JPS5923410B2 - tatsuchi keyboard - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a touch keyboard in which touch switches that utilize capacitance, that is, switches that detect when a human body touches them and perform a predetermined operation, are arranged in a matrix. The present invention relates to a structure for correcting capacitance imbalance when there is a missing part, that is, an unnecessary part of a switch.

Touch keyboards that utilize capacitance matrices are used to reduce the size and weight of operation switch panels and keyboards for electronic devices.

In such a capacitance matrix configuration, sensing cells may be missing. To compensate for this, it is common to externally mount a molded capacitor corresponding to the capacitance of the sensing cell on the peripheral circuit.However, in this method, the drive line and receive line If the routing method is not uniform and the distribution of force stray capacitance becomes unbalanced, there is a risk that the S/N of the Tuchi keyboard will decrease.In order to prevent this, the present invention adds a dummy on the matrix. This is to stabilize the compensation characteristics by arranging embedded pads.This will be explained in detail below with reference to the drawings.

Figure 1 shows the basic circuit configuration of a touch switch using a capacitance matrix.V) 1 is a sensing block;
2 is a driving circuit, 3 is a sensing circuit, 4 is a driving (drive) line, 41 is a drive pad, 5 is a touch pad, 6 is a sensing (receiving) line, and 61 is 5 receiving pad.

As shown in Figure 1, the intersections of the drive lines and receive lines form a matrix, and the intersections are as shown in Figure 1.
The drive line and the so-receive line are capacitively coupled.

If the touchpad 5 is completely floating, the pulse signal applied to the drive line will be transmitted to the receive line, but if the touchpad is grounded by the human body, almost no pulse signal will be transmitted to the receive line. Therefore, by sequentially applying voltage pulses to each drive line from the drive circuit 2 for scanning, and by sequentially switching and selecting each receive line using the sensing circuit 3 and observing the reception amplitude of the voltage pulse, it is possible to determine which touch pad is being selected. It can be detected when a human body is in contact with it.

In this way, a keyboard is generally arranged in a matrix of NXm (N, m are positive integers), but in some cases it may not be possible to have an NXm arrangement.

Furthermore, even if the total number of keys is NXm, there are cases where the function of each key and the layout of the design result in a matrix with some keys missing, as shown in Figure 2. do. If no processing is done in such a case, there will always be no pulse transmission between the drive line and the receive line if the missing part is present, and therefore the sensing circuit will always wonder if that part is in contact with the human body. It will be detected as follows. Although it is possible to memorize the position of such a missing part in the matrix in advance by some method and ignore the detection output from that part, the circuit is complicated, so the conventional approach was as shown in Figure 2. A common solution was to connect an external capacitor C between the drive line and the receive line to ensure pulse transmission at all times. In this case, the value of C is of course equal to the series composite value of the capacitance Cd between the drive pad and the touch pad and the capacitance Cr between the touch pad and the receive pad. However, attaching the capacitor C externally in this way not only increases the number of work steps, but also has the disadvantage of lowering the S/N due to the unbalance of the stray capacitance, which is not desirable.

Therefore, in the present invention, dummy receive pads and drive pads are provided in the matrix to eliminate the need for compensation with external capacitors, thereby reducing the number of work steps and achieving high operational stability due to uniform load capacitance. FIG. 3 shows one embodiment of the present invention; FIG. 3a is a perspective view showing the arrangement of each pad in each layer, and FIG. 3b is a sectional view taken along line A-A'.

The touch pads 5 shown by dotted lines are arranged in a matrix on the first layer (surface layer), but there are some parts that are not present.

Drive pads 41 indicated by solid lines and hatched are provided in the third layer and connected by drive lines 4 in each column. Further, in the area where the touch pad 5 is not present, a dummy drive pad 42 having an area one-fourth of the normal drive pad 41 is provided. Receive pads 61 shown by chain lines are provided in the second layer and are connected by receive lines 6 in each row. Further, in the area where the touch pad 5 is not present, a dummy receive pad 62 having an area half that of the normal receive pad 61 is provided. The area of each pad is explained as follows.

Assuming that the spacing and dielectric constant between each layer are the same, if the area of the pad 61 in the second layer is half the area of the pad 41 in the third layer, the capacitance Cd between the drive pad 61 and the touch pad 5 will be The capacitance Cr between the receive pad 61 and the touch pad 5 is approximately the same. Therefore, touch pad 5
When the pad is floating, the capacitance between the drive pad 41 and the receive pad is Cd/2 (or Cr/2).

Therefore, the dummy drive pad 42 and receive pad 6
In order to make the capacitance between the two pads approximately equal to this, the area of the dummy pads 42 and 62 should be half the area of the second layer pad 61, that is, a quarter of the area of the third layer pad 41. It must be 1. In this example, the drive pad was provided in the third layer and the receive pad was provided in the second layer, but
Needless to say, this may be reversed. The board 10 may be of any material as long as it has appropriate mechanical strength and dielectric constant, but a glass epoxy multilayer printed wiring board is used, and each pad is fabricated in the same process as printed wiring for other peripheral circuits. This not only reduces man-hours, but also has great benefits such as smaller size, lighter weight, and increased reliability due to fewer connections.

As described above, the present invention eliminates the need for an external compensating capacitor by providing dummy drive pads and receive pads in the second and third layers in the missing parts of the touch keyboard using a three-layer electrostatic matrix. Not only does it reduce man-hours, but since there is no wiring, stray capacitance can be equalized and stable operation can be achieved.

Further, since nothing appears on the surface (first layer) due to the missing portions, no problem arises in terms of appearance.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a touch keyboard using a capacitance matrix, Fig. 2 is an example of the arrangement of touch pads, and Fig. 3 is an embodiment of the present invention. , b are cross-sectional views. In each figure, 1 is the sensing block, 2 is the 7 drive circuit, and 3 is the sensing block.
41 is a sensing circuit, 41 is a drive pad, 5 is a touch pad, 61 is a receive pad, 42 is a dummy drive pad, and 62 is a dummy receive pad.

Claims (1)

[Scope of Claims] 1. The touch pad has a touch pad in the first layer, a drive pad or a receive pad in the second layer, and a receive pad or drive pad in the third layer, and the touch pad is activated by reducing the amplitude of the pulse signal from the drive pad that is sensed by the receive pad. A touch keyboard comprising a plurality of touch switches arranged in a matrix for detecting that a touch switch is grounded, characterized in that dummy drive pads and receive pads are provided at positions where touch pads are missing in the matrix arrangement. 2 The drive pad or receive pad of the second layer has an area approximately half that of the receive pad or drive pad of the third layer, and the dummy drive pad and receive pad have the same area and approximately half the area of the drive pad or receive pad of the second layer. 2. The touch keyboard according to claim 1, wherein the touch keyboard has an area of . 3 The first layer, second layer, and third layer are the surface layer, second layer, and third layer of a glass epoxy multilayer printed wiring board,
3. A touch keyboard according to claim 1, wherein each pad is formed by printed wiring technology.