JPH06326941A - Television signal receiver - Google Patents

Abstract

PURPOSE:To prevent the generation of malfunction due to a harmonic noise generated in an AGC circuit. CONSTITUTION:An RF signal in a MUSE signal inputted from an input terminal 1 is frequency-converted into an IF signal by a tuner 2, the IF signal is detected by a video detecting circuit 4 through an IF amplifier 3, the detected signal is amplified by an image amplifier 5, and the amplified signal is outputted from an output terminal 6 as a MUSE base band signal. A part of an output from the circuit 4 is attenuated at its harmonic noise by a low pass filter(LPF) 9 and supplied to an RF-AGC circuit 7 to prepare RF-AGC control voltage. Similarly IF-AGC control voltage is also prepared. These AGC control voltages are used for controlling the RF amplification of the tuner 2 and the gain of the IF amplifier 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to CATV transmitted A
The present invention relates to a television signal receiving apparatus most suitable for a CATV receiver that receives an M-modulated MUSE signal.

[0002]

2. Description of the Related Art As a method of transmitting a MUSE signal, 1
Sanyo Giho Vol.24 No.1 "MUSE-" issued in February 992
VSB. There is CATV transmission by the AM system as described in "AM system CATV reception system".

The AGC circuit in the receiver of the above system has a structure as shown in FIG. That is, the RF signal input from the input terminal 1 is frequency-converted into an IF signal by the tuner 2, detected by the video detection circuit 4 via the IF amplifier 3, amplified by the video amplifier 5, and output as a MUSE baseband signal. It is output from 6. A part of the output of the video detection circuit 4 is composed of a reference voltage generating circuit 71, a comparator 71 for comparing the reference voltage with the input signal level, and a low pass filter 72 for smoothing the comparison output.
It is supplied to the F-AGC circuit 7 and an RF-AGC control voltage is created. Similarly, an IF-AGC control voltage is also created.
These AGC control voltages control the gains of the RF amplifier and the IF amplifier 3 of the tuner 2. Then, these AGC circuits, as shown in FIG.
Is a peak value type AGC for comparing the level of the peak (lower end) of the frame pulse or the video signal with a reference level and controlling the amplifier with the comparison output.

[0004]

On the other hand, in the above CATV system, the MU on the transmission side (head end) is used.
Since the SE signal source is an FM mode signal that has been subjected to emphasis suitable for normal FM modulation, the SE signal source has an amplitude of 1 to 8 MH having an amplitude equal to or higher than the peak value level of the video signal as shown in FIG.
Harmonic noise of z may be mixed in. This harmonic noise causes the AGC to malfunction.

The present invention provides a television signal receiving apparatus which solves the above drawbacks.

[0006]

The present invention is directed to a received RF.
A tuner that converts a signal into an IF signal, an IF amplifier that amplifies this IF signal, a video detection circuit that detects the output of this IF amplifier, and an RF-AGC that controls the gain of the RF amplifier of the tuner by this video detection output. In a television signal receiving device including a circuit and an IF-AGC circuit that controls the gain of the IF amplifier by the video detection output, a low-pass filter that attenuates a harmonic component of the video detection output is provided, and the low-pass filter output To the RF-AGC circuit and / or the IF-AGC circuit.

[0007]

In the present invention, since the harmonic noise mixed in the video detection output is attenuated by the low pass filter,
The AGC circuit does not malfunction due to the harmonic noise.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A television signal receiving apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of the apparatus of this embodiment, and FIG.
The same parts as those in FIG.

The feature of this embodiment is that the video amplifier 5 and the RF-
A low-pass filter 9 is arranged between the AGC circuit 7 and the IF-AGC circuit 8. This low-pass filter 9 is for attenuating the harmonic noise mixed in the video-detected MUSE signal shown in FIG. 2, and its cutoff frequency is set to 500 kHz. As shown in FIG. 3, the output has a harmonic noise amplitude of 1 in the second line.
Attenuated to be less than the peak level in the flat portion of 2 to 215 samples.

Therefore, the RF-AGC circuit 7 and the IF-A
The GC circuit 8 can detect the DC component of the peak level of the second line or the peak level of the video signal to generate an accurate AGC control voltage.

[0012]

As described above, according to the present invention, in the CATV system, the MU on the transmission side (head end)
Even if the SE signal source is an FM mode signal subjected to emphasis suitable for FM modulation, harmonic noise mixed in the video detection output on the receiving side is attenuated by the low-pass filter. It does not malfunction due to harmonic noise.

[Brief description of drawings]

FIG. 1 is a block diagram of a television signal receiving apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of a MUSE signal before noise attenuation.

FIG. 3 is a diagram showing a waveform of a MUSE signal after noise attenuation.

FIG. 4 is a block diagram of a television signal receiving device in a conventional example.

[Explanation of symbols]

 2 tuner 3 IF amplifier 4 video detection circuit 5 video amplifier 7 RF-AGC circuit 8 IF-AGC circuit 9 low-pass filter

Claims (1)

[Claims] 1. A tuner for converting a received RF signal into an IF signal, an IF amplifier for amplifying the IF signal, a video detection circuit for detecting the output of the IF amplifier, and an RF amplifier of the tuner by the video detection output. Of an RF-AGC circuit that controls the gain of the video signal and an IF-AGC circuit that controls the gain of the IF amplifier by the video detection output, a low-pass filter that attenuates a harmonic component of the video detection output. A filter is provided, and the output of this low-pass filter is the RF
-A television signal receiving device provided to an AGC circuit and / or an IF-AGC circuit.