Noise characterization of MOSFET current mirror circuit on high impedance application using DAQ card PCI-6221

Abstract

The distinction and characterization of noise have been carried out in the current mirror (CM) circuit as a part of a biosensor system with some main components of MOSFET type BS250 and two resistors at the input (Rref) and output (RL) of the circuit. This evaluation is important since the biosensor module has very high impedance due to the low conductivity sample measured and the high loading resistance for current to voltage conversion. This high impedance leads to the rise of high noise due to thermal noise which is proportional to the resistance, in addition, the type and the specifications of the MOSFET determine the noise due to semiconductor properties. Therefore, this evaluation can be used to reduce the resulted noise to obtain high Signal to Noise Ratio (SNR). The experiment was performed by applying Rref and RL with some values of 1 kν, 100 kν and 1 Mν while maintaining the voltage source at 1 V, which causes the input current to vary accordingly. This experiment was adjusted to meet the range of current in the biosensor application, which is relatively very small. The measurement is acquired by a DAQ card PCI-6221 that has been integrated with a LabVIEW program based on Fast Fourier Transform (FFT). The noise response analysis is performed within a bandwidth of 0.1 Hz to 100 kHz and a frequency resolution of 0.1 Hz. This bandwidth is sufficient to describe the noise in the CM circuit applied to the biosensor device. The results show that the noise characteristics vary with the applied resistance. Thus, it can be considered to determine an appropriate loading resistance, which could be used to build a high SNR current mirror circuit for the biosensor system.