Stylus for operating a digitizer system
An apparatus includes a housing, a tip configured to move with respect to the housing based on contact pressure applied the tip, and a circuit. The circuit detects pressure applied on the tip based on movement of the tip. The circuit includes a variable current source configured to drive a sensor, a transimpedance amplifier (TIA) configured to receive current from the sensor and an analog to digital converter configured to sample output from the TIA.
1. An apparatus comprising:
a housing;
a tip configured to move with respect to the housing based on contact pressure applied the tip;
a capacitive based sensor configured to vary capacitance based on movement of the tip, wherein the capacitive based sensor is associated with a sub-circuit including:
a current mirror configured to invert a pulse polarity of the current source; and
a resistor configured to detect current drained from the current mirror; and
a circuit configured to detect pressure applied on the tip based on movement of the tip, wherein the circuit includes:
a current source configured to drive the sensor, wherein the current source is variable;
a transimpedance amplifier (TIA) configured to receive current from the sensor; and
an analog to digital converter configured to sample output from the TIA.
2. The apparatus of claim 1 , wherein amplitude of the output decreases with increase contact pressure applied on the tip.
3. The apparatus of claim 1 , wherein the capacitive based sensor includes a first electrode of the capacitor that moves with respect to a second electrode based on the movement of the tip.
4. The apparatus of claim 1 , wherein the capacitive based sensor includes a deformable electrode that deforms based on the contact pressure applied on the tip.
5. The apparatus of claim 4 , wherein the deformable electrode is an elastomer formed with a protrusion.
6. The apparatus of claim 5 , wherein the deformable electrode is formed with at least one protrusion.
7. The apparatus of claim 1 , wherein the capacitive based sensor comprises:
a first electrode coated with solid dielectric layer, wherein a portion of the dielectric layer is patterned with a conductive pad that is exposed;
a second electrode formed at least in part with elastic material, wherein the second electrode contacts the conductive pad patterned on the dielectric layer; and a support element that moves together with the tip of the apparatus and presses against the second electrode in response to pressure applied on the tip.
8. The apparatus of claim 7 , wherein the first electrode is embedded in a printed circuit board assembly (PCBA) and the conductive pad is patterned on a surface of the PCBA.
9. The apparatus of claim 8 , wherein the first electrode is patterned on a first layer of the PCBA and the dielectric layer is a second layer of the PCBA, which coats the first layer of the PCBA.
10. The apparatus of claim 8 , wherein the PCBA is fixed to the housing.
11. The apparatus of claim 7 , wherein the second electrode is supported by the support element that that moves together with the tip.
12. The apparatus of claim 1 , wherein the sub-circuit comprises a capacitor and resistor configured to match input impedance to the TIA.
13. The apparatus of claim 1 , wherein the circuit includes a variable gain and voltage offset for the TIA.
14. The apparatus of claim 1 , wherein the variable gain and voltage offset is adjusted based on the sensor.
15. The apparatus of claim 1 , wherein the output based on the movement of the tip is non-linear.
16. The apparatus of claim 1 , wherein both the housing and the tip include a conductive portion and wherein the tip is configured to be electrically connected to the conductive portion of the housing based on contact pressure being below a defined threshold.
17. The apparatus of claim 16 , wherein the tip is configured to be electrically disconnected to the conductive portion of the housing based on contact pressure being above the defined threshold.