JPH01318330A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To improve the S/N of a stereo signal and to obtain high sound quality by switching noninverting/inverting IF signal so as to apply FM demodulation. CONSTITUTION:A positive IF signal and a negative IF signal whose polarity in frequency shift is positive and negative due to modulation are obtained from an IF stage of an FM modulation wave and a switch 24 outputs alternately the positive IF signal and the negative IF signal by using a prescribed switching pulse. A signal in response to the stereo signal (ER-EL) is obtained from the output of the switch 24 and a signal in response to a monaural signal (ER+EL) is obtained from the IF stage of the FM modulation wave. Then a matrix circuit 28 obtains a right ear signal and a left year signal from the signal corresponding to the (ER-EL) and the (ER+EL). Thus, the effect of high frequency noise attended with the FM demodulation is eliminated and the stereo listening with high S/N is attained even from the reception of a weak electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a stereo switch type FM stereo receiving apparatus.

B0 Overview of the invention Two types of I”M modulated waves with positive and negative frequency deviations
Create an IF and use the PLL method to calculate cos2ωpt (2f
,, : 38 kllz) switch pulse is generated, the positive and negative IFs are switched, the output is FM demodulated, 0 to 15 kHz is extracted, and Es
(= (ER-EL)/2), while positive IF
FM demodulate the 0 to 15k) (take out the low frequency component of z, set it as EM (= (ER+EL)/2), and use the matrix circuit to convert it to ER=(ES+EM)/2
, EL = (EM ES )/2 right ear signals and left ear signals are generated.

C6 conventional technology The baseband signal of FM broadcasting takes the form of equation (1).

+ p coS2ωpt ・・・・・・・・・
(1) f, = 19kHz Since the FM demodulated baseband signal is expressed as formula (1),
ER and -EL can be separated by switching at cos 2ω, t (38 to 7 subcarriers). 38k
The Hz switch pulse is p CO
It is sufficient to take out the pilot signal (19kHz) of 8ω, t and create a frequency double this, but with the correct phase, equation (1)
) will cause distortion and deterioration of the degree of separation between ER and EL. Therefore, in recent years, P L L (Phase Lo
A stereo decoding method based on CKED, LOOP) has been put into practical use.

Figure 4 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, 3 is the frequency converter, 4 is the local oscillator, and 5 is the FM demodulator-1
, 6 is a decoder, 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 a 76 kHz VCO (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 an EL
represents the output.

The antenna power l 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 F゛M demodulator-15 is sent to the stereo decoder circuit 6.
added to. The output of amplifier 7 is applied to phase comparators 8 and 17. The output of the phase comparator 8 passes through a DC amplifier 10 to 4f.

= 76klly, in addition to the nearby vCO11, through each flip-flop 13.14, 19kl (z) of 1/4 frequency of the output of vCOll is returned to the phase comparator 8, and the output of the low frequency amplifier 7 is 19kl.
kHz, that is, the phase of pcosωpt. On the other hand, the phase comparator 17 has a flip-flop 1
3.15, the phase is compared with the signal of 19kl (z), and the stereo switch pulse (this is the output of the flip-flop 13 and 38 kHz) is generated by the stereo switch pulse generator 16 through the trigger circuit 18.

Since sinωp1 is used in the phase comparator 8 and is orthogonal to cosωp1 of the output of the low frequency amplifier 7, if the phase of vCO is correct, the input to the DC amplifier 10 becomes O, and vCo 11 is stable. On the other hand, the output of the stereo switch pulse generator 16 is cosω,
, t, which matches the phase of the subcarrier in the second term of equation (1), completing rheo decoding. That is, the low frequency amplifier 7
The baseband signal of the output of the stereo switch pulse generator 16 is supplied to the decoder 19, and the cos of the output of the stereo switch pulse generator 16 is
Switch at 2ωp1.

D0 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, FM demodulator
Since the output of
The subcarrier modulation component degrades the S/N ratio by about 20 dB. 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 an FM broadcast receiving apparatus using a PLL stereo switch method, which improves the SN ratio of a stereo signal and makes it possible to obtain high sound quality.

E8 Means for Solving Problems In order to achieve the above object, the FM stereo receiving device according to the present invention has a positive polarity IF signal and a negative polarity of the frequency shift due to modulation from the IF stage of the FM modulated wave. means for obtaining a stereo IF signal; a switch circuit for alternately outputting the positive IF signal and the negative IF signal using a predetermined switching pulse; and means for obtaining a signal corresponding to a stereo signal (EREL) from the output of the switch circuit. And a monaural signal (E
means for obtaining a signal corresponding to (R+-EL);
The gist of the present invention is to include a matrix circuit that obtains a right ear signal and a left ear signal from a signal corresponding to L) and a signal corresponding to (ER+EL).

A stable stereo signal can be switched by generating switching pulses by the F0 action PLL.
Switch the IF signal and demodulate the FM. That is,
A stereo signal gate pulse of 38k&(cos2ωpt) is generated by the PLL, but the FM modulated wave of the IF stage is gated instead of the baseband signal.

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, reference numbers common to those in FIG. 4 represent the same or corresponding parts, and 22 is Frequency converter, 23 is fixed oscillator (2f+o), 24 is IF switch, 25
FM demodulator-2, 26, 27 are low-pass filters (0~15kllz), and 28 is a matrix.

From the following, the operation of the above embodiments will be explained.

Similar to the apparatus shown in FIG. 4, the output of the FM demodulator 15, which demodulates the output of the frequency converter 3, is used as the input signal to the PLL 6.

The IF output of frequency converter 3 is added to frequency converter 22 and fixed frequency oscillator (2f+o) 2
Generate the frequency subtracted from the output of 3. If the frequency of the output of the frequency converter 3 is fl, and the frequency of the output of the frequency converter 22 is f1', then L' + " f Io + Δf ・
-(2) flo: Frequency Δf without modulation: Frequency shift due to modulation f+' = 2f+oft = flo-Δf (3), and formula (1) and formula (2) As is clear from Δf
The polarity of is reversed in equation (2). The output of the frequency converter 3 and the output of the frequency converter 22, which are two types of IF, are added to the IF switch 24 to generate the stereo switch signal co of the stereo switch generator 16.
s 2ωI, switch at synchronous 1/2f at t.

The output is FM demodulator-2 (discriminator) 2
5 to perform FM demodulation and low-pass filter (0 to 15kHz
)26 by Es” (ER-EL)/2
get.

On the other hand, the output of the FM demodulator-15 is also passed through the low-pass filter 2
7, we obtain EM = (ER+EL)/2. The matrix 28 of the output of the low-pass filter 26.27 plus the right ear signal ER20 and the left ear signal E
Obtain L21.

=8- FIG. 2 shows signal waveforms at various parts of the device shown in FIG. 1 (in (a) and (c), the vertical axis is frequency). (a) is an F'M modulated wave (FM modulated wave in equation (1)), but the pilot signal is omitted. (b) is the switch pulse cos2ω,t which is the output of the stereo switch generator 16. (b) switches (c). The solid line in (c) is the output of frequency converter 3,
This is the positive phase IF (Equation (2)), and the broken line is the output of the frequency converter 22, which is the negative phase IF of Equation (3). By switching (c) with (b), solid lines and broken lines, such as thick lines, appear alternately, for example. (c) Thick line FM
When the signal is demodulated by a demodulator-225 and passed through a low-pass filter 26, Es shown in (d) is obtained. The output of the low-pass filter 27 of the FM demodulated signal of the frequency converter 3 is (
e).

The matrix 28 obtains the right ear signal ER shown in (f) from (d)+(e), and the left ear signal EL shown in (g) from (e)-(d).

Figures 3 and 5 show the noise distribution according to the present invention and the conventional method, respectively.
23 to 53 kHz centered around 35 kHz to M
There is noise from FM demodulation, and in the conventional method, the stereo signal E
This shows that the noise of s is significantly larger than that of EM. In the present invention, EM is the same as that shown in Fig. 5, and ES is shown in Fig. 3, which is similar to EM at 15 k< therefore, there is no drop in the SN ratio compared to monaural reception even in stereo reception.

As described in detail of the H0 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 noise distribution diagram according to the present invention. , Figure 4 shows the conventional PLL system.
FIG. 5, which is a block diagram showing the configuration of an FM stereo receiver, is a noise distribution diagram according to a conventional system. 1...Antenna input, 2...High frequency amplifier, 3...Frequency converter, 4...
・・・Local oscillator, 5... ・F"M demodulator-
1, 6...Decoder, 7...Low frequency (baseband signal) amplifier, 8...Phase comparator, 9...Low pass filter, 10...・・・・・・
・DC amplifier, 11... ・76 kl (z
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 high output 21...
・・・・・・EL high output 22・・・・・・Frequency converter, 23・・・Fixed oscillator (2f+o),
24...IF switch, 25...FM
Demodulator - 2, 26, 27...Low pass filter (O ~ Patent applicant Clarion Co., Ltd.

Claims (1)

[Scope of Claims] (a) Means for obtaining a positive polarity IF signal and a negative polarity IF signal in which the polarity of the frequency shift due to modulation is positive and negative from an IF stage of an FM modulated wave, (b) The above positive polarity IF signal and A switch circuit that alternately outputs negative polarity IF signals using predetermined switching pulses; (c) A stereo signal (E_R
-E_L); (d) means for obtaining a signal corresponding to the monaural signal (E_L) from the IF stage of the FM modulated wave;
(E_R+E_L); and (e) means for obtaining a signal corresponding to (E_R-E_L) and (E_R+
An FM stereo receiving device comprising a matrix circuit that obtains a right ear signal and a left ear signal from a signal corresponding to E_L.