Two data series of disk integrated solar irradiance, taken by the Variability of the solar IRradiance and Gravity Oscillations (VIRGO) experiment on board the Solar and Heliospheric Observatory (SoHO) mission, corresponding to epochs of minimum and maximum solar activity have been analysed in order to study the background signal of the associated power spectra. We fit the most apparent convective structures that appear at low frequencies in the spectrum as well as non-periodic components. We aim to compare the results found in the three observed bands (centered in λ=402nm, λ=500nm and λ=862nm) as well as to find dependences of the non-periodic convective structures parameters with the solar cycle.