Design and simulation of a high-gain organic operational amplifier for use in quantification of cholesterol in low-cost point-of-care devices

This paper presents circuit design and simulations of a high gain organic Op-Amp, for use in quantification of real cholesterol, in the range of 1-9 mM. A 7-stage inverter chain is added onto the design so as to enhance the amplifier gain. The circuit adapts p-channel transistors only (PMOS) design architecture with saturated loads, simulated on a conventional platform, using appropriate OTFT model and associated parameters. The effect of variation in threshold voltage on circuit operation is also examined. For a supply voltage of ±15 V, the DC output voltage is found to be within an acceptable range of -1 V to -12.5 V, with a highest open loop gain of 83 dB. The closed loop gain is also in agreement with theoretical values, in the range of 1.5 dB to 39 dB, with corresponding bandwidths of 770 Hz to 275 Hz respectively. The latter gain of 39 dB and/or gain-bandwidth product of 10.63 kHz is currently the highest reported in the literature, for this lower supply voltage. The amplifier offers adequate quantification factor, with linear sensitivity of -0.7 V/mM. This paper is the first to adapt organic circuit designs in quantification of cholesterol, with promising outputs, for implementation in low-cost sensor systems.