JPH0553523A - Signal noise reducing circuit - Google Patents

Abstract

PURPOSE:To guarantee accurate signal transmission by reducing a noise, generated through a cable, by a capacitor and further shortening the rising time and falling time of an electric signal, which become long, by the capacitor. CONSTITUTION:The capacitor 16 which is grounded at one end, a 1st Schmitt trigger circuit 17 which has its input terminal connected to the other terminal of the capacitor 16, and a 2nd Schmitt trigger circuit 18 which has its input terminal connected to the output terminal of the 1st Schmitt trigger circuit 17 are provided; and an enable signal which is sent from a central processing part 11 through a cable 14 is inputted to the connection point between the capacitor 16 and 1st Schmitt trigger circuit 17 and outputted from the output terminal of the Schmitt trigger circuit to a liquid crystal display 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal noise reduction circuit for an electronic device which inputs an electric signal via a cable.

[0002]

2. Description of the Related Art Conventionally, in an electronic device for inputting an electric signal through a cable, there is a possibility that malfunction may occur due to noise generated in the process of transmitting the electric signal through the cable. For example, as shown in FIG. There was a signal noise reduction circuit.

In FIG. 3, reference numeral 1 is a central processing unit 1 on the transmitting side.
Is. In the central processing unit 1, the enable signal output terminal Eo of the gate array 2 outputs the enable signal for the display device. This enable signal is transmitted to the cable 4 having the cable length L [m] via the damping resistor 3. This cable 4 connects the central processing unit 1 and the display device unit 5 in order to transmit an electric signal such as an enable signal to the display device unit 5 arranged at a distance from the central processing unit 1. ing.

The enable signal transmitted from the central processing unit 1 is input via the cable 4 to the other end of the capacitor 5 whose one end constituting the signal noise reduction circuit is grounded in the display device unit 5. .. Further, the enable signal input terminal Ei of the liquid crystal display 7 is connected to the other end of the capacitor 5.

The enable signal has the noise generated in the cable 4 smoothed by the charging / discharging action of the capacitor 5 and the enable input terminal E of the liquid crystal display 7.
It is designed to be input to i.

[0006]

In the liquid crystal display, in order to capture the rising and falling signals of the enable signal, the level of the enable signal must change within the threshold level range within a specified time.

However, when the capacitance of the capacitor 5 is large, the signal waveform is also smoothed at the rising or falling of the enable signal, so that the rising and falling waveforms are also smoothed, and thus the rising The time and fall time will be extended. Then, there is a possibility that the rise time or fall time of the enable signal may not fall within the specified time for capturing the rise and fall of the signal of the liquid crystal display 7. In such a case, since the falling edge and the falling edge of the enable signal are not taken in, the data transmitted on the transmitting side is transmitted to the liquid crystal display 7.
There is a problem that can not be displayed accurately in.

Further, when the capacitance of the capacitor is small, there is a problem that the data transmitted on the transmission side cannot be displayed accurately on the liquid crystal display 7 because the noise cannot be sufficiently smoothed.

Therefore, according to the present invention, the noise generated through the cable can be reduced by the capacitor, and the long rising and falling times of the electric signal can be shortened by the capacitor, so that accurate signal transmission is guaranteed. It is an object of the present invention to provide a signal noise reduction circuit that operates.

[0010]

According to the present invention, there is provided a capacitor having one end grounded, a first Schmitt trigger circuit having an input terminal connected to the other end of the capacitor, and the first Schmitt trigger circuit.
And a second Schmitt trigger circuit having an input terminal connected to the output terminal of the Schmitt trigger circuit, and the electric signal input via the cable is input to the connection point between the capacitor and the first Schmitt trigger circuit, An electric signal is output from the output terminal of the second Schmitt trigger circuit.

[0011]

In the present invention having such a structure, the noise generated in the electric signal transmitted through the cable is smoothed by the capacitor.

The electric signal whose noise is smoothed is inverted by the first Schmitt trigger circuit and converted into a rectangular wave,
Further, it is inverted by the second Schmitt trigger circuit, converted into a rectangular wave, and output.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the central processing unit is applied to control the display unit arranged at a distance. In FIG. 1, 11 is a central processing unit, and the central processing unit 11 has a gate array. An enable signal output terminal Eo of 12 outputs an enable signal for the display device. This enable signal is applied to damping resistor 1
3 is transmitted to the cable 14 having the cable length L [m]. The cable 14 is used to transmit an electric signal such as an enable signal to the display device section 15 arranged at a distance from the central processing unit 11.
And the display unit 15 are connected to each other.

The enable signal transmitted from the central processing unit 11 is input to the other end of the capacitor 16 whose one end is grounded and the first Schmitt trigger circuit 17 in the display unit 15 through the cable 14. It is input to the connection point with the terminal. This first Schmitt trigger circuit 1
The output terminal of the second Schmitt trigger circuit 1 is connected to the input terminal of the second Schmitt trigger circuit 18.
8 output terminals are connected to the enable signal input terminal Ei of the liquid crystal display 19.

In this embodiment having such a configuration, the enable signal output from the enable signal output terminal Eo of the gate array 12 provided in the central processing unit 11 is
For example, at the detection point S1, the signal is output as a noise-free signal as shown in FIG. The waveform a is an example of a signal that maintains a low level, and the waveform b is an example of a falling signal. Of course, the enable signal also includes a signal that maintains a high level and a rising signal.

The output enable signal is transmitted to the cable 14 via the damping resistor 13. In this cable 14, noise is generated due to electromagnetic influence around the cable. At this time, as for the waveform a and the waveform b at the detection point S1, an irregular noise waveform is partially seen at the detection point S2 as shown in FIG.

The noise generated in the cable 14 is smoothed by the capacitor 16 provided in the display device section 15, and becomes smooth at the detection point S3 as shown in FIG. On the other hand, as shown in the waveform b, the falling signal has a gentle slope and a long falling time.

The enable signal whose noise is smoothed by the capacitor 16 is input to the input terminal of the first Schmitt trigger circuit 17, converted into an inverted rectangular wave, and output from the output terminal thereof. At the detection point S4, as shown in FIG. 2, the waveform a becomes a waveform in which noise is completely disappeared and the high level is maintained, and the waveform b is completely depleted in noise. The waveform is inverted.

Then, by the second Schmitt trigger circuit 18, at the detection point S5, as shown in FIG.
The inverted waveform of the waveform seen in FIG.
It can be seen that almost the same waveform can be obtained for the waveform of 1.

As described above, according to the present embodiment, the noise can be smoothed by the capacitor 16, and the fall time and the rise time extended by the capacitor of the enable signal can be used for the first and second Schmitt trigger circuits 1.
It can be shortened by 7,18.

Moreover, the noise waveform that could not be completely reduced by the capacitor 16 can be completely eliminated by using the first and second Schmitt trigger circuits 17 and 18.

Therefore, a signal having no noise on the liquid crystal display 19 allows the rise time and rise time of the signal to be within the specified time for capturing the signal of the liquid crystal display 19.
An accurate display can be made based on the transmitted data.

In addition, this signal noise reduction circuit includes one capacitor 16 and two Schmitt trigger circuits 17 and 1.
In addition, even if the noise reduction by the capacitor is not perfect, the noise is completely reduced by the Schmitt trigger circuit and a large capacity capacitor is not required. is there.

[0024]

As described in detail above, according to the present invention,
Provides a signal noise reduction circuit that ensures accurate signal transmission by reducing the noise generated via the cable with a capacitor, and further shortening the rise time and fall time of the electrical signal that is extended by the capacitor. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of a main part of an embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms detected at respective detection points S1 to S5 of the same embodiment.

FIG. 3 is a diagram showing a circuit configuration of a main part of a conventional example.

[Explanation of symbols]

11 ... Central processing part, 14 ... Cable, 16 ... Capacitor, 17 ... 1st Schmitt trigger circuit, 18 ... 2nd Schmitt trigger circuit, 19 ... Liquid crystal display.

Claims (1)

[Claims] 1. A capacitor having one end grounded, a first Schmitt trigger circuit having an input terminal connected to the other end of the capacitor, and an input terminal connected to an output terminal of the first Schmitt trigger circuit. A second Schmitt trigger circuit is provided, and an electric signal input via a cable is input to a connection point between the capacitor and the first Schmitt trigger circuit, and an electric signal is output from an output terminal of the second Schmitt trigger circuit. A signal noise reduction circuit characterized by outputting a signal.