Effect of quantization noise on the accuracy of Langmuir probe Measurements using DSO

Abstract

With the recent advancement in digital electronics, a wide range of Digital Storage Oscilloscopes (DSO) are widely used instead of conventional analog oscilloscope. In-spite of having numerous advantages, the DSO’s has also some disadvantages. DSO converts the incoming analog signal into digital form by sampling and quantization. This phenomena leads to data inaccuracy due to amplitude quantization in DSO; which can be viewed as a form of random noise. The effect of this noise reduces the accuracy of measurements performed in plasma systems, particularly during low values of SNR. To highlight the quantization effect of data in a noisy plasma environment; in this paper, experimental results are presented to demonstrate the reduction in the accuracy of Langmuir probe measurements carried in a capacitively driven RF plasma. The dependency of SNR with various parameters namely the number of quantization bits, dynamic voltage range and background noise level have been simulated using MATLAB under experimental conditions. A qualitative discussion has been presented to account the uncertainty in the values of positive ion saturation current measurements using Langmuir probes.