Simulation and Calibration of Op-Amp Nonidealities in the Voltage Feedback Method for a Cross-Point Resistive Sensor Array

Sensor integration is widely demanded in many applications. For sensor fabrications, a cross-point structure is beneficial because of its low cost, while the readout interface circuit suffers from sneak currents, which can lead to enormous readout error. In this study, the developing electric olfaction system which integrates over 1,000 gas sensors was introduced. Compared to previous works, the array size tends to become large, and resistance values can be widely distributed. We employed the conventional voltage feedback method for the interface circuit because it can measure a wide range of resistance. However, since it constitutes the voltage divider circuit with the selected resistor and the reference resistance by an op-amp unity gain feedback, the readout accuracy is affected by its large load sensor resistance. Therefore, a calibration technique for the voltage feedback method was proposed. The feedback error caused by the load resistance and op-amp nonidealities was analyzed with a simplified circuit, in which circuit parameters such as an array scale, a reference resistance, and an op-amp output impedance were variable. The sneak currents were estimated in the calibration by utilizing the op-amp input difference, and their effects were eliminated. The simulation results showed that the readout error of 32×32 resistive array with 10% distributed resistance could be decreased from around 3% to less than 0.005%. The dependency of the readout accuracy on an op-amp's gain input offset voltage was evaluated systematically to apply the calibration to a practical system.