JPH02260805A - Fm demodulator - Google Patents

Abstract

PURPOSE:To eliminate interference due to an adjacent channel by providing 1st and 2nd voltage controlled oscillators, a phase comparator and an amplifier, and outputting an output signal of a 2nd amplifier as a demodulation signal. CONSTITUTION:When a desired signal and an interference signal are inputted from an input terminal 1, a phase comparator 3 compares a phase of a 1st oscillation signal and the phase of the desired signal and a 1st phase comparison signal is outputted from the phase comparator 3. Moreover, a phase comparator 7 compares the phase of the 1st oscillation signal and the phase of a 2nd oscillation signal and the phase comparator 7 outputs a 2nd phase comparison signal. The signal is outputted as a demodulation signal from an output terminal 9 after being amplified, inputted to a VCO 6 to control the frequency of the 2nd oscillation signal. A phase locked loop comprising circuit elements 2-4 is locked by the desired signal only and a loop comprising circuits elements 6-9 is locked by the 1st oscillation signal only, only a composite video signal of the base band is outputted from the output terminal 9. Thus, the interference by the adjacent channel is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application J This invention relates to an FM demodulator for demodulating a composite video signal from a high frequency signal frequency modulated by the composite video signal in a television receiver or the like that receives satellite broadcasting.

[Prior art] Fig. 3 is a block diagram showing an example of the construction of a conventional FM demodulator. In this figure, "" indicates an intermediate frequency obtained by frequency-converting the received desired channel signal by a converter (not shown). An input terminal into which a signal (frequency = 403 MHz) (hereinafter referred to as desired signal) is manually input, 2 is a voltage controlled oscillator (VCO) that outputs a 403 MHz oscillation signal, 3 is a comparison between the phase of the desired signal and the phase of the oscillation signal 4 is a DC amplifier that amplifies the output signal of the phase comparator 3, 5 is an output terminal, and the output signal of the DC amplifier 4 is output as a demodulated signal from the output terminal 5. At the same time, it is also manually input to the control voltage input terminal of VCO2. This controls the frequency of the oscillation signal.

"Problems to be Solved by the Invention" By the way, in the above-mentioned converter (not shown), as shown in FIG.
At the same time as the frequency is converted to curve a), the signal of the adjacent channel is also frequency converted to a signal (hereinafter referred to as an interference signal) near the desired signal (curve b).

Therefore, when these signals are input to the input terminal 1, the phase comparator 3 performs a demodulation operation because the oscillation signal is locked to the desired signal, but performs a demodulation operation for the interference signal. take action. As a result, the baseband composite video signal (curve a in FIG. 5) and the difference component between the interference signal and the oscillation signal (curve b in the same figure) are output from the output terminal 5. In this case, since the difference component between the interfering signal and the oscillation signal is frequency modulated, there is a problem in that the spectrum extends to low frequencies and interferes with the composite video signal.

This invention was made against this background, and is an FM system that can eliminate interference caused by adjacent channels.
tl! The purpose is to provide an Ill device.

"Means for Solving the Problems" An FM demodulator according to the present invention includes first and second voltage controlled oscillators that output first and second oscillation signals, respectively, and a phase and phase difference of a frequency-modulated high-frequency signal. ! a first phase comparator that compares the phase of the oscillation signal with the first phase comparison signal and outputs a first phase comparison signal, and amplifies the first phase comparison signal and controls the frequency of the first oscillation signal by the output signal. 1st
a second phase comparator that compares the phase of the first oscillation signal and the phase of the second oscillation signal and outputs a second phase comparison signal; and a second phase comparator that amplifies the second phase comparison signal. It is characterized by comprising a second amplifier that controls the frequency of the second oscillation signal by the output signal thereof, and outputting the output signal of the second amplifier as a demodulated signal.

"Operation" According to the above configuration, when the desired signal and the interference signal are input to the first phase comparator, the first phase comparator
The phase of the first oscillation signal and the phase of the desired signal are compared, and a first phase comparison signal is output from the first phase comparator. Further, in the second phase comparator, the phase of the first oscillation signal and the phase of the second oscillation signal are compared, and a second phase comparison signal is output from the second phase comparator. next,
The second phase comparison signal is amplified in the second amplifier, output as a demodulated signal, and controls the frequency of the second oscillation signal.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an FM demodulator according to an embodiment of the present invention.
Components corresponding to those in the figures are given the same reference numerals, and their explanations will be omitted. In FIG. 1, the output terminal 5 is removed and the VC outputs the second oscillation signal of 403 MHz.
O6, a phase comparator 7 that compares the phase of the output signal of the VCO2 (hereinafter referred to as the first oscillation signal) with the phase of the second oscillation signal and outputs a second phase comparison signal, and a second phase comparison A DC amplifier 8 and an output terminal 9 for amplifying the signal are newly provided. Note that the output signal of the phase comparator 3 will be referred to as a first phase comparison signal.

In such a configuration, when a desired signal and an interference signal having the spectrum shown in FIG. 4 are input from the input terminal I, the phase of the first oscillation signal and the phase of the desired signal are compared in the phase comparator 3. The first phase comparison signal is output from the phase comparator 3. Further, in the phase comparator 7, the phase of the first oscillation signal and the phase of the second oscillation signal are compared, and the phase comparator 7 outputs a second phase comparison signal. Next, the second phase comparison signal is amplified in the DC amplifier 8, outputted as a demodulated signal (see FIG. 2) from the output terminal 9, and inputted to the control voltage input terminal of the vCO 6. This controls the frequency of the second oscillation signal.

As explained above, even if a desired signal and an interference signal having the spectrum shown in FIG. Since the phase low-7 quadruple consisting of circuit elements 6 to 9 is locked to only the first oscillation signal, only the baseband composite video signal having the spectrum shown in Fig. 2 is output from output terminal 9. be done. Therefore, high quality television images can be viewed without interference from adjacent channels.

"Effect of the Invention J As explained above, the present invention has the effect of being able to eliminate interference caused by adjacent channels. Therefore, it has the effect of allowing high-quality television images to be viewed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an FM demodulator according to an embodiment of the present invention, FIG. 2 is a diagram showing the spectrum of the signal output from the output terminal 9 of FIG. 1, and FIG.
A block diagram showing an example of the configuration of the M demodulator, FIG.
FIG. 5 is a diagram showing the spectrum of the signal inputted to the input terminal 1 of the 1im device, and FIG. 5 is a diagram showing the spectrum of the signal output from the output terminal 5 of FIG. 3. 2.6...VCO13,7...phase comparator,
4.8...DC amplifier, 9...Output terminal. Newcomer Alps Electric Co., Ltd. Representative Masataka Kataoka Figure 1 Figure 3 Figure 4v! 5 Figure 2 Figure 5

Claims (1)

[Claims] first and second voltage controlled oscillators that respectively output first and second oscillation signals;
a first phase comparator that outputs a phase comparison signal; a first amplifier that amplifies the first phase comparison signal and controls the frequency of the first oscillation signal by its output signal; a second phase comparator that compares the phase of the oscillation signal with the phase of the second oscillation signal and outputs a second phase comparison signal; and a second phase comparator that amplifies the second phase comparison signal and uses its output signal to An FM demodulator, comprising a second amplifier that controls the frequency of a second oscillation signal, and outputs an output signal of the second amplifier as a demodulated signal.