Driving variable capacitive loads

Circuitry for driving a variable capacitive load, the circuitry comprising:

• the variable capacitive load, wherein at any time the variable capacitive load comprises an active subset of a set of capacitive loads and wherein the capacitance of each capacitive load is predetermined;
• a digital control circuit configured to generate a digital drive signal;
• and
• a drive circuit configured to convert the digital drive signal into an analogue drive signal, the analogue drive signal forming a drive waveform for charging the variable capacitive load, the drive circuit comprising a slewing circuit configured to drive a time dependent voltage component of the drive waveform;
• wherein the digital control circuit is configured to, for each charging cycle:
• receive an indication of the active subset of capacitive loads for that charging cycle;
• determine the variable capacitive load for that charging cycle based on the active subset of capacitive loads for that charging cycle and the predetermined capacitance of each capacitive load;
• and
• modify the digital drive signal so as to match the time dependent voltage component of the drive waveform to the variable capacitive load.