Mitigating distortion in coded light

Apparatus for controlling a current flowing through an illumination source, the driver circuitry comprising:

• current measurement circuitry arranged to take a current measurement measuring the current flowing through the illumination source;
• a current controller configured to output a current control signal to control the current flowing through the illumination source, and thereby control an amount of illumination emitted by the illumination source;
• power circuitry arranged to receive the current control signal and in dependence thereon to drive the current through the illumination source, the current controller being configured to adjust the current control signal based on an error signal representing a comparison between an input set-point and the current measurement fed back from the current measurement circuitry, in order to thereby keep said current through the illumination source on average substantially steady at a level specified by said input set-point;
• a coded light injector arranged to modulate the current control signal output by the current controller in order to cause a sequence of data symbols to be modulated into the current flowing through the illumination source, and to thereby cause the sequence of data symbols to be embedded in the emitted illumination;
• and
• a compensation filter arranged to receive an indication of the presently transmitted data symbol and apply a compensation to the error signal based thereon, to at least partially remove an effect of a distortion of the current measurement caused by the modulation of the data symbols into said current through the illumination source by means of the compensation.