KR100189518B1 - Switching circuit of cable television - Google Patents

Abstract

A circuit for switching the first, second, and third broadcast signals applied at different frequencies in response to a preset external switching signal includes a switch unit for applying a switching signal according to an application state of the switching signal, and the switch unit ( An oscillator and a delay unit connected to 100) and having an oscillator for providing an oscillation frequency for processing color signals of the first, second, and third broadcast signals, and a line delayer for delaying the color signals on a line-by-line basis; A chroma processing IC connected to a delay unit and the switching signal to process the color signal, and connected between the switch unit and the oscillation and delay unit, and the chroma processing unit IC is connected to the 1, 2 and 3 broadcast signals in response to the switching signal. Switching the outputs of the oscillator and the line delay to the corresponding terminals of the chroma processing IC so as to process the color signal according to It consists of a switching IC.

Description

Switching Circuit of Cable Television

1 is a switching circuit diagram according to the present invention

* Explanation of symbols for main parts of the drawings

50: microcomputer 100: switch unit

200: switching IC 250: oscillation and delay unit

300: chroma processing IC

The present invention relates to the switching of three systems (NTSC, PAL-N, PAL-M) of a CTV (Cable Television), and more particularly to a switching circuit suitable for switching the CHROMA portion of the CTV.

In general, the NTSC, PAL-N, and PAL0M send signals are different in frequency and number of horizontal lines per frame. In order to receive these different broadcast signals as one TV, a switching operation is required for processing each video signal. It can be seen.

In the related art, a complicated configuration using bias and ground is used for switching the chroma unit for three systems, and a mechanical switch is used instead of a transmitter. Therefore, there is a problem that noise occurs on the screen during switching. It was very inconvenient to use.

These problems have caused the user to feel the necessity of enabling the system switching to a transmitter (hereinafter referred to as a remote controller) using a microcomputer.

Accordingly, the present invention is to provide a switching circuit that can solve the above conventional problems.

Another object of the present invention is to provide a switching circuit suitable for switching a chroma unit in a CTV.

Still another object of the present invention is to provide a switching circuit capable of improving reception quality and increasing usability.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of the present invention, and is a circuit for switching first, second and third broadcast signals applied at different frequencies in response to a preset external switching signal. A microcomputer 50 for generating a switching signal according to a user's selection signal received from a remote controller (not shown), a switch unit 100 for applying a switching signal according to an application state of the switching signal, and the switch unit ( An oscillator and delay unit (250) connected to 100 and having an oscillator for providing an oscillation frequency for processing the color signals of the first, second, and third broadcast signals, and a line delay unit for delaying the color signals on a line basis; A chroma processing IC 300 connected to the oscillation and delay unit 250 and the switching signal to process the color signal, and connected between the switch unit 100 and the oscillation and delay unit 250, and the switching signal. In response, the chroma processing unit IC 300 outputs the oscillator and the line delay unit to the corresponding terminals of the chroma processing IC 300 so that the chroma processing unit 300 can process the color signals according to the first, second, and third broadcast signals. It is composed of a switching IC (200) for each switching.

Here, the first, second and third broadcast signals are composed of NTSC, PAL-N and PAL-M signals.

The switch unit 100 includes first and second transistors that turn on or off according to the switching state.

The switching IC 200 switches the terminal 1 or the terminal 2 of the input terminal to the output terminal 15 according to the switching signal of the second transistor Q ₂ , and also connects the terminal 12 to the terminal 13. ) Or switch to terminal (14).

In addition, the 1-3 oscillators (X ₁ -X ₂ ) of the oscillation and delay unit 250 provide clocks for processing PAL-M, PAL-N, and NTSC broadcast signals, respectively. 251 and 252 are line delays outputting a color (or chroma) signal by one horizontal line delay.

The chroma processing IC 300 employs a known TA-8659 IC manufactured by Toshiba, Japan.

In addition, the resistors R1-R14, which are not described, are resistors for protection or voltage drop, and the capacitors C1-C4 are coupling and charging capacitors.

An embodiment of the preferred operation of the present invention will be described in detail based on the above configuration.

First, the present invention can remove the screen noise and simplify the circuit configuration. The present invention is configured as shown in FIG. 1, and for convenience of description, the micom 150 and the PAL-N, PAL-M, and NTSC broadcast inputs. The conditions of the terminals of the chroma processing IC 300 were defined as shown in Table-1 below.

TABLE 1

Referring to the conditions of Table-1 and FIG. 1, when NTSC is selected as the transmitter, high is always input to terminal C of the chroma processing IC 300 of FIG. Since the output of the port B of the microcomputer is Low as shown in Table-1, Low is applied. At this time, the terminal i outputs an NTSC crystal drive, and accordingly, the third oscillator X ₃ is oscillated and input to the terminal h. Therefore, the CHROMA signal in NTSC is processed.

On the other hand, when PAL-N is selected, the terminal c is always in a high state, and high is applied to the terminals a and b since the output of the port B of the microcomputer is high as shown in Table-1. At this time, since the output of the port A of the microcomputer is high, the second transistor Q ₂ of the switch unit 100 is turned on, and thus the terminals 9 and 10 of the switching IC 200 are low. Since the oscillation drive output of the terminal i of the chroma IC 300 oscillates the second oscillator X ₂ , which is a PAL-N oscillator, the terminals 1 and 15 of the switching IC 200 are in a state. Is switched. The oscillation output through the terminal 15 is input to the terminal g, while the chroma signal output from the terminal d is transmitted through the delay line 252 for PAL-N and the terminal 12 and ( 14) is switched. The signal of the terminal 14 is input to the terminal f of the chroma processing IC 300 through the capacitor C3 to process the chroma signal of the PAL-N signal.

In a similar manner, when the PAL-M is selected, the terminal (c) is continuously high and the terminals (a, b) are input high because the output of the port (B) of the microcomputer is high. Since the output of A) is low, the second transistor Q ₂ is turned off, and the terminals 9 and 10 of the switching IC 200 are in a high state, and the terminal 15 is switched to the terminal 1. At this time, the oscillation drive output output from the terminal i is input to the terminal g through the terminal 15 by oscillating the first oscillator X ₁ , which is an oscillator for PAL-M, and the terminal 13 is The chroma signal connected to the terminal 14 and passing through the PAL-M delay unit 251 is input to the terminal through the terminal 14 and the capacitor C3 to process the chroma signal of the PAL-M.

That is, it can be seen that the circuit as described above is operated as a chroma processing circuit applied to the switching of three systems (PAL-N, PAL-M, NTSC).

As described above, the present invention has the advantage of implementing a switching circuit suitable for chroma signal processing of CTV, and also has the advantage of having a reception quality and a simple circuit configuration.

Claims (3)

(Correction) A cable television switching circuit for switching first, second, and third broadcast signals applied at different frequencies in response to a preset external switching signal, wherein the switching signal is applied according to an application state of the switching signal. An oscillator connected to the switch unit 100 and the switch unit 100 to provide an oscillation frequency for processing the color signals of the first, second and third broadcast signals, respectively, and a line for delaying the color signals in line units. An oscillation and delay unit 250 having a delay unit, a chroma processing IC 300 connected to the oscillation and delay unit 250 and the switching signal to process the color signal, the switch unit and the oscillation and delay unit ( The oscillator and the line delay so that the chroma processing unit IC 300 can process the color signals according to the 1, 2 and 3 broadcast signals in response to the switching signal. And a switching IC (200) for respectively switching the output of the device to a corresponding terminal of the chroma processing IC (300). (Correction) The circuit according to claim 1, wherein the first, second and third broadcast signals are NTSC, PAL-N and PAL-M signals. (Correction) The circuit according to claim 1, wherein the switch unit (100) comprises first and second transistors which turn on or off according to the switching state.