An active voltage divider ensures constant gain up to a mean anode current of 100 µA, the maximum permitted in most photomultiplier types. Power consumption is typically 100 mW making them particularly suited to portable instrumentation. An active divider consists of a string of high impedance resistors connected in parallel with a string of FETs. The resistors provide reference voltages for each stage of the active string to pick off and apply to the dynodes. An ideal active divider is one that can sense these voltages over the full dynamic range of anode currents without unwanted load effects.