Capacitive switch having high accuracy

Patent metadata

Field	Value
Publication number	US-2018006647-A1
Application number	US-201715703927-A
Country	US
Kind code	A1
Filing date	Sep 13, 2017
Priority date	Dec 10, 2014
Publication date	Jan 4, 2018
Grant date	—

Abstract

A capacitive switch includes a drive circuit, a detection circuit, a reference circuit and an identification unit. The drive circuit outputs a drive signal and a switching signal, wherein the drive signal is outputted to a first node and a second node. The detection circuit is sequentially coupled to the first node and the second node according to the switching signal and generates a first detection signal according to the drive signal. The reference circuit is sequentially coupled to the second node and the first node according to the switching signal and generates a second detection signal according to the drive signal. The identification unit includes a first input terminal and a second input terminal respectively coupled to the first node and the second node, and identifies a phase shift between inputted detection signals received by the first input terminal and the second input terminal.

First claim

What is claimed is:

1 . A capacitive switch, comprising:
a drive circuit configured to output a drive signal to a first circuit path and a second circuit path; a capacitive detection circuit configured to be coupled to the first circuit path at a first time to generate a first detection signal, and coupled to the second circuit path at a second time to generate a second detection signal; a capacitive reference circuit configured to be coupled to the second circuit path at the first time to generate a third detection signal, and coupled to the first circuit path at the second time to generate a fourth detection signal; and an identification unit electrically connected to the first circuit path and the second circuit path, and configured to identify a first phase shift between the first detection signal and the third detection signal, identify a second phase shift between the second detection signal and the fourth detection signal, and calculate a difference value between the first phase shift and the second phase shift.

2 . The capacitive switch as claimed in claim 1 , wherein when the difference value exceeds a difference threshold, the identification unit is further configured to output an identified signal indicating a touch detected by the capacitive detection circuit.

3 . The capacitive switch as claimed in claim 1 , further comprising a register coupled to the identification unit and configured to store information related to the first phase shift.

4 . The capacitive switch as claimed in claim 3 , wherein the first time is prior to the second time.

5 . The capacitive switch as claimed in claim 1 , further comprising:
a first switching element configured to couple the capacitive detection circuit to the first circuit path or the second circuit path; and a second switching element configured to couple the capacitive reference circuit to the second circuit path or the first circuit path.

6 . The capacitive switch as claimed in claim 1 , further comprising a delay extension circuit configured to extend the first phase shift and the second phase shift.

7 . The capacitive switch as claimed in claim 1 , further comprising a comparison unit configured to convert the first detection signal, the second detection signal, the third detection signal and the fourth detection signal to square waves.

8 . The capacitive switch as claimed in claim 7 , wherein the comparison unit comprises a slicer, an inverter or a buffer.

9 . The capacitive switch as claimed in claim 1 , wherein the capacitive reference circuit is a replica circuit of the capacitive detection circuit.

10 . The capacitive switch as claimed in claim 1 , wherein the identification unit comprises a time to digital converter, a phase detector, a D flip-flop or an AND gate configured to identify the first phase shift and the second phase shift.

11 . A capacitive switch, comprising:
a drive circuit configured to output a drive signal to a first circuit path and a second circuit path; a capacitive detection circuit electrically connected to the first circuit path; a capacitive reference circuit electrically connected to the second circuit path; and an identification unit comprising a first input terminal and a second input terminal, wherein
the first input terminal is coupled to the first circuit path at a first time to receive a first detection signal generated by the capacitive detection circuit and coupled to the second circuit path at a second time to receive a second detection signal generated by the capacitive reference circuit,
the second input terminal is coupled to the second circuit path at the first time to receive a third detection signal generated by the capacitive reference circuit and coupled to the first circuit path at the second time to receive a fourth detection signal generated by the capacitive detection circuit, and
the identification unit is configured to identify a first phase shift between the first detection signal and the third detection signal, and identify a second phase shift between the second detection signal and the fourth detection signal.

12 . The capacitive switch as claimed in claim 11 , wherein the identification unit is further configured to
compare a difference value or a ratio between the first phase shift and the second phase shift with a difference threshold, and output an identified signal indicating a detection state of the capacitive detection circuit.

13 . The capacitive switch as claimed in claim 11 , further comprising:
a first switching element set configured to couple the first input terminal to the first circuit path or the second circuit path; and a second switching element set configured to couple the second input terminal to the second circuit path or the first circuit path.

14 . The capacitive switch as claimed in claim 11 , wherein the capacitive reference circuit is a replica circuit of the capacitive detection circuit.

15 . The capacitive switch as claimed in claim 11 , further comprising a register coupled to the identification unit and configured to store information related to the first phase shift.

16 . The capacitive switch as claimed in claim 11 , further comprising a delay extension circuit configured to extend the first phase shift and the second phase shift.

17 . The capacitive switch as claimed in claim 11 , further comprising a comparison unit configured to convert the first detection signal, the second detection signal, the third detection signal and the fourth detection signal to square waves.

18 . The capacitive switch as claimed in claim 11 , wherein the identification unit comprises a time to digital converter, a phase detector, a D flip-flop or an AND gate configured to identify the first phase shift and the second phase shift.

19 . A capacitive switch, comprising:
a drive circuit configured to output a drive signal to a first circuit path and a second circuit path; a multiplexer, a plurality of capacitive detection circuits, one of the plurality of capacitive detection circuits being configured to be coupled to the first circuit path via the multiplexer at a first time to generate a first detection signal, and coupled to the second circuit path via the multiplexer at a second time to generate a second detection signal; a capacitive reference circuit configured to be coupled to the second circuit path at the first time to generate a third detection signal, and coupled to the first circuit path at the second time to generate a fourth detection signal; and an identification unit electrically connected to the first circuit path and the second circuit path, and configured to identify a first phase shift between the first detection signal and the third detection signal and identify a second phase shift between the second detection signal and the fourth detection signal.

20 . The capacitive switch as claimed in claim 11 , wherein the plurality of capacitive detection circuits is sequentially coupled to the first and second circuit paths by the multiplexer.

Assignees

• Pixart Imaging Inc

Inventors

• Kao Hong-Sing

Classifications

• H03K2217/960745

  Capacitive differential; e.g. comparison with reference capacitance · CPC title

• H03K17/962 Primary

  Capacitive touch switches · CPC title