JP2742685B2 - Apparatus for receiving FM multiplex signal - Google Patents

Description

A. Field of the Invention The present invention relates to a demodulator for demodulating an IF signal, a filter for separating a predetermined signal from the demodulated signal, and a stereo demodulator for stereo demodulating the separated signal. The present invention relates to an FM multiplex signal receiving apparatus provided. B. Summary of the Invention At the IF (intermediate frequency) stage of an FM multiplex broadcast receiver, a delay line, a multiplication circuit, and a bandpass filter (separate the sum frequency component or difference frequency component of the product of the IF wave product of the IF) ) And a 1/2 frequency divider circuit that averages the frequency shift of FM, suppresses the stereo difference component and sum component of the audio, and multiplexes the digital signal four times the frequency of the pilot signal. A circuit that emphasizes the FM component corresponding to the signal. C. frequency distribution of the baseband signal of an FM multiplex broadcast ART nearby broadcast is started, as shown in FIG. 10, 76 kHz (4f _p in a frequency band 0~53kHz conventional stereo sound, f _p = A data signal having a 19 kHz pilot signal as a carrier is multiplexed. Form of multiplex signals using a carrier wave cos 4ω _p t in the form of binary. As an example, as shown in FIG. 11, cos 4ω _p t
And, to use the 2 value of -cos 4ω _p t. In the conventional receiving method, as shown in FIG.
The FM demodulator 32 uses the baseband signal shown in Fig. 10 and filters
Separating the audio signal and multiplex signal in 33, the multiplexed signal of the filter 34, for example, from the pilot signal cos omega _p t extracted by the band filter 35 is multiplied by 4 by the frequency multiplication circuit 36 cos
4Omega _p make t, and synchronous detection output of the filter 34 at the frequency detector 37, a positive or negative digital signal to recover the information input by the D / A converter 38. In such a conventional method, if the broadband FM demodulator 32 is required and the circuit shown in FIG. 12 is provided in a device having an existing demodulator for an audio signal, the audio portion is doubled, It is uneconomical, and has the drawback that a part corresponding to the audio part is added as a demodulator even when it is desired to use only the FM multiplex signal. D. Problems to be Solved by the Invention It is an object of the present invention to provide an FM multiplex signal receiving apparatus that separates and demodulates a multiplex signal with an IF signal of an FM receiver. E. Means for Solving the Problems In order to achieve the above object, an FM multiplexed signal receiving device according to the opening paragraph according to the present invention is provided with an IF signal from a received FM multiplexed signal on which an FM modulation signal of digital data is multiplexed. Means for delaying the IF signal by a time corresponding to the reciprocal of the carrier frequency of the digital data, and outputting a first delayed IF signal; the first delayed IF signal and the IF signal A first multiplier for multiplying the output of the first multiplier, a first signal extracting means for extracting a sum component signal from an output of the first multiplier,
A second delay unit that outputs a second delay IF signal obtained by delaying the IF signal by half the time of the first delay unit, and a second delay unit that multiplies the sum component signal by the second delay IF signal And a multiplier of
Extracting a difference component signal from an output of the second multiplier;
And a digital data demodulator for FM demodulating the difference component signal. In a preferred embodiment of the present invention, the separating circuit is configured by combining a plurality of delay elements, a plurality of multiplying circuits, and a plurality of bandpass filters. F. Function On the transmitting side of FM multiplex broadcasting,
It modulates 76kHz with digital data or the like to a stereo program, adds it, performs FM (frequency modulation), and transmits it. Second
The figure conceptually shows FM multiplex transmission, in which 54 is an FM stereo program, 55 is digital data, etc., 56 is an adder, 57
Represents an FM modulation transmitter, and 58 represents a transmitting antenna. Figure 10 shows
2 is a frequency distribution at a point A in FIG. 2 before being applied to an FM modulation transmitter. On the receiving side, the FM stereo program and digital data are separated in the reverse process. FIG. 1 is a block diagram showing the configuration of an FM multiplex receiver according to the present invention, in which 1 is a receiving antenna, 2 is a tuner unit frequency converter, 3 is a local oscillator, 4 is an FM demodulator, and 5 is
53 kHz low-pass filter, 6 is an FM multiplexed signal separation circuit, 7 is a stereo demodulator, 8 and 9 are stereo demodulated signals E _R and
E _L and 10 are digital data decoders, and 11 is a data output signal. The output of antenna 1 is applied to frequency converter 2,
The difference in frequency from the local oscillator 3 is obtained, and the signal reaches the IF stage B. In a general receiver, the B signal is applied to the FM demodulator 4.
The frequency distribution of the output of the FM demodulator 4 is shown in FIG. Therefore, the signal is separated into a stereo modulated signal and a digital signal by the FM multiplex signal separating circuit 6, and the output of the low-pass filter 5 is converted into signals of the right and left ears of E _R 8 and E _L 9 by the stereo demodulator 7. On the other hand, the output of the FM multiplexed signal separation circuit 6 is applied to a digital data decoder 10, and a data signal 11 is obtained. In the present invention, the IF stage of B is added to the FM multiplexed signal separation circuit 6 to separate the FM modulated signal (IF stage) of digital data in the form of an IF signal modulated by FM. The output of the FM multiplex signal separation circuit 6 is applied to an FM demodulator for digital data.
The data signal is extracted. Unlike a stereo signal, this demodulator may be a simple demodulator that does not require strict characteristics such as linearity. 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. When an FM signal is separated into an audio signal and a multiplexed (data) signal at the IF signal stage and demodulated by independent FM demodulators, (i) the linearity of frequency versus amplitude is improved, and an audio signal with less distortion can be obtained. (Ii) Since the multiplexed signal is binary, there is an advantage that a simple FM demodulator for binary, which does not require a gradation, can be used, and (iii) only demodulation of a data signal can be handled. However, in the IF band, the signal is an FM signal, and the signal having the baseband frequency distribution shown in FIG. 10 cannot be separated by a filter. In this case, a method using a delay line, a multiplication circuit, and a band filter is applied to filter separation of an IF band FM signal converted into a base band. The characteristics of the filter using the delay line in the base band will be described with reference to FIGS. In FIG. 3, τ ₁ and τ ₂ are delay elements, + is an adder circuit, 1/2 is an attenuator for setting a low frequency gain to 1, and a triangle is an operational amplifier. When the input is represented by E (0), τ of the signal E (t) of the filter having the structure shown in FIG.
_Since the component delayed by _two is E (τ ₂ ), the sum of its input and output is E (0) + E (τ ₂ ). At frequencies where ω _τ2 = π (2n + 1), n = integer, E (0) and E (τ ₂ ) are in opposite phases, and E (0) and E (τ ₂ ) are zero. This isゝ, when the τ ₂ = 1 / 4f _p, the gain 0 at _{f = 38kHz (= 2f p)} × (2n + 1). That is, the frequency characteristic of the circuit of FIG. 3A is a comb filter characteristic in FIG. 4A. Further, in FIG. 3 (b), E (0) and 2.tau ₁ the average value of the sum of the delayed signal E (2τ ₁₎ FIG. 4B shows the same characteristics as FIG. 4A.
Was Isuzu, and because a childゝis set to _{τ 1 = 1 / 16f p,} f = 76kHz × (2n + 1) in the gain becomes zero, the gain at 76 kHz × 2n becomes 1. Third
In FIG. (B), a combination of the components and tau ₁ delay E (τ ₁₎ Is obtained, the characteristic becomes as shown in FIG. 4 (c). The gain becomes 0 at 76 kHz × 2n and becomes a comb filter having a gain of 1 at 76 kHz × (2n + 1). FIG. 4 is for the baseband signal, but in the IF band.
With respect to the FM signal, the configuration shown in FIG. 5 can have the same characteristics. In FIG. 5, 24 is an IF signal (FM) M
(T), 25 is a delay line: τ ₂ , 26 is a multiplying circuit, 27 is a bandpass filter (sum frequency component), 28 is a 1/2 frequency dividing circuit (for example, flip-flop), and 29 is an output. When the multiplication circuit 26 multiplies M (0) and M (τ), and the sum frequency component of the product is taken out by the bandpass filter 27, the baseband signal is obtained by the processing shown in FIG.
(0) + E (τ). In addition, 1 /
2 corresponds to the frequency dividing circuit 28, for example, a flip-flop.
Therefore, output 29 is Of the FM signal. The same applies to FIG. 3 (b), but a specific configuration will be described in detail with reference to FIG. FIG. 6 is a block diagram showing the configuration of the multiplexed signal separation circuit 6 in the IF stage, in which 31 is an IF signal, and 39 is a delay element τ ₂ = 1 /
4f _p, 40 a multiplier circuit, the bandpass filter (sum frequency component) 41, 42 and 43 are delay elements _{τ 1 = 1 / 16f p,} 44,48 and
50 is a multiplication circuit, 45 is a bandpass filter (sum frequency component), 46
Is a frequency dividing circuit, 47 is a carrier signal cos ω ₁ t, 49 is a bandpass filter (sum frequency component), 51 is a bandpass filter (difference frequency component), 52 is an output, and 53 is a frequency dividing circuit. 31 is a IF signal at FM, τ _{2 =} 1 / 4f delay elements _p 3
9, the multiplying circuit 40, the band-pass filter (sum frequency component) 41, and the frequency dividing circuit 53 are as described in FIG. It should be noted, chose to delay time τ _{2 =} 1 / 4f _p is, the voice signal 38kHz (= 2f
Since stereo difference signal centered at _p) are multiplexed, in order to attenuate as the baseband signal around 2f _p Fig. 4 (a). The delay elements 42 and 43 of FIG. 6 τ _{1 = 1} / 16f _p multiplication circuit 44
And when converted to baseband by the band filter 45 of the sum frequency component, constituting a comb filter multiple carrier 4f _p = 76 kHz is zero. The frequency dividing circuit 46 performs baseband average processing. Tau ₁ delay signal which is the output of the delay element 42 is multiplied by the multiplier circuit 48 and the carrier signal cos ω ₁ t47, bandpass filter
49 takes the sum component in, for converting the frequency from omega of the output of the delay element 42 omega + omega _1. Output of frequency divider 46 and bandpass filter
The output of 49 is multiplied by a multiplying circuit 50, and the difference frequency component is extracted by a band-pass filter 51 to obtain an output 52. This processing is performed in the baseband by using ΔE in FIG. 3 (b).
This corresponds to taking the difference between (0) + E (2τ ₁ )｝ / 2 and E (τ ₁ ). If cos ω ₁ t of the carrier signal 47 is not used, the difference frequency of the multiplying circuit 50 is prevented from becoming almost zero in the IF band where the frequency modulation is performed. The process of Figure 3 is at baseband (b), a characteristic emphasizing 4f _p = 76 kHz of FIG. 4 (c). Therefore, the overall characteristics of the base band in FIG.
Becomes Figure (a) and the product of (c), the components around the carrier 4f _p multiple signal as FIG. 7 can be separated by the IF band. FIG. 8 shows an example of the usefulness of the multiplex signal separation of the present invention. In this case, for convenience of explanation, the parts 31 to 53 in FIG. 6 are brought after the processing, but this is a linear processing and there is no problem. FIG. 8 (a) shows a binary coded multiplexed signal of 1,0. (B) is a signal obtained by polar modulating a 76 kHz carrier. An FM signal FM-modulated with a signal obtained by multiplexing the signal (b) with the audio signal becomes an IF signal. Here, a change in the multiplexed signal at the baseband is shown. (C) is the delay of 1 / 8f _p of (b), (e) is the delay of 1 / 16f _p. (D) is the average (baseband) of (b) and (c),
The subtraction of (e) and (d) becomes (f). The above is shown in FIG.
This is a baseband signal corresponding to the processing of 42 to 51. On the other hand, in 31 to 53 of FIG.
Suppress components with _p = 38 kHz as the carrier. Of Figure 8 a (f) 1 / 4f _p delayed make (g), (f) and (g)
(H). At point A where the amplitude of (h) increases positively, the sign changes from 0 to 1 and B increases negatively.
At this point, assuming that the value changes from 1 to 0, the data signal (binary) of (i) is restored, which has a distribution equal to that of FIG. 8 (a). Note that a simple frequency detection circuit is sufficient for generating the signals (h) to (i). Figure 9 is modulated wave audio stereo component 2f _p is 6 Figure 31
~ 53 indicates how much remains. The low-frequency component of the stereo component becomes almost zero in the processing of FIGS. When stereo difference signal is high, components remaining in cancellation with a delay of 1 / 4f _p comes increased. FIG. 9 (a) shows cos (2π × 2f _p
An example is shown in which the carrier for stereo in t) is modulated at 9.5 kHz. The solid line in FIG. 9 (a) is the stereo component, and the broken line is
It is a delayed signal of 1 / 4f _p. Therefore, when the processing of 31 to 53 in FIG. 6 is performed in the IF stage, the baseband signal becomes as shown in FIG. 9 (b),
It is significantly attenuated as compared to FIG. 9 (a), and the influence of the amplitude in FIG. 8 (h), and therefore the IF stage, can be easily eliminated as compared to the frequency shift. H. Effects of the Invention As described above, according to the present invention, an FM stage is not demodulated by a FM multiplex broadcast receiver and then separated into an audio signal and a multiplex (data) signal. Multiplexed signal can be separated from the audio signal, so that each FM demodulation is easy, and since only the FM multiplexed component can be extracted at the IF stage, it is possible to apply a simple FM demodulator. Is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an FM multiplex receiver according to the present invention, FIG. 2 is a conceptual diagram of FM multiplex transmission, and FIG. 3 shows a configuration of a delay signal combining circuit in an IF band. FIG. 4 is a block diagram, and FIG.
FIG. 13 is a block diagram showing the configuration of a processing circuit using an IF signal.
FIG. 7 is a block diagram showing the configuration of a multiplexed signal separation circuit in the IF stage, FIG. 7 is a baseband overall characteristic diagram, FIG. 8 is a waveform diagram showing an example of signal processing, and FIG. 9 is the effect of an audio stereo signal. FIG. 10 is a frequency distribution diagram of the FM multiplex signal, and FIG.
Figure waveform diagram showing an example of the code display by cos 4ω _p t, the first
FIG. 2 is a block diagram showing an example of the FM multiplex signal separation method. 1 ... Reception antenna, 2 ... Tuner section frequency converter, 3 ... Local oscillator, 4 ... FM demodulator, 5 ... 53kHz
Low-pass filter, 6 FM multiplex signal separation circuit, 7 stereo demodulator, 8, 9 stereo demodulated signal, E _R , E _L , 10
Digital data decoder, 11 data output signal,
31 ...... IF signals, 39 ...... delay elements _{τ 2 = 1 / 4f p,} 40 ...... multiplier circuit, 41 ...... band filter (the sum frequency component), 42, 43 ...
... delay _{element, τ 1 = 1 / 16f p} , 44,48,50 ...... multiplication circuit, 45
…… Band filter (sum frequency component), 46 …… Division circuit,
47: Carrier signal cos ω ₁ t, 49: Band filter (sum frequency component), 51: Band filter (difference frequency component), 52
…… Output, 53 …… Division circuit, 54 …… FM stereo program, 55
… 56 digital data, etc. adder, 57 FM transmitter, 58 transmitting antenna.

Claims (1)

(57) [Claims] Means for obtaining an IF signal from a received FM multiplexed signal in which an FM modulation signal of digital data is multiplexed; and 1
Delay means, a first multiplier for multiplying the first delayed IF signal by the IF signal, and a first multiplier for extracting a sum component signal from an output of the first multiplier.
Signal extracting means, and a second signal obtained by delaying the IF signal by half the time of the first delay means.
A second delay unit that outputs a delayed IF signal of the following: a second multiplier that multiplies the sum component signal by the second delayed IF signal; and a difference component signal from the output of the second multiplier. Second to extract
And a digital data demodulator that performs FM demodulation of the difference component signal.