Capacitive sensing for paper tray

A system for measuring paper characteristics for paper within a paper tray using capacitive sensing, comprising:

• the paper tray including at least two capacitive sensors with respective capacitive electrodes CIN1 and CIN2, each with a ground plane at a paper tray bottom, with CIN1 and CIN2 at a top of the paper tray
• CIN1 and CIN2 oriented relative to a width dimension of the paper in the paper tray such that the paper covers CIN1, and partially covers CIN2, with CIN2 having a length a2=a2p+a2a, where a2p is a portion of the CIN2 length a2 that is over the paper, and a2a is a portion of the CIN2 length a that is not over the paper;
• a capacitance-to-digital converter (CDC) configured to acquire capacitance measurements from the capacitive sensors, and to convert capacitance measurements into sensor date representative of paper width;
• the CDC configured to acquire capacitance measurements based on:
• with no paper in the paper tray, measuring a capacitance CA0=CIN1 to the ground plane, and
• with paper in the paper tray,
• measuring a capacitance CA1=CIN1 to ground,
• measuring a capacitance CA2=CIN2 to ground;
• and
• the CDC is configured to convert these capacitance measurements into sensor data for:
• determining CDIFF_w=CA1*(1−a2p/a2)−CA0*(aa/a), and
• determining paper width based on:
• a2=a2p+a2a,
• a2p=a2−a2a,
• a2a=(a2*CDIFF_w)/(CA1−CA0);
• with paper width corresponding to a percentage (a2p/a) of CIN2 covered by paper.

A capacitance-to-digital converter (CDC) for use in a system for measuring paper characteristics for paper within a paper tray using capacitive sensing, the paper tray including at least two capacitive sensors with respective capacitive electrodes CIN1 and CIN2, each with a ground plane at a paper tray bottom, with CIN1 and CIN2 at a top of the paper tray, and with CIN1 and CIN2 oriented relative to a width dimension of the paper in the paper tray such that the paper covers CIN1, and partially covers CIN2, with CIN2 having a length a2=a2p+a2a, where a2p is a portion of the CIN2 length a2 that is over the paper, and a2a is a portion of the CIN2 length a that is not over the paper, the CDC comprising:

• acquisition circuitry configured to acquire capacitance measurements, including:
• with no paper in the paper tray, a capacitance CA0=CIN1 to the ground plane, and
• with paper in the paper tray,
• a capacitance CA1=CIN1 to ground,
• a capacitance CA2=CIN2 to ground;
• and
• conversion circuitry configured to convert these capacitance measurements into sensor data for:
• determining CDIFF_w=CA1*(1−a2p/a2)−CA0*(aa/a), and
• determining paper width based on:
• a2=a2p+a2a,
• a2p=a2−a2a,
• a2a=(a2*CDIFF_w)/(CA1−CA0);
• with paper width corresponding to a percentage (a2p/a) of CIN2 covered by paper.