Analog Integrated Circuits and Signal Processing, 20, 11±23 (1999) # 1999 Kluwer Academic Publishers, Boston. Manufactured in The Netherlands. AVery Low Voltage Bipolar Op-Amp for Sensor Applications G. FERRI AND M. FACCIO University of L'Aquila, Localita' Monteluco di Roio, 67040, L'Aquila, Italy G. STOCHINO Ericsson Telecomunicazioni, Via Anagnina 203, 00040 Roma, Italy A. D'AMICO University of Roma Tor Vergata, Via della Ricerca Scienti®ca, 00133 Roma, Italy D. ROSSI AND G. RICOTTI SGS-Thomson, Via Tolomeo 1, 20100 Cornaredo, Milano, Italy Received November 15, 1995; Revised October 7, 1996; Accepted October 14, 1996 Abstract. A new bipolar four-quadrant operational ampli®er operating at a power supply voltage of 0.8 V and with a supply current of 800 mA is here presented and illustrated. It features low input offset, low bias current, low noise, low crossover distortion and a rail-to-rail output swing. Control circuits ensuring minimum and maximum current limits for the output transistors have been incorporated. The biasing circuitry follows a PTAT scheme. A simple compensation topology allows the reduction of the area. The chip, whose area is about 2 mm 2 , has been fabricated in HF2CMOS 2 m/6 GHz technology. Finally, Spice simulations and experimental results, which con®rm the expected overall performances of the low voltage op-amp, are reported. Key Words: analog circuit design, operational ampli®ers, low voltage, low power 1. Introduction In the last few years, integrated circuit technology has been continuously pushed towards lower and lower operating supply voltages. The reason for this trend is mainly the increasing use of battery-operated portable electronics and wireless systems, which call for low power consumption, small size and low weight. Also the need to reduce power dissipation in modern digital systems, which are very complex and fast, plays an important role in determining this trend. Moreover, a further push is given by the cultural scienti®c interest to explore the technological and physical limits of the integrated devices [1±4]. Consequently, analog as well as digital designers have been forced to redesign a number of functions and subsystems capable of operating at supply voltages as low as two (2.4 V) or even one (1.2 V) cell voltage. The ®rst low voltage bipolar op-amp, capable of operating by a total supply voltage of 1 V and featuring a rail-to-rail output swing, was proposed by R. Widlar in 1978 [5]. Subsequently, in the early 1990s, the Huijsing group developed a number of structures, still working down to 1 V [6±10]. A 1 V op- amp with rail-to-rail input and output swing was also proposed [6], albeit the extension of rail-to-rail operation down to 1 V has been exchanged for a deterioration of such input characteristics as noise performances and offset. As is well known, in the design of low voltage analog circuits, bipolar technology offers some advantages when compared to MOS devices (even if these have their own advantages, e.g. low gate and offset currents): a higher transconductance, a base- emitter voltage which is more stable and predictable Author for correspondence: Giuseppe Ferri, Universita' L'Aquila, Italy, Localita' Monteluco di Roio, 67040 Poggio di Roio. Phone:  39 0862 434446. Fax:  39 0862 434403. E-mail: ferri@dsiaq1.ing.univaq.it