JP4455785B2 - Pilot signal extraction circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pilot signal extraction circuit that separates and extracts a pilot signal included in a composite signal after FM detection.
[0002]
[Prior art]
The FM receiver has an FM demodulation circuit that reproduces the L signal and the R signal from the stereo composite signal after FM detection. This FM demodulator circuit is roughly divided into a matrix system and a switching system, and both systems are common in that L signals and R signals are extracted using a pilot signal superimposed on a stereo composite signal. ing.
[0003]
[Problems to be solved by the invention]
By the way, since the pilot signal described above is very weak and has voltage fluctuation due to other components, it is difficult to extract the pilot signal simply by comparing with a predetermined threshold voltage. For this reason, it is necessary to generate a signal synchronized with the weak pilot signal by using a PLL (phase locked loop) circuit, which causes a problem that the configuration is complicated.
[0004]
The present invention has been created in view of such a point, and an object thereof is to provide a pilot signal extraction circuit capable of extracting a pilot signal with a simple configuration.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problem, the pilot signal extraction circuit according to the present invention receives an FM modulated wave signal on which a pilot signal is superimposed in order to separate and extract the pilot signal superimposed on the FM modulated wave signal. Pilot signal removing means for removing the pilot signal contained therein, and analog subtracting means for outputting the difference between the signals before and after the pilot signal is removed by the pilot signal removing means. With a simple configuration in which the difference between the signals before and after the pilot signal is removed is output, it is possible to extract only the pilot signal by removing the influence of voltage fluctuations other than the pilot signal.
[0006]
The pilot signal removing means described above is preferably a band elimination filter that removes only the frequency component corresponding to the pilot signal. When observing the signal that has passed through the band elimination filter, the phase changes greatly in the vicinity of the frequency of the pilot signal that is the stopband, but when obtaining the difference between the signals before and after passing through this filter, Since only the pilot signal included in the signal is output, the pilot signal whose phase has not changed can be extracted. In particular, if only a pilot signal is extracted using a bandpass filter, the phase changes greatly in the passband of this filter, that is, in the vicinity of the frequency of the pilot signal to be passed, and a configuration for adjusting the phase is necessary. However, the pilot signal extraction circuit of the present invention does not require a configuration for performing such adjustment, and the configuration can be simplified.
[0007]
Further, it is desirable to further include an amplifier that amplifies the output signal of the analog subtracting means described above and a voltage comparator that compares the voltage of the signal amplified by the amplifier with a predetermined threshold voltage. Removes the effects of voltage fluctuations other than the pilot signal and extracts the pilot signal with no phase change, and generates a pulse signal synchronized with the pilot signal with a simple configuration that includes an amplifier and voltage comparator. It becomes possible to do.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a pilot signal extraction circuit according to an embodiment to which the present invention is applied will be described in detail.
FIG. 1 is a diagram illustrating a configuration of an FM receiver including a pilot signal extraction circuit according to the present embodiment. The FM receiver shown in FIG. 1 includes a high frequency amplifier circuit 11, a mixing circuit 12, a local oscillator 13, an intermediate frequency filter 14, 16, an intermediate frequency amplifier circuit 15, a limit circuit 17, an FM detection circuit 18, and a stereo demodulation circuit 19. It consists of
[0009]
After the FM modulated wave signal received by the antenna 20 is amplified by the high frequency amplifier circuit 11, the local oscillation signal output from the local oscillator 13 is mixed to convert the high frequency signal into an intermediate frequency signal. The intermediate frequency filters 14 and 16 are provided before and after the intermediate frequency amplifier circuit 15, and extract only a predetermined band component from the input intermediate frequency signal. The intermediate frequency amplifier circuit 15 amplifies a part of the intermediate frequency signal that passes through the intermediate frequency filters 14 and 16.
[0010]
The limit circuit 17 amplifies the input intermediate frequency signal with high gain. The FM detection circuit 18 performs FM detection processing on a signal having a constant amplitude output from the limit circuit 17. The stereo demodulation circuit 19 performs a stereo demodulation process on the stereo composite signal after the FM detection output from the FM detection circuit 18 to generate an L signal and an R signal.
[0011]
FIG. 2 is a diagram showing a detailed configuration of the stereo demodulation circuit 19, and shows a schematic configuration when, for example, a switching method is adopted. As shown in FIG. 2, the stereo demodulation circuit 19 includes an amplifier 21, a pilot signal extraction circuit 22, a multiplication circuit 23, and a switching unit 24.
[0012]
The amplifier 21 amplifies the stereo composite signal (composite signal) input from the FM detection circuit 18 in the previous stage. The pilot signal extraction circuit 22 separates and extracts the 19 kHz pilot signal superimposed on the stereo composite signal.
The multiplier circuit 23 generates a 38 kHz signal that is synchronized with the pilot signal and has a double frequency. The switching unit 24 performs a switching operation in synchronization with the 38 kHz signal output from the multiplier circuit 23 on the amplified stereo composite signal input from the amplifier 21, so that L included in the stereo composite signal is included. The signal and the R signal are separated.
[0013]
FIG. 3 is a diagram showing a detailed configuration of the pilot signal extraction circuit 22. As shown in FIG. 3, the pilot signal extraction circuit 22 includes a band elimination filter (BEF) 30, an analog subtractor 31, an amplifier 32, and a voltage comparator 33.
[0014]
The band elimination filter 30 removes only the frequency component near 19 kHz corresponding to the pilot signal and passes the other frequency components. This band elimination filter 30 corresponds to pilot signal removal means. The analog subtractor 31 receives the stereo composite signal input from the FM detection circuit 18 and the signal obtained by removing the pilot signal from the stereo composite signal by passing through the band elimination filter 30. Outputs the differential voltage of the signal. This analog subtractor 31 corresponds to analog subtracting means.
[0015]
The amplifier 32 amplifies the output voltage of the analog subtractor 31. The voltage comparator 33 compares the output voltage of the amplifier 32 with a predetermined threshold voltage Vref, and sets the output to a high level when the output voltage is equal to or higher than the threshold voltage Vref.
FIG. 4 is a diagram showing input / output waveforms of each part of the pilot signal extraction circuit 22 of the present embodiment. FIG. 4A shows the waveforms of the stereo composite signals input to the band elimination filter 30 and the analog subtractor 31, respectively. FIG. 4B shows the waveform of the output signal of the band elimination filter 30. FIG. 4C shows the waveform of the output signal of the analog subtractor 31.
[0016]
The stereo input signal before removing the pilot signal (FIG. 4A) and the stereo output signal after removing the pilot signal (FIG. 4B) are input to the two input terminals of the analog subtractor 31. Therefore, the analog subtractor 31 can extract only the pilot signal by outputting the differential voltage between these two input signals (FIG. 4C). Since the pilot signal extracted in this way is not affected by voltage fluctuations or the like due to other frequency components, the voltage level is amplified by the amplifier 32 at the subsequent stage, and then a predetermined threshold voltage Vref and By comparing, it becomes possible to easily generate a pulse signal synchronized with the pilot signal.
[0017]
As described above, the pilot signal extraction circuit 22 according to the present embodiment has the simple configuration necessary for outputting the differential voltage of the stereo composite signal before and after the removal of the pilot signal, thereby affecting the influence of voltage fluctuations other than the pilot signal. It is possible to extract only the pilot signal. For this reason, the configuration can be simplified as compared with the conventional case where a PLL circuit is used.
[0018]
When the signal passing through the band elimination filter 30 is observed, the phase changes greatly in the vicinity of the frequency of the pilot signal that is the stop band. Since only the pilot signal included in the signal before passing is output, it is possible to extract the pilot signal whose phase has not changed. In particular, if only a pilot signal is extracted using a bandpass filter, the phase changes greatly in the pass band of this filter, that is, in the vicinity of the frequency of the pilot signal to be passed, and a configuration for adjusting the phase is necessary. However, the pilot signal extraction circuit of the present embodiment does not require a configuration for performing such adjustment, and can further simplify the configuration.
[0019]
Further, the analog subtractor 31 can remove the influence of voltage fluctuations other than the pilot signal, and can output a pilot signal having no phase change. Therefore, the amplifier 32 and the voltage comparator 33 are further added. Thus, a pulse signal synchronized with the pilot signal can be generated.
[0020]
【The invention's effect】
As described above, according to the present invention, only the pilot signal is extracted by removing the influence of voltage fluctuations other than the pilot signal by a simple configuration of outputting the difference between the signals before and after removing the pilot signal. Is possible.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an FM receiver including a pilot signal extraction circuit according to an embodiment.
FIG. 2 is a diagram illustrating a detailed configuration of a stereo demodulation circuit.
FIG. 3 is a diagram showing a detailed configuration of a pilot signal extraction circuit.
FIG. 4 is a diagram showing input / output waveforms of each part of the pilot signal extraction circuit;
[Explanation of symbols]
18 FM detection circuit 19 Stereo demodulation circuit 21, 32 Amplifier 22 Pilot signal extraction circuit 23 Multiplication circuit 24 Switching unit 30 Band elimination filter (BEF)
31 Analog subtractor 33 Voltage comparator

Claims (1)

In a pilot signal extraction circuit that separates and extracts a pilot signal superimposed on an FM modulated wave signal,
Pilot signal removing means for receiving the FM modulated wave signal on which the pilot signal is superimposed, and removing the pilot signal included therein;
Analog subtracting means for outputting a difference between signals before and after the pilot signal is removed by the pilot signal removing means;
An amplifier for amplifying the output signal of the analog subtracting means;
A voltage comparator that compares the voltage of the signal amplified by the amplifier with a predetermined threshold voltage;
Wherein the pilot signal removing means, a pilot signal extraction circuit, wherein a band elimination filter der Rukoto removing only the frequency component corresponding to the pilot signal.

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