JPS6314508Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an FM receiving device that prevents interference waves of specific frequency components in an input signal from an antenna from entering the front end.

As a conventional device of this type, the present inventor has proposed the one shown in FIG. In the figure, 1 is an antenna, 2 is a trap circuit whose tuning frequency can be varied by voltage, 3 is a front end, 4 is an intermediate frequency stage/detector, 5 is a multiplex (MPX) demodulator, 6 is a high-pass filter, and 7 is a 8 is a minimum value detector, 9 is a sawtooth generator, 10 is a voltage memory, and 11 is a changeover switch.

The antenna 1, trap circuit 2, front end 3, intermediate frequency stage/detector 4, and MPX demodulator 5 constitute a normal receiving device.
The high frequency signal inputted from the is a mixed signal of a desired signal and an interference signal. In particular, proximity interference signals are demodulated to a higher frequency band than the audio signal band,
Since it is converted to an audio band during multiplex demodulation, it becomes a problem in receiving high-quality sound. Therefore, in the illustrated apparatus, in order to eliminate this interference signal, a trap circuit 2 having a narrow band elimination characteristic is tuned to this interference signal, thereby enabling reception with a higher S/N ratio.

Normally switch 11 selects the output of sawtooth generator 9 and applies it to trap circuit 2 as a control input. While the output of the sawtooth generator 9 sweeps from its minimum value to its maximum value, the tuning frequency of the trap circuit 2 is swept over a predetermined range. At this time, a high-pass filter 6 extracts a noise component caused by proximity interference from the output of the intermediate frequency stage/detector 4, and a rectifier 7 converts it into a DC voltage.
This DC voltage changes depending on the proximity jamming signal,
When the interference signal is small, its voltage value becomes small.
Therefore, the time when the DC output voltage of the rectifier 7 is minimum while the trap circuit 2 sweeps a predetermined frequency range corresponds to the time when the interference signal is reduced the most.

When the output voltage of the rectifier 7 is input to the minimum value detector 8, the minimum value is detected by the minimum value detector 8, and the output voltage of the sawtooth generator 9 when this minimum value is obtained is stored in the voltage memory. 10 is stored. Therefore, when the sawtooth wave generator 9 outputs a waveform with one period or more, the trap control voltage for the most reduction is obtained at the output of the voltage memory 10, and the switch 11 is changed to output the voltage memory 10. By selecting the output, you can receive with the least amount of interference.

As mentioned above, since the interfering signal is demodulated in a frequency band very close to the desired signal, the high-pass filter 6 needs to have steep characteristics, which has the disadvantage of complicating the configuration.

Furthermore, in a range where the S/N ratio exceeds a certain level, the interference signal component becomes extremely small, making it difficult to detect the optimum trap control voltage, which also has the disadvantage that optimum interference reduction cannot be achieved.

The present invention was made to eliminate the drawbacks of the conventional ones as described above, and its purpose is to detect and rectify the high-frequency noise component of the demodulated signal, but instead to detect and rectify the high-frequency noise component of the demodulated signal. It is an object of the present invention to provide an FM receiver which achieves the same effect as the conventional one with a simpler configuration by performing detection rectification, and which also enables interference detection when the S/N ratio is good.

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 21 is an antenna, 22 is a trap circuit whose tuning frequency is controlled by voltage,
The high frequency signal inputted from the antenna 21 via the trap circuit 22 is applied to a normal receiving device consisting of a front end 23, an intermediate frequency stage/detector 24, and an MPX demodulator 25.

The output of the front end 23 is also input to the AM detector 26, where it is subjected to AM detection.
The output of the AM detector 26 is connected to a rectifier 27,
The output of the rectifier 27 is input to a minimum value detector 28.

Furthermore, a sawtooth wave generator 29 is provided, the output of which is connected to a voltage memory 30, and the output of the minimum value detector 28 is connected to a control input of the voltage memory 30. One of the outputs of the sawtooth wave generator 29 and the output of the voltage memory 30 is selected by a changeover switch 31 and connected to the control input of the trap circuit 22.

By the way, the high frequency signal inputted from the antenna 21 is a mixed signal of a desired signal and an interference signal,
In particular, the proximity interference signal generates a beat with the desired signal, giving an AM modulation component to the envelope of the desired signal. Since this AM modulation component has a frequency difference between the desired signal and the nearby interference signal as a component, it has a frequency component that is an integral multiple of 100 KHz, according to the current FM broadcast channel plan. Normally, proximity interference exceeding ±300KHz is removed by the IF filter in the intermediate frequency stage, so 100KHz,
Only the 200KHz and 300KHz AM components are generated by close interference.

That is, when there is near interference, the output of the front end 3 will have 10.7M as shown in Figure 3a.
A signal waveform is obtained in which a Hz FM wave is modulated by a beat component due to proximity interference. In a normal FM receiver, the AM component is suppressed by a limiter.
FM demodulation is performed, but the above AM modulated FM wave is AM
It is demodulated by the detector 26, and its output is shown in Fig. 3b.
A signal with the waveform shown in is obtained. This demodulated signal is converted into a DC signal by a rectifier 27 as shown in FIG. 3c.
converted to voltage. This DC voltage corresponds to the proximity interference signal and becomes smaller as the interference signal becomes smaller.

Now, when the switch 31 selects the output of the sawtooth wave generator 29 and applies it to the trap circuit 22, the sawtooth wave generator 29 changes from its minimum value to its maximum value as shown in FIG. When the output voltage is swept up to 1, the tuning frequency of the trap circuit 22 is swept within a predetermined range, and the rectifier 27 rectifies the near disturbance component to the tuning frequency of the trap circuit 22 at that voltage value.
A DC voltage with a waveform as shown in Figure b is obtained. The time when this DC voltage is the smallest is the time when the proximity interference is most reduced, and the control voltage output from the sawtooth wave generator 29 at this time is stored in the voltage memory 30.
In order to store the value, the output of the rectifier 27 is applied to a minimum value detector 28, where minimum value detection is performed.

The minimum value detector 28 outputs an H level while the voltage applied to its input is lower than before;
When the voltage is higher than the previous voltage, the output becomes L level, and in response to the application of the DC voltage shown in Fig. 4b, an output signal as shown in Fig. 4c is sent out.
This is applied to the control input of the voltage memory 30. Voltage memory 30 has H at its control input.
While the level signal is being applied, the output of the sawtooth wave generator 29 is received as an input, a voltage corresponding to this input voltage is memorized, and when the control input becomes L level, the sawtooth wave generator 29 The output from the sawtooth wave generator 29 is not received, but the voltage that was received and stored from the sawtooth wave generator 29 immediately before is held and continues to be output. Therefore, when the sawtooth wave generator 29 sweeps one cycle or more as described above,
At the output of the voltage memory 30, a voltage having a waveform as shown in FIG. 4(d) is generated, and ultimately a trap control voltage that can most effectively reduce the proximity disturbance is obtained. In this situation, switch 20
By switching the output of the voltage memory 30 to the trap circuit 22, a good S/N ratio can be achieved.
reception can be achieved.

As described above, according to the present invention, the level of the AM component in the output signal of the front end is detected, and the optimal control voltage of the trap circuit is automatically set according to the minimum level. Therefore, there is no need to use a high-pass filter that was required in the past, and the optimum reception condition can be obtained with a simple configuration. Moreover, even in a high S/N state where the S/N exceeds a certain level, the optimum control voltage can be maintained. This makes it possible to detect and reduce interference better than before.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example, Fig. 2 is a block diagram showing an embodiment of the present invention, and Figs. 3 and 4 are waveform diagrams for explaining the operation of the embodiment of Fig. 2. be. 21... Antenna, 22... Trap circuit, 2
3...Front end, 26...AM detector, 2
8... Minimum value detector, 29... Sawtooth wave generator,
30...Voltage memory.

Claims (1)

[Scope of utility model registration request] It is installed between the antenna and the front end, and the tuning frequency can be varied by the applied control voltage.
a trap circuit for trapping the tuning frequency component in the input signal from the antenna; a sweep voltage generating means for generating the control voltage for sweeping the tuning frequency of the trap circuit in a predetermined range; AM detection means for detecting the AM component of the AM component; minimum value detection means for detecting the minimum value of the level of the AM component detected by the AM detection means; and the sweep voltage generation means when the minimum value is detected by the minimum value detection means. and means for applying a voltage equal to the voltage being generated to the trap circuit as the control voltage.