JPH0355996Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to an RGB signal input circuit in video equipment such as television receivers and color display devices.

<Summary of the invention> This invention is based on an RGB signal input circuit in a video device equipped with an RGB input terminal, which includes a level detection circuit that detects the level of an RGB signal, and a level detection circuit that detects the level of the RGB signal and detects the input of the RGB input terminal according to a control signal of the level detection circuit. Equipped with an impedance conversion circuit that converts impedance and a switch that selects whether or not to go through the level conversion circuit according to the control signal of the level detection circuit, eliminating the need for switching operations due to differences in RGB signal levels. It was made so that it could be done.

<Prior art> In general, RGB input for television receivers, color displays, etc. is not possible with personal computers.
TTL level, character multiplex adapter has analog level. TTL input from an RGB display makes it easy to interface with a personal computer, and the configuration up to the CRT drive circuit is simple. Analog television circuits convert the TTL level of a personal computer. Furthermore, since the signal from the character multiplexing adapter is an analog input, it is necessary to perform DC reproduction and blanking processing at the RGB interface 1F. In this way, as an RGB input signal,
There are two types: TTL level and analog level.

However, since the TTL level is 4 to 5V _pp and the analog level is 1V _pp or less, there is a large level difference between the TTL level and the analog level, so if the TTL level is output from a personal computer, for example, it is necessary to convert the TTL level. Conventionally, an RGB signal input circuit as shown in FIG. 2 has been used. In this RGB signal input circuit, dedicated
Equipped with RGB input terminals 7 and 8, TTL level RGB
After the signal is converted to an analog level by the level conversion circuit 5, the changeover switch 8 is manually switched to output the signal to the processing circuit 6.

<Problems to be solved by the invention> For this reason, the changeover switch must be manually changed each time depending on the level of the RGB signal, resulting in a problem that the operation becomes complicated.

<Means for solving the problem> The RGB signal input circuit of this invention includes a level detection circuit that detects the level of the RGB signal, and converts the input impedance of the RGB input terminal according to a control signal of the level detection circuit. and a changeover switch that selects whether or not to go through the level conversion circuit in accordance with the control signal of the level detection circuit.

<Operation> Therefore, the input impedance and signal level can be automatically adjusted according to the level of the RGB signal.

<Embodiment> FIG. 1 shows the circuit configuration of an RGB signal input circuit according to an embodiment of the present invention. In this diagram,
1 is an input terminal common to TTL level and analog level. 2 is an input signal level detection circuit that determines whether the signal input from input terminal 1 is a TTL level or an analog level and outputs a corresponding control signal, and 3 is an output signal from level detection circuit 2. 4 is an impedance conversion circuit composed of a transistor Tr ₁ and a resistor R _1. The base of this transistor Tr ₁ is connected to the control output of the level detection circuit 2, and the collector is connected to the control output of the level detection circuit 2. is connected to input terminal 1, and its emitter is grounded via resistor _R1 . 5 is a level conversion circuit that converts a TTL level signal to an analog level signal, 6 is a processing circuit for displaying an RGB signal on a CRT, and the input of this processing circuit 6 is the analog side of the changeover switch 3. Output and level conversion circuit 5
connected to the output of

Next, the operation of the automatic level conversion circuit in the case of TTL level and analog level input will be explained.

(a) When using TTL level input 5V _PP (Peak to peak) TTL to input terminal 1
When a level signal is input, the level detection circuit 2 determines that the input signal is a TTL level, and accordingly outputs a control signal to switch the changeover switch 3 to the TTL side, and also outputs a control signal to switch the changeover switch 3 to the TTL side. The base potential of transistor Tr ₁ is set to a low level so that the impedance is high. Therefore, the input impedance of input terminal 1 is suitable for TTL level signals.
After that, this TTL level signal is converted into a signal similar to an analog level signal by a level conversion circuit 5.
It is converted to a level of 1.0V _PP and output to the processing circuit 6.

(b) For analog input When a 1V _PP analog level signal is input to input terminal 1, level detection circuit 2 determines that the input signal is at analog level, and accordingly switches switch 3 to analog At the same time, the base potential of the transistor Tr ₁ is set to a high level so that the impedance of the impedance conversion circuit 4 becomes low. Therefore, the input impedance of input terminal 1 is suitable for analog level signals. Thereafter, this analog level signal is output to the processing circuit 6 without level conversion.

<Effects of the invention> As explained above, according to the invention, even if the level difference between the TTL level and the analog level is large, the level of the RGB input signal can be automatically adjusted with a simple circuit configuration. Furthermore, since the input impedance is automatically switched, impedance matching can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an RGB signal input circuit according to an embodiment of this invention, and FIG. 2 is a circuit diagram of a conventional RGB signal input circuit. 1... Input terminal, 2... Input signal level detection circuit, 3... Changeover switch, 4... Impedance conversion circuit, 5... Level conversion circuit.

Claims (1)

[Scope of utility model registration request] a level detection circuit that detects whether the level of the RGB signal input from the RGB input terminal is a TTL level or an analog level;
The RGB signal changes the input impedance of the input terminal.
an impedance conversion circuit that converts to high impedance when the RGB signal is at TTL level and to low impedance when the RGB signal is at analog level; It consists of a changeover switch that outputs the RGB signal to the RGB signal processing circuit via a level conversion circuit when the RGB signal is at TTL level, and outputs it directly to the RGB signal processing circuit when the RGB signal is at analog level. RGB signal input circuit.