JPH0495423A - Fm multiplex receiver - Google Patents

Abstract

PURPOSE:To demodulate a data without being affected by noises even at a weak electric field by using a couple of changeover means so as to select a limiter output continuously, FM-demodulating the data and extracting a data signal. CONSTITUTION:An output of a limiter 5 is switched by a couple of electronic switches 14, 21 in the FM multiplex receiver, FM-demodulated by frequency discriminators 15, 16, 22, 23 and LPFs 19, 26 extract data signals DI, DQ. Thus, the data signals DI, DQ not affected by high frequency noise (51-91KHz band) attended with FM demodulation are obtained. Since the data is switched by using a narrow pulse tau2 by electronic switches 18, 25 and given to an LPF, the effect of fluctuation based on a phase of an FM carrier and either of leading and trailing of a switching pulse from a cos4omegapt generator 8 and a 90 deg. phase shifter 9 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM multiplex reception device that allows listening to a plurality of programs.

[Prior Art] In FM transmission, the baseband signal EB before FM modulation is expressed by the following equation.

EB=ElvI+Pcosωpt+EScos 2ω
pt+D1cos4 ωpt+DQsin4 ωpt
-(1) Here, E gate: monaural signal P cosωpt: pilot signal, fp=19KHz
, E5CO52ωpt Stereo signal modulation wave, DI
, DQ' data signal (4-phase DPSK cos 4ωpt
Note that the data signal is shown as D, but since 4-phase DPSK is used, it is shown separately into two orthogonal signals Dr and DQ. Further, EB is expressed as in the following equation.

EB= E, )+ D1 cos4 ωpt+ 5i of D
n4 ωpt-(2) where EO: audio signal, expressed as in the following equation.

E□=EM+Pcosωpt+E5cos2ωpt
-(3) By extracting the second and third terms of the baseband signal in equation (2), the data signal can be obtained using a data demodulator.

Figure 3 shows the configuration of a conventional FM multiplex receiver.
1 is a receiving antenna, 2 is a local oscillator, 3 is a frequency converter, 4 is a bandpass filter (center frequency 10.7M
H2), 5 is a limiter, 6 is a frequency discriminator, 7 is a band pass filter (band frequency 61 to 91
KHz).

In addition, 8 is a C084ωpt generator, and 9 is a 90' phase shifter (
sin4 ωpt generator), 28.29 is a synchronous detection circuit, 30.31 is a low-pass filter (band frequency 0 to 1
5), 32 is a decoder, and 33 is a data output.

With the above configuration, the received signal received by the receiving antenna 1 is mixed with the output signal of the local oscillator 2 by the frequency converter 3, converted to an IF (intermediate frequency), and then output to the bandpass filter 4. After the amplitude is made constant by this IF signal and the limiter 5, it is applied to the frequency discriminator 6, and the baseband signal EB is restored according to the above equation (1) or (2). Here, we will focus only on data signals.

The output signal of the frequency discriminator 6 is applied to a bandpass filter, and the components from 6 to 91 KHz are extracted and applied to a cos 4ωpt generator 8. Instead of this cos 4ωpt generator 8, two costas circuits or two square circuits may be used. cos4ωpt generator 8
The output signal of is applied to a 90' phase shifter 9 and cos 4ω
pt is converted to sin 4ωpt. In addition, cost
The as circuit provides both CO5 and sin outputs.

The output signal of the bandpass filter 7 is a signal corresponding to the second and third terms of the above equation (2), and the synchronous detection circuit 28
The component DI of os 4ωpt is obtained by the low-pass filter 30, and similarly the component DQ of 5in4ωpt is obtained by the synchronous detection circuit 29 and the low-pass filter 31. @ DII Both components of DQ are added to the decoder 32 and processed by the digital signal processing system. Restored data output 3
3 is obtained.

If the output signal of the frequency discriminator 6 contains noise with a --like spectral distribution during reception, noise will occur during FM demodulation. D ICO54ωpt+DQsin4ω
Since the pt data signal is suppressed to 2.5% of the total amplitude, the SN ratio is significantly worse than that of the audio signal. Furthermore, mobile reception becomes difficult because the SN ratio of the data channel is poor.

[Problem II to be solved by the invention] However, in the conventional FM multiplex receiver shown in FIG.
Is there no problem as long as the received electric field strength is high enough?If the electric field is weak, the received noise becomes large, and during FM demodulation, the problem was that the original data could not be restored due to the influence of that noise, so-called triangular noise proportional to the frequency. .

The present invention has been made in response to the above-mentioned problems.
An object of the present invention is to provide an FM multiplex receiver capable of demodulating data without being affected by noise even in a weak electric field.

[Means for Solving the Problems] In order to achieve the above object, the FM multiplex reception device of the present invention converts a received signal of an FM modulated wave into an IF signal of an intermediate frequency, demodulates the FM, and generates an FM multiplexed baseband signal. FM to get
a demodulating means; a frequency detecting means for detecting the Fp signal of the pilot frequency component from the baseband signal;
a phase difference means for inputting the P signal and outputting a phase difference signal with a phase difference of 90 degrees; inputting the Fp signal and the phase difference signal, and switching the IF signal and on/off based on the respective signals; a first switching means for outputting two intermediate frequency signals having a phase difference; and inputting the two intermediate frequency signals;
a frequency detection means for converting the two signals into F-V and outputting a difference component signal through arithmetic processing, and inputting the Fp signal;
a frequency conversion means for converting into a pulse signal with a cycle smaller than that of the signal and outputting the signal; and a frequency converting means for inputting the pulse signal and intermittently switching the difference component signal based on the signal to extract only the DC component and producing a data signal. and a second switching means for outputting.

[Operation: Separate 4 fp multi-carrier waves, switch the FM IF, distribute them to 2 channels, and then perform FM frequency detection. Moreover, the difference between the two channels is further increased by 8
By turning off the transient portion caused by the switch with a switch pulse having a period of fp, fluctuations after demodulation due to mismatch between the phase of the FM carrier wave and the timing of the switch pulse are removed. Furthermore, the switched FM is applied to a frequency discriminator and then passed through a low-pass filter. This avoids the influence of high frequency noise due to FM demodulation, and data demodulation can be performed without being affected by noise, especially in weak electric fields.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the FM multiplex receiver of the present invention, where l is a receiving antenna, 2 is a local oscillator, 3 is a frequency converter, 4 is a band pass filter (center frequency 10.7 MHz), and 5 is a limiter, 6 is a frequency discriminator, 7 is a band pass filter (band frequency 61
91KHz), 8 is cos4ct+pt generator, 9
is 90″ phase shifter (Sin 4ωpt generator), 10 is c
os 8ωpt generator.

11 is a switch pulse (pulse width τ,), 12 is cos
8ωpt generator, 13 is a switch pulse (pulse width τ
, ), 14.21 is an electronic switch (pulse width τ, ), 1
5, 16, 22.23 are frequency discriminators, 1
7.24 is a differential amplifier, 18.25 is an electronic switch (pulse width τ,), 19°26 is a low-pass filter (band frequency O to 15), 20 is an output, and 27 is a DQ output.

With the above configuration, the reception signal received by the reception antenna 1 is mixed with the output signal of the local oscillator 2 by the frequency converter 3 and converted into an IF (intermediate frequency) signal, and then passed through the bandpass filter 4 and limiter 5 to the frequency disk. It is input to the liminator 6.

In this frequency discriminator 6, the above formula (1) or (
2), the baseband signal EB is restored, and components of 61 to 91 KHz are extracted from this output signal by a bandpass filter 7 and applied to a cos 4ωpt generator 8. fp is a 19 KHz FM stereo pilot frequency, and 4fp is 76 KHz, which is a subcarrier for data broadcasting. The cos4ωpt generator 8 may be replaced by a costas circuit or a square circuit.

The configuration up to this point is the same as the conventional configuration.

In this embodiment, the IF ratio output electronic switch 14 from the limiter 5 controls the cos4ωpt generator 8.
(clpt: a side of 1 or cos4 ωpt= −
Allocate to side b of 1. Figure 2(a) shows cos 4ωp
The switch pulse of the output of the t generator 8 is shown, and its period is 4 fp. Further, the pulse width τ is 1/8 fp.

FIGS. 2(b) and 2(C) show each output when the switch pulse of FIG. 2(a) is used to distribute the IF ratio output of the limiter 5.

FIG. 2(d) shows the output of the limiter 5, with the amplitude of the baseband signal or the frequency of the IF on the vertical axis.

Each signal distributed to a and b by the electronic switch 14 is subjected to frequency-voltage (f-V) conversion by a frequency discriminator 15, 16, and then input to a differential amplifier 17. Figure 2(e) shows the frequency discriminator 1
5 is shown.

FIG. 2(f) shows the output of the differential amplifier 17, in which the difference components of the discriminators 15 and 16 are output.

The output of the differential amplifier 17 is applied to an electronic switch 18,
Electronic switch 18 switches its output under control of switch pulse 11.

The cos 4ωpt pulse of the output of the C084ωpt generator 8 is applied to the cos 8ωpt generator 10 and the cos
A pulse of 8ωpt is generated, which is switch pulse 1
1, resulting in a waveform as shown in FIG. 2(g). The period τ1 of this waveform is 8 fp, but the period during which the electronic switch 18 is turned on is set to τ8<τ1. ] Figure 2 (h
) becomes the output of the electronic switch 18.

For example, this output waveform is such that the rising and falling edges of the output of the frequency discriminator 15 shown in FIG. 2(e) are F.
It is not constant but varies depending on the phase of the M carrier wave. It also removes transient components of noise, which is the key to this embodiment.

In FIG. 2(1), the low frequency switched components such as the stereo signal component in FIG. 2(h) can be removed by the later low-pass filter 19, so if they are removed in advance and only the data component is shown, the result is as shown in FIG. 2(1). Furthermore, by passing it through a low-pass filter]9, the output shown in FIG. 2 (j) is obtained.

is obtained. In addition, the 90' phase shifter 9 converts the output of the cos 4ωpt generator 8 from cos 4ωpt to sin 4ωpt.
is generated, and the output of the limiter 5 is switched by the electronic switch 21. 90″ phase shifter 9 to -cos 8ωpt generator] 2 and electronic switch 25 with switch pulse 13
generation of switch pulses, electronic switches 21°25,
Frequency discriminator 22, 23, differential amplifier 24
, the course of the low-pass filter 26 is cos4ωpt and 5i
This is the same as FIG. 2 except that the phase of n4 ωpt is shifted by 90e, and illustration is omitted.

The output of the low-pass filter 26 becomes DQ.

According to this embodiment, the limiter output is switched by a pair of electronic switches 14.21, FM demodulated by frequency discriminators 15, 16, 22. ,D
Since Q is extracted, high frequency noise (51
to 91KH2 band) data signals DI, DQ that are not affected by
can be obtained. Moreover, since it is switched by the narrow pulse τ of the electronic switch 18.25 and then passed through a low-pass filter, the phase of the FM carrier wave and cos 4
ωpt generator 8.90″ It is possible to remove the influence of the fluctuation based on either the rising or falling edge of the switch pulse of the phase shifter 9.

[Effects of the Invention] As described above, according to the present invention, data can be demodulated without being affected by noise even in a particularly weak electric field.
M multiple receivers can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the FM multiplex reception device of the present invention, Fig. 2 (a) to (j) are signal waveform diagrams showing the operation of the device of this embodiment, and Fig. 3 shows a conventional example. It is a block diagram. 4.7...Band pass filter, 5. Limiter, 6.15.16.22.23-...
...Frequency discriminator, 8...
cos 4ωpt generator, 9...906 phase shifter, 10 river old cos 8ωpt generator, 11.1
3...Switch pulse, 12. . ---cos 8 (11ptJlj generator, 14.18
, 21.25-=...Electronic switch, 19.2
6... Kawaguchi-pass filter, 20...
・DI output, 27... DQ specific output patent applicant Clarion Co., Ltd. Figure 2

Claims (1)

[Claims] FM demodulation means for converting a received signal of an FM modulated wave into an IF signal of an intermediate frequency and performing FM demodulation to obtain an FM multiplexed baseband signal; and Fp of a pilot frequency component from the baseband signal.
a frequency detection means for detecting a signal; and a phase difference means for inputting the Fp signal and outputting a phase difference signal with a phase difference of 90 degrees;
In an FM multiplex reception device that converts a signal into a predetermined subcarrier signal and detects a data signal that becomes an I signal and a Q signal, the Fp signal and the phase difference signal are input, and the IF signal is generated based on the respective signals. a first switching means that outputs two intermediate frequency signals having a phase difference by switching intermittently;
Frequency detecting means for converting and outputting a difference component signal through arithmetic processing; Frequency converting means for inputting the Fp signal and converting it into a pulse signal with a smaller period than the signal and outputting it; inputting the pulse signal. FM multiplex reception apparatus, characterized in that it has a second switching means for intermittently switching the difference component signal based on the signal, extracting only the DC component, and outputting the data signal.