APPARATUS USING A DIFFERENTIAL ANALOG-TO-DIGITAL CONVERTER

• US 20100328226A1
• Filed: 06/26/2009
• Published: 12/30/2010
• 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
• Granted Patent: US 8,253,706 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• 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 method comprising:

acquiring a first response from an output line, the first response being a signal derived from a rising edge of a waveform;

acquiring a second response from the output line, the second response being a signal derived from a falling edge of the waveform; and

manipulating the first response and the second response to reject noise at frequencies less than a frequency associated with the waveform.

2. The method of claim 1, wherein:

acquiring a first response from an output line includes acquiring the first response from an output line of a matrix touch screen, the first response being a capacitively induced signal derived from a rising edge of a pulse applied to an input line of the matrix touch screen;

acquiring a second response from the output line includes acquiring the second response from the output line of the matrix touch screen, the second response being a capacitively induced signal derived from a falling edge of the pulse applied to the input line of the matrix touch screen; and

manipulating the first response and the second response to reject noise at frequencies less than a frequency associated with the waveform includes manipulating the first response and the second response to reject noise at frequencies less than a frequency associated with the pulse.

3. The method of claim 2, wherein manipulating the first response and the second response includes a subtraction between a digital representation of the first response and a digital representation of the second response.

4. The method of claim 2, wherein manipulating the first response and the second response includes:

applying the first response and the second response to sample and hold circuits;

applying outputs from the sample and hold circuits to a differential analog-to-digital converter such that an output of the differential analog-to-digital converter includes a measure of charge associated with the first and second responses

5. The method of claim 4, wherein applying outputs from the sample and hold circuits to the differential analog-to-digital converter includes applying two voltages to the differential analog-to-digital from the sample and hold circuits.

6. An apparatus comprising:

a waveform capture circuit configured to capture a waveform having a characteristic varying in one direction and to capture an associated characteristic varying in a different direction; and

a differential analog-to-digital converter coupled to the waveform capture circuit, the differential analog-to-digital converter having inputs to receive a representation of the characteristic varying in the one direction and to receive a representation of the associated characteristic varying in the different direction.

7. The apparatus of claim 6, wherein the waveform is a response to a pulse, the characteristic varying in one direction is a rising edge of the response to the pulse, and the associated characteristic varying in a different direction is a falling edge of the response to the pulse.

8. The apparatus of claim 7, wherein the waveform capture circuit includes a sample and hold circuit.

9. The apparatus of claim 7, wherein the waveform capture circuit includes an amplifier coupled to two sample and hold circuits, the waveform capture circuit arranged to provide a representation of the rising edge of the pulse and a representation of the falling edge of the pulse.

10. The apparatus of claim 9, wherein the amplifier includes a virtual earth amplifier.

11. 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 capacitively induced signal derived from a waveform applied to the input line of the matrix touch screen;

a waveform capture circuit configured to capture characteristics of the capacitively induced signal including a characteristic varying in one direction and an associated characteristic varying in a different direction; and

a differential analog-to-digital converter coupled to the waveform capture circuit, the differential analog-to-digital converter having inputs to receive a representation of the characteristic varying in the one direction and to receive a representation of the characteristic varying in the different direction.

12. The system of claim 11, wherein the waveform is a pulse, the characteristic varying in one direction is a rising edge of a response to the pulse, and the characteristic varying in a different direction is a falling edge of the response to the pulse.

13. The system of claim 12, wherein the waveform capture circuit includes a sample and hold circuit.

14. The system of claim 12, wherein the waveform capture circuit includes a virtual earth amplifier coupled to the output line to receive the capacitively induced signal and coupled to two sample and hold circuits to send a representation of the rising edge of the pulse and a representation of the falling edge of the pulse to the two sample and hold circuits.

15. The system of claim 14, wherein the two sample and hold circuits are coupled to the differential analog-to-digital converter.

16. The system of claim 14, wherein the system includes a control circuit to synchronize generation of the pulse with operation of the two sample and hold circuits.

17. The system of claim 11, wherein the differential analog-to-digital converter is configured with the waveform capture circuit such that the differential analog-to-digital converter operatively removes DC offsets from measurement of charge from the capacitively induced signal.