constant-gm operational amplifier for video applications

  • Authors:

  • Juan M. Carrillo;J. Francisco Duque-Carrillo;José L. Ausín;Guido Torelli

  • Affiliations:

  • Department of Electronics and Electrical Engineering, University of Extremadura, Avda. de Elvas S/N, 06071 Badajoz, Spain;Department of Electronics and Electrical Engineering, University of Extremadura, Avda. de Elvas S/N, 06071 Badajoz, Spain;Department of Electronics and Electrical Engineering, University of Extremadura, Avda. de Elvas S/N, 06071 Badajoz, Spain;Department of Electronics, University of Pavia, Via Ferrata 1, 27100 Pavia, Italy

  • Venue:
  • Integration, the VLSI Journal
  • Year:
  • 2004

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Abstract

This paper presents an operational amplifier (op-amp) with input/output rail-to-rail capability suitable for video applications. The input stage, which is based on two complementary differential pairs, provides a constant transconductance over the entire input common-mode voltage range, whereas a class-AB output stage with an accurate control of the quiescent current ensures rail-to-rail output swing even in the presence of a heavy load. Both the input stage transconductance and the output stage quiescent current are controlled by means of static loops, which allows high-frequency operation of the amplifier. In addition, the proposed constant-transconductance technique does not depend on the I-V characteristics of the input transistors--it is therefore compatible with modern submicron CMOS devices--and does not rely on any accurate matching between the complementary input pairs. The op-amp was designed to operate with 3 V of supply voltage and fabricated in 0.8-µm CMOS technology. The measured open-loop gain and unity gain-bandwidth for a 100-Ω||100-pF load are 60 dB and 32 MHz, respectively, while the output swing with the same output load reaches 83% of the total supply voltage.