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Unformatted text preview: 1144 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-20, NO. 6, DECEMBER 1985 Low-Voltage Operational Amplifier with Rail-to-Rail Input and Output Ranges JOHAN H. HUIJSING, SENIOR MEMBER, IEEE, AND DANIEL LINEBARGER, MEMBER, IEEE Abstract — An operational amplifier is described which can perform precision signal operations in nearly the full supply voltage range, even when thk range is as slow as 1.5 V totally. The untrimmed input offset voltage is typically 0.3 mV in an input common-mode (CM) voltage range which extends beyond both supply voltages for about 200 mV. The ,output voltage can reach each supply rail within 150 mV. A nested-loop frequency-compensation scheme yields a stable unity-gain bandwidth of 0.6 MHz while the low-frequency open-loop voltage gain is 110 dB. The op amp is integrated in a standard low-cost bipolar process and the chip measures 1.5 X 1.7 mmz. I. INTRODUCTION o PERATIONAL amplifiers for low supply voltages should be able to utilize the largest possible part of the supply-voltage range for input and output signal oper- ations in order to get the best signal-to-noise ratio. Usually, base–emitter or gate–source voltages prevent the input and/or output from reaching the positive and/or negative supply voltages within about 0.7 V . This becomes a problem when the supply voltage is low as in battery- powered systems or in low-power applications. The operational-amplifier design presented here includes three new solutions to low supply-voltage operation: firstly, an input stage with a rail-to-rail common-mode input-volt- age range which achieves a constant transconductance over the full common-mode range; secondly, a rail-to-rail class- All output stage; and thirdly, a simple overall frequency compensation structure that allows a large gain with three or more common-emitter stages in cascade. With these measures an operational amplifier capable of performing precision operations on signals in the nearly full supply- voltage range has been obtained. II. INPUT STAGE Rail-to-rail common-mode voltage swing at the input can only be obtained by using two input stages in parallel such that the common-mode (CM) voltage of one can reach the positive supply rail and that of the other the negative supply rail. An example of such an existing input stage is given in Fig. 1. , . Two complementary emitter-coupled tran- Manuscript received April 15, 1985; rewsed August 7, 1985. J. H Huijsing was with the Signetlcs Corporation, Sunnyvale, CA 94086 He is now with the Delft Umversity of Technology, Department of Electrical Engineering, Mekelweg 4,2628 DC Delft, Holland, D Linebarger is with the Slgnetlcs Corporation, Sunnyvale, CA 94086, sister pairs are connected in parallel to the input. The input of the n-p-n pair Ql, Q1 can reach the positive supply provided the voltage drops across the collector resistances RIO and Rll do not cause significant saturation of these transistors. Similarly, the input of the p-n-p pair” Q3, Q4 can...
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