JPH0542853B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a receiving device having a noise interpolation function that suppresses the effects of impulse noise and multipath interference.

B. Summary of the Invention In an FM receiver, in order to reduce the effects of multipath, in particular, during a period in which the amplitude modulation signal of an intermediate frequency signal is larger than a predetermined value, the input signal is Replace it with the output of a sine wave oscillator. At that time, the frequency of the audio (sound) electrical signal to be detected by FM is separated using a narrow band filter that is logarithmically divided into approximately equal intervals.
Each of the plurality of components thus obtained is represented by a sinusoidal signal at the center frequency of the narrowband filter, and its amplitude is equal to The signal level for each output.

C. Prior Art When impulse noise is added to FM broadcast waves or multipath interference is present, the quality of received and reproduced sound deteriorates. In particular, when multipath interference is present in mobile reception (in-vehicle radio), the signal strength of the received radio waves fluctuates depending on the speed of movement, causing noise. In response to this, receiving apparatuses have been proposed in which various countermeasures have been taken.

For example, when impulse noise is present,
The impulse part is identified from the excessive envelope of the intermediate frequency signal of the received FM wave and the high frequency component of the detection output, and the detection output for that period is removed through a gate circuit, and during that period, the signal before removal is removed as shown in Figure 3a. The DC level of the trailing edge of the signal is maintained and the removed portion is interpolated. In addition, in response to multipath interference, the intermediate frequency signal becomes an amplitude modulated wave, so when the amplitude modulation is detected and it exceeds a certain value, the detection output will not change until the amplitude fluctuation is below the certain value. Maintains the DC level of the signal.

FIG. 5 is a block diagram showing the configuration of a conventional multipath mitigation circuit that performs such interpolation.
A signal from the antenna ANT is converted into an intermediate frequency signal by a front end 1, passes through a limiter and an FM detector 2, and then becomes L and R channel signals by a stereo demodulator 3. In this case, if there is multipath interference, an amplitude modulation (AM) component will occur in the intermediate frequency signal. Therefore, the AM component of the intermediate frequency is detected by the AM detector 4 with AGC, and its magnitude is determined by the reference power source 6.
When the voltage E exceeds ₁ , an output is produced in the comparator 5,
This causes the sample and hold circuits 7 and 8 to operate, and for the period τ during which the comparator 5 operates, L, R
Maintains DC level on both channels. In the figure, 9
and 10 represent the outputs of L and R, respectively.

D Problems to be Solved by the Invention An example of compensation for pulse noise obtained by the apparatus shown in FIG. 5 is shown in FIG. FIG. 6a shows the period τ of the pulse noise. Figure b shows an audio signal, in which the broken line portion corresponds to the noise period τ, and the thick line portion indicates the DC interpolation portion. If the interpolation period τ is smaller than the signal period, DC interpolation may be used, but
When τ becomes larger than the period, an audible sense of abnormality occurs during the period τ.

An object of the present invention is to interpolate the detection output when there are level fluctuations due to impulse noise or multipath interference during FM reception, by using a sine wave signal similar to a normal detection output signal, rather than a simple DC component. It is an object of the present invention to provide a receiving device that can perform interpolation and reduce audible abnormalities.

E. Means for Solving the Problems In order to achieve the above object, a receiving device according to the present invention includes an amplitude detecting means for detecting an amplitude level of an amplitude modulation component signal caused by noise from a received signal that is equal to or higher than a certain value; a detection means for detecting a received signal to obtain a detection signal; and an interpolation signal generation means for generating a predetermined interpolation signal according to the frequency component and signal level of the detection signal immediately before the amplitude level of the predetermined value or more is detected. , an interpolation means for replacing the detection signal with the interpolation signal when detecting an amplitude level equal to or higher than the predetermined value.

The interpolation means includes a gain control circuit to which the detection signal is applied and which sets the gain of the detection signal to zero when an amplitude level equal to or higher than the certain value is detected, and an output of the gain control circuit and the interpolation signal generation. and an addition circuit for adding the outputs of the means.

Further, the interpolation signal generation means has a plurality of sine wave oscillators with different frequencies, and controls and adds the gains of the sine wave signals from the sine wave oscillators according to the frequency components and signal levels of the detected signal. It is also possible to generate the interpolated signal by doing so.

F Effect In the receiving device of the present invention, an interpolated signal is generated according to the frequency component and signal level of the detected signal obtained when detecting the amplitude level of the amplitude modulated signal,
This detected signal is replaced with this interpolated signal.

G Example It is known that many narrowband transmission systems exist in parallel in the human hearing system. In psychoacoustics, these narrowband transmission systems are called critical bands. In other words, the auditory transmission band is 20Hz
This band is said to be ~20 kHz, and as shown in FIG. 7, this band is considered to be a collection of many narrow band filters. Two frequencies within one critical band should originally be indistinguishable, but
They can be distinguished because the proportions of critical bands on both sides are different. For example, in FIG. 8, frequencies ₁ and ₂ can be distinguished not because of the b ₁ and b ₂ of _{the b} channel, but because of the difference in the components a ₁ and c ₂ of the _a and _c of the adjacent channels on both sides. Approximately, it can be considered that frequencies within one critical band sound approximately equal. The present invention has been accomplished based on the findings of the inventors.

FIG. 1 shows an embodiment of the receiving device of the present invention, which is designed to reduce multipath noise, in which 1 is a front end, 2 is a limiter and an FM detector, and corresponds to the detection means. 4 is AM detector with AGC,
A comparator 5 constitutes the amplitude detection means. 1
Reference numeral 1 denotes a group of sine wave generators, which corresponds to the interpolation signal generating means. 12 is a gain control circuit, and 13 is an adder circuit, which constitutes the interpolation means.

The sine wave generator group 11 is, for example, a circuit having the configuration shown in FIG. 2b. The FM detection output signal of the limiter and FM detector 2 is transmitted to the filter group 15-1, 1.
5-2, . . . 15-n. Figure 2a shows the frequency characteristics of those filters. The center frequencies of these filters are ₁ , ₂ , ..., _o , and are equally distributed at logarithmic frequencies.
For example, if you divide 50Hz to 12.8kHz by 33,
₁ = 50Hz, ₂ = 59.5Hz, ₃ = 70.7Hz, ₄ = 84Hz,
_Five
=100Hz,..., ₉ =200Hz,..., ₁₃ =400Hz,
..., ₁₇ = 800Hz, ..., ₂₁ = 1600Hz, ...,
₂₅ = 3200Hz, ..., ₂₉ = 6400Hz, ..., ₃₃ =
It becomes 12.8kHz.

16-1, 16-2, ..., 16-n are amplitude detectors for each frequency component, 17-1, 17-2,
..., 17-n are amplitude detectors 16-1, 16-
This is a sample and hold circuit with levels of 2, . . . , 16-n. Comparator 5 determines this hold.
This is the output of That is, the sine wave signal is held while the amplitude modulation of the intermediate frequency exceeds the reference voltage _E1 . On the other hand, 19-1, 19-2,...
..., 19-n are frequencies ₁ , ₂ , ..., _o , respectively
The output is a sine wave oscillator whose amplitude is determined by gain limiting circuits 18-1, 18-2, . be done. In addition, the output of the limiter and FM detector 2 is connected to the gain limiting circuit 1.
2, during the period when the output of the comparator 5 exists, that is, the period when the amplitude modulation component of the intermediate frequency exceeds the reference value, by setting the gain to zero and adding it to the adder circuit 13, the output 14 of the adder circuit 13 is normal. condition fm
The composite wave (output of the adder 20) of the demodulated output and the sine waves of center frequencies ₁ , ₂ , ..., _o of each critical band during the period when the AM component of the intermediate frequency is large due to the presence of multipath interference is automatically generated. The value will be changed automatically.

If you create a sound field with output 14 using speakers etc.,
Although the output of the sine wave generator group 11 and the input of the gain control circuit 12 are slightly different as electrical signals, since the auditory sense consists of critical bands, they cannot be distinguished from each other in terms of the auditory sense.

In the case of stereo, narrowband filter groups 15-1, 15-2, . . . are provided for both L and R channels.
...15-n, amplitude detectors 16-1, 16-2,...
...16-n, sample hold circuit 17-1, 1
7-2, ..., 17-n, gain controller 18-1,
18-2,..., 18-n, adder 20 is required, but sine wave oscillators 19-1, 19-2,...
..., 19-n may be common to R and L.

Figures 3a and 3b show output waveforms interpolated by the prior art and the present invention, respectively, to provide an intuitive understanding of the spirit of the present invention. In the figure,
The broken line shows the original audio signal including noise, and the thick line shows the interpolated audio signal. represent.

When sampling and holding the signal from the comparator 5, the oscillators 19-1, 19-2, ..., 19-n
is the output of the limiter and demodulator 2.
If the FM demodulated signals are not in phase, a click will occur during switching. As a countermeasure, as shown in FIG.
The phase of the sine wave oscillator 19 may be coupled with the demodulated output to make the output of the narrowband filter 15 and the phase of the sine wave oscillator 19 continuous.

If there is pulse-like noise instead of multipath interference, by extracting the period in which the amplitude is excessively large in intermediate frequency amplitude detection and using the sine wave signal according to the present invention for interpolation, it will be possible to eliminate the pulse-like noise. Interference can be reduced.

H. Effects of the Invention As explained above, according to the present invention, since the auditory sense has a critical band structure, even if the disturbed portion of the input audio signal is replaced with a sine wave signal of discontinuous frequency, Interpolation is hardly discernible to the auditory sense.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a multi-path noise reduction circuit according to the present invention in the case of monaural;
FIG. 2 is a diagram showing the configuration of the sine wave generator group in FIG. 1, FIG. 3 is a diagram comparing output waveforms interpolated by the conventional technique and the present invention, and FIG. 4 is a diagram showing the present invention. 5 is a block diagram showing the structure of a conventional multipath noise reduction circuit, and FIG. 6 is a block diagram showing the structure of a conventional multipath noise reduction circuit obtained by the apparatus shown in FIG. FIG. 7 is a diagram showing an example of compensation for pulse noise, FIG. 7 is a schematic diagram of the auditory critical band, and FIG. 8 is a diagram for explaining the relationship between the critical band and the auditory sense. 1...Front end, 2...Limitsuta and
FM detector, 4... AM detector with AGC, 5...
Comparator, 6...Reference power supply, 11...Sine wave oscillator group, 12...Gain controller, 13...Addition circuit, 1
4...Output, 15, 15-1, 15-2,...1
5-n...Narrow band filter, 16-1, 16-
2,...,16-n...amplitude detector, 17-1,
17-2,..., 17-n... Sample hold circuit, 18-1, 18-2,..., 18-n...
Gain limiting circuit, 19, 19-1, 19-2,...
..., 19-n... sine wave oscillator, 20... adder.

Claims (1)

[Scope of Claims] 1. An amplitude detection means for detecting an amplitude level of an amplitude modulation component signal generated by noise from a received signal that is equal to or higher than a certain value; a detection means for detecting the received signal to obtain a detected signal; and the certain value. interpolation signal generation means for generating a predetermined interpolation signal according to the frequency component and signal level of the detected signal immediately before the amplitude level above is detected; A receiving device having a noise interpolation function, comprising: interpolation means for replacing the interpolation signal with the above interpolation signal. 2. The interpolation means includes: a gain control circuit to which the detection signal is applied and sets the gain of the detection signal to zero when detecting an amplitude level equal to or higher than the certain value; and an output of the gain control circuit and the interpolation signal generation means. 2. A receiving device having a noise interpolation function according to claim 1, comprising: an adding circuit for adding the outputs of the signal and the output of the signal. 3. The interpolation signal generating means has a plurality of sine wave oscillators with different frequencies, and controls and adds the gains of the sine wave signals from the sine wave oscillators according to the frequency components and signal levels of the detected signal. 2. A receiving device having a noise interpolation function according to claim 1, wherein the interpolation signal is generated by using a noise interpolation function.