Apparatus using a differential analog-to-digital converter

• US 9,692,439 B2
• Filed: 08/24/2012
• Issued: 06/27/2017
• Est. Priority Date: 06/26/2009
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Simmons, Martin John
• Primary Examiner(s): Sasinowski, Andrew
• Assistant Examiner(s): WOO, KUO-KONG
• Application Number:
  US13/593,982
• Publication Number:
  US 20120319995A1
• Time in Patent Office: 1,768 Days
• Field of Search: 345173, 345 87, 345 94, 345156, 345157, 345174, 341156
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03M 1/1245 Details of sampling arrangements or methods

Abstract

Electronic apparatus and methods of operating the electronic apparatus include less than a frequency associated with a generated waveform. In various embodiments, an apparatus using a differential analog-to-digital converter can perform low frequency noise rejection that can be implemented in a variety of applications. Additional apparatus, systems, and methods are disclosed.

Claims

1. A circuit comprising:

an amplifier having an output;

a first sample and hold circuit having an input and an output, the input of the first sample and hold circuit coupled to the output of the amplifier;

a second sample and hold circuit having an input and an output, the input of the second sample and hold circuit coupled to the output of the amplifier;

a differential analog-to-digital converter (ADC) having first and second inputs and an output, the first input of the differential ADC coupled to the output of the first sample and hold circuit, and the second input of the differential ADC coupled to the output of the second sample and hold circuit, the ADC operable to;

receive a first voltage offset from the first sample and hold circuit;

receive a second voltage offset from the second sample and hold circuit; and

measure a difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit; and

a control unit operable to control a pulse generation based on the difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit.

2. The circuit of claim 1, wherein the amplifier is operable to:

collect a first charge on a receive electrode of a touch screen and generate the first voltage offset of a first polarity in response to a first edge of a pulse on a drive electrode of the touch screen; and

collect a second charge on the receive electrode and generate the second voltage offset of a second polarity in response to a second edge of the pulse on the drive electrode of the touch screen.

3. The circuit of claim 2, wherein:

the first edge comprises a rising edge of the pulse applied to the drive electrode; and

the second edge comprises a falling edge of the pulse applied to the drive electrode.

4. The circuit of claim 2, wherein the differential ADC is operable to measure the difference by subtracting the first edge from the second edge, wherein the first edge is represented by S_P, where S_P=−

M+L, and the second edge is represented by S_N, where S_N=+M+L, and where M is a measurement and L is a low frequency interference.

5. The circuit of claim 1, wherein the first sample and hold circuit is operable to hold a maximum value of the first voltage offset in a first direction.

6. The circuit of claim 1, wherein the second sample and hold circuit is operable to hold a maximum value of the second voltage offset in a second direction.

7. The circuit of claim 1, wherein the amplifier comprises a virtual earth amplifier.

8. A method comprising:

coupling an input of a first sample and hold circuit to an output of an amplifier;

coupling an input of a second sample and hold circuit to the output of the amplifier;

coupling an output of the first sample and hold circuit to a first input of a differential analog-to-digital converter (ADC);

coupling an output of the second sample and hold circuit to a second input of the differential ADC;

coupling an output of the differential ADC to an input of a control unit;

receiving, by the differential ADC, a first voltage offset from the first sample and hold circuit;

receiving, by the differential ADC, a second voltage offset from the second sample and hold circuit; and

measuring, by the differential ADC, a difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit; and

controlling, by the control unit, a pulse generation based on the difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit as measured by the differential ADC.

9. The method of claim 8, further comprising:

collecting, by the amplifier, a first charge on a receive electrode of a touch screen;

generating, by the amplifier, the first voltage offset of a first polarity in response to a first edge of a pulse on a drive electrode of the touch screen;

collecting, by the amplifier, a second charge on the receive electrode; and

generating the second voltage offset of a second polarity in response to a second edge of the pulse on the drive electrode of the touch screen.

10. The method of claim 9, wherein:

the first edge comprises a rising edge of the pulse applied to the drive electrode; and

the second edge comprises a falling edge of the pulse applied to the drive electrode.

11. The method of claim 9, further wherein measuring the difference comprises subtracting the first edge from the second edge, wherein the first edge is represented by S_P, where S_P=−

M+L, and the second edge is represented by S_N, where S_N=+M+L, and where M is a measurement and L is a low frequency interference.

12. The method of claim 8, further comprising holding, by the first sample and hold circuit, a maximum value of the first voltage offset in a first direction.

13. The method of claim 8, further comprising holding, by the second sample and hold circuit, a maximum value of the second voltage offset in a second direction.

14. The method of claim 8, wherein the amplifier comprises a virtual earth amplifier.

15. A system comprising:

a matrix touch screen having an input line and an output line, the output line configured with respect to the input line to acquire a signal;

a circuit coupled to the output line of the matrix touch screen, the circuit comprising;

an amplifier having an input and an output, the input coupled to the output line of the matrix touch screen;

a first sample and hold circuit having an input and an output, the input of the first sample and hold circuit coupled to the output of the amplifier;

a second sample and hold circuit having an input and an output, the input of the second sample and hold circuit coupled to the output of the amplifier;

a differential analog-to-digital converter (ADC) having first and second inputs and an output, the first input of the differential ADC coupled to the output of the first sample and hold circuit, and the second input of the differential ADC coupled to the output of the second sample and hold circuit, the ADC operable to;

receive a first voltage offset from the first sample and hold circuit;

receive a second voltage offset from the second sample and hold circuit; and

measure a difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit; and

a control unit operable to control a pulse generation based on the difference between the first voltage offset from the first sample and hold circuit and the second voltage offset from the second sample and hold circuit.

16. The system of claim 15, wherein the amplifier is operable to:

collect a first charge from a receive electrode of the matrix touch screen and generate the first voltage offset of a first polarity in response to a first edge of a pulse on a drive electrode of the touch screen; and

collect a second charge from the receive electrode of the matrix touch screen and generate the second voltage offset of a second polarity in response to a second edge of the pulse on the drive electrode of the touch screen.

17. The system of claim 16, wherein:

the first edge comprises a rising edge of the pulse applied to the drive electrode of the matrix touch screen; and

the second edge comprises a falling edge of the pulse applied to the drive electrode of the matrix touch screen.

18. The system of claim 16, wherein the differential ADC is operable to measure the difference by subtracting the first edge from the second edge, wherein the first edge is represented by S_P, where S_P=−

M+L, and the second edge is represented by S_N, where S_N=+M+L, and where M is a measurement and L is a low frequency interference.

19. The system of claim 15, wherein:

the first sample and hold circuit is operable to hold a maximum value of the first voltage offset in a first direction; and

the second sample and hold circuit is operable to hold a maximum value of the second voltage offset in a second direction.

20. The system of claim 15, wherein the amplifier comprises a virtual earth amplifier.