  We investigate gate voltage dependence of electrical readout noise in
high-speed rf reflectometry using gallium arsenide quantum dots. The fast
Fourier transform spectrum from the real time measurement reflects build-in
device noise and circuit noise including the resonator and the amplifier. We
separate their noise spectral components by model analysis. Detail of gate
voltage dependence of the flicker noise is investigated and compared to the
charge sensor sensitivity. We point out that the dominant component of the
readout noise changes by the measurement integration time.
