Use of resistive touch screen as a proximity sensor

1. A touch screen proximity sensing apparatus comprising:

a touch screen comprising a bottom layer and a top layer wherein the top layer and bottom layer are oriented such that they are separate but capable of being temporarily pressed together by a user;

a control circuit operatively connected to the touch screen;

a plurality of measurement circuits comprising:

a first measurement circuit comprising a resistive sensor circuit; and

a second measurement circuit comprising a proximity capacitance sensor circuit;

wherein the proximity capacitance sensor circuit detects an object by determining an equivalent capacitance between the touch screen and the object, and comprise a bias circuit configured to apply a particular voltage to the bottom layer of the touch screen, said particular voltage being substantially the same as the voltage applied to the top layer;

wherein the resistive sensor circuit measures a touch position by measuring a voltage along a voltage gradient on at least one of the top layer and bottom layer;

wherein the control circuit selectively connects the touch screen with one of the plurality of measurement circuits; and

wherein the control circuit disables the first measurement circuit when said object is detected, said object being a face of said user, the control circuit only enabling the first measurement circuit when said object is no longer detected.

2. The apparatus of claim 1 wherein the control circuit further comprises an isolation circuit configured to isolate the touch screen from the plurality of measurement circuits.

3. The apparatus of claim 1 wherein the control circuit sequentially connects the touch screen with each one of the plurality of measurement circuits.

4. The apparatus of claim 3 wherein the control circuit connects the touch screen with each one of the plurality of measurement circuits in a sequence that repeats periodically.

5. The apparatus of claim 4 wherein a period of the sequence that repeats periodically is approximately five milliseconds.

6. The apparatus of claim 1 control circuit further comprising an event driven control for selectively connecting the touch screen and at least one of the plurality of measurement circuits;

wherein the event driven control determines which member of the plurality of measurement circuits to connect to the touch screen based at least in part on a recently measured input from the touch screen.

7. The apparatus of claim 1 wherein the top layer and the bottom layer comprise a resistive material.

8. The apparatus of claim 1 wherein the top layer comprises a conductive material and the bottom layer comprises a resistive material.

9. The apparatus of claim 1 wherein the bottom layer comprises a conductive material and the top layer comprises a resistive material.

10. In a system comprising a touch screen comprising a bottom layer and a top layer, and a plurality of measurement circuits comprising a capacitive proximity circuit and a resistive touch circuit, a method for proximity detection using the touch screen comprises the steps of:

performing a resistive touch operation by a user comprising the steps of:

disabling the plurality of measurement circuits that are not the resistive touch circuit;

operatively connecting the resistive touch circuit and the touch screen; and

measuring touch information obtained by the touch screen;

performing a proximity capacitive sensing operation comprising the steps of:

disabling the plurality of measurement circuits that are not the capacitive proximity circuit;

operatively connecting the capacitive proximity circuit and the touch screen;

applying a particular voltage to the bottom layer of the touch screen, the particular voltage being substantially the same as the voltage applied to the top layer of the touch screen; and

measuring proximity information obtained by the touch screen;

generating a mode selection signal comprising a touch state and a proximity state, said mode selection signal being maintained in said proximity state when a face of said user is detected to be in contact with said touch screen by said capacitive proximity circuit;

performing the resistive touch operation when the mode selection signal is in the touch state; and

performing the proximity capacitive sensing when the mode selection signal is in the proximity state.

11. The method of claim 10 further comprising the step of sequentially performing the resistive touch operation and the proximity capacitive sensing operation.

12. The method of claim 11 wherein the sequence of performing the resistive touch operation and the proximity capacitive sensing operation repeats periodically.

13. The method of claim 11 wherein the resistive touch operation and the proximity capacitive sensing operation repeat periodically with a period of approximately five milliseconds.

14. The method of claim 10 wherein the mode selection signal is generated at least in part by an input from the touch screen.

15. The method of claim 10 wherein the step of disabling the plurality of measurement circuits further comprises the step of electrically isolating at least one measurement circuit from the touch screen.