Apparatus using a differential analog-to-digital converter

• US 8,253,706 B2
• Filed: 06/26/2009
• Issued: 08/28/2012
• 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): Patel, Nitin
• Application Number:
  US12/492,856
• Publication Number:
  US 20100328226A1
• Time in Patent Office: 1,159 Days
• Field of Search: 345156-173
• 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 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 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 pulse.

2. The method of claim 1, 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.

3. The method of claim 2, where the subtraction between the digital representation of the first response and the digital representation of the second response is performed by a digital subtraction unit.

4. The method of claim 1, 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. The method of claim 4, wherein the measure of charge associated with the first and second responses comprises S_N−

S_P, the first response represented by a positive edge S_P, where S_P=−

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

7. The method of claim 1, wherein manipulating the first response and the second response comprises:

applying the first and second response to an analog-to-digital converter such that an output of the analog-to-digital converter includes a first digital representation of the first response and a second digital representation of the second response; and

applying the output from the analog-to-digital converter to a digital subtraction unit such that an output of the digital subtraction unit includes a measure of charge associated with the first and second responses based on a subtraction between the first digital representation of the first response and the second digital representation of the second response.

8. An apparatus comprising:

a waveform capture circuit configured to;

capture a response to a pulse having a characteristic varying in one direction, the characteristic varying in the one direction comprising a rising edge of the response to the pulse; and

capture an associated characteristic varying in a different direction, the associated characteristic varying in the different direction comprising a falling edge of the response to the pulse; 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.

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

10. The apparatus of claim 8, 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.

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

12. The system of claim 10, wherein the system comprises a control circuit configured to synchronize generation of the pulse with operation of the two sample and hold circuits.

13. 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 pulse 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, the characteristic varying in the one direction comprising a rising edge of a response to the pulse, and an associated characteristic varying in a different direction, the associated characteristic varying in the different direction comprising a falling edge of the response to the pulse; 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.

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

15. The system of claim 13, 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.

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

17. The system of claim 15, wherein the system includes a control circuit to synchronize generation of the pulse with operation of the two sample and hold circuits.

18. The system of claim 13, 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.