JPH06152551A - Fm receiver - Google Patents

Abstract

PURPOSE:To cancel a multipath interference on an auditory sense by interpolating (signal processing) an omitted signal generated due the multipath interference. CONSTITUTION:An envelope detector circuit 12 amplitude-detects an IF component signal, and obtains an amplitude detection signal. An amplitude comparing circuit 13 detects a weak electric field time less than a reference voltage (er) based on the amplitude detection signal. A control pulse generator 15 outputs a control signal corresponding to the reference voltage (er) level based the amplitude detection signal. A noise generator 30 generates a replacement signal (noise) corresponding to the amplitude detection signal. Then, an electronic switcher 16 replaces the level signal of an FN modulated signal or right-and-left ear signals 11 and 10 with the noise at the time of the weak electric field based on the control signal from the control pulse generator 15. Thus, the voice quality due to the multipath interference can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver, and more particularly to an FM receiver having a multipath interference suppressing circuit.

[0002]

2. Description of the Related Art FIG. 7 shows a principle block diagram of a conventional FM receiver after an IF (intermediate frequency) stage. IF signal (FM
The frequency of the wave 1 is converted into a voltage by a frequency discriminator (FM demodulator) 2, demodulated and restored as a baseband signal. FM broadcasting is mainly stereo broadcasting, and a pilot signal cosωpt (fp = 19 KHz) is extracted by a BPF (bandpass filter) 3 and 2 fp.
= 38KHz by controlling the phase of sub-carrier generator 4
The subcarrier cos2ωpt of Hz is generated.

Further, as shown in FIG. 7, the baseband output from the frequency discriminator 2 is the signal cos2ωpt = 1 and c from the subcarrier generator 4 in the electronic switcher 5.
os2ωpt = -1 sampling, band 0 ~ 15KHz
Of the right ear signal 10 (ER) and left ear signal 11 (EL) through a LPF (low-pass filter) 6 or LPF 7 and a kind of integration performed by the de-emphasis circuit 8 or 9.
To get

[0004]

FIG. 8A is a distribution diagram of the IF envelope detection output and shows the demodulated signal distribution of the IF signal with respect to the fluctuation of the received electric field when there is multipath interference. Further, the electric field strength and the S / N of the FM demodulated baseband signal in the conventional FM receiver are as shown in FIG. 9, and the S / N gradually decreases with the decrease of the electric field strength up to the threshold point P. However, there is a drawback that the S / N is rapidly deteriorated when the threshold falls below the point P.

As shown in FIG. 8A, this is the conventional F
In the M receiver, when the electric field strength of the IF signal decreases, the noise becomes larger than that of the IF signal, and the FM as shown in FIG.
This is because click noise is generated during demodulation. For example, in multi-path, I = I between t = t1 to t2 and t3 to t4
When the F amplitude decreases and the threshold falls below er, the S / N of the FM demodulated baseband signal deteriorates and the sound quality is unbearable for listening.

In this case, if the envelope of the signal 10 is detected in FIG. 7 and t1 to t2 and t3 to t4 below er are detected.
As shown in FIG. 11A, a control pulse is generated between them to switch off t1 to t2 and t3 to t4 at which click noise occurs as shown in FIG. 10 to gate the audio signal 111 so that noise is not output. Can be done (Fig. 5
A solid line portion 55 of A, hatched portions 61 and 63 of FIG. 6A
reference). However, such noise reduction of t1 to t2 causes an unnatural feeling when the frequency is high although the noise disappears, and the abrupt on / off of the switch at t1, t2, t3, and t4 of the audio signal is another. There is a problem in that a feeling of strangeness occurs when a click occurs and the frequency of signal loss increases as in multipath.

The present invention has been made in view of the above drawbacks and problems, and in an FM receiver, a missing signal generated due to multipath interference is interpolated (signal processing) so that the multipath interference is audibly perceived. The purpose is to eliminate it.

[0008]

In order to achieve the above object, the present invention provides t1 to t2 and t as shown in FIG. 11B.
When the noise 112 is embedded between 3 and t4, the noise is hardly perceived in the sense of hearing, and the auditory phenomenon in which the audio signals 112, ... Specifically, the FM receiver according to the first invention converts the FM received signal into a predetermined IF component signal, performs FM demodulation, and outputs the demodulated signal to the left and right ear component signals based on a predetermined subcarrier signal. In an FM receiver for extracting and obtaining a stereo signal, an amplitude detection means for amplitude-detecting an IF component signal to obtain an amplitude detection signal, and a level for detecting a weak electric field at a predetermined level or lower based on the amplitude detection signal to obtain a detection signal A detection unit, a control signal output unit that outputs a control signal corresponding to the level based on the amplitude detection signal, a replacement signal generation unit that generates a predetermined replacement signal corresponding to the amplitude detection signal, and a control signal Based on the above, when the amplitude detection signal is a weak electric field equal to or lower than a predetermined level, there is provided a signal replacement means for replacing the level signal of the FM demodulation signal or the left and right ear side component signals with the replacement signal. .

In the FM receiver according to the second aspect of the invention, in the FM receiver of the first aspect of the invention, the replacement signal generating means has a delay means for obtaining a delayed signal obtained by delaying the demodulated signal by a predetermined time, The delay signal is used as a replacement signal except when the electric field is weak.

[0010]

With the above construction, in the FM receiver according to the first aspect of the invention, the amplitude detecting means amplitude-detects the IF component signal to obtain the amplitude detecting signal, and the level detecting means weakens the amplitude to a predetermined level or lower based on the amplitude detecting signal. When the electric field is detected and a detection signal is obtained, the control signal output means outputs a control signal corresponding to a predetermined level based on the amplitude detection signal, and the replacement signal generation means performs predetermined replacement corresponding to the amplitude detection signal. Generate a signal. Then, based on the control signal, the signal replacement means replaces the level signal of the FM demodulation signal or the left and right ear side component signals with the replacement signal when the amplitude detection signal is at a predetermined level or lower, thereby reducing the sound quality due to multipath interference. Reduce.

In the FM receiver according to the second aspect of the invention, in the FM receiver of the first aspect of the invention, the replacement signal generating means obtains a delayed signal obtained by delaying the demodulated signal by the delay means for a predetermined time, and the weak signal is weak. The delayed signal is used as a replacement signal except when the electric field is applied.

[0012]

EXAMPLES The present invention will be described below with reference to examples.
In addition, as for the first invention, Examples 1-1 and 1-2 are given.
The second invention will be described in the second embodiment. Further, in each of the drawings of the following embodiments, it is meant that the portions having the same symbols have the same configurations (for example, the portions having the same symbols as those shown in FIG. 7 have the same configurations as those in FIG. 7). Means).

<Embodiment 1-1> FIG. 1A shows the basic components of an FM receiver according to the first invention (IF of the FM receiver).
FIG. 2B is a block diagram showing a configuration of an embodiment (portions after the intermediate frequency stage), and FIG. 2B is a configuration example of a level control unit for controlling the output level of the noise generator. Is an envelope (amplitude) detector, 13 is an amplitude comparison circuit and corresponds to level detection means, 14 is a reference voltage (V = er), 15 is a control pulse generator, 16 is an electronic switcher and corresponds to signal replacement means, Reference numeral 20 is an envelope detector, 21 is a memory (hold memory), 22 is a gain control circuit, 30 is a noise generator, which corresponds to replacement signal generating means, and 31 is a noise level control unit.

The present embodiment is an example in which a noise signal is used as the interpolation signal 112 (see FIG. 11B). The IF signal 1 is detected by the envelope detector 12, and the IF signal shown in FIG.
Obtain the envelope detection output. Then, the output is applied to the amplitude comparator 13, and the control pulse of the control pulse of FIG. The output of the frequency discriminator 2 is generated at the time of a strong electric field ~ t1, t2 ~ t3, t4 ~.
The contact of 6 is a, and the output of the frequency discriminator 2 (baseband signal) is the output of the electronic switcher 16. When the electric field is weak, the contact point of the electronic switcher 16 is set to b at t1 to t2 and t3 to t4, and the band is 0 to 53 KHz.
The output of the noise generator 30 is used as the output of the electronic switcher 16.

The output level of the noise generator 30 shown in FIG. 1A is controlled by the noise level control section 31 shown in FIG. 1B. The noise level control unit 31 uses the envelope detector 2
0, a memory 21, and a gain control circuit 22, and the output of the frequency discriminator 2 (baseband signal)
The amplitude of is detected by the envelope detector 20, and the
Holds its amplitude, and the gain control circuit 22 controls the noise level of the output of the noise generator 30. This noise level control does not have to be accurate level control, and may be the average value of the “certain section” of the output of the frequency discriminator 2. The envelope detector 20 may be replaced with the envelope detector 13, and the output of the envelope detector 12 may be added to the memory 21 to hold its amplitude.

In the circuit of FIG. 1A, t1 to t2 and t3 to t4.
During this period, the input of the switcher 5 becomes noise, so that the output signals 10 and 11 also become noise. However, in this case, BPF3
Since the output of is also mainly noise, it is necessary for the subcarrier generator 4 to generate an approximate 38KHz subcarrier even if the output from the BPF 3 is not an accurate 19KHz pilot signal. Therefore, the subcarrier generator 4 is preferably of a type in which a 38 KHz oscillator is phase-controlled by the output of the BPF 3.

FIG. 3 shows a waveform after noise interpolation according to the first aspect of the present invention. In the case of a short time (t1 to t2, t3 to t4; in mobile reception, there are often 10 ms (millisecond) and outside), almost no noise is heard in the sense of hearing. do not feel.

<Embodiment 1-2> FIG. 2 is a block diagram showing the construction of another embodiment of the basic constituent parts of the FM receiver according to the first invention. Bands 17 and 18 are 0 to 15 KHz.
The noise generator corresponds to the replacement signal generating means, and 19 is the double-pole double-throw electronic switcher corresponding to the signal replacing means. Note that the noise generators 17 and 18 may be one noise generator. The present embodiment is an example in which noise interpolation is performed for each of the right ear signal ER and the left ear signal EL (signals 10 and 11 in FIG. 2), and the control pulse from the control pulse generator 15 causes the contact point of the bipolar switcher 19 to be in a strong electric field. Control is performed so that the side a is set to the side b when the electric field is weak. Bipolar switcher 19
If it is provided before the de-emphasis circuits 8 and 9, discontinuity at the time of switching is reduced. In addition, the noise generators 17, 1
The noise level of 8 is controlled by the output levels of LPFs 6 and 7 by noise level control units 31 ′ and 31 ″ similar to those shown in FIG. 1B.

<Embodiment 2> FIG. 4 is a block diagram showing the configuration of an embodiment of the basic components of the FM receiver according to the second invention (the portion after the IF (intermediate frequency) stage of the FM receiver). In the figure, 41 is an IF envelope detector, 42 is a comparison circuit corresponding to a level detecting means, and 43 is a reference voltage (V
= Er), 44 is a control pulse generator, 45, 46, 4
7, 48 are electronic switchers, 49, 50 are delay time T
The electronic switchers 47 and 48 correspond to signal replacement means, and the electronic switcher 45 and the delay element 49, and the electronic switcher 46 and the delay element 50 respectively form replacement signal generation means. The electronic switchers 45 to 48 may be one quadrupole electronic switch, and memories may be used instead of the delay elements 49 and 50.

The present embodiment is an example in which an interpolation signal that repeats at a period τ of FIG. 8B is inserted into the missing signal of FIG. 8A. The envelope of the IF signal 1 is detected by the IF envelope detector 41, and the output is added to the comparison circuit 42. When the output of the IF envelope detector 41 is the signal of FIG. 8A, the (reference) voltage of the reference voltage 43 is er shown by the alternate long and short dash line in FIG. 8A. Therefore, the control pulse generator 44 is driven by the output of the comparison circuit 42 and t1 to t2, t as shown in FIG. 2B.
A control pulse for 3 to t4 is generated.

LPF demodulated by FM and stereo
The audio signal from 6 is applied to the contact a of the electronic switcher 45 and the contact a of the electronic switcher 47, and the output of the electronic switcher 45 is applied to the contact b of the electronic switcher 47 via the delay circuit 49. Similarly, the audio signal from the LPF 7 is applied to the contact a of the electronic switcher 46 and the contact a of the electronic switcher 48, and the output of the electronic switcher 46 is applied to the contact b of the electronic switcher 48 via the delay circuit 50.

Electronic switchers 45, 46, 47, 48
Selects contact point a when the IF signal level is at or above threshold er, and the IF signal level is at threshold e
When dividing r, the contact b is selected (that is, when dividing the threshold, t1 to t2 and t3 to t in FIG. 8b).
Select contact b with pulse 4). Therefore, the electronic switchers 45, 46, 47 and 48 can also be realized by four-pole type switches.

The output signal from the LPF 6 is the IF signal er.
If the envelope is above, it is directly output to the de-emphasis circuit 8. When the envelope of the IF signal divides er, the electronic switcher 47 selects the contact b side and outputs the delay signal of the delay time Tms of the delay circuit 19 for Tms. Furthermore, since the electronic switcher 45 is connected to the output of the delay circuit 19, the b contact of the electronic switcher 47 is an LPF.
When Tms immediately before switching off the output of 6 is repeatedly output and the IF signal becomes an envelope of er or more, LPF is output.
The output of 6 is applied to the de-emphasis circuit 9.

Similarly, the output signal from the LPF 7 is directly output to the de-emphasis circuit 9 if the IF signal has an envelope of er or more. When the envelope of the IF signal divides er, the electronic switcher 48 selects the contact b side and outputs the delay signal of the delay time Tms of the delay circuit 20 for Tms. Further, since the electronic switcher 46 is connected to the output of the delay circuit 20, the b contact of the electronic switcher 48 repeatedly outputs Tms immediately before the switch-off of the output of the LPF 6 and I
When the F signal has an envelope of er or more, the output of the LPF 7 is added to the de-emphasis circuit 9.

In FIG. 5B, at the time t = t1 following the signal 57 at the broken line portion, the signal 58 at the solid line portion is a delayed signal of Tms, and from the subsequent t2-T to t2, the signal delayed by 2T in FIG. Will be used.

FIG. 6 is an explanatory diagram of the interpolation by the interpolation signal. In FIG. 6A, t0-t1 (interval T) becomes t0-t1 of the insertion signal of FIG. 6B, and the shaded portion from t0 + T to t2 (FIG. 6B). ), The part of t0-t0 'of FIG. 6A is repeated. 6A and 6B are switched at t = t1 and t2, clicks are likely to occur, but in FIG. 4, the de-emphasis circuit subsequent to the electronic switchers 47 and 48 is a kind of integrating circuit and suppresses high frequency components. Does not stay in my ears. Also, by inserting the same kind of signals for both the right ear signal ER and the left ear signal EL, it is possible to listen to a high-quality audio signal without causing a sense of discomfort.

[0027]

As described above, according to the first invention, when a voice (acoustic) signal, which is one of the characteristics of human hearing, is missing for a short time, a noise signal is inserted in the missing section. Since the original audio signal can be listened to without being damaged, the circuit is configured so that noise can be formed in a short time audio signal missing portion due to multipath interference of the FM receiver. It is possible to improve the reception sound quality.

Further, according to the second aspect of the invention, similarly, the auditory interpolation characteristic is utilized to remove the voice signal at the time of low amplitude of the IF signal by the FM multipath interference and interpolate the signal immediately before it. As a result, the sound is interpolated without a sense of discomfort, and deterioration of sound quality due to FM multipath interference can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a basic configuration part (a part after an IF (intermediate frequency) stage of the FM receiver) of an FM receiver according to the first invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the basic components of the FM receiver according to the first invention.

FIG. 3 is a waveform after noise interpolation according to the first invention.

FIG. 4 is a block diagram showing a configuration of an example of a basic component part (a part after the IF (intermediate frequency) stage of the FM receiver) of the FM receiver according to the second invention.

FIG. 5 is an explanatory diagram of a baseband signal dropout portion due to multipath interference and an interpolation signal.

FIG. 6 is an explanatory diagram of interpolation using an interpolation signal.

FIG. 7 is a principle configuration diagram after an IF (intermediate frequency) stage of a conventional FM receiver.

FIG. 8 is an explanatory diagram showing a relationship between fluctuations in a received electric field and control pulse generation.

FIG. 9 is a diagram showing a relationship between electric field strength and S / N.

FIG. 10 is a diagram showing an example of noise due to multipath interference.

FIG. 11 is an explanatory diagram of a signal missing portion and an interpolation signal due to noise processing due to multipath interference.

[Explanation of symbols]

1 IF signal 10 Left ear signal 11 Right ear signal 12,41 Envelope detector (amplitude detection means) 13,42 Amplitude comparison circuit (level detection means) 15,44 Control pulse generator (control signal output means) 1,18, 30 noise generator (replacement signal generation means) 49, 50 delay circuit (delay means (replacement signal generation means)) 16, 19, 47, 48 electronic switcher (signal replacement means)

Claims (2)

[Claims] 1. An FM receiving apparatus for obtaining a stereo signal by converting an FM received signal into a predetermined IF component signal, performing FM demodulation, and extracting the demodulated signal from left and right ear component signals respectively based on a predetermined subcarrier signal. An amplitude detection means for amplitude-detecting the IF component signal to obtain an amplitude detection signal; a level detection means for detecting a weak electric field at a predetermined level or lower based on the amplitude detection signal to obtain a detection signal; and the amplitude detection signal Control signal output means for outputting a control signal corresponding to the level, replacement signal generation means for generating a predetermined replacement signal corresponding to the amplitude detection signal, and the amplitude based on the control signal. Signal replacement means for replacing the level signal of the FM demodulation signal or the left and right ear side component signals with the replacement signal when the detected signal is a weak electric field of a predetermined level or less;
An FM receiver comprising: 2. The FM receiver according to claim 1, wherein
An FM receiver, wherein the replacement signal generation means has a delay means for obtaining a delay signal obtained by delaying the demodulated signal by a predetermined time, and uses the delay signal as a replacement signal except when a weak electric field is present.