JPS62245733A - Unbalanced transmission circuit - Google Patents

Abstract

PURPOSE:To obtain a high quality picture regardless of transmission range by adding an output of a sender side TTL and an output being the differentiation of the output of the TTL by a differentiation circuit and sending the sum to a transmission line so as to attain the long range transmission of an RGB picture signal. CONSTITUTION:The differentiation circuit comprising a capacitor 6 and a resistor 7 is connected to the output of the sender side TTL 1 and the end of turn of the secondary winding of a transformer 5 is connected. The start of turn of the primary winding of the transformer 5 is connected to the output of the sender TTL 1, and the end of turn is used as the transmission output and the start of turn of the secondary winding is connected to a reference potential. The differentiation circuit comprising the capacitor 6 and the resistor 7 differentiates the output of the sender side TTL 1 and the transformer 5 has a function adding the output of the sender TTL 1 and the output of the differentiation circuit. Thus, a received waveform is close to a square wave, the long range transmission of the RGB picture signal is attained and high quality picture is obtained independently of the transmission range.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to RGB (Red Green 31u
e) This relates to an unbalanced transmission circuit suitable for long-distance transmission of RGB input signals of a television set having an input.

<Prior art> Television sets that support RGB input have red (R),
Green (G), blue (8) color signals,! ! It has five dialects for direct line signals and horizontal synchronization signals.

Each input signal is Ttransister T
It is a binary signal equivalent to the output level of the Ransister 1-09iC) circuit, and can be directly driven by a general-purpose TTL circuit, which is convenient. However, this TT
Since the L output level is a low voltage, the distance over which the signal can be transmitted while maintaining sufficient resolution is short, at most 10m8.
It was degree.

FIG. 5 shows an example of a conventional unbalanced transmission circuit that performs such a transmission operation.

This unbalanced transmission circuit, for example, transmits FJfl of color signal @R.
1 is a transmitting side TTL, 2u is a receiving TTL of the receiving side TV set, 3 is a constant voltage diode that protects the receiving TTL from overvoltage surges, and 4 is a transmission line, for example, a pair of AM.

FIG. 6 shows a waveform diagram representing the operation when transmitting and receiving the color signal R on this n path.

All (△), (B), and (C) represent the waveforms of point A, point 8, and point 0 in the @ path shown in FIG.
As for the waveforms at points 8 and 0, *Kan indicates the case where the transmission distance is long, and the broken line indicates the case where the transmission distance is short.

Furthermore, the waveforms at point B and point 0 are aligned in phase with the transmitted waveform at point A by correcting the propagation delay time depending on the transmission distance. A
The dashed line in the point waveform and 8-point waveform indicates the received T T i 2
It represents the threshold level of 0.8V according to the standard.
~2V, but normally it is about 1.2V.

Now, in the circuit shown in FIG.
Transmit the pattern of the M I N binary signal.

The transmitting side TTL1 converts the internal signal into a TTL level and sends it to the transmission line 4. Received TTL2 is the transmitted TT
The L level image pattern is converted into an internal signal within this TV set and used as a luminance signal.

On the receiving side, the overvoltage surge is limited to a constant voltage υj and the reception T
It is common to include a constant voltage diode 3 that protects TL2.

When the transmitted waveform has a pattern as shown in Figure 6 (A>), the 8-point received waveform is as shown by the broken line when the transmission distance is short,
As the transmission distance increases, the waveform becomes thicker and distorted, becoming like a solid line. As a result, since the threshold level of the reception TTL2 is low, there is a significant delay in the transition from the B point waveform ゛TODO' to "L II", and the waveform of the output (C) of the reception TTL2 is after the bright point. This generates a phenomenon in which the edges are extended and the dark areas are collapsed.In addition, the threshold level of reception TTL2 has individual differences for R, G, and B, and the reception waveform (B
) is not steep, the delay at the trailing edge of the 38 bright spots tends to vary, resulting in color shift or blurring at the edges of the image.
This was causing low quality images.

In this way, the conventional image information transmission using TTL level RGBI signals could only be used for transmission between very close devices.

<Problem to be solved by the invention> The problem to be solved by the invention is to enable long-distance transmission of RGB image signals, and its purpose is to obtain a quality image regardless of the transmission distance. The objective is to realize an unbalanced transmission circuit that can

Means for Solving the Problems The present invention solves the above problems by changing the reference potential to II L
II level output, a drive circuit that sets a positive voltage higher than the TTL threshold voltage to "H" level, a differentiation circuit that differentiates the transmission output of this drive circuit, and adds the output of the drive circuit and the output of the differentiation circuit. This is an unbalanced transmission circuit which has a boosting means and uses the output of the boosting means as a transmission signal.

Effect> The unbalanced transmission circuit of the present invention adds the output of the transmitting side TTL and the output obtained by differentiating this output with a differentiating circuit and sends the result to the transmission line, so the received waveform becomes close to a square wave. .

<Embodiment> FIG. 1 shows an example of an unbalanced transmission circuit in which the present invention is implemented.

In this figure, components having the same symbols as the conventional circuit shown in FIG. 4 have the same functions.

In the unbalanced transmission circuit of the present invention, a differentiating circuit consisting of a capacitor 6 and a resistor 7 is connected to the output side of the transmitting side TTLI, and the end of the secondary winding of the transformer 5 is further connected. The transformer 5 connects the beginning of the primary winding to the output side of the transmission side TTL1, and uses the end of the winding as a transmission output. The beginning of the secondary winding is connected to a reference potential.

A differentiating circuit consisting of a capacitor 6 and a resistor 7 is connected to the transmitting side TT.
The transformer 5 has a function of differentiating the output of L1 and adding the output of the transmitting side TTL1 and the output of the differentiating circuit.

Note that the time constant of the differentiating circuit including the capacitor 6 and the resistor 7 is selected to be shorter than the time corresponding to the minimum resolution of the display Wit1. Further, the inductance of the transformer 5 is set to a value that does not cause ringing, taking into consideration the characteristics of the peripheral circuits.

The operation of the unbalanced transmission circuit of the present invention constructed in this way will be explained using FIG. 2.

FIG. 2 shows each part (Ao >, (A+), (A)) when an image signal is transmitted over a long distance from the transmitting side.

These are the output waveforms of (B) and (C).

In this figure, a differential waveform corresponding to the output of the transmitting side TTL1 at point Ao is generated at point A+, and is applied to the secondary winding of transformer 5. As a result, a similar waveform is induced in the primary winding, and the waveform obtained by adding the differential waveform to the original image signal at point Ao becomes A
occurs at a point. This output (A) becomes a transmission signal to the receiving TV set.

The output waveform shown at point A is integrated by the line capacitance while propagating on the transmission line (twisted wire pair) 4, and the waveform becomes dull, but since the differential waveform is superimposed on this transmission signal, When transmitting signals over the same distance, receive! The received waveform at the RIB point is closer to a square wave than in the conventional example, and image quality does not deteriorate on the receiving side.

FIG. 3 shows the output waveforms of each section when an image signal is transmitted over a short distance from the transmitting side.

In this figure, the waveform at point A on the transmitting side tends to be the same as that in FIG. 2, but the waveform is limited to a certain voltage or less by the protection diode 3 inserted on the receiving side.

At the same time, the differential waveform at point A1 becomes the waveform shown in the figure, and the resistor 7 constituting the differential circuit is at this time
It functions as a 4-flow limiting resistor and prevents overload on the transmitting side TTL1.

The time constant of the differential element in this circuit is set to be shorter than the minimum resolution of the image, that is, the time corresponding to one dot of a picture or character, and the same effect can be obtained for any image pattern.

In this way, according to this circuit, in a format compatible with TTL level RGB signals, which is a short-distance interface,
It is possible to extend its transmission distance.

FIG. 4 shows another example of implementing the present invention.

In this example, a differentiating circuit including a capacitor 6 and a resistor 7 is driven by an inverter 8 in a phase opposite to that of the transmission signal. Since the differentiating circuit has an opposite phase, the connection of the transformer 5 is reversed from that of the circuit shown in FIG. 1, but the basic operation is the same.

As described above, the unbalanced transmission circuit of the present invention has TTL
TVt with level RGB input terminal? It is possible to drive the set from a long distance without deteriorating the image, and if the input ml is at the T"l level, it is possible to drive the same long distance even if it is not a TV set. In addition, the elements used as the drive elements are made of special materials. Instead, common TTL can be used.

<Effects of the Invention> The unbalanced transmission circuit of the present invention adds the output of the transmitting side TTL and the output obtained by differentiating this output with a differentiating circuit, and sends the result to the transmission line, so that the received waveform is close to a square wave. Therefore, R
An unbalanced transmission circuit that can enable long-distance transmission of GB image signals and obtain high-quality images regardless of the transmission distance can be developed.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an unbalanced transmission circuit embodying the present invention, Figs. 2 and 3 are waveform diagrams showing the operation of the unbalanced transmission circuit embodying the present invention, and Fig. 4 shows another unbalanced transmission circuit embodying the present invention. FIG. 5 is a block diagram showing an example of a balanced transmission circuit, FIG. 5 is a block diagram showing a conventional unbalanced transmission circuit, and FIG. 6 is a waveform diagram showing the operation of the conventional unbalanced transmission circuit. 1... Sending side TTL, 2... Receiving TTL, 3...
Protection diode, 4... Transmission line, 5... Transformer, 6... Capacitor, 7... Resistor, 8... Inverter. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] a drive circuit that outputs a reference potential at "L" level and outputs a positive voltage equal to or higher than the TTL threshold voltage as "H"level;
An unbalanced transmission circuit comprising: a differentiating circuit for differentiating a transmission output of the driving circuit; and an adding means for adding the output of the driving circuit and the output of the differentiating circuit, and using the output of the adding means as a transmission signal.