JPH01288124A - Fm stereo broadcast receiver - Google Patents

Abstract

PURPOSE:To improve the S/N of a stereo signal by switching two kinds of different frequencies being 0 delay and tau delay with respect to an intermediate frequency at a time tau and demodulating the resulting signal. CONSTITUTION:The delay time tau of a delay circuit 6 is 13.15mus (=1/4fp) and outputs of the delay circuit 6 and a frequency converter 7 are fed to a frequency converter 9. Moreover, the output of the delay circuit 6 is fed to a frequency converter 12 and then fed to a frequency converter 13. An electronic switch 14 uses a signal Cos2omegapt being an output of a pulse generator 18 to switch outputs of the frequency converters 9, 13, a stereo signal ES is obtained by giving the result to an FM demodulator 19 to obtain a stereo signal ES, it is synthesized with a monaural signal EM being an output of a monaural separator 16 at a matrix 20 thereby obtaining a right ear signal ER 21 and a left ear signal EL 22.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a device for receiving FM stereo broadcasts.

Summary of B0 invention In FM stereo broadcast receiving equipment, *.

(1), a component is created by delaying the IF signal by τ = 13.15 μs.

(2) Create a delay sum-wavenumber component from the IF delay component of 0, and demodulate this by FM demodulation to obtain a monaural signal from the low frequency component.

(3) In (2), extract the 19kHz pilot signal and send it to the subway t! Create a pulse of tcos, 2ω, t.

(4) Create two types of difference frequency components: 0 delay and τ delay of IF. That is, 0 delay minus τ delay and τ delay minus 0 delay.

(5) The two types of IP in (4) are used as CO52ωp1 in (3)
The output is FM demodulated and a stereo signal is obtained from the low frequency components.

(6) Combine the outputs of (2) and (5) to create a right ear signal and a left ear signal.

C0 Conventional technology The FM stereo signal is converted into a monaural signal (0 to 15 kHz) Es at the baseband as shown in Figure 5.38
kHz subcarriers are balanced modulated and multiplexed, and a sine wave of f=19 kHz is added as a pilot signal.

Therefore, the baseband signal E before FM modulation is expressed by equation (1).

E = EM + Et, cos 21Jpt+
p cos (+Jpi +++++++++
+ (1) In the FM receiver, by performing FM demodulation, Equation (1)
, separate each component with a filter, extract the pilot cosω,t from the third term of Equation (1), frequency-multiply it to create cos 2ω9t, and now Equation (1)
The second term Es cos 2 ωpt is synchronously detected to obtain a stereo signal ES.

The monaural signal EM of equation (1) and the stereo signal E obtained above
s is matrix-synthesized to produce a right ear signal ER and a left ear signal Et,
get.

D0 Problem to be Solved by the Invention During FM demodulation, noise proportional to the frequency of the baseband signal called triangular noise is generated, and therefore, Equation (1)
The noise distribution shown in FIG. 6 is obtained for each component of . When receiving a weak electric field, the S/N ratio of the stereo signal Es deteriorates by about 20 dB compared to the S/N ratio of the monaural signal EM, and stereo reception becomes impossible in a weak electric field mainly due to this deterioration of the S/N ratio of the stereo signal.

[Objective of the Invention] The object of the present invention is to increase the stereo reception component in receiving FM stereo broadcasting, improve the S/N ratio during FM demodulation, and enable stereo listening even with weak electric field reception. An object of the present invention is to provide an FM stereo broadcast receiving device.

80 Means for Solving the Problems In order to achieve the above object, the FM stereo broadcast receiving apparatus according to the present invention includes means for creating a delayed IF multiplied signal by delaying the IF multiplied signal of the FM stereo receiver by a predetermined time;
The above-mentioned IF multiplied signal delay means for creating an IF multiplied signal sum frequency component, a first demodulator for demodulating the sum component, and means for obtaining a monaural signal from the demodulated signal obtained from the first demodulator; Obtain a pilot signal from the demodulated signal, and il
means for obtaining a J carrier wave; means for creating a difference frequency component between the IF signal and the delayed IF signal; switching means for switching the IF multiplied signal delayed IF multiplied signal by the subcarrier; and demodulating the signal selected by the switching means. The gist of the present invention is to include a second demodulator for obtaining a stereo signal, and means for obtaining left and right ear signals based on the outputs of the first and second demodulators.

The SN ratio of the monaural signal is improved by FM demodulating the monaural signal from the sum frequency of the delays using the zero delay of the F0 effect IF. Further, by switching two difference frequencies of the IF O delay and τ delay by τ and demodulating the switched signal, the S/N ratio of the stereo signal is improved, and at this time, the influence of the monaural signal is also reduced.

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 stereo broadcast receiving apparatus according to the present invention. In the figure, 1 is an antenna input;
2 is a high frequency amplifier, 3 is a frequency converter, 4 is a local oscillator, 5 is a limiter, 6 is a delay circuit (τ = 1
3.15 μs), 7 is the frequency converter (sum)
, 8 is a fixed oscillator, 9 is a frequency converter (sum, difference),
10 is the sum frequency, 11 is the difference frequency, 12 is the frequency converter (sum), 13 is the frequency converter (difference), 1
4 is an electronic switch, 15 is an FM demodulator-1, 16 is a monaural separator (15kHz low-pass filter), 17
is f, = 19 is the 7 pilot separation filter, 18 is 2f, = 38 is the 7 pulse generator, 19 is the FM demodulator-2, 20 is the matrix, 21 is the right ear signal ER122
represents the left ear signal EL.

The operation of the above embodiment will be explained below.

The antenna power 1 is high-frequency amplified by the high-frequency amplifier 2.
A difference frequency component is created by the frequency of the local oscillator 4 and the frequency converter 3, and the amplitude is made constant by the limiter 5. The delay time of delay circuit 6 is τ = 13.15 μs
(= 1/4 fp). The IF signal output from the limiter 5 is normally 10.7 MHz, but if it does not match the band of the delay circuit, the IF signal may not necessarily be set to 1.
There is no need to set it to 0.7 MHz. Here, the carrier wave frequency of IF is set to flo. Let the frequency of the fixed oscillator 8 be fl. How to output limiter 5 and fixed oscillator 8
From the output of the frequency converter 7, the sum frequency (f□.+
Make fl). Delay circuit 6 and frequency converter 7
The frequency converter 9 adds the output of the frequency converter 9 to the frequency converter 9, which outputs the sum of frequencies 1° and the difference 11 of the outputs of the delay circuit 6 and the frequency converter 7.

Frequency converter 9 sum frequency output 1o to FM
In addition to the demodulator-115, the demodulated output is sent to the monaural separator 1
Separate the monaural signal EM with a 0-15 kHz low-pass filter.

On the other hand, the output of the FM demodulator-115 is f, = 19k) I
z pilot separation filter 17 plus eO3ω
, 1 is separated, multiplied by 2 by the pulse generator 18, and 2f
, = 38 kHz pulses are generated.

The output of the delay circuit 6 is added to the frequency converter 12 to obtain the sum frequency of the outputs of the delay circuit 6 and the fixed oscillator 8, and in addition to the frequency converter 13, the frequency difference between the frequency converters 12 and 7 is obtained to obtain the electronic switch 14.
Add to. Each frequency is displayed as a change in time, fso (
It is expressed as jL fto(t-t) (τ delayed signal).

Output of delay circuit 6 f to (t-τ) Output of frequency converter 7 fro (t) + f□ Output of frequency converter 12 flo (t-τ) + fs Output of frequency converter 13 fso (t-t) - fto (t)+f.

Output of frequency converter 9 10 f so (t ) + f to (t-, t ) + f
.

Output of frequency converter 9 11 fto(t)-fso(t-v)+, f1 Eventually electronic switch 14 has output of frequency converter 13 ft
o(t-i) flo(t)+ft and the output of frequency converter 9 fso(t) ft.

(with -)+fl is added to 0. Both become fl when no modulation is performed. Electronic switch 14 is a pulse generator
Switch the outputs of frequency converters 9 and 13 at cos 2ω9t of the output of 18.

In addition to FM demodulation-219, a stereo signal ES is obtained, which is synthesized with the monaural signal EM output from the monaural separator 16 in the matrix 20 to produce a right ear signal ER21, a left ear signal Ec,
Get 22.

The vertical axis in FIG. 2 corresponds to the frequency of the IF stage or the amplitude when demodulated to a baseband signal.

FIG. 2(a) shows the IF signal fso(t).

(b) is the output of the delay circuit 6 delayed by τ.

(c) is the difference frequency component between the two ((a) and (b)). Note that (c) corresponds to FIG. 1, which is the output of the frequency converter 9 or 13, and the frequency is shifted by fl due to frequency conversion. (d) is the switching output of the outputs of frequency converters 9 and 13, and the IF of the positive phase shown by the solid line and the reverse phase shown by the broken line is expressed as τ
The signal indicated by the thick line is output by switching each time.

(e) is the switching pulse cos 2ω, t and is the output of the pulse generator 18 . The stereo signal is converted to a low frequency by Fig. 2(d), and the residual monaural signal EM
is modulated with a 35' kHz subcarrier. Therefore, if the signal shown in FIG. 2(d) is demodulated by FM demodulation@-219, a stereo signal will be obtained at that low frequency.

Figure 3 shows the noise distribution of FM demodulation in this case, with 15
The noise of the stereo signal of kHz or less is similar to that of the monaural signal in FIG. 6, and is significantly reduced compared to the noise of the stereo signal in FIG.

FIG. 4 shows the effects of summation and subtraction in the frequency domain of the input and output of the delay τ of the present invention using a baseband signal. The sum signal shown by the dashed line in FIG. 4 (FIG. 1, 10) becomes zero at 38K, and the gain doubles at low frequencies. This improves the S/N ratio for demodulating the monaural signal EM.

The solid line in Figure 4 is the subtraction characteristic, and the stereo signal has a gain of 2 centered around 38 kl (z), which decreases at low frequencies,
Suppress monaural signals. Therefore, due to this filter effect, the monaural signal component at the time of switching by the electronic switch 14 in FIG. 1 is affected only by the high frequency component. Naturally, the monaural signal is removed by the low-pass filter at the output of the FM demodulator-2.

As described in detail about the H0 invention, the present invention has the advantage that the S/N ratio during FM demodulation is improved and stereo listening becomes possible even in a weak electric field.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an FM stereo broadcast receiver according to the present invention, Fig. 2 is a waveform diagram explaining switching of the IF signal, Fig. 3 is a noise distribution diagram of FM demodulator-2, and Fig. 4 is an IF processing filter characteristic diagram converted to a baseband signal, FIG. 5 is a frequency distribution (baseband) diagram of FM broadcasting, and FIG. 6 is a noise distribution diagram of FM demodulation using the conventional method. 1...Antenna input, 2...
...High frequency amplifier, 3...Frequency converter, 4...Local oscillator, 5...
...Limiter, 6...Delay circuit (τ
= 13.15 μs), 7...... Frequency converter (sum), 8...... Fixed oscillator, 9...... Frequency converter (sum) ,difference),
10.......sum frequency, 11........
・・Difference frequency, 12・・・・・・・Frequency converter (sum), 13・・・・・・・Frequency converter (
difference). 14......Electronic switch, 15...
...FM demodulator-1, 16...Monaural separator (15k seven low-pass filters), 17...
...... j, = 19kHz pilot separation filter, 18...2fp = 38 kHz
z pulse generator, 19...FM demodulator-
2, 20... Matrix, 21...
...Right ear signal ER, 22...Left ear signal EL. Patent applicant Clarion Co., Ltd.

Claims (1)

Claims: (a) means for creating a delayed IF signal by delaying the IF signal of an FM stereo receiver by a predetermined time; (b) means for creating a sum frequency component of the IF signal and the delayed IF signal. (c) a first demodulator for demodulating the sum component; (d) means for obtaining a monaural signal from the demodulated signal obtained from the first demodulator; (e) obtaining a pilot signal from the demodulated signal and subcarrier. (f) means for creating a difference frequency component between the IF signal and the delayed IF signal; (g) switching means for switching between the IF signal and the delayed IF signal using the subcarrier; (h) a frequency component selected by the switching means; a second demodulator for demodulating the received signal to obtain a stereo signal; and (i) means for obtaining left and right ear signals based on the outputs of the first and second demodulators. Stereo broadcasting and receiving equipment.