JPH01180123A - Fm multiplex broadcast receiver - Google Patents

Abstract

PURPOSE:To decode a multiplex channel signal with high quality by using a frequency modulated wave of multiplex channel only, approaching the frequency of the side band of the FM modulation wave to the carrier frequency of the FM wave, applying the carrier of the FM wave and demodulating the signal through the amplitude limit device. CONSTITUTION:An output of an IF converter 1 is fed to an amplitude limit device 2, an FM demodulator 3 and a demultiplexer 4 separate a voice signal 5. The voice signal 5 is fed to the VCO 7, the output of the VCO 7 and the output of the limiter 2 are fed to a multiplier circuit 8, and a BPF 9 extracts the FM modulation wave of multiplex channel only. Moreover, the carrier of an fR generator 12 is multiplexed by the multiplex circuit 11 through a carrier trap filter 10 and the side band frequency of the frequency modulated wave is approached to the carrier frequency of the FM wave through a BPF 14. Then the carrier extracted by the filter 10 is added by the adder circuit 15 and demodulated by an FM demodulation circuit 16 through an amplitude limiter 16. Then the multiplex channel signal with high quality is decoded at the output of the data decoding circuit 18.

Description

[Detailed description of the invention] A. Industrial application field The present invention relates to a receiving device for FM multiplex broadcasting.

B0 Summary of the Invention In a receiving device for FM multiplex broadcasting, (1) FM demodulated audio channel signals (signals other than multiplex channels) are
The product of the M-modulated FM modulated wave and the IF output FM modulated wave is passed through a filter to create a multichannel-only FM modulated wave, and the FM modulated wave obtained in (2) and (1) and its carrier are removed to perform multiplexing. Channel subcarrier frequency ω76 (7
By multiplying the carrier wave ω with a frequency below 6kHz), F
The frequency of the sideband wave of the FM modulated wave is reduced by ωR through a bandpass filter centered on the carrier wave of the M modulated wave.
After adding the carrier wave of the FM wave close to the carrier frequency of the wave, it is demodulated through an amplitude limiter. In this way, the subcarrier frequency of the ω78 multiplex signal is isometrically reduced to ω − ωk.

C0 Conventional technology Multiplexing data or audio (digital signals) onto FM broadcast waves The frequency distribution of FM multiplexing is as shown in Figure 7, where the audio stereo signal is centered around 38kHz, and the multiplexed data is centered around 38kHz.
76 k& is distributed as a carrier wave. In the receiver,
As shown in Fig. 8, the converter 1 converts the input signal into an intermediate frequency signal IF, the amplitude limiter 2 suppresses the influence of interference waves, and the FM demodulator 3 synthesizes the audio stereo signal and multiplexed data signal. A zero frequency demultiplexer 4 which obtains the components shown in FIG.

D0 Problems to be solved by the invention In this method, a single FM demodulator demodulates an audio signal and a data signal.
The FM demodulation noise of the data signal at the center) increases,
The amplitude of the data signal is 5% or less of the audio signal (for example, 2.
5%), this combined with the drawback of deteriorating the S/N ratio. In particular, when receiving mobile signals onboard a vehicle, noise generated from various parts of the vehicle may cause insufficient SN.
There is a drawback that it cannot be compared.

An object of the present invention is to provide a receiver for FM multiplex broadcasting that performs FM demodulation of multiplexed data signals so as to reduce the influence of noise.

Means for Solving the E0 Problem In order to achieve the above object, the present invention comprises: a first converter for converting a received signal into an intermediate frequency signal; a demodulator for FM demodulating the intermediate frequency signal; F equipped with a demultiplexer that separates the demodulated signal into low frequency components and high frequency components.
The M multiplex broadcast receiving apparatus includes a second converter that converts the voltage change of the low frequency component into a frequency signal, and a second converter that multiplies the input side signal to the demodulator by the frequency signal from the second converter. 1 multiplier, means for obtaining a frequency difference component from the multiplied signal of the first multiplier, means for extracting a predetermined component from the frequency difference component, and multiple channels! a second multiplier for multiplying the predetermined component by a predetermined frequency equal to or lower than the second subcarrier frequency; means for extracting a signal band corresponding to the carrier wave of the FM modulated wave; The gist of the present invention is to include an adding means for adding a carrier wave, and a demodulator for demodulating the signal added by the adding means.

FIG. 2 shows an example of the waveform of the FM multiplexed baseband signal of FIG. 7. However, the pilot signal of fp=19kHz is omitted. The stereo difference signal L-R is amplitude modulated (AM) at 38k7 (=2f9) and multiplexed to the stereo sum signal L+H, resulting in the distribution shown by the solid line.Furthermore, the fs=76kHz shown by the broken line is modulated with the data signal. Components are multiplexed.

Generally, FM modulated wave M(t) is expressed by equations (1) and (2).

M, (t) = A sin ((Llct = A [
JO(Δ(11/(1)) sinωct+J,(Δ
ω/ωH5in(ω0+ω)t-5in(ω0-ω)1
) +J2(Δω/ω)(5in(ωo+2ω)t-5in
(ωO−2ω)1) + ・・・・・・ ] ・・・・・・・・・(
2) In 2\, ωC=carrier frequency, Δω: maximum frequency deviation for the modulated signal, ω: angular frequency of the modulated signal, JOtJi+J2...: Bessel function.

On the other hand, if noise of frequency ω1 is present when receiving M (t), the output signal E of FM demodulation becomes Equation (3).

E=(ω1-ω) cos (ωl-ω)t...
(3) When formula (3) is illustrated, it becomes FIG. 3, and it can be seen that the level of demodulation noise increases in proportion to the frequency of the modulation signal. When FIG. 3 and FIG. 7 are superimposed, it can be seen that in receiving FM multiplex broadcasting, multiplexed data centered around a 76 kHz carrier wave is disadvantageous against noise in the propagation path compared to audio signals.

The present invention allows this data signal to be demodulated even in the presence of noise.

From equation (3), it can be seen that the carrier frequency ωs (=2πts) for multiplexing can be made isometrically lower than 76 kHz at the receiving stage. For that purpose, here is the following
Configure the FM demodulation method.

(1) Remove the audio signal from the received signal and separate the FM modulated wave of the multiplexed signal only.

(2) FM demodulation is performed after lowering the carrier frequency ω using the FM modulated wave of the multiplexed signal.

G. EXAMPLES The present invention will be explained in more detail below using examples with reference to the drawings, but these are merely illustrative and various modifications and improvements can be made without going beyond the scope of the present invention. Of course it is possible.

FIG. 1 is a block diagram showing the configuration of an FM multiplex broadcast receiving apparatus according to the present invention. In the figure, reference numbers common to those in FIG. 8 represent parts that are the same as or correspond to those in FIG. is a voltage controlled oscillator (VCO), 8 is a multiplication circuit, 9 is a bandpass filter, 10 is a carrier trap filter, 11 is a multiplication circuit, 12 is an fR generator, 13 is fR (7 in 19), 14 is a bandpass filter , 15 is a carrier adder circuit, 16 is an amplitude limiter, 17
18 represents an FM demodulation circuit, and 18 represents a data decoding circuit.

The output of the intermediate frequency stage IF converter 1 of the FM receiver is added to the amplitude limiter 2, the FM demodulator 3, and the splitter 4.
The place where the audio signal 5 is separated is the normal F in Fig. 8.
It has the same configuration as the M receiver. Audio signal 5 to V CO
(Voltage Control
rvoltage controlled oscillator) or FM modulator 7 to convert the voltage changes of the audio signal into frequency. At this time, the voltage is controlled so that the output frequency matches the frequency of the audio portion input to the duplexer 4. VCO7 output and amplitude limiter 2
When the output of the filter 9 is added to the multiplier circuit 8 and the frequency difference component is taken out by the band pass filter 9, only the FM modulated component with the FM multiplexed data signal remains in the output of the filter 9.

Equation (1) is modified to provide a form modulated by an audio signal (including a pilot) and a multiplexed data signal.

M(t) = A sin ((11, t“°”°−(
4] 2N, ωC: carrier angular frequency, also applies to the frequency of IF.

Δω,: maximum angular frequency deviation of the audio channel, ω1: angular frequency of the audio channel, Δω3: maximum angular frequency deviation of the multichannel signal, ω3:
Angular frequency of multichannel signal, ω76: Angular frequency of multichannel subcarrier.

Of the FM demodulator 3 shown in FIG.
5).

a = a cosω1t ・・・・・・
(5) a: Amplitude of demodulated signal corresponding to frequency deviation Δω1.

In reality, there is not a single audio channel, but (L+
R) and pilot f, = 19 to 7 and voice subcarrier 2f
, = 38 kHz as stereo component (L - R)
It consists of amplitude-modulated components, but in order to simplify the explanation, it is represented by equations (4) and (5). Let Ms(t) be the modulated wave that is FM-modulated again using the VCO 7 according to e in equation (5).

Ml(t) = A sin (ωc1tωc1:
Carrier angular frequency of output of vco 7.

The output of the multiplier circuit 8 in FIG. 1 is the product of M(t) in equation (4) and Ml(t) in equation (6).

Since M(t)・Mx(t) is the sum component and difference component of the frequencies of equations (4) and (6), extract the difference component with the bandpass filter 9. Let this component be M2(t). , the amplitude is normalized by A.

M2 (t) = A sin [('(1101-Δ
ωt)t (7) Equation (7) indicates that M2(t) is only a multichannel FM signal. That is, the F of only the multi-channel signal excluding the audio signal from the received signal is the part (1) of the present invention up to the output of the band pass filter 9.
Achieving M modulated waves. As for the baseband signal, (a) to (b) in Fig. 4 are removed and (c) is used. In Fig. 4, (a) is the FM of the amplitude limiter 2.
wave baseband signal, (b) is the F of the output of VCO7
M-wave baseband signal, (c) is F of multiplier circuit 8
Represents an M-wave baseband signal.

Next, the process (2) will be explained.

The carrier wave trap filter 10 in FIG. 1 is the output of the bandpass filter 9, that is, the carrier wave (ω.−
ω. 1), and is generally a narrowband trap filter.

Note that Δω3 in equation (7) is the frequency shift for the multiplexed signal, and the standard is several percent of the frequency shift for the audio signal shown by Δω1 in equation (6).

Generally, when the frequency deviation is small for FM modulated waves (Δω1
/ωs<0.5), the FM modulated wave consists of a carrier wave and a first sideband wave, and it is known that the second sideband wave and above can be ignored. For FM broadcasting, Δω, = 75kHz
Because it is.

Δω3〈4 k7, ω7a=76 to 7, that is Δω3
/ω76<0.05, and the multichannel FM wave consists of only the carrier wave and the first sideband wave.

AJo(Δ”) a/ (1) 7o)s in M2(t)
in(ω, + (1) ci)t+AJ1(Δ(113
/ (1) 76) sin(ωC-(L) cs-C7
6) t-AJ, (Δ(i)3/c+)7e) Sin(
ωc−ωct”ω7a)t+ ・・・・・・
(8) However, JotJl is the carrier wave eO8ωRt of the fR generator 12 except for the first term of equation (8) at the carrier wave trap filter 1o of the Heracell function in Fig. 1.
Since it is the product of cosωRt and the second and third terms of equation (8) multiplied by the multiplier circuit 11, its output M2'(t) becomes equation (9).

M2'(t) = AJ, (Δω3/ω7e) sin(ωC-ωc1-ωR
-ω76)t+AJ, (Δ(113/ (1176)s
in((110-<11 c1+(11R-(1) 7
6) t-AJl(Δωs/C76) sun(ω, +
(1) C1-(11R+C76)t-AJl(Δ
(1) 3/ (&l 76) Sin((11C-(1
) c1+ ω, + (IJ 76)t・・・・・・
... (9) Bandpass filter In 14, the second and third terms of equation (9)
Extract only the term.

This will be explained using FIG. FIG. 5(a) shows the output of the bandpass filter 9, and the carrier wave fc
The first sideband waves are distributed upward and downward by +/-76& with fcl as the center. (b) is the distribution with f c f cl removed by trap, (c) is the distribution with trap filter 10
The output of the bandpass filter (
fc-fI± fx, f〈76 k7) at 14 (d)
The second and third terms of equation (9) are extracted as follows.

Addition circuit 15 in FIG. 1 adds carrier wave AJo (Δω3/ω76) extracted by trap filter 10 to
Adding Sin(ω.-ω.1)1, the FM modulated wave M2 is generated again.
”(t).

M2”(t) = AJo(Δ(113/ (1) 7
6) sin(ωC-CIJ C1)t+AJ, (Δ(1
13/ (1) 7e) sin((il c-ωc1÷
ωR-CI) 7e) -AJ, (Δω3/ω7e)s
in(ω0-ωc1-ωR+ω76)t・・・・・・
・・・・・・(10) =A sin[(ωc−ωe1)t ・・・・・・・・・(11) Even if the amplitude of the carrier wave is not a sufficient proportion compared to the sideband wave,
By passing through the amplitude limiter 16, equation (11) is established. In other words, M2''(t) in Equation 1 (11) means that the subcarrier of the multichannel is from C76 (76k7) to (C76-ω
R).

In the explanation so far, the three items in parentheses in equation (4) are sinω3τ and sinω76τ, but when subcarrier ω76 is used, the sideband wave of the AM wave is located around C76, so The result is as shown in Fig. 5, and C76 is used in equation (8) and thereafter.

In addition, in Fig. 1, the output of the duplexer 4 is connected to the ωR oscillator 12
3, f, = 19kHz, fR:
2f, = 38 k7, 3f.

It is also possible to set the frequency to 57kHz.

FIG. 6 shows the noise distribution of the FM demodulator 17 shown in FIG. 1, taking as an example the above-mentioned case of fR=57 kHz at the knee. The horizontal axis in Fig. 6 is the baseband frequency, ■ indicates the noise due to the conventional method, and ■ indicates the noise due to the method of the present invention.1 In the original demodulation of Fig. 8, the multichannel is f76 = 76.
The area where the level of triangular noise centered at kHz is high is used to obtain the integral value of I. fa=57kH
If we take z, we get (C76-ω1□)/2π=19k7, which becomes ■ in Figure 6, which is 1/4 compared to ■.
However, if the frequency of the multichannel modulation signal sinω3t of the subcarrier ω76 is 19kHz or more, ωR/2π<57 must be set, and there is no effect in Fig. 6, but n<1 holds, S of the data signal
This results in a significant improvement in the N ratio.

Effects of the H0 Invention In FM demodulation, noise in a low electric field becomes triangular noise, which increases in proportion to the frequency from the carrier wave of the FM wave. The multichannel frequency is 76 kHz away from the center frequency (carrier wave), and the level is several percent of that of an FM voice signal, so the influence of noise is large.

According to the present invention, by isometrically reducing the deviation from the center frequency of the FM wave, the noise in FM demodulation of a multi-channel signal can be reduced by that amount, and the multi-channel signal can be produced with good quality. The advantage is that it can be restored.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an FM multiplex broadcast receiving apparatus according to the present invention, Fig. 2 is a baseband signal waveform diagram of FM multiplexing, Fig. 3 is a noise distribution diagram of FM demodulation, and Fig. 4 is a diagram of the data signal. Separation explanatory diagram, Figure 5 is a diagram of FM wave band change of multiplexed data, Figure 6 is a diagram of change in FM demodulation noise distribution,
Fig. 7 is a frequency distribution diagram of the baseband signal of FM multiplex broadcasting, and Fig. 8 is a diagram of the FM multiplex reception system. 1... IF converter, 2...
・・・・・・Amplitude limiter, 3・・・・・・FM demodulator, 4・・・・・・Brancher, 5・・・・・・・・・
・Audio signal, 7... Voltage controlled oscillator (V
CO), 8...Multiplication circuit, 9...
... Band pass filter, 10 ... Carrier trap filter, 11 ... Multiplier circuit, 12 ... fR generator, 13・・・・・・
・・・・・・fR (19kHz), 14・・・・・・・・・
・Band pass filter, 15...Carrier adder circuit, 16...Amplitude limiter, 17...
......FM demodulation circuit, 18...
Data decoding circuit. Patent applicant Clarion Co., Ltd.

Claims (1)

[Claims] A first converter that converts a received signal into an intermediate frequency signal;
In an FM multiplex broadcast receiving device comprising a demodulator that performs FM demodulation of the intermediate frequency signal, and a duplexer that separates the demodulated signal into a low frequency component and a high frequency component, (a) a voltage of the low frequency component; a second converter for converting the change into a frequency signal; (b) a first multiplier for multiplying the input signal to the demodulator by the frequency signal from the second converter; (c) the first multiplier for multiplying the frequency signal by the second converter; (d) means for extracting a predetermined component from the frequency difference component; (e) multiplying the predetermined component by a predetermined frequency equal to or lower than the subcarrier frequency of the multichannel; (f) means for extracting a signal band corresponding to the carrier wave of the FM modulated wave; (g) means for adding the carrier wave of the FM wave to the extracted signal band; and (h) the addition means for adding the carrier wave of the FM wave to the extracted signal band. An FM multiplex broadcast receiving apparatus comprising a demodulator for demodulating a signal applied by the means.