Touch keypad with key scanning

Patent metadata

Field	Value
Publication number	US-10505564-B2
Application number	US-201615015118-A
Country	US
Kind code	B2
Filing date	Feb 3, 2016
Priority date	Feb 3, 2015
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

Touch/key sensing with N-1 key scan averaging, for use with an N-key touch input apparatus, including a key matrix of N touch-key sense circuits, including: (a) continuously scanning the key matrix at a first bandwidth to determine a respective touch-key baseline sense signal, independent of a key-press condition, and a related touch-key baseline value based on successive baseline sense signals; and (b) during successive key-scan periods, scanning the key matrix at a second bandwidth greater than the first bandwidth, and for each touch key N, determining a touch-key sense signal, generating an N-1 key-scan average value by averaging the touch-key baseline values for the other N-1 touch keys, comparing the Nth touch-key sense signal to a key-press threshold based on the N-1 key-scan average value; and (c) signaling a key-press condition if the touch-key sense signal is greater in magnitude than the N-1 key-scan average value by the key-press threshold.

First claim

The invention claimed is:

1. A method for use with an N-key touch input apparatus including a touch surface defining N touch keys each with an associated touch-key area, the touch surface overlying a key-matrix of N touch-key sense circuits, each associated with a respective touch-key area for a respective touch key, to provide a touch-key sense signal based on sensing the associated touch key, including sensing a key-press condition in response to depressing the associated touch-key area, the method comprising:
continuously scanning at a first bandwidth each of the N touch-key sense circuits of the key-matrix, and for each touch key:
determining a respective touch-key baseline sense signal, independent of a key-press condition; and
determining a respective touch-key baseline value based on successive touch-key baseline sense signals; and

during successive key-scan periods, scanning at a second bandwidth greater than the first bandwidth each of the N touch-key sense circuits of the key-matrix, and for each touch key:
determining a touch-key sense signal from an associated one of the N touch-key sense circuits;
averaging the touch-key baseline values for the other N-1 touch keys to generate a respective N-1 key-scan average value;
comparing the touch-key sense signal for the touch key to a key-press threshold value based on the N-1 key-scan average value for the other N-1 touch keys; and
signaling a key-press condition if the touch-key sense signal is greater in magnitude than the respective N-1 key-scan average value by the key-press threshold value.

2. The method of claim 1 , wherein, during each key-scan period, for each touch key, generating a respective touch-key baseline value comprises generating a normalized touch-key baseline value, including suppressing offset.

3. The method of claim 2 , wherein generating the normalized touch-key baseline value for each touch key comprises:
incrementing the touch-key baseline value if the touch-key sense signal is greater than the touch-key baseline value;
decrementing the touch-key baseline value if the touch-key sense signal is less than the touch-key baseline value; and
generating the normalized touch-key baseline value by subtracting the touch-key baseline value from the touch-key sense signal.

4. The method of claim 1 , further comprising signaling a multi-touch condition for multiple key-press conditions.

5. The method of claim 1 , wherein the baseline value corresponds at least in part to temperature drift.

6. A device including an N-key touch input apparatus, comprising:
a touch key apparatus including a touch surface defining N touch keys each with an associated touch-key area;
a key-matrix including N touch-key sense circuits, each associated with a respective touch-key area for a respective touch key, to provide a touch-key sense signal based on sensing the associated touch key;
a touch-key sensor unit coupled to the N touch-key sense circuits;
the touch-key sensor unit operable to continuously scan at a first bandwidth each of the N touch-key sense circuits of the key-matrix, and for each touch key:
to determine a respective touch-key baseline sense signal, independent of a key-press condition; and
to determine a respective touch-key baseline value based on successive touch-key baseline sense signals; and

the touch-key sensor unit operable, during successive key-scan periods, to scan at a second bandwidth greater than the first bandwidth each of the N touch-key sense circuits of the key-matrix, and for each touch key:
to determine a touch-key sense signal from an associated one of the N touch-key sense circuits;
to generate a respective N-1 key-scan average value based on averaging the touch-key baseline values for the other N-1 touch keys;
to compare the touch-key sense signal for the touch key to a key-press threshold value based on the N-1 key-scan average value for the other N-1 touch keys; and
to signal a key-press condition if the touch-key sense signal is greater in magnitude than the respective N-1 key-scan average value by the key-press threshold value.

7. The system of claim 6 , wherein each generated touch-key baseline value is normalized to suppress offset.

8. The system of claim 6 , wherein the touch-key sensor unit generates the touch-key baseline value for each touch key by:
incrementing the touch-key baseline value if the touch-key sense signal is greater than the touch-key baseline value;
decrementing the touch-key baseline value if the touch-key sense signal is less than the touch-key baseline value; and
generating the touch-key baseline value by subtracting the touch-key baseline value from the touch-key sense signal.

9. The system of claim 8 , wherein each generated touch-key baseline value is normalized to suppress offset.

10. The system of claim 6 , wherein the touch-key sensor unit is operable to signal a multi-touch condition for multiple key-press conditions.

11. The device of claim 6 , wherein the baseline value corresponds at least in part to temperature drift.

12. A touch-key circuit for use in a touch-on-metal N-key input system that includes a touch surface defining N touch keys each with an associated touch-key area for a respective touch key, and a key-matrix including N touch-key sense circuits, each associated with a respective touch-key area to provide a touch-key sense signal based on sensing the associated touch key, the touch-key sensor unit comprising:
baseline scanning circuitry coupled to the N touch-key sense circuits of the key-matrix, and operable to continuously scan at a first bandwidth each of the N touch-key sense circuits, and for each touch key:
to determine a respective touch-key baseline sense signal, independent of a key-press condition; and
to determine a respective touch-key baseline value based on successive touch-key baseline sense signals; and

touch-key scanning circuitry coupled to the N touch-key sense circuits, and operable, during successive key-scan periods, to scan at a second bandwidth greater than the first bandwidth each of the N touch-key sense circuits of the key-matrix, and for each touch key:
to determine a touch-key sense signal from an associated one of the N touch-key sense circuits;
to generate a respective N-1 key-scan average value based on averaging the touch-key baseline values for the other N-1 touch keys;
to compare the touch-key sense signal for the touch key to a key-press threshold value based on the N-1 key-scan average value for the other N-1 touch keys; and
to signal a key-press condition if the touch-key sense signal is greater in magnitude than the respective N-1 key-scan average value by the key-press threshold value.

13. The circuit of claim 12 , wherein each generated touch-key baseline value is normalized to suppress offset.

14. The circuit of claim 12 , wherein the baseline scanning circuitry generates the touch-key baseline value for each touch key by:
incrementing the touch-key baseline value if the touch-key sense signal is greater than the touch-key baseline value;
decrementing the touch-key baseline value if the touch-key sense signal is less than the touch-key baseline value; and
generating the touch-key baseline value by subtracting the touch-key baseline value from the touch-key sense signal.

15. The circuit of claim 14 , wherein each generated touch-key baseline value is normalized to suppress offset.

16. The circuit of claim 12 , wherein the touch-key sensor circuit is operable to signal a multi-touch condition for multiple key-press conditions.

17. The circuit of cla

Assignees

• Texas Instruments Inc

Inventors

• Liu Dongtai

Classifications

• H03K17/975

  using a capacitive movable element · CPC title

• H03M11/20 Primary

  Dynamic coding, i.e. by key scanning (H03M11/26 takes precedence) · CPC title

• H03K2217/94026

  Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input · CPC title

• H03K17/9622

  using a plurality of detectors, e.g. keyboard · CPC title

• H03K17/98

  having a plurality of control members, e.g. keyboard · CPC title