Ground switching technique for silkscreened digitizer grids

• US 4,853,499 A
• Filed: 12/12/1988
• Issued: 08/01/1989
• Est. Priority Date: 12/12/1988
• Status: Expired due to Fees

• Current Assignee: GTCO Corporation (GTCO Calcomp, Incoporated)
• Original Assignee: CalComp, Inc. (Martin Marietta Corporation)
• Inventors: Watson, James S.
• Primary Examiner(s): Schreyer, Stafford D.
• Application Number:
  US07/283,509
• Time in Patent Office: 232 Days
• Field of Search: 178/18, 178/19, 382/13
• US Class Current: 178/20.02
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

A method and associated circuitry for use in an electromagnetic digitizer having a plurality of first grid conductors connected from a first multiplexer controlled by a first enable input to ground and a plurality of second grid conductors connected from a second multiplexer controlled by a second enable input to ground and crossing over the first grid conductors at multiple points for eliminating errors caused by capacitively coupled signals between the grid conductors at the cross over points. The method comprises, connecting a first switch having a control input for switching the first switch to a closed position in series with the connection of the first grid conductors to ground; connecting a second switch having a control input for switching the second switch to a closed position in series with the connection of the second grid conductors to ground; applying the first enable input simultaneously to the control input of the second switch and the first multiplexer whereby the connection to ground of the second grid conductors is broken when the first multiplexer is enabled; and, applying the second enable input simultaneously to the control input of the first switch and the second multiplexer whereby the connection to ground of the first grid conductors is broken when the second multiplexer is enabled.

Claims

1. In an electromagnetic digitizer having a plurality of first grid conductors connected from a first multiplexer controlled by a first enable input to ground and a plurality of second grid conductors connected from a second multiplexer controlled by a second enable input to ground and crossing over the first grid conductors at multiple points, the improvement for eliminating errors caused by capacitively coupled signals between the grid conductors at the cross over points comprising:

(a) first switching means connected in series with the connection of the first grid conductors to ground and including a control input for breaking the connection to ground of the second grid conductors when the first multiplexer is enabled by the first enable input; and

,

(b) second switching means connected in series with the connection of the second grid conductors to ground and including a control input for breaking the connection to ground of the first grid conductors when the second multiplexer is enabled by the second enable input.

2. The improvement to an electromagnetic digitizer of claim 1 wherein:

said first and second switching means each comprises a switching transistor.

3. In an electromagnetic digitizer having a plurality of first grid conductors connected from a first multiplexer controlled by a first enable input to ground and a plurality of second grid conductors connected from a second multiplexer controlled by a second enable input to ground and crossing over the first grid conductors at multiple points, the improved method of operation for eliminating errors caused by capacitively coupled signals between the grid conductors at the cross over points comprising the steps of:

(a) connecting a first switching means having a control input for switching the first switching means between an open and a closed position in series with the connection of the first grid conductors to ground;

(b) connecting a second switching means having a control input for switching the second switching means between an open and a closed position in series with the connection of the second grid conductors to ground;

(c) applying the first enable input simultaneously to the control input of the second switching means and the first multiplexer whereby the connection to ground of the second grid conductors is broken when the first multiplexer is enabled by the first enable input; and

,

(d) applying the second enable input simultaneously to the control input of the first switching means and the second multiplexer whereby the connection to ground of the first grid conductors is broken when the second multiplexer is enabled by the second enable input.

4. In an electromagnetic digitizer of the loopback grid variety having a plurality of first grid conductors connected to a first multiplexer controlled by a first enable input and crossing a working surface of the digitizer twice to a ground connection and a plurality of second grid conductors connected to a second multiplexer controlled by a second enable input and crossing the working surface of the digitizer twice while crossing over the first grid conductors at multiple points to a ground connection, the improvement for eliminating errors caused by capacitively coupled signals between the grid conductors at cross over points where the conductors turn to recross the working surface of the tablet comprising:

(a) first switching means connected in series with a connection of the first grid conductors to ground disposed after their second crossing of the working surface and including a control input for breaking said connection to ground of the second grid conductors when the first multiplexer is enabled by the first enable input; and

,

(b) second switching means connected in series with a connection of the second grid conductors to ground disposed after their second crossing of the working surface and including a control input for breaking said connection to ground of the first grid conductors when the second multiplexer is enabled by the second enable input.

5. The improvement to a loopback grid electromagnetic digitizer of claim 4 wherein:

said first and second switching means each comprises a switching transistor.