Methods and circuits for detecting an ion current in a mass spectrometer are described. A circuit and a method may involve converting, over a length of integration time, the ion current to a voltage ramp by an integrating circuit having a gain setting. The circuit and the method may also involve determining a slope of the voltage ramp. The circuit and the method may also involve determining a magnitude of the ion current based on the slope of the voltage ramp and the gain setting. The circuit and the method may further involves determining an out-of-range state based on the voltage ramp and adjusting the gain setting of the integrating circuit, or the length of integration time or both, in response to the determining of the out-of-range state.