Self-referencing capacitive key cell structure and switchcore matrices formed therefrom
First Claim
1. In a capacitive key cell of the type including a contact switch in series with a key cell capacitor for use in a matrix of similar capacitive key cells, the improvement wherein each key cell further includes an intracell coactive loading capacitor connected between a low impedance source of constant voltage and the junction of the contact switch with the key cell capacitor.
4 Assignments
0 Petitions
Accused Products
Abstract
In a capacitive switchcore of the type in which each key cell includes a contact switch in series with a key cell capacitor, an improvement is disclosed in which an intracell coactive loading capacitor is added to each key cell. The intracell coactive loading capacitor is connected between ground and the junction of the contact switch with the key cell capacitor. A matrix of key cells so formed is self-referencing, in that the need for a separate reference capacitor to load the sense line is eliminated. Instead, loading is provided intrinsically by the effect of the intracell coactive loading capacitors acting through multiple key cells connected to a sense line. A preferred embodiment in a capacitive membrane switchcore is described.
-
Citations
10 Claims
- 1. In a capacitive key cell of the type including a contact switch in series with a key cell capacitor for use in a matrix of similar capacitive key cells, the improvement wherein each key cell further includes an intracell coactive loading capacitor connected between a low impedance source of constant voltage and the junction of the contact switch with the key cell capacitor.
-
6. A membrane switchcore comprising:
-
a plurality of drive lines; one or more sense lines; a ground line; a plurality of key cells, each key cell being connected to the ground line and to a unique combination of one drive line and one sense line, in which at least one sense line is connected to two or more of said plurality of key cells, and in which each key cell includes;
a contact switch, with one end of the contactswitch being connected to one drive line, and the other end of the contact switch being connected to a floating junction point, the contact switch having a high impedance open state and a low impedance closed state; actuating means for changing the contact switch between the open and closed states; a key cell capacitor, with one end of the key cell capacitor being connected to said at least one sense line, and the other end of the key cell capacitor being connected to the floating junction point; and an intracell coactive loading capacitor connected between the floating junction point and the ground line; wherein when an interrogating pulse is applied to one of the drive lines connected to a first key cell on said at least one sense line, the remainder of the key cells on said at least one sense line, other than the first key cell, provide substantial loading for said at least one sense line, regardless of the state of the contact switches in said remainder of key cells. - View Dependent Claims (7, 8, 9, 10)
-
Specification