A readout circuit is provided. The readout circuit is coupled to a pixel circuit for reading out signals from the pixel circuit. The readout circuit includes a biasing circuit. The biasing circuit includes a cascode transistor and a biasing transistor. A first terminal of the cascode transistor is coupled to an output terminal of the biasing circuit and the pixel circuit. A second terminal of the cascode transistor is coupled to a first terminal of the biasing transistor. A second terminal of the biasing transistor is coupled to a negative voltage.