Solid state capacitive switch

• US 6,225,711 B1
• Filed: 08/13/1999
• Issued: 05/01/2001
• Est. Priority Date: 10/21/1997
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Kramer, Alan Henry, Gupta, Bhusan
• Primary Examiner(s): Jackson, Stephen W.
• Assistant Examiner(s): Deberadinis, Robert L.
• Application Number:
  US09/374,716
• Time in Patent Office: 627 Days
• Field of Search: 203/343, 203/512, 341/33, 307/125, 307/116, 340/573.1, 340/554.4, 340/562, 361/181
• US Class Current: 307/125
• 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 solid state toggle switch, comprising:

a silicon member having an exposed surface;

first and second ungrounded, electrically isolated, and closely physically spaced, capacitor plates covered by a thin layer of said silicon member in a manner to place said exposed surface within a dielectric field-influence of said first and second capacitor plates;

a solid state amplifier formed as a first portion of said silicon member, said amplifier having an ungrounded input node and an ungrounded output node;

a feedback circuit connecting said first capacitor plate to said amplifier input node and said second capacitor plate to said amplifier output node, such that a signal at said output node is responsive to the presence/absence of an ungrounded object on said exposed surface;

a solid state comparator formed as a second portion of said silicon member, said comparator having a noninverting input, an inverting input, and an output, said inverting input being connected to a reference voltage, and said noninverting input being connected to said amplifier output node;

a solid state flip-flop formed as a third portion of said silicon member, said flip-flop having an input and an output;

said comparator output being connected to said flip-flop input;

said flip-flop responding to a first association of an ungrounded object with said exposed surface to assume a set condition and responding to a second association of an ungrounded object with said exposed surface to assume a reset condition.

2. The solid state toggle switch of claim 1 wherein said amplifier is a signal inverting amplifier.

3. The solid state switch of claim 2 including an external lead for applying operating power to said amplifier, said comparator, and said flip-flop;

an external ungrounded switch output lead;

an external grounded switch output lead connected to said flip-flop output.

4. The solid state switch of claim 3 wherein said signal comparator shorts said ungrounded switch output lead to said grounded switch output lead when said flip-flop is in said set condition.

5. The solid state toggle switch of claim 1 wherein said exposed surface, said first capacitor plate, and said second capacitor plate form a compound capacitor connected to provide negative feedback from said amplifier output node to said amplifier input node, a capacitance of said compound capacitor varying as a function of a proximity of an ungrounded object to said exposed surface.

6. The solid state switch of claim 1 including:

a solid state cyclically operable control formed as a fourth portion of said silicon member, connected to cyclically (1) short said amplifier output node to said amplifier input node, and (2) apply a reference voltage to said amplifier input node, said cyclically operable control rendering said amplifier sensitive to a proximity of an ungrounded object to said exposed surface during said application of said reference voltage to said amplifier input node.

7. The solid state switch of claim 1 including a thin film of electrically nonconducting plastic sealing said silicon member.

8. The solid state switch of claim 1, including a solid state power transistor formed as a fourth portion of said silicon member;

circuit means connecting an input electrode of said power transistor to said flip-flop output.

9. The solid state switch of claim 8 further comprising:

an external lead for applying operating power to said amplifier, said comparator, and said flip-flop;

a first external output lead connected to a first output lead of said power transistor, and

a second external output lead connected to a second output lead of said power transistor.

10. The solid state switch of claim 9 including a solid state cyclically operable control formed as a fifth portion of said silicon member, said cyclically operable control being connected to cyclically (1) momentarily short said amplifier output node to said amplifier input node, and (2) thereafter apply a reference voltage to said amplifier input node, said cyclically operable control operating to render said amplifier sensitive to the proximity of an ungrounded object to said exposed surface during said application of said reference voltage to said amplifier input node.

11. The solid state switch of claim 1 including a thin film of electrically nonconducting plastic environmentally sealing said silicon member.