JPS6065687A - Catv receiver - Google Patents

Abstract

PURPOSE:To obtain a stable video signal by inputting an output signal of an integration circuit to a microprocessor and using its output signal to switch an AGC circuit in a CATV receiver. CONSTITUTION:A scramble decoding signal is obtained by a detecting circuit 18, the signal is subject to waveform shaping 19, the result is converted into a DC voltage by the integration circuit 20 and the voltage is applied to the microprocessor (CPU)21. The CPU21 detects the broadcast system by using an inputted signal thereto and sends a switching signal to an AGC switching circuit 17 accordingly. The AGC circuit 16 acts like the peak AGC system at a general broadcast and like the keyed AGC system in a charging broadcast by using the switching signal. Thus, the gain control of an RF or an IF amplifier circuit is performed in both the general broadcast and the charging broadcast.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a CATVfl+ receiver with an AGC diversion path.

Conventional Structure and Problems There are two types of CATV broadcasting: general broadcasting and paid broadcasting (broadcasting for which you pay an additional fee in addition to your subscription fee). In paid broadcasting, video is scrambled using various methods to prevent eavesdropping by subscribers other than the subscriber. However, depending on the scrambling method, wiretapping may be easier.

In the scramble method, which makes eavesdropping difficult.

For example, there are methods such as shifting the video synchronization signal level or randomly inverting the video signal.

For these reasons, if the same AGC circuit is used for both general broadcasting and billing broadcasting in a CATV receiver,
Problems such as changes in contrast occur, resulting in the disadvantage that clear images cannot be obtained.

Purpose of the Invention The present invention is capable of operating an AGC circuit well in both general broadcasting and charge-based broadcasting, and is capable of stably receiving good, clear images in both cases. The purpose is to provide a CA, TV receiver that can perform the following functions.

Structure of the Invention In the present invention, it is possible to detect whether a received signal is a general broadcast or a billing broadcast and to switch the AGC circuit accordingly. By generating a pulse signal and using this pulse signal to switch the AGC circuit, an AGC circuit that can obtain stable images for both general broadcasting and billing broadcasting is realized.

DESCRIPTION OF EMBODIMENTS The following describes a CATV in an embodiment of the present invention based on the drawings.
Explain the receiver.

FIG. 1 is a block diagram of a general AG'C circuit.

11d: CATV amplified here by the IF amplifier circuit
The IF multiplied signal of the received signal is converted into a composite video signal by the video detection circuit 2. The composite video signal is amplified by a video amplification circuit 3. For the purpose of keeping the composite video signal constant even if the reception level fluctuates, the composite video signal is used to connect the IF-A.
A control voltage for controlling the gain of the IF amplifier circuit is created in the GC circuit 4 to control the gain of the IF amplifier circuit 1, and further,
By controlling the gain of the RF amplifier circuit together with the RFAGC circuit 5, the composite video signal voltage is always kept constant.

Figure 2 shows the RF amplifier circuit 1 that responds to fluctuations in the input signal level.
This figure shows changes in the gain 6 of the IF amplifier circuit and the gain 7 of the IF amplifier circuit.

FIG. 3 shows an overall block diagram of a CATV receiver according to an embodiment of the present invention, in which the input signal selected by the tune undergoes frequency conversion, and the IF amplification circuit 10 amplifies the IF multiplied signal. . A composite video signal is obtained from the amplified IF multiplied signal in a video detection circuit 11. Furthermore, it is amplified by the first video amplification circuit 12 f15. First video amplification circuit 1
The synthesized video signal from 2 is sent to the IF amplification circuit 1 by the AGC circuit 16.
A control voltage is created to control the gain of 0.

Here, the waveform of the U: composite video signal is different between general broadcasting and billing broadcasting. In other words, as mentioned above, in general broadcasting, a composite video signal that can be received by all CATV subscribers is sent, but in paid broadcasting, the composite video signal is scrambled so that only subscribers can receive it. has been made into

The scrambled composite video signal has a waveform as shown in a of FIG. 5, for example, and the waveform of a of FIG.
0 is shifted and the video signals 31, 32 . Sync signal 3
0 is randomly flipped. Therefore, it is not possible to obtain a constant video signal using the same AGC circuit for general broadcasting and billing broadcasting.

To this end, in this receiver, the AGC circuit 16 is switched between two types of AGC systems.

In billing broadcasting, a scramble decoding signal is obtained by a detection circuit 18 which extracts the scramble decoding signal from the IF multiplied signal, and a waveform shaping circuit 19 shapes the waveform of the scramble decoding signal. The waveform-shaped scramble decoding signal is converted into a DC voltage by the integrating circuit 20, and then
The data is sent to the processor 21 (hereinafter referred to as CPU). The CPU 21 detects the broadcast system based on the input signal and sends a switching signal to the AGC switching circuit 17 accordingly. In the case of general broadcasting, the CPU 21 sends a high level switching signal to the AGC switching circuit 17.

The AGC switching circuit 17 sends a low level to the AGC circuit 16, and the AGC circuit 16 operates as a peak AGC method.
The amplification gain and the gain of the IF amplification circuit 10 are controlled to keep the video signal output constant.

In the case of paid broadcasting, CPU 217) and A
A low level signal is sent to the GC switching circuit 17, and the AGC
The switching circuit 17 sends a high level to the AGC circuit 16 to set the AGC circuit 16 to the keyed AGC system. key A
The pulse signal necessary for the GC method is a pulse signal Vl obtained by the pulse signal generation circuit 22 from the scramble decoded signal obtained by the waveform shaping circuit 19, and has a waveform as shown in FIG. 5b, and the timing is as shown in FIG. In other words, in the scrambled composite video signal [Fig. 5a], the peak AG
In the C method, since the synchronization signal 30 is inverted, the control voltage of the AGC circuit 16 fluctuates each time the synchronization signal 30 is inverted, resulting in changes in the RF amplification gain and the gain of the IF amplification circuit 10. Since the signal changes and problems such as changing the contrast of the TV screen occur, this receiver uses the pulse signal shown in Figure 5b for charge broadcasting.
AGC is performed using the keyed AGC method according to the timing shown in Figure 5.
A control voltage is generated in a circuit 16 to control the RF amplification gain and the gain of the IF amplification circuit 10 to keep the composite video signal constant.

13 is a 4.5MHz audio trap circuit, and 92
This prevents interference from audio signals such as 0 KHz beats.

14 is a second video amplification circuit, and the composite video signal is increased by 1@ only in the case of general broadcasting. In the case of fee-charging broadcasting, it passes through the third video amplification and video processing circuit 15 and is sent to the CPU 2.
The composite video signal copy is restored to its original state by the control signal from 1.

FIG. 4 is a configuration diagram of the AGC method switching circuit 17.
It should be noted that m=description of the same reference numerals will be omitted.

25 is an AGC switching determination circuit, and the switch circuit 26 is controlled by this output signal. Further, 27 is a peak AGC comparison voltage circuit, and 28 is a keyed AGC comparison voltage circuit. In the peak AGC method, the switch circuit 26
The GC circuit 16 and the peak AGC comparison voltage circuit 27 are electrically connected. In addition, in the keyed AGC method, the switch circuit 26 includes the AGC circuit 16 and the keyed AGC comparison voltage circuit 28.
It conducts with.

FIG. 6 is a circuit diagram of the AGC switching determination circuit 25.

35 is a NOR gate to which a signal from the CPU 21 and a signal for fixing the AGC method only for a few seconds during channel selection are input, and the output signal of the NOR gate 35 controls the switch circuit 26 by the inverter gate 1.36. I'm getting a signal to do that. Furthermore, the AGC circuit 16 is controlled by the NOR gate 37.
The AGC method is switched by sending a signal to

Effects of the Invention As is clear from the above explanation, according to the present invention, AG
By dividing the C system into general broadcasting and charge-based broadcasting, and switching to the peak AGC method for general broadcasting and the keyed AGC method by generating a pulse signal from the scramble decoding signal for chargeable broadcasting, general broadcasting 9 Appropriate for both paid broadcasting, RF amplification circuit, I
This has the excellent effect of being able to control the gain of the F amplifier circuit and obtain a stable video signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a general AGC circuit, FIG. 2 is a characteristic diagram showing the operation of the circuit in FIG. 1, FIG. 3 is a circuit block diagram of a CATV receiver according to an embodiment of the present invention, and FIG. The diagram is the AG
FIG. 3 is a configuration diagram of a C-scheme switching circuit. FIG. 5 is a waveform diagram of the video signal and the signal for billing broadcasting, and FIG. 6 is a circuit diagram of the AGC switching determination circuit. 16-AGC circuit, 17...Switching circuit, 18...Detection circuit, 19...Waveform shaping circuit, 20...Integrator circuit, 21...Microprocessor, 22...
-Pulse generation circuit.

Claims (1)

[Claims] a detection circuit that detects a scramble decoded signal, a waveform shaping circuit that shapes the output signal of the detection circuit, and a pulse generation circuit that generates a signal using the shaped output signal;
CATV equipment characterized by comprising an integrating circuit that integrates the shaped output signal, and a switching circuit that receives an output signal of the integrating circuit into a microprocessor and switches an AGC circuit based on the output signal of the microprocessor. Receiving machine.