Stylus and stylus circuitry for capacitive touch screens
A stylus for a capacitive touch screen includes an inverting charge integrator circuit is connected to a conductive tip for providing an output signal proportional to a charge induced at the conductive tip. An inverting amplifier generates an amplified signal proportional to the signal output from the inverting charge integrator. A conductive contact provides electrical or capacitive coupling between the amplified signal and an exterior of the stylus which may provide electrical or capacitive coupling with a person holding the stylus. In other embodiments, the order of the inverting charge integrator and the inverting amplifier may be reversed. A power supply circuit powers the inverting charge integrator and the inverting amplifier. Shielding may be implemented to isolate the stylus circuitry and prevent oscillation. The provided circuitry may enable a ball point or other fine point stylus tip configurations.
1. A circuit for a capacitive touch screen stylus, the circuit comprising:
a. a conductive tip for providing capacitive coupling with a capacitive touch screen;
b. an amplifier circuit for providing an output signal proportional to a current induced at the conductive tip when it is placed near the capacitive touch screen;
c. an integrator circuit for generating an output voltage proportional to the output signal of the amplifier circuit; and
d. a conductive contact for providing electrical or capacitive coupling between the output voltage and an exterior of the stylus.
2. The circuit of claim 1 wherein a positive transition in potential at the conductive tip results in a positive transition in voltage at the conductive contact.
3. The circuit of claim 1 wherein a negative transition in potential at the conductive tip results in a negative transition in voltage at the conductive contact.
4. The circuit of claim 1 , further comprising shielding between the conductive tip and the integrator circuit for isolating at least the connection between the tip and the integrator circuit.
5. The circuit of claim 4 wherein the shielding is connected to a ground of the stylus circuit.
6. The circuit of claim 4 wherein the shielding comprises a conductive enclosure having a circular cross-section and extending along an axis of at least a portion of the stylus.
7. The circuit of claim 4 wherein the shielding comprises a conductive wrapping around at least a portion of the stylus circuit.
8. The circuit of claim 4 wherein the shielding comprises a substantially continuous conducting layer of a circuit board for the stylus circuit.
9. The circuit of claim 4 wherein the shielding comprises one or more conducting planes above and/or below a plane of the stylus circuit.
10. The circuit of claim 4 wherein the shielding comprises one or more conducting planes in a plane of the stylus circuit.
11. The circuit of claim 1 wherein the conductive contact is connected or coupled to an external surface of a stylus.
12. The circuit of claim 1 wherein the integrator circuit and the amplifier circuit are combined.
13. The circuit of claim 1 wherein the conductive tip is metallic.
14. The circuit of claim 1 wherein the conductive tip comprises a conductive polymer.
15. A stylus for a capacitive touch screen, the stylus comprising:
an elongated barrel with an opening therein adapted to receive a stylus circuit;
a conductive tip extending through an end of the elongated barrel;
an amplifier circuit housed within the elongated barrel, the amplifier circuit providing an output signal proportional to a current induced at the conductive tip when the conductive tip is placed near a voltage source;
an integrator circuit housed within the elongated barrel, the integrator circuit generating an output voltage at an output proportional to the output signal of the amplifier circuit; and
a conductive contact on an exterior surface of the elongated barrel, the conductive contact electrically or capacitively coupled to the output of the integrator circuit.
16. The stylus of claim 15 , wherein the conductive tip has a cross-section projected onto the touch screen of less than 3.5 millimeters.
17. The stylus of claim 15 , further comprising a power supply circuit housed within the elongated barrel, the power supply circuit comprises one or more batteries.
18. The stylus of claim 17 , wherein the one or more batteries are rechargeable.
19. The stylus of claim 15 , wherein the conductive tip comprises a ball point.
20. The stylus of claim 15 , wherein a positive change in voltage at the conductive tip results in a positive change in voltage at the conductive contact and a negative change in voltage at the conductive tip results in a negative change in voltage at the conductive contact.