JPH01318331A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To improve the S/N of a stereo signal and to obtain high sound quality by using two FM demodulators so as to apply direct FM demodulation to FM modulation waves respectively corresponding to a right ear signal and a left ear signal. CONSTITUTION:An IF signal of a frequency converter 3 is fed to an electronic switch 22 and a switch pulse being an output of a stereo switch generator 16 switches signals for FM demodulators 23, 24. Then the output of the FM demodulator 23 is fed to a low pass filter 25 to obtain a right ear signal ER. This is applied similarly to the left ear signal EL. Thus, the effect of high frequency noise attended with FM demodulation is avoided and the stereo listening with high S/N is attained even in a weak electric field reception.

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention is directed to a PLL FM stereo decoding method.
M relates to a stereo receiving device.

B9 Summary of the Invention In an FM stereo broadcast receiving device, intermediate frequency (I
F)'s FM modulated wave is switched at cO82ωpt (f: pilot signal frequency, 19 kHz, 2fp: subcarrier frequency), and two intermittent FM modulated waves that alternate in T = 1/4 fp period are sent to each FM demodulator. (discriminator), and its output is passed through a low-pass filter to form a right ear signal ER and a left ear signal EL. In addition, the outputs of the two FM demodulators are summed to form the input signal of the PLL, and the 19 k signal generated by the 76 kHz vCO is
The phase is compared with the signal of &, and the switch signal cos 2ω9t of the intermediate frequency FM demodulated wave is generated.

C0 conventional technology The baseband signal of FM broadcasting takes the form of equation (1).

+p cos2ωp1 (1
) The baseband signal demodulated by 7 FM at fp=19 is expressed as formula (1), so
ER and EL can be separated by switching at cos2ωpt (38kHz subcarrier). 38
The switch pulse of kHz is p from the signal of equation (1).
Co! It is possible to extract the pilot signal (19kl(z)) of ω2t and create a frequency twice this, but if equation (1) is not switched with the correct phase, it will cause distortion and deterioration of the degree of separation between ER and EL.Therefore, in recent years, P L L (Phas
A stereo decoding method using e Locked Loop has been put into practical use.

Figure 5 is an explanatory diagram of the conventional system centered on PLL.
In the figure, 1 is the antenna input, 2 is the high frequency amplifier, and 3 is the antenna input.
is a frequency converter, 4 is a local oscillator, 5 is an FM demodulator, 1 and 6 are decoders, 7 is a low frequency (baseband signal) amplifier, 8 is a phase comparator, 9 is a low pass filter, 10 is a DC amplifier, 11 is 76kHz VC
O (voltage controlled oscillator), 12 is a VCO adjustment circuit, 13゜14.15 is a flip-flop, 16 is a stereo switch generator, 17 is a phase comparator, 18 is a trigger circuit, 19 is a decoder, 20 is an ER output, 21 is EL
represents the output.

The antenna power 1 is high-frequency amplified by a high-frequency amplifier 2,
The difference frequency with the output of local oscillator 4 is converted into a frequency converter.
3, with an intermediate frequency (10.7 MHz). The output of frequency converter 3 is an FM modulated wave,
This is added to the FM demodulator-15 to restore the baseband signal of equation (1).

The output of the FM demodulator-15 is applied to a stereo decoder circuit 6. The output of amplifier 7 is applied to phase comparators 8 and 17. The output of the phase comparator 8 passes through the DC amplifier 1o to the VCO 11 near 4fp=76kHz.
In addition, through each flip-flop 13.14, the frequency of 1/4 of the output of VCO 11 is 19kHz.
This is returned to the phase comparator 8, and the low frequency amplifier 7
19kl (z, i.e., PcO8ω, , of the output of
Match the phase of t. On the other hand, the phase comparator 17 has a 19k
The phase is compared with the signal of 1-1z, and the stereo switch pulse generator 16 generates a stereo switch pulse (this is the output of the flip-flop 13 and has a frequency of 38 kHz) via the trigger circuit 18.

The phase comparator 8 uses sin ω9t, which is orthogonal to the cosω,,t of the output of the low frequency amplifier 7, so if the phase of the VCO is correct, the input to the DC amplifier 10 will be O, and the VCO 11 will be stable. There is. on the other hand,
The output of the stereo switch pulse generator 16 is cosω
p1 and matches the phase of the subcarrier in the second term of equation (1), so we take E = E in equation 0, %cos2ωpt = -1,
Complete stereo decoding. That is, the baseband signal of the output of the low frequency amplifier 7 is supplied to the decoder 19, and the baseband signal of the output of the stereo switch pulse generator 16 is supplied to the decoder 19.
Switch with os2ωpt.

D1 Problems to be Solved by the Invention This method uses PLL and has advantages such as good symmetry of the 38 kHz signal. On the other hand, since the output of the FM demodulator-15, that is, FM demodulation, involves triangular noise, in weak electric field reception, the SN ratio of the subcarrier modulation component of the second term deteriorates by about 20 dB compared to the first term of equation (1). . Therefore, even in stereo decoding using the apparatus shown in FIG. 4, the S/N ratio inevitably decreases in a weak electric field.

[Object of the Invention] An object of the present invention is to provide a PLL stereo switch type FM broadcast receiving device that improves the SN ratio of a stereo signal and makes it possible to obtain high sound quality.

Means for Solving Problem E1 In order to achieve the above object, the FM stereo receiving device according to the present invention includes a switching circuit that alternately switches and outputs the FM modulated wave in the IF stage using a predetermined switching pulse, and a switching circuit of the switching circuit. a first demodulator for demodulating one output; a second demodulator for demodulating the other output of the switching circuit; means for obtaining a right ear signal from the first demodulator output; and means for obtaining a left ear signal from the demodulator output.

Two F0 effect FM demodulators (discriminators) are used to directly FM demodulate the intermittent FM modulated wave corresponding to the right ear signal ER and the FM modulated wave corresponding to the left ear signal EL, respectively.

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 receiver according to the present invention. In the figure, the reference numbers common to those in FIG. 5 represent the same or corresponding parts, and 22 is IF switch, 23 represents FM demodulator-2, 24 represents FM demodulator-3, 25, and 26 represent low-pass filters (0 to 15 kHz).

The operation of the above embodiment will be explained below.

In this case, the baseband signal which is the output signal of the FM demodulator-15 is PLLed to generate cos 2ωp1.
It is used to make the circuit work. The IF signal of the frequency converter 3 has the frequency distribution shown in (,) in FIG. 2, but the pilot signal of pCO8ωp1 is omitted here. Adding this to the electronic switch 22 and cos 2ωpt of the output of the stereo switch generator 16
switch pulse -7 = (Fig. 2(b)) to switch FM demodulator -223 and FM demodulator -
324 signal.

In FIG. 2(c), the solid line shows the switch signal at cos 2ωp1 (vertical axis: two-layer wave number) and its output from the FM demodulator-223 (vertical axis: amplitude).

The output of the FM demodulator-223 is filtered by a low-pass filter 25 (
0 to 15 kHz) plus a right ear signal ER20.

The same applies to the left ear signal EL.

The FM demodulation shown in Fig. 2(c) is not affected by triangular noise. In other words, the high-frequency components of triangular noise coexist in the high-frequency components of the shaded area in FIG. This can be seen in the noise distribution of FM demodulation in Figure 4. In other words, cos
The present invention eliminates the noise affecting ER-EL 2 cos2ωpt centered around 2ωp1(38kl(z)).

The device shown in Fig. 1 is good in principle, but the FM demodulator (
Discriminator) has the disadvantage of requiring three units.

FIG. 3 is an example in which the number of FM demodulators is reduced to two.

FM demodulator-223 and FM demodulator-3 in Fig. 1
The outputs of 24 are added by an adder 27 as shown in FIG. Second
The baseband in Figure (,) is restored, but if only p cosω2t omitted in (,) is taken out and illustrated, it becomes Figure 2 (f), where the output of the FM demodulator-223 is shown as a solid line and the demodulation is shown as a broken line. This signal is a combination of the outputs of the amplifier 324 and is input to the low frequency amplifier 7. Demodulator-22
3 and the output of the demodulator-324 are low-pass filtered.
Similarly, the right ear signal ER20 and the left ear signal EL21 are passed through 5 and 26.

H1 As described in detail in the invention, according to the present invention, F of a stereo signal is
M demodulation has the advantage that it is not affected by high frequency noise associated with FM demodulation, and stereo listening with a high S/N ratio is possible even with weak electric field reception.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an FM stereo receiving device according to the present invention, FIG. 2 is a signal waveform diagram at various parts of the device shown in FIG. 1, and FIG. 3 is a simplified f@according to the present invention. A block diagram showing the configuration of an FM stereo receiver, Fig. 4 is an FM demodulation noise distribution diagram, and Fig. 5 is a PL
FIG. 2 is a block diagram showing the configuration of an L-scheme FM stereo receiver. 1 antenna input, 2... high frequency amplifier, 3
...Frequency converter, 4...Local oscillator, 5...FM demodulator-1, 6...
Decoder, 7...Low frequency (baseband signal)
Amplifier, 8... Phase comparator, 9... Low pass filter, 10... DC amplifier, 11... 76
kHz VCO (voltage controlled oscillator), 12-...-VCO adjustment circuit, 13, 14. 15... flip-flop, 16... stereo switch generator, 17... phase comparator, 18... trigger circuit, 19... ...Decoder, 20...ER output, 21...E
L output, 22... IF switch, 23...
... FM demodulator-2, 24... FM demodulator-3, 25, 26...... Low-pass filter (O
~15k7). Patent applicant Clarion Co., Ltd.

Claims (3)

[Claims] (1) (a) A switching circuit that alternately switches and outputs the FM modulated wave in the IF stage using a predetermined switching pulse, (b) A first demodulator that demodulates one output of the switching circuit, (c) The above switching circuit. a second demodulator for demodulating the other output of the circuit; (d) means for obtaining a right ear signal from said first demodulator output;
and means for obtaining a left ear signal from the output of the second demodulator. (2) Claim 1, wherein the switching pulse is a signal from a decoder that decodes a demodulated signal from a third demodulator that demodulates the FM modulated wave in the IF stage. FM stereo receiver. (3) The FM according to claim 1, wherein the switching pulse is a signal from a decoder that decodes a sum signal of the first demodulator output and the second demodulator output. Stereo receiver.