High gain, rail-to-rail input/output operational amplifier design

Operational amplifier is a main integrated circuit which has critical importance for the design of analog circuits in many areas such as electronics, communications, optics, medical etc. It is needed in many applications such as analog to digital conversion or vice versa, differentiation and integration, addition and subtraction, active filter, comparator and so on. The principle work of this integrated circuit is to amplify the difference of signals applied to its inputs. Speed, accuracy, and voltage range of this conversion vary according to characteristic features of the operational amplifier. Hence, it is necessary that circuit blocks forming the operational amplifier should be designed according to the needed characteristic properties. In addition, the importance of portable, low power, efficient and fast electronic circuits has increased with the progress of technology. From past to present, CMOS technology is widely used to make high performance integrated circuit designs. Thus, custom solutions for particular requirements can be developed. In this thesis work, an operational amplifier which has high gain, rail-to-rail input and output is designed for battery-powered and having wide input / output voltage range applications. The most important feature of the designed operational amplifier is that amplifying operation remains constant during the input common mode voltage range. Its characteristic properties such as gain, bandwidth, phase margin, and slew rate are not heavily affected from input voltage variations. Moreover, a self-compensated circuit for the operational amplifier to work stable, and self-biased voltage and current sources to decrease power consumption are designed. In order to avoid any stabilization problems, simple electronic circuits have been utilized. Simulations of the designed operational amplifier are done and its operating performance on the required applications is examined. Besides, the proposed design is compared to various examples in the literature. The developed design with CMOS technology having small channel length occupies less space than similar designs. Also, a design was developed for low-voltage / high performance portable devices, which will allow them to both fulfill their low current and voltage amplifying functions and to ensure their operation within a wide voltage range. By means of the design which utilized 130 nm CMOS technology and 1.5 V single-sourced supply voltage, following results were obtained: gain over 100 dB; input common mode voltage range between 0.05 V and 1.45 V; output swing between 0.05 V and 1.45 V; bandwidth higher than 10 MHz; phase margin larger than 45º; 4.2 V / µs slew rate; more than 80 dB CMRR and PSRR; power consumption lower than 1 mW.