An optical receiver is described. This optical receiver includes a digital feedback circuit that biases a front-end circuit, which receives an optical signal, so that an analog electrical signal output by the front-end circuit is calibrated relative to a reference voltage corresponding to a decision threshold of a digital slicer in the optical receiver. In particular, during a calibration mode the feedback circuit may determine and store a calibration value that calibrates the analog electrical signal relative to the reference voltage. Then, during a normal operating mode, the feedback circuit may output a current corresponding to the stored calibration value that specifies a bias point of the front-end circuit.