Solid state capacitive switch

• US 5,973,623 A
• Filed: 10/21/1997
• Issued: 10/26/1999
• Est. Priority Date: 10/21/1997
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Gupta, Bhusan, Kramer, Alan Henry
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): WONG, ALBERT KANG
• Application Number:
  US08/957,972
• Time in Patent Office: 735 Days
• Field of Search: 341/33, 341/26, 400/600, 382/124, 345/173, 345/174, 307/116, 361/181
• US Class Current: 341/33
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

A fingertip-operated solid state capacitance switch detects a capacity change that is induced by the physical contact of an ungrounded fingertip to an external dielectric surface of the solid state switch. The input and output of a solid state signal-inverting amplifier are respectively connected to two relatively large and ungrounded capacitor plates that are associated with, but electrically isolated from, the switch'"'"'s external dielectric surface. An ungrounded fingertip forms a third capacitor plate on the switch'"'"'s external surface. The solid state amplifier detects the presence of a fingertip on the switch'"'"'s external surface by way of a change in capacitance within a compound, three plate, capacitor that includes the two ungrounded capacitor plates and the ungrounded fingertip that is resident on the switch'"'"'s external surface. An automatic gain control circuit is provided to adjust the value of an amplifier reference voltage when the solid state switch is not operating, thereby allowing the solid state switch to adapt to changeable ambient conditions. A momentary switch and a toggle flip-flop latched switch are provided. A linear switch array having a movable control knob and a linear LED indicator array is provided. The momentary solid state switch is constructed to operate as a temporal code detector that detects a coded sequence of switch-taps and a coded time interval between adjacent switch-taps.

Claims

1. A momentary switch, comprising:

a dielectric layer having an exposed surface;

an amplifier having an ungrounded input node and an ungrounded output node;

first and a second capacitor plates covered by a thin layer of said dielectric layer to place said exposed surface within an electric field-influence of said first and second capacitor plates, said first capacitor plate being connected to said input node and said second capacitor being connected to said output node;

wherein a magnitude of a signal at said output node is responsive to a proximity of an ungrounded object to said exposed surface;

and a signal comparator for comparing a signal at said output node of said amplifier to a reference voltage.

2. The momentary switch of claim 1 wherein said amplifier is a signal inverting amplifier.

3. The momentary switch of claim 1 wherein said exposed surface, said first capacitor plate, and said second capacitor plate form a compound capacitor that is connected to provide negative feedback from said output node to said input node of said amplifier, a capacitance value of said compound capacitor being a function of a proximity of an ungrounded object to said exposed surface.

4. The momentary switch of claim 1 including an external lead for applying operating power to said amplifier and said signal comparator;

a grounded output lead; and

an ungrounded output lead connected to an output of said signal comparator.

5. The momentary switch of claim 4 wherein said signal comparator operates to short said ungrounded output lead to said grounded output lead when an ungrounded object is in a predetermined proximity to said exposed surface.

6. The momentary switch of claim 1 including:

a cyclically operable control to (1) short said output and input node of said amplifier and (2) apply a reference voltage to said input node, in repeating cycles;

said a cyclically operable control to render said amplifier sensitive to the presence of an ungrounded object on said exposed surface during periods of application of said reference voltage to said input node of said amplifier.

7. The momentary switch of claim 6 wherein:

said amplifier is a signal inverting amplifier, and

said exposed surface, said first capacitor plate, and said second capacitor plate form a compound capacitor that is connected to provide negative feedback from said output node to said input node of said amplifier, a capacitance value of said compound capacitor being a function of a proximity of an ungrounded object to said exposed surface.

8. The momentary switch of claim 7 including an external lead for applying operating power to said amplifier, said signal comparator, and said cyclically operable control means;

a grounded output lead; and

an ungrounded output lead connected to an output of said signal comparator.

9. The momentary switch of claim 8 wherein said signal comparator shorts said ungrounded output lead to said grounded output lead when an ungrounded object is in the presence of said exposed surface.

10. The momentary switch of claim 1 wherein said dielectric layer comprises a silicon member, and including:

a thin film of electrically nonconducting plastic sealing said silicon member.