Touch-on-Metal Keypad with N-1 Key Scan Averaging

Patent metadata

Field	Value
Publication number	US-2016226521-A1
Application number	US-201615015118-A
Country	US
Kind code	A1
Filing date	Feb 3, 2016
Priority date	Feb 3, 2015
Publication date	Aug 4, 2016
Grant date	—

Abstract

For touch-on-metal (ToM) apparatus, an N-1 key scan averaging (with baseline drift compensation) technique, including: (a) during successive key-scan periods, scanning each N key-touch sense circuits, to determine a respective touch-key sense signal, including a key-press sense signal, determine a respective touch-key baseline value based on the touch-key sense signal independent of any key-press condition; and (b) during each key-scan period, for each touch key 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 to a threshold value based on the respective N-1 key-scan average value, and signaling a key-press condition if at least one touch-key output signal is greater in magnitude than the respective N-1 key-scan average value by the threshold value. Touch-key baseline values can be determined 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 normalized touch-key baseline value by subtracting the touch-key baseline value from the touch-key sense signal.

First claim

1 . A method suitable for use with a touch-on-metal N-key input apparatus including a metal fascia defining N touch-key areas, overlying a key-matrix of N key-touch sensor circuits associated with a respective touch-key area, and each key-touch sensor circuit is configured to provide a touch-key sense signal, including a key-press sense signal in response to depressing the metal fascia above the key-touch circuit, the method comprising
during successive key-scan periods, scanning each N key-touch sense circuits, to
determine a respective touch-key sense signal, including a key-press sense signal,
determine a respective touch-key baseline value based on the touch-key sense signal independent of any key-press condition; and
during each key-scan period, for each touch key
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 to a threshold value based on the respective N-1 key-scan average value, and
signaling a key-press condition if at least one touch-key output signal is greater in magnitude than the respective N-1 key-scan average value by the 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, with suppressed 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.

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

• H03K17/98

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

• H03K17/962 Primary

  Capacitive touch switches · CPC title

• H03K17/9622

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