JPH0322644A - Pilot signal eliminating system - Google Patents

Abstract

PURPOSE:To eliminate the need for the adjustment of the addition rate of triangular waves by controlling an elimination signal so that a pilot signal is completely eliminated. CONSTITUTION:A level detection circuit 11 is connected to an output terminal 14 and the output of the level detection circuit 11 is connected to a comparator 10, the output of the level detection circuit 12 with no input is connected to the comparator, as well which compares the output of the level detection circuit 11 with the output of the level detection circuit 12 and the amplification factor of a variable gain amplifier 6 is controlled with its difference. Thus, a pilot elimination signal level at the output terminal 14 is operated to be the input of the level detection circuit 12, i.e., no signal. Thus, a stereoscopic signal at the output terminal 14 from which a pilot signal component is eliminated is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pilot signal cancellation system. [Prior art] General FM (Frequency Modulat)
ion) In stereo broadcasting, there is a 19KHz sine wave pilot signal. The pilot signal is P L L (Phase Loc
However, since it is included in the input signal, if it is simply demodulated, it will also appear in the output of the demodulator, causing problems in terms of hearing. Therefore, it is necessary to remove this 19KHz pilot signal. Figure 2 shows a conventional 19KHz pilot signal removal system. The system consists of a triangular wave converter 16. A variable gain amplifier 18, an adder 20, and a level detection circuit 22 are used. The stereo signal is input from the terminal 13, passes through the adder 8, and is output to the output 14-.

In reality, the adder 8 adds triangular wave and sine wave pilot signals that are 180 degrees opposite in phase to the pilot signal, and removes the pilot signal. For the above-mentioned triangular wave with an opposite phase, a square wave with a phase difference of 90' from the pilot signal in the PLL is used, the square wave is converted into a triangular wave by the triangular wave converter 16, and the capacitor provided in the triangular wave converter 16 is normally used. Input terminal 1 of the triangular wave converter 16 for converting into a triangular wave by charging and discharging (not shown)
The relationship between the square wave input to the input circuit and the triangular wave output from the triangular wave converter 16 is as shown in FIGS. 2(a) and 2(b). A phase difference occurs, resulting in a 180° phase difference with the pilot signal. The triangular wave converter output S3 is connected to the variable gain amplifier 6, and the amplification factor of the variable gain amplifier 6 is controlled by the level detection circuit 22, and the input terminal A triangular wave corresponding to the pilot signal level of 13 is output to the output terminal 7 of the variable amplifier, input to the adder 8, added to the stereo signal, and added to the pilot signal, so the pilot signal of the input terminal 13 is always the same. This is a system that enables removal according to the level. [Problem to be solved by the invention] However, in the conventional pilot removal system described above, the addition rate of the triangular wave in the adder is reduced due to variations in the gain of the level detection circuit. Therefore, when using the conventional pilot removal system mentioned above, it is necessary to adjust the variation. Also, when the conventional pilot removal system is integrated into an integrated circuit, terminals and external elements (usually [Means for Solving the Problem] In the pilot signal removal system of the present invention, the output of the triangular wave converter is connected to the input of the variable gain amplifier, and is connected to one input of a two-input adder, the other input of the two-input adder is an input terminal of a pilot signal removal system, and the output of the two-input adder is connected to an input of a first level detection circuit. are connected, the output of the first level detection circuit is connected to the first input of the two-level comparator, the output of the second level detection circuit is connected to the second input, and the output of the two-level comparator is connected to the second input. The output of the variable gain amplifier is connected to the amplification factor control terminal of the variable gain amplifier, and the output signal of the two-input adder is used as the output signal of the pilot signal removal system. [Embodiment] Next, the present invention will be explained in the drawings. 1 is a block diagram of an embodiment of the present invention. The system includes a triangular wave converter 2, a variable gain amplifier 6, a level detection circuit 11, a level detection circuit 12, a comparator 10, and an adder. The stereo signal is input from the terminal 13, passes through the adder 8, and is output to the output terminal 14.As for the triangular wave having the opposite phase to the pilot signal, the pilot signal and the 90° ``Use a square wave with a phase difference. That is, the square wave S1 input to the terminal 1 is converted into a triangular wave by the triangular wave converter 2. Since the triangular wave conversion is performed by charging and discharging the capacitor, the relationship between the input terminal 1 and the output terminal 3 of the triangular wave converter 2 is similar to the conventional one shown in FIG. 3(a). (b)
is the same, and compared to the phase of the square wave, the phase of the triangular wave is further 9
The output signal S3 of the triangular wave converter 2 is connected to the variable gain amplifier 6. The amplification factor of the variable gain amplifier 6 is the same as that of the output terminal 14. Control is performed using the pilot removal signal level so that a triangular wave always at the same level as the pilot signal level at the input terminal 13 is output from the output 7 of the variable gain amplifier 6. For this purpose, a level detection circuit 11 is connected to the internal output terminal l4. , the output of the level detection circuit 11 is connected to the comparator 10, the output of the level detection circuit 12 with no input is also connected to the comparator 10, and the output of the level detection circuit 11 and the output of the level detection circuit 12 are connected in the comparator 10. The comparison is made and the amplification factor of the variable gain amplifier 6 is controlled based on the difference. This operates so that the pilot removal signal level at the output terminal 14 becomes the input to the level detection circuit 12, that is, no signal. Since the pilot signal component at the output terminal 14, which is the output of the adder 8, always operates in the direction of disappearing, the stereo signal at the output terminal 14 is always output with the pilot signal component removed.Integrated circuit When used in the level detection circuit 11 and the level detection circuit 12, since the level detection circuit 11 and the level detection circuit 12 each produce the same level of variation, it is sufficient to consider the output of the comparator 10 excluding the variation in each level detection circuit. Even if a triangular wave to sine wave conversion circuit is inserted between the variable gain amplifier 6 and the variable gain amplifier 6 in order to increase pilot rejection, the effects of the present patent can be obtained in the same way. [Effects of the Invention] As explained above, the present invention In the pilot signal removal system in , the removal signal is controlled to completely remove the pilot signal, so there is no need to adjust the addition rate of the triangular wave in the conventional system, making it possible to eliminate adjustment man-hours on the set. Furthermore, when it is integrated into an integrated circuit, the number of adjustment terminals can be reduced, and the pilot signal rejection rate is high, making it possible to maintain stability and continue operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an example of a conventional pilot signal removal system, and FIG. 3 is a signal waveform diagram of the blocks in FIG. 2. 1... Square wave input terminal, 2... Triangular wave converter, 3...
... Triangular wave converter output/terminal, 6... Variable gain amplifier, 7... Variable gain amplifier output terminal, 8... Adder,
9... Variable gain amplifier control terminal, 10... Comparator,
11, 12.22... Level detection circuit, 13... Stereo signal input terminal, 14... Output terminal.

Claims (1)

[Claims] The output of the triangular wave converter is connected to the input of a variable gain amplifier, the output of the variable gain amplifier is connected to one input of a two-input adder, and the other input of the two-input adder is connected to the input of a pilot signal cancellation system. a terminal, an input of a first level detection circuit is connected to the output of the two-input adder, an output of the first level detection circuit is connected to a first input of a two-level comparator, and a second input is connected to the output of the second level detection circuit, the output of the two-level comparator is connected to the amplification factor control terminal of the variable gain amplifier, and the output signal of the two-input adder is connected to the output of the pilot signal removal system. A pilot signal removal system characterized in that the signal is a pilot signal.