KR950008281Y1 - Self testing circuit in catv channel demodulator - Google Patents

Abstract

No content.

Description

Self-Diagnosis Circuit of Channel Demodulator for Cable TV

1 is a conventional demodulator circuit diagram.

2 is a circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

1: Tuner part 2: Middle frequency filter

3: Nyquist Filter 4: Audio

5: automatic gain control unit 6: video unit

10: peak detector 11, 12, 13: first to third amplifiers

14, 15, 16: first to third display units 20, 30, 40: first to third detection units

The present invention relates to a channel demodulator for a cable television (hereinafter referred to as CATV), and more particularly to a self-diagnosis circuit of a channel demodulator for CATV that determines whether the automatic gain control unit is normal.

The conventional demodulator circuit shown in FIG. 1 includes a tuner section 21, an intermediate frequency filter 22, a Nyquist filter 23, an audio section 24, and a video section. Since it is a well-known circuit which consists of 26 and the automatic gain control part 25, it demonstrates easily. The automatic gain control unit 25 always outputs a constant video and audio output regardless of the magnitude of the input television signal. In addition, there was a function to cut the audio and video output when the modulation level measurement and the demodulator input a signal lower than the size of the desired television signal. However, this function has a problem in that it is not possible to find this abnormal part quickly when an error occurs in the demodulator with a distorted audio and video signal output.

Accordingly, an object of the present invention is to provide a self-diagnosis circuit of a demodulator capable of determining whether the automatic gain control unit is normal while determining and displaying whether a local oscillation frequency signal is appropriate in a channel demodulator for CATV.

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

FIG. 2 is a circuit diagram of the present invention, in which a tuner part 1 which receives a television signal and converts an intermediate frequency to generate a first local oscillation frequency signal a, and an output signal of the tuner part 1 are inputted. In the intermediate frequency filter (2) for removing signals outside the frequency band, the Nyquist filter (3) for inputting the output signal of the intermediate frequency filter (2) to have an intermediate frequency characteristic, and in the intermediate frequency filter (2) An audio unit 4 for inputting an output intermediate frequency to generate a second local oscillation frequency signal c, the tuner unit 1, the intermediate frequency filter 2, the Nyquist filter 3, and the audio unit ( 4) and the first local oscillation frequency signal a of the tuner section 1, the sync signal b of the Nyquist filter 3, and the audio section 4 of the audio section 4, with automatic gain control of the video section 6; First and second local oscillation signals a1 and c1 for adjusting the automatic gain by receiving the two local oscillation frequency signals c. Automatic gain control from the automatic gain control unit 5 for generating the sync signal b1, the video unit 6 generating a video signal under the control of the automatic gain control unit 5, and the automatic gain control unit 5 from the automatic gain control unit 5. The regulated first and second local oscillation signals a1 and c1 and the sync signal b1 are input to generate the voltages of the first and second local oscillation signals a1 and c1 and the voltage of the sync signal b1 in response thereto. In order to display the detected signal by comparing the output of the peak detector 10 and the voltage of the first local oscillation signal a1 generated from the peak detector 10 with the first reference signal, the resistances R1 and R2 and The voltage and the second reference signal of the first detection unit 20 including the variable resistor R3, the first amplifier 11, and the first display unit 14, the sink signal b1 generated from the peak detector 10. A second detection unit 30 including resistances R4 and R5 and variable resistors R6 and a second amplifier 12 and a second display unit 15 to display the detected signal by comparing with In order to display the detected signal by comparing the voltage of the second local oscillation signal c1 generated from the peak detector 10 with the second reference signal, the resistors R7 and R8 and the variable resistor R9 and the third amplifier are displayed. And a third detection unit 40 consisting of a 12 and a third display unit 16.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings based on the above-described configuration. First, the television signal is input to the tuner unit 1 and converted into an intermediate frequency signal. Thereafter, the intermediate frequency signal is input to the intermediate frequency filter 2 to filter only signals of the intermediate frequency band, and apply the filtered signal to the Nyquist filter 3 and to the audio unit 4 at the same time. In order to perform the above-described process, the tuner unit 1 and the audio unit 4 respectively generate a first local oscillation frequency signal a at 101 MHz and a second local oscillation frequency signal c at 45.75 MHz, respectively. The audio signal of the frequency signal and the base band are extracted. In addition, the first and second local oscillation frequency signals a and c are applied to the automatic gain control unit 5, and the automatic gain control unit 5 includes the tuner unit 1, the intermediate frequency filter 2, and the Nyquist. Automatic gain control of the filter 3, the audio section 4 and the video section 6 is performed respectively. However, in order to perform the above operation normally, the first and second local oscillation frequency signals a and c need to be more than a predetermined size.

That is, the peak detector 10 and the first detector 20 detect the magnitude of the first local oscillation frequency signal a and notify the detection result to the first display unit 14 in the first detector 20. The amplitude of the sync signal b is detected through the peak detector 10 and the second detector 30, and the detection result is notified to the second display unit 15 in the second detector 30, and the peak detector ( 10) and the third detection unit 40 detect the magnitude of the second local oscillation frequency signal c and notify the detection result to the third display unit 16 in the third detection unit 40.

Hereinafter, the detection and display operations of the peak detector 10 and the first to third detectors 20, 30, and 40 will be described in detail. First, when the first and second local oscillation signals a1 and c1 and the sync signal b1 are input to the peak detector 10 through the automatic gain control unit 5, the first and second local oscillation signals a1 and c1 may be input to the peak detector 10. The voltages of the two local oscillation signals a1 and c1 are generated. The voltages of the first and second local oscillation signals a1 and c1 are input to the inverting input terminals of the first and third amplifiers 11 and 13 through the resistors R1 and R7, respectively.

Accordingly, the first amplifier 11 receives the first reference signal, which is the partial voltage of the power supply voltage Vcc, through the resistor R2 and the variable resistor R3 as the non-inverting input terminal, and the inverting input terminal through the resistor R1. The display driving of the first display unit 14 is controlled by comparing the voltage of the first local oscillation signal a1 inputted to the first reference signal with an output voltage corresponding to the comparison state. For example, when the voltage of the first local oscillation signal a1 is greater than the first reference signal, the first display unit 14 may be driven to be displayed in response to the comparison state. The third amplifier 11 receives the third reference signal, which is the partial voltage of the power supply voltage Vcc, as the non-inverting input terminal through the resistor R8 and the variable resistor R9, and the inverting input terminal through the resistor R7. The display driving of the third display unit 16 is controlled by comparing the voltage of the second local oscillation signal c1 inputted to the third reference signal with the output voltage corresponding to the comparison state.

In this case, the first and third reference signals for comparing the magnitudes of the first and second local oscillation signals a1 and c1 are varied by the variable resistor R3 and the variable resistor R9, respectively.

In this case, when the voltage applied to the inverting input terminal is higher than the first or third reference signal, the first or third amplifiers 11 and 13 may compare the output voltage of the “high” state with the first or third amplifier. It is applied to the third display units 14 and 16 so as to be driven to indicate that the magnitude of the first local oscillation signal a1 or the second local oscillation signal c1 is greater than or equal to the reference level. On the contrary, when the voltage applied to the inverting input terminals of the first or third amplifiers 11 and 13 is lower than the first or third reference voltage, the output voltage of the "low" state is determined according to the comparison result. Alternatively, the third display unit 14 or 16 is turned off.

Therefore, the user can easily determine whether there is an abnormality of the local oscillator.

On the other hand, the automatic gain control unit 5 has an integrated circuit for processing an input signal, and the integrated circuit outputs a constant video sync signal b1 when automatically adjusted. The constant sync signal b1 generates a voltage of the sync signal b1 via the peak detector 10. Thereafter, the second amplifier 12 receives the second reference signal, which is the partial voltage of the power supply voltage Vcc, through the resistor R4 and the variable resistor R6 as a non-inverting input terminal, The voltage of the corresponding sink signal b1 is applied to the inverting input terminal through the resistor R4 to compare the voltage levels of the two input voltages and generate and output an output voltage corresponding to the fertilizer state to display the second display unit 15. Controls the display drive of In this case, the second amplifier 12 and the second display unit 15 operate similarly to the first or third amplifiers 11 and 13 and the third display unit 16.

Accordingly, the user may check the level state of the sync signal b1 through the second display unit 15.

In this case, the first to third display units 14, 15, and 16 may use, for example, light emitting devices such as LEDs that emit light.

As described above, the present invention has the advantage that the user can easily detect the abnormal part by judging whether the automatic gain control unit is properly operated while judging and displaying whether the local oscillation frequency signal size is appropriate in the demodulator. .

Claims (1)

In the channel demodulator circuit, a cable television comprising a tuner unit 1, an intermediate frequency filter 2, a Nyquist filter 3, an audio unit 4, an automatic gain control unit 5, and a video unit 6 is provided. The first and second local oscillation signals a1 and c1 and the sync signal b1 that are output from the automatic gain control unit 5 are input, and correspond to the magnitudes of the input signals, respectively. a peak detector 10 for generating and outputting a voltage of c1 and a voltage of the sink signal b1, and a predetermined first reference signal, and applying a voltage of the first local oscillation signal a1 from the peak detector 10; And a first detector 20 for comparing the voltage level with the first reference signal and displaying the comparison result, and a predetermined second reference signal. The voltage of the sink signal b1 is obtained from the peak detector 10. A second detection unit 30 which is applied and compares the voltage level with the second reference signal and displays the comparison result; A third detector 40 having a third reference signal and receiving a voltage of the second local oscillation signal c1 from the peak detector 10 to compare the voltage level with the third reference signal and display the comparison result; Self-diagnosis circuit of a channel demodulator for cable television, characterized in that the configuration.