Active pen signal detection

A processing system for a capacitive sensing input device and an active pen, said processing system comprising:

• a charge integrator;
• a demodulator;
• an analog-to-digital convertor (ADC);
• and
• at least one signal detection filter, wherein said processing system is configured to:
• receive, with said charge integrator, a signal from said active pen to a achieve an integrated signal;
• perform at least one of downconverting with said demodulator and aliasing with said analog-to-digital convertor to achieve a resulting signal from said integrated signal;
• and
• detect, using said at least one signal detection filter, one of a plurality of possible resulting signal frequencies present in said resulting signal, wherein said detected resulting signal frequency is associated with a particular one of a plurality of possible transmission frequencies of said signal, and wherein each of said plurality of transmission frequencies of said signal represents information about operation of said active pen.

A capacitive sensing input device, comprising:

• a capacitive sensor;
• an active pen configured for outputting a signal at a first frequency in response to a user interaction with said active pen;
• and
• a processing system comprising an analog-to-digital convertor (ADC) configured to:
• receive a signal from said active pen;
• perform at least one of downconverting and aliasing to achieve a resulting signal from said signal;
• and
• detect one of a plurality of possible resulting signal frequencies present in said resulting signal, wherein said detected resulting signal frequency is associated with a particular one of a plurality of possible transmission frequencies of said signal, and wherein each of said plurality of transmission frequencies of said signal represents information about operation of said active pen.