Methods, devices and systems for providing a high-precision and fast changing driving current for a gradient coil to generate a gradient magnetic field to acquire a high-quality image in an MRI device are provided. An example gradient amplifier includes a controller, a power amplifying circuit and a filtering circuit. The controller is configured to output pulse signals. The power amplifying circuit includes a first H bridge circuit and a second H bridge circuit and is configured to perform power conversion on an input power supply according to the pulse signals to output a driving current to a gradient coil. The filtering circuit is configured to filter the driving current output by the power amplifying circuit. A phase difference between the pulse signals output by the controller to drive switching tubes on a same position in the first H bridge circuit and the second H bridge circuit is a particular degree.
