A reference signal generator circuit for an analog-to-digital converter, the circuit having a signal-generation stage to generate a first reference signal on a first reference terminal, and a filtering circuit arranged between the generator stage and the analog-to-digital converter to determine a filtering of disturbance present on the first reference signal and supply at output on a second reference terminal a second filtered reference signal, the filtering circuit having a switching circuit to connect the first reference terminal to the second reference terminal directly during startup of the reference signal generator circuit and then through the filtering circuit once the startup step is terminated.