An evolutionary-based design methodology for performance enhancement of a folded-cascode OTA using symbiotic organisms search algorithm and g m /I D technique

In this paper, a new population-based evolutionary technique namely symbiotic organisms search (SOS) optimisation algorithm is proposed to optimize the design variables of transistors used in analog circuit. Here length and width of the transistors are considered to be the design variables, the optimisation of which minimizes the input-referred noise, total MOSFET area, and power consumption. This algorithm is quite useful in solving optimization problems but it suffers from higher computational time. Thus in order to minimize the computational time along with SOS algorithm, gm/ID design methodology is used. The proposed method not only guarantees appropriate bias conditions but also estimates the reduced search spaces for the design variables of the MOSFETs. To analyse the performance of SOS algorithm along with gm/ID design methodology, a low noise differential folded-cascode operational transconductance amplifier has been designed and verified using Cadence Spectre circuit simulator in UMC 0.18 µm CMOS process and MATLAB. From the optimisation results, it is observed that the gm/ID method combined with SOS algorithm converges earlier than SOS alone. The total computational time of simulation obtained using the proposed method is 8.59 s while errors found are less than 8%. Hence, this method not only reduces computational time but also improves the accuracy of the circuit design.