JP2673299B2 - FM multiplex broadcast receiver - Google Patents

Description

The present invention relates to a receiver for FM multiplex broadcasting.

B. Outline of the Invention In a receiver for FM multiplex broadcasting, (1) the product of an FM modulated wave of the FM demodulated voice channel signal (a signal other than the multiplex channel) and the IF modulated FM modulated wave is multiplexed through a filter. The FM-modulated wave of only the channel is used, and the product of the FM-modulated wave obtained in (2) and (1) and its carrier is removed, and the carrier ω _R of the frequency below the sub-carrier frequency ω ₇₆ (76 kHz) of the multi-channel. Through a band pass filter centered on the carrier wave of the FM modulated wave, and the carrier wave of the FM wave is added by bringing the frequency of the sideband wave of the FM modulated wave close to the carrier frequency of the FM wave by ω _{R and then} passed through an amplitude limiter. Demodulate. This way ω
Subcarrier frequency of ₇₆ multiplexed signal drops equivalently ω-ω _R.

C. Conventional technology The frequency distribution of FM multiplexing that multiplexes data or voice (digital signal) into the FM broadcast wave. As shown in Fig. 7, the voice stereo signal is centered at 38kHz and the multiplexed data is distributed with 76kHz as the carrier. ing. In the receiver, as shown in FIG. 8, the converter 1 frequency-converts the input signal into the intermediate frequency signal IF, the amplitude limiter 2 suppresses the influence of the interfering wave, and the FM demodulator 3 multiplexes with the audio stereo signal. The components shown in FIG. 7 are obtained by combining the data signals. Low frequency component (53kH
z or less) 5 is the high-frequency component (61
(-91kHz) is a data signal, so it is sent to the data decoder 6.

D. Problems to be solved by the invention In this method, a single FM demodulator demodulates a voice signal and a data signal. However, the FM demodulation noise of the data signal at a high frequency (centered at 76 kHz) is larger than the voice band. The amplitude of the data signal is less than 5% of the voice signal (eg 2.5%).
There was a drawback that the deterioration of the SN ratio came together with the small thing. In particular, there is a drawback that a sufficient signal-to-noise ratio cannot be obtained due to noise generated from each part of the vehicle when moving and receiving in a vehicle.

An object of the present invention is to reduce the influence of noise on a multiplexed data signal in a receiver of FM multiplex broadcasting.
It is to provide a receiver for FM demodulation.

E. Means for Solving the Problems To achieve the above object, a first converter for converting a received signal into an intermediate frequency signal, and a demodulator for FM demodulating the intermediate frequency signal according to the present invention, An FM multiplex broadcast receiver including a demultiplexer for separating the demodulated signal into a low frequency component and a high frequency component, a second modulator for converting a voltage change of the low frequency component into a frequency signal, and the above A first multiplier for multiplying the input side signal to the demodulator by the frequency signal by the second converter; a means for obtaining a frequency difference component from the multiplication signal of the first multiplier; and the frequency difference component Means for extracting a predetermined component from the second multiplier, a second multiplier for multiplying a predetermined frequency equal to or lower than the subcarrier frequency of the multiplex channel by the predetermined component, and means for extracting a signal band corresponding to the carrier wave of the FM modulated wave. , Add the FM wave carrier to the extracted signal band And that adding means, and summarized in that includes a demodulator for demodulating a signal applied by said adding means.

F. Action FIG. 2 is an example of the waveform of the FM multiplex baseband signal of FIG. However, the pilot signal of f _p = 19 kHz is omitted. The stereo difference signal L + R is amplitude-modulated (AM) at 38 kHz (= 2f _p ) and multiplexed with the stereo sum signal L + R to form a solid line distribution, and f _S = 76 kHz indicated by a broken line.
Are modulated with a data signal and multiplexed.

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

_{= A [J 0 (Δω /} ω) sinω c t + J 1 (Δω / ω) {sin (ω 0 + ω) t -sin (ω 0 -ω) t} + J 2 (Δω / ω) {sin (ω 0 + 2ω) t −sin (ω ₀ −2ω) t} + ... ······· (2) Here, ω _{c is the} carrier frequency, Δω is the maximum frequency deviation with respect to the modulation signal, and ω is the modulation. Angular frequency of signal, J ₀ , J ₁ , J ₂ …: Bessel function.

On the other hand, when noise of frequency ω _n exists when M (t) is received, the output signal E of FM demodulation is given by equation (3).

E = (ω _n −ω) cos (ω _n −ω) t (3) When Equation (3) is shown in FIG. 3, the demodulation noise level increases in proportion to the frequency of the modulation signal. You can see that It can be seen from the superposition of FIG. 3 and FIG. 7 that in the reception of FM multiplex broadcasting, the multiplexed data centered on the carrier of 76 kHz is more disadvantageous to the noise in the propagation path than the audio signal. 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 for multiplexing ω _s (= 2πt _s ) should be equivalently lower than 76 kHz at the receiving stage. Therefore, the following FM demodulation method is configured here.

(1) Along with the audio signal from the received signal, only the multiplexed signal
Separate FM modulated waves.

(2) FM demodulation is performed after the carrier frequency ω _s is lowered by the FM modulated wave of the multiplexed signal.

G. Examples Hereinafter, the present invention will be described in more detail by way of examples with reference to the drawings, but these are merely examples, and various modifications and improvements can be made without departing from the scope of the present invention. Of course, this is possible.

FIG. 1 is a block diagram showing a configuration of an FM multiplex broadcast receiving apparatus according to the present invention. In the figure, reference numerals common to FIG. 8 indicate the same or corresponding portions as those in FIG. Is a voltage controlled oscillator (VCO), 8 is a multiplication circuit, 9 is a band pass filter, 10 is a carrier trap filter, 11 is a multiplication circuit, 12 is an f _R generator, 13 is f _R (19 kHz), 1
4 is a band pass filter, 15 is a carrier addition circuit, 16 is an amplitude limiter, 17 is an FM demodulation circuit, and 18 is a data decoding circuit.

The place where the output of the IF receiver IF converter 1 of the FM receiver is added to the amplitude limiter 2 and the audio signal 5 is separated by the FM demodulator 3 and the demultiplexer 4 is similar to the ordinary FM receiver of FIG. It is the structure of. Audio signal 5 is VCO (Voltage Control Oscillato)
(r voltage controlled oscillator) or FM modulator 7, and converts the voltage change of the audio signal into frequency. At this time, the voltage is controlled so that the output frequency matches the frequency of the voice part of the input of the duplexer 4. When the output of the VCO 7 and the output of the amplitude limiter 2 are applied to the multiplication circuit 8 and the frequency difference component is taken out by the band pass filter 9, the output of the filter 9 remains only the component FM-modulated by the FM multiplex data signal.

Transforming equation (1), the audio signal (including pilot)
And modulated with multiple data signals.

Here, ω _c is also applied to carrier angular frequency and IF frequency.

Δω _{1 is} the maximum angular frequency deviation of the voice channel, ω _{1 is} the angular frequency of the voice channel, Δω _{3 is} the maximum angular frequency deviation of the multi-channel signal, ω _{3 is} the angular frequency of the multi-channel signal, ω _{76 is the} multi-channel sub Angular frequency of carrier wave.

Of the FM demodulator 3 shown in FIG. 1, the low frequency component 5 extracted by the demultiplexer 4 is the two items of the equation (4), and the equation (5)
Becomes

e = a cos ω ₁ t (5) a: The amplitude of the demodulated signal corresponding to the frequency shift Δω ₁ .

Actually, the voice channel is not a single channel, but (L
+ R) and pilot f _p = 19kHz and voice subcarrier 2f _p = 38kH
It is composed of a component in which z is amplitude-modulated by a stereo component (LR), but here, for simplicity of description, it is represented by equations (4) and (5). VCO7 with e in equation (5)
Let M ₁ (t) be the modulated wave that was FM-modulated again using.

ω _c1 : Carrier frequency of VCO7 output.

The output of the multiplication circuit 8 in FIG. 1 is the product of M (t) in equation (4) and M ₁ (t) in equation (6). Since M (t) · M ₁ (t) is the sum component and the difference component of the frequencies of the formulas (4) and (6), the band pass filter 9 extracts the difference component. This component is M ₂ (t), and the amplitude is normalized by A.

Expression (7) indicates that M ₂ (t) is only the multi-channel FM signal. That is, up to the output of the band-pass filter 9 is the part (1) of the present invention, in which the FM modulated wave of only the multi-channel signal obtained by removing the voice signal from the received signal is achieved. The baseband signal is to be (c) by removing (b) from (a) in FIG.
In FIG. 4, (a) is the FM wave baseband signal of the amplitude limiter 2, (b) is the FM wave baseband signal of the VCO 7 output,
(C) represents the baseband signal of the FM wave of the multiplication circuit 8.

 Next, the process (2) will be described.

The carrier trap filter 10 of FIG. 1 is the output of the bandpass filter 9, that is, the carrier (ω _c −ω _c1 ) of the equation (7).
Is a demultiplexing circuit, and is generally a narrow band trap filter.

It should be noted that Δω ₃ in Expression (7) is the frequency deviation for the multiplexed signal, and the standard is several% of the frequency deviation for the audio signal represented by Δω ₁ in Expression (6). It is generally known that when the frequency shift of the FM modulated wave is small (when Δω ₁ / ω ₁ <0.5), the FM modulated wave consists of the carrier and the first sideband, and the second sideband and above can be ignored. In FM broadcasting, Δω
_{Since 1} = 75 kHz, Δω ₃ <4 kHz, ω ₇₆ = kHz, that is, Δω ₃ / ω ₇₆ <0.05, and the multi-channel FM wave consists of the carrier wave and the first sideband wave only.

M ₂ (t) ≈ AJ ₀ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _{c 1} ) t + AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _{c 1} −ω ₇₆ ) t −AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _c1 + ω ₇₆ ) t + …………………… (8) where J ₀ and J ₁ are the Hessian function in the carrier trap filter 10 of the formula (1). 1) of 8)
Except for the term, the carrier wave cosω _R t of the f _R generator 12 and the multiplication circuit 11
Multiply by. The second and third terms of equation (8) and cosω _R t
And the output M ₂ ′ (t) is given by equation (9).

M ₂ ′ (t) = AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _c1 −ω _R −ω ₇₆ ) t + AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _c1 + ω _R − ω ₇₆ ) t −AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _{c 1} −ω _R + ω ₇₆ ) t −AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _{c 1} + ω _R + ω ₇₆ ) t + ... (9) The band pass filter 14 extracts only the second and third terms of the equation (9).

This will be described with reference to FIG. FIG. 5 (a) shows the output of the bandpass filter 9, in which the first sideband is vertically distributed at ± 76 kHz around the carrier wave f _c −f _c1 .
(B) is a distribution in which f _c −f _c1 is removed by a trap, (c) is the output of the trap filter 10, that is, equation (9),
A band-pass filter (f _c −f ₁ ± f _K , f _K <76 kHz) 14 is used to extract the second and third terms of the equation (9) as shown in (d). In addition to this, the addition circuit 15 in FIG.
Carrier wave AJ ₀ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω extracted in 10
_c1 ) t is added and the FM modulated wave M ₂ ″ (t) is obtained again.

M ₂ ″ (t) = AJ ₀ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _c1 ) t + AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _{c 1} + ω _R −ω ₇₆ ) t −AJ ₁ (Δω ₃ / ω ₇₆ ) sin (ω _c −ω _c1 −ω _R + ω ₇₆ ) t
…………(Ten) Even if the amplitude of the carrier wave is not a sufficient ratio as compared with the sideband wave, the expression (11) is established by passing through the amplitude limiter 16. That is, M ₂ ″ (t) in the equation (11) indicates that the subcarriers of the multiple channels are reduced from ω ₇₆ (76 kHz) to (ω ₇₆ −ω _R ).

In addition, in the above description, the three items in () of the equation (4) are sinω ₃ τ · sinω ₇₆ τ, but the subcarrier ω
_{When 76} is used, the sideband of the AM wave is located around ω ₇₆ , so that the result is as shown in FIG. 5, and ω ₇₆ is used in equation (8) and thereafter.

Further, in FIG. 1, the frequency is coupled to the ω _R oscillator 12 to the output 13 of the demultiplexer 4, f _p = 19 kHz, and f _R = 2f _p = 38 kHz, 3f _p =
It is also possible to set it to 57kHz.

FIG. 6 shows the noise distribution of the FM demodulator 17 of FIG. 1, and here, the case of f _R = 57 kHz is taken as an example. The horizontal axis of FIG. 6 is the baseband frequency, where I is the conventional system and II is the noise of the system of the present invention. In the original demodulation of FIG. 8, the multiple channel uses the place where the level of the triangular noise centered at f ₇₆ = 76 kHz is large and becomes the integral value of I. f _R = 57kH
Taking z gives (ω ₇₆ −ω ₁₂ ) / 2π = 19kHz,
II, which is 1/4 of I. However, the frequency of the modulated signal sin ω ₃ t of the subcarrier ω ₇₆ is 19 kHz.
In the above case, ω _R / 2π <57kHz must be set, which is not as effective as in FIG. 6, but II <I holds and the data signal
This is a significant improvement in the SN ratio.

H. Effect of the invention In the FM demodulation, the noise in the electric field stopping is triangulated noise and increases in proportion to the frequency of the FM carrier wave. The multiple channels are separated from the center frequency (carrier wave) by 76 kHz, and F
The level is a few percent of the M voice signal, and the influence of noise is large. According to the present invention, noise in FM demodulation of a multi-channel signal can be correspondingly reduced by equivalently reducing the deviation of the FM wave from the center frequency, and a high-quality multi-channel signal can be restored. The advantage is that you can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an FM multiplex broadcasting receiver according to the present invention, FIG. 2 is a FM multiplex baseband signal waveform diagram, FIG. 3 is a noise distribution diagram of FM demodulation, and FIG. 4 is a data signal diagram. Separation explanatory diagram, Fig. 5 is band change diagram of FM wave of multiplex data, Fig. 6 is change diagram of FM demodulation noise distribution, Fig. 7 is frequency distribution diagram of baseband signal of FM multiplex broadcast, and Fig. 8 is It is an FM multiplex reception system diagram. 1 ... IF converter, 2 ... amplitude limiter, 3 ... FM demodulator, 4 ... demultiplexer, 5 ... voice signal, 7 ... voltage controlled oscillator (VCO), 8 ... multiplier circuit, 9 ... Band pass filter, 10 ... Carrier trap filter, 11 ... Multiplier, 12 ... F _R generator, 13 ... F _R (19kHz), 14 ... Band pass filter, 15 ... Carrier adder , 16 …… Amplitude limiter, 17 …… FM demodulation circuit, 18 …… Data decoding circuit.

Claims (1)

(57) [Claims] 1. A first converter for converting a received signal into an intermediate frequency signal.
And a demodulator for FM demodulating the intermediate frequency signal,
In an FM multiplex broadcasting receiver including a demultiplexer for separating the demodulated signal into a low frequency component and a high frequency component, (a) a second converter for converting a voltage change of the low frequency component into a frequency signal , (B) a first multiplier that multiplies the input signal to the demodulator by the frequency signal from the second converter, and (c) obtains a frequency difference component from the multiplication signal of the first multiplier. Means, (d) means for extracting a predetermined component from the frequency difference component, (e) a second multiplier for multiplying a predetermined frequency equal to or lower than a subcarrier frequency of multiple channels by the predetermined component, (f) FM modulation Means for extracting a signal band corresponding to the carrier wave of the wave, (g) adding means for adding the carrier wave of the FM wave to the extracted signal band, and (h) a demodulator for demodulating the signal added by the adding means. FM multiplex broadcasting receiver characterized by including