Gradient Power Amplifier
The gradient amplifier is used to supply the current to the gradient coils. Since it's the fields we care about, and the fields are proportional to current, this amplifier can be viewed as a voltage to current transducer; it takes a voltage waveform from the console and creates a current proportional to that voltage in the gradient coil. It is similar to a common audio power amplifier except that it must also be able to output DC currents. It uses a power op-amp followed by a current sensor. The output of the current sensor is compared to the input voltage to ensure that the current itself is proportional to the input voltage. A current sensor is created by measuring the voltage across a small resistor in series with the output.