COMBINED TOUCH SENSOR AND LED DRIVER WITH N-TYPE MOSFET PROTECTING TOUCH SENSOR

• US 20090174686A1
• Filed: 01/09/2008
• Published: 07/09/2009
• Est. Priority Date: 01/09/2008
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Leadin Technology Co., Ltd.
• Inventors: Lee, Eun Jin, Jeon, Yung Jin
• Granted Patent: US 8,723,807 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/04 Display protection
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A combined touch sensor and light-emitting-diode (LED) driver comprises a touch sensor circuit configured to detect a touch, where the touch sensor circuit is coupled to a common node and configured to operate with a first operating voltage, an LED driver circuit configured to drive an LED if the LED is coupled to the common node, where the LED driver circuit is also coupled to the common node and configured to operate with a second operating voltage is higher than the first operating voltage, and an n-type field effect transistor (FET) connected in series between the common node and the touch sensor. The n-type FET prevents the higher operating voltage of the LED driver from affecting the operation of the touch sensor, when a port of the combined touch sensor and LED driver IC is used to drive an LED. The touch sensor may be a capacitance-to-digital converter.

Claims

1. A combined touch sensor and light-emitting-diode (LED) driver, comprising:

a touch sensor circuit configured to detect a touch, the touch sensor circuit coupled to a common node and configured to operate with a first operating voltage;

an LED driver circuit configured to drive an LED if the LED is coupled to the common node, the LED driver circuit also coupled to the common node and configured to operate with a second operating voltage that is higher than the first operating voltage; and

an n-type field effect transistor connected in series between the common node and the touch sensor circuit.

2. The combined touch sensor and LED driver of claim 1, wherein the n-type field effect transistor is n-type MOSFET (Metal Oxide Silicon Field Effect Transistor).

3. The combined touch sensor and LED driver of claim 1, wherein the n-type field effect transistor prevents the second operating voltage from affecting operation of the touch sensor circuit if the LED is coupled to the common node.

4. The combined touch sensor and LED driver of claim 1, wherein the n-type field effect transistor is turned on and off in accordance with a non-overlapping, two-phase clock signal.

5. The combined touch sensor and LED driver of claim 1, wherein the common node is connected to a shared port of an integrated circuit.

6. The combined touch sensor and LED driver of claim 1, wherein the touch sensor circuit is a capacitance-to-digital converter (CDC) circuit configured to detect charges stored on a sense capacitor coupled to the common node and generate a digital value corresponding to the detected charges.

7. The combined touch sensor and LED driver of claim 6, wherein the CDC circuit comprises:

an integrator;

a reference capacitor coupled to a predetermined voltage;

a first switch coupled in series to the reference capacitor to connect or disconnect the reference capacitor to or from the integrator according to a first clock signal;

and

a second switch coupled in series to the n-type field effect transistor to connect or disconnect the sense capacitor and the field effect transistor to or from the integrator according to a second clock signal, wherein

the first clock signal is at logic high while the second clock signal is at logic low, and the second clock signal is at logic high while the first clock signal is at logic low, and the n-type field effect transistor is turned on according to the first clock signal and the second clock signal.

8. The combined touch sensor and LED driver of claim 7, further comprising:

a third switch coupled in parallel to the reference capacitor and turned on or off according to the second clock signal.

9. The combined touch sensor and LED driver of claim 7, further comprising:

a third switch coupled in parallel to the series-connected n-type field effect transistor and the sense capacitor, the third switch turned on or off according to the first clock signal.

10. The combined touch sensor and LED driver of claim 9, wherein the sense capacitor is discharged to ground through the n-type field effect transistor and the third switch when the third switch is turned on according to the first clock signal.

19. The combined touch sensor and LED driver of claim 1, wherein the common node is connected to an anode of the LED, and the LED driver circuit is configured to drive the anode of the LED.

11. A combined capacitance-to-digital converter (CDC) and light-emitting-diode (LED) driver, comprising:

an LED driver circuit configured to drive an LED, if the LED is coupled to a common node of the combined CDC and LED driver, the LED driver circuit coupled to the common node;

a CDC circuit configured to detect charges stored on a sense capacitor coupled to the CDC circuit and generate a digital value corresponding to the detected charges, if the sense capacitor is coupled to the common node of the combined CDC and LED driver, the CDC circuit coupled to the common node; and

an n-type MOSFET (Metal Oxide Silicon Field Effect Transistor) connected in series between the CDC circuit and the common node,

wherein the CDC circuit comprises;

an integrator;

a reference capacitor coupled to a predetermined voltage;

a first switch coupled in series to the reference capacitor to connect or disconnect the reference capacitor to or from the integrator according to a first clock signal; and

a second switch coupled in series to the n-type MOSFET to connect or disconnect the sense capacitor and the field effect transistor to or from the integrator according to a second clock signal,

the first clock signal being at logic high while the second clock signal is at logic low, and the second clock signal being at logic high while the first clock signal is at logic low, and

the n-type MOSFET being turned on according to the first clock signal and the second clock signal.

12. The combined CDC and LED driver of claim 11, wherein the CDC circuit further comprises:

a third switch coupled in parallel to the reference capacitor and turned on or off according to the second clock signal.

13. The combined CDC and LED driver of claim 11, wherein the CDC circuit further comprises:

a third switch coupled in parallel to the series-connected n-type MOSFET and the sense capacitor, the third switch turned on or off according to the first clock signal.

14. The combined CDC and LED driver of claim 13, wherein the sense capacitor is discharged to ground through the n-type MOSFET and the third switch when the third switch is turned on according to the first clock signal.

15. The combined CDC and LED driver of claim 11, wherein the CDC circuit is configured to operate with a first operating voltage and the LED driver circuit is configured to operate with a second operating voltage that is higher than the first operating voltage.

16. The combined CDC and LED driver of claim 15, wherein the n-type MOSFET prevents the second operating voltage from affecting operation of the CDC circuit if the LED is coupled to the combined CDC and LED driver.

17. The combined CDC and LED driver of claim 11, wherein both the CDC circuit and the LED driver circuit are configured to be connected to a shared port of an integrated circuit.

18. The combined CDC and LED driver of claim 11, wherein the common node is connected to an anode of the LED, and the LED driver circuit is configured to drive the anode of the LED.

20. A combined touch sensor and light-emitting-diode (LED) driver, comprising:

a touch sensor circuit configured to detect a touch, the touch sensor circuit coupled to a common node and configured to operate with a first operating voltage; and

an LED driver circuit configured to drive an LED, the LED driver circuit also coupled to the common node and configured to operate with a second operating voltage that is higher than the first operating voltage,

wherein the common node is connected to an anode of the LED, and the LED driver circuit is configured to drive the anode of the LED.