A multi-bit continuous-time sigma-delta analog-to-digital converter (ADC) has an input stage which receives an analog input signal current. A multi-bit feedback current digital-to-analog converter (IDAC) generates a multi-level feedback current depending on a feedback signal. An integrator integrates a sum of the generated current and input signal current on a continuous-time basis. The IDAC has a first output branch including a first biasing current source and a second output branch including a second biasing current source. The biasing current sources supply a bias current to a respective branch of the IDAC to bias the input stage in a mid-scale condition. The biasing current sources are connected to the branches via chopping switches which connect the biasing current sources to the branches in a first configuration and a second, reversed, configuration. The integrator amplifier can also be chopper-stabilized, although preferably only the first stage is chopper-stabilized.