Force sensing semiconductive touchpad

A touchpad assembly for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly, the touchpad assembly comprising:

• a pad having a touch surface;
• a first sensor layer;
• a first pair of spaced apart conductive traces running across opposite ends of the first sensor layer in a first direction such that a first resistance between the opposite ends of the first sensor layer connects the first pair of conductive traces;
• a second sensor layer;
• a second pair of spaced apart conductive traces running across opposite ends of the second sensor layer in a second direction generally perpendicular to the first direction such that a second resistance between the opposite ends of the second sensor layer connects the second pair of conductive traces;
• the second sensor layer being disposed beneath the first sensor layer such that the first and second sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad, wherein the contact point is connected to each conductive trace by a pressure resistance associated with the first and second sensor layers and position resistances of the first and second sensor layers, wherein the pressure resistance varies inversely as a function of the pressure asserted and the position resistances vary proportionally as a function of the distance of the contact point from the conductive traces;
• a first pair of timing capacitors each connected to a respective one of the first pair of conductive traces;
• a second pair of timing capacitors each connected to a respective one of the second pair of conductive traces;
• and
• a microprocessor operative with the timing capacitors, wherein the microprocessor controls and monitors charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.

A touchpad assembly for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly, the touchpad assembly comprising:

• a pad having a touch surface;
• an X position sensor layer having a pair of spaced apart X conductive traces running across opposite ends of the X sensor layer along a Y direction such that a resistance RX between the opposite ends of the X sensor layer connects the pair of X conductive traces;
• a Y position sensor layer having a pair of spaced apart Y conductive traces running across opposite ends of the Y sensor layer along an X direction generally perpendicular to the Y direction such that a resistance RY between the opposite ends of the Y sensor layer connects the pair of Y conductive traces, wherein the Y sensor layer is disposed adjacent the X sensor layer such that the X and Y sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad, wherein the contact point is connected to each conductive trace by a pressure resistance RZ associated with the X and Y sensor layers and position resistances of the X and Y sensor lavers, wherein the pressure resistance RZ varies as a function of the pressure asserted and the position resistances vary as a function of the distance of the contact point from the conductive traces;
• a first pair of timing capacitors each connected to a respective one of the pair of X conductive traces;
• a second pair of timing capacitors each connected to a respective one of the pair of Y conductive traces;
• and
• a microprocessor operative with the timing capacitors, wherein the microprocessor controls and monitors charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.

A method for providing a signal to a computer representative of a position and asserted pressure of an object touching a touchpad having X and Y position sensor layers, wherein the X and Y sensor layers are Z pressure sensitive and come into contact at a contact point when the object touches the touchpad, the method comprising:

• providing a pair of spaced apart X conductive traces running across opposite ends of the X sensor layer along a Y direction such that a resistance RX between the opposite ends of the X sensor layer connects the pair of X conductive traces;
• providing a pair of spaced apart Y conductive traces running across opposite ends of the Y sensor layer along an X direction generally perpendicular to the Y direction such that a resistance RY between the opposite ends of the Y sensor layer connects the pair of Y conductive traces;
• driving the X conductive traces to a given voltage so that current flows from the contact point through a pressure resistance RZ across position resistances to the pair of Y conductive traces;
• determining the position of the object along a Y direction on the Y sensor layer as a function of the current flowing from the contact point to the pair of Y conductive traces, wherein the current varies as a function of the pressure resistance RZ and the position resistances connecting the pair of Y conductive traces to the contact point;
• driving the Y conductive traces to a given voltage so that current flows from the contact point through a pressure resistance RZ across position resistances to the pair of X conductive traces;
• determining the position of the object along an X direction on the X sensor layer as a function of the current flowing from the contact point to the pair of X conductive traces, wherein the current varies as a function of the pressure resistance RZ and the position resistances connecting the pair of X conductive traces to the contact point;
• and
• determining the Z pressure of the object touching the touchpad from the currents flowing from the contact point to the pairs of X and Y conductive traces.