Noise Analysis and Measurement for Current Mode and Voltage Mode Active Pixel Sensor Readout Methods
A detailed experimental and theoretical investigation of noise in both current mode and voltage mode amorphous silicon (a-Si) active pixel sensors (APS) has been performed in this study. Both flicker (1/f) and thermal noise are considered. The experimental result in this study emphasizes the computation of the output noise variance, and not the output noise spectrum. This study determines which mode of operation is superior in term of output noise. The current noise power spectral density of a single a-Si TFT is also measured in order to find the suitable model for calculating the flicker noise. This experimental result matches Hooge’s model. The theoretical analysis shows that the voltage mode APS has an advantage over the current mode APS in terms of the flicker noise due to the operation of the readout process. The experimental data are compared to the theoretical analysis and are in good agreement. The results obtained in this study apply equally well to APS circuits made using polycrystalline silicon (poly-Si) and single crystal silicon.