JPS603239A - Stereophonic demodulator - Google Patents

Abstract

PURPOSE:To improve the separation of a stereophonic signal by making a composite signal outputted from an FM demodulator and an output multiplied with a subcarrier signal almost coincident with the phase of a main signal in the composite signal. CONSTITUTION:The composite signal S1 inputted to an input terminal IN is supplied to synthesis circuits 3, 5 as a signal S10 via a phase lag circuit 10. A subcarrier signal in synchronization with a pilot signal is outputted from a subcarrier wave generator 1. This subcarrier wave signal is multiplied with the composite signal by a multiplier 2 and becomes a signal S2. The signal S2 and the signal S10 are synthesized by the synthesizing circuit 3. Further, the signal S2 is passed through a phase lead circuit 11 and a phase inverter 4 to form a signal S4 and the signals S10 and S4 are synthesized by the synthesizer circuit 5. In adjusting the transfer function of the phase lag circuit 10 and the phase lead circuit 11, a right channel output signal and a left channel signal are not mixed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stereo demodulator used in an FM receiver.

(Prior Art) A conventional stereo demodulator of a so-called matrix type is shown in FIG. , a DSB signal (hereinafter simply referred to as a DSB signal) in which the subcarrier is AM suppressed carrier modulated by the subcarrier by multiplying the subcarrier signal generated by the subcarrier generator 1 and the composite signal supplied to the input terminal IN. a multiplier 2 for demodulating the composite signal, a combining circuit 3 for combining the composite signal and the output of the multiplier 2, a phase inverter 4 for inverting the phase of the output of the multiplier 2, and a combination of the composite signal and the phase inverter 4. It was configured to include a synthesis circuit 5 for synthesizing the output from the synthesis circuit 3.5, and a low-pass filter 6.7 for extracting only signals in a predetermined frequency band from the output of the synthesis circuit 3.5.

Note that 8 and 9 are de-emphasis circuits.

When using a conventional stereo demodulator configured as described above, compared to a switching type stereo demodulator that requires two switching circuits for each left and right channel,
There is an advantage that only one switching circuit is required for sub-signal demodulation. However, since there is no switching circuit on the main signal side line and a switching circuit exists on the sub signal side line, the phase of the sub signal is delayed due to the phase delay caused by the multiplier. As a result, there was a drawback that the degree of separation at high frequencies deteriorated as shown by the solid line in FIG.

In addition, the selection element in the intermediate frequency amplification stage also has a DS
The phase of the B signal is shifted by 1tyi, which causes the problem of deteriorating the degree of separation, similar to the above.

Furthermore, there is also the drawback that the degree of separation in the right channel audio signal deteriorates due to the phase delay in the phase inverter.

(Objective of the Invention) The present invention has been made in view of the above problems, and an object of the present invention is to provide a stereo demodulator that eliminates the above-mentioned drawbacks and improves the degree of separation.

According to the present invention, this purpose is achieved by providing a phase compensation means for substantially matching the phases of the main signal in the composite signal supplied to the first synthesis circuit and the output of the η multiplier, or This is achieved by providing another phase compensation means for substantially matching the phases of the main signal in the composite signal supplied to the second combining circuit and the output of the phase inverter.

Hereinafter, the present invention will be explained by examples.

(Configuration of the Invention) FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention.

In one embodiment of the present invention, the conventional stereo demodulator shown in FIG. is supplied, and the output of the multiplier 2 is supplied to the phase inverter 4 via the phase lead circuit 11.

(Operation of the Invention) The operation of the embodiment of the present invention configured as described above will be explained.

The composite signal SI supplied to the input terminal IN is ωC 81=(L+11.)+(L−R)sir+ωct+p
sun ``t = - (1). (1
) The first term in the equation represents the main signal (M=L+几), the second term represents the D8'B signal, and the third term represents the pilot signal, ωC is the angular frequency of the subcarrier, and p is the pilot signal. The amplitude of (LR) is the sub-signal S.

The subcarrier generator 1 outputs a subcarrier signal having an angular frequency ωC synchronized with the pilot signal.

The subcarrier signal output from the subcarrier generator 1 is supplied to a multiplier 2, where it is multiplied by a composite signal.

The following description will be made with the pilot signal omitted.

Now, focusing on the phase delay caused by multiplier 2, the transfer function of multiplier 2 regarding the phase characteristics can be approximately expressed as 1/(1+jω'
v1) Torsult multiplier 2 output S2 Sz = ~''(2
Msicu. t + 8-8 cos 2 G) Ct
) 93. (2) 1+JωT1. Here, multiplier 2 is assumed to output via an amplifier with a gain of 2, and the transfer function of this amplifier is also '/ (1+j
o+Tl).

On the other hand, if the transfer function of the phase delay circuit 10 is 1/(1+jωT2), the output 810 of the phase delay circuit 10 is 510=-(M+5sinG)(t)-(3)1+
”ωT2.

Therefore, the output S3 of the synthesis circuit 3 is ■ S3= 1+jcoT1 (2M5f+ωct+S-8
QllIS 2ωc1) Only band components are extracted.

The output S6 of the low-pass filter 6 is becomes.

Here, if the transfer function of the phase delay circuit 10 is set to be Tl-T2, the output S6 will be, and the right channel output signal will not mix with the left channel output signal.

Also, the transfer function of the phase inverter 4 is -1/(1+jωT3
), and the transfer function of the phase lead circuit is (1+''ωT4), then the output S4 of the phase inverter 4 becomes 1S −5 cos 2 ωct ) −−−−, (force).

Therefore, the output S5 of the synthesis circuit 5 is S5:S10+84+S-8C1ys2ω. t) Old...(8), and only the necessary frequency band components are extracted by the low-pass filter.

The output S7 of the low-pass filter is ...(9) becomes.

Here, if the transfer function of the phase lead circuit 11 is set so that T4=T3, the output S7 will be as follows, and the left channel output signal will not be mixed into the right channel output signal.

Therefore, by inserting the phase delay circuit 10 and the phase advance circuit 11, the degree of separation of the stereo demodulator is greatly improved compared to the conventional case, as shown by the broken line in FIG.

Further, as mentioned above, the composite signal S1 supplied to the stereo demodulator is influenced by the frequency band characteristics at the stage before the stereo demodulator in the FM receiver, and
The B signal is normally delayed in phase. Therefore, this phase delay can also be compensated by the phase delay circuit 10.

Next, what about the phase lag circuit 10 and the phase lead circuit 11? ! 11 dawn.

FIGS. 4A and 4B are circuit diagrams showing specific examples of the phase delay circuit 10 and the phase lead circuit 11.

The phase delay circuit 10 includes an operational amplifier 20, resistors 21, 22 . It can be composed of a capacitor 23. If the gain of the operational amplifier 20 is ■, then
The transfer function is. Here, 几 represents the resistance value of the resistors 21 and 22, and C represents the capacitance of the capacitor 23.

Further, the phase advance circuit 11 can be composed of an operational amplifier 20, resistors 24, 25, and a capacitor 26, as shown in FIG. 4(1). In this case, the transmission is jωC1+1 1 . Here, R1 is the resistance value of resistors 24 and 25, and C1
is the capacitance of the capacitor 26.

Next, other embodiments of the present invention will be described.

FIGS. 5 and 6 are block diagrams showing the configurations of other embodiments of the present invention, respectively.

In another embodiment of the present invention shown in FIG. The composite signal is supplied to the combining circuit 3 and the phase lead circuit 11, and the composite signal and the phase lead circuit 12 are combined in the combining circuit 3.
It is configured to combine the output of

In another embodiment of the present invention shown in FIG. The configuration is such that the output of the phase delay circuit 10 and the output of the phase lead circuit 13 are combined in the synthesis circuit 3.

In another embodiment of the present invention shown in FIG. It will be clear from the effects of one embodiment of the present invention that the degree of separation is improved.

In another embodiment of the present invention shown in FIG. 6, the phase delay caused by the phase inverter 4 is compensated for by the phase advance caused by the phase lead circuit 13, and the degree of separation is improved. This will be clear from the operation in one embodiment.

In the embodiment and other embodiments of the present invention described above, a case is exemplified in which the phase delay caused by the phase inverter 4 is also compensated, but the DSB due to the circuit before the stereo demodulator is
The phase delay of the signal is larger than the phase delay caused by the phase inverter 4, and even just compensating for the phase delay of the DSB signal caused by the circuit before the stereo demodulator and the phase delay caused by the multiplier 2 can have an effect of improving the degree of separation. Therefore, in this case, the phase lead circuits 11 and 13 may be omitted.

(Effects of the Invention) As explained above, according to the present invention, the first phase compensating means or the first phase By providing the compensation means and the second phase compensation means for compensating for the phase delay of the phase inverter, the degree of separation of the stereo demodulated output is improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional stereo demodulator. FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a characteristic diagram for explaining the operation of an embodiment of the present invention. FIGS. 4(a) and 4(b) are circuit diagrams showing an example of a phase delay circuit and a phase lead circuit. FIG. 5 and FIG. 6 are block diagrams showing the configuration of other embodiments of the present invention, respectively. 1. Subcarrier generator, 2. Multiplier, 3 and 5...
Synthesis circuit, 10... Phase delay circuit, 11.12 and 13... Phase lead circuit. Patent applicant Trio Co., Ltd. Agent Patent attorney Nobuo Sunako

Claims (1)

[Claims] (a multiplier that multiplies the composite signal by a subcarrier signal synchronized with a pilot signal in a composite signal output from an 11FM demodulator; and a phase inverter that inverts the phase of the output of the multiplier. , a stereo demodulator comprising a first combining circuit that combines the composite signal and the output of the multiplier, and a second combining circuit that combines the composite signal and the output of the phase inverter, A stereo demodulator characterized by comprising phase compensation means for substantially matching the phases of the main signal in the composite signal supplied to the first synthesis circuit and the output of the multiplier. (2) The phase compensation means comprises: The stereo demodulator according to claim 1, characterized in that the stereo demodulator is a phase delay circuit that delays the phase of the composite signal supplied to the first and second combining circuits. The stereo demodulator according to claim 1, characterized in that the stereo demodulator is a phase advance circuit that advances the phase of the multiplier output supplied to the synthesis circuit of claim 1. (4) In the composite signal output from the FM demodulator. a multiplier that multiplies the composite signal by a subcarrier signal synchronized with the pilot signal of A stereo demodulator comprising a synthesis circuit and a second synthesis circuit that synthesizes the composite signal and the output of the phase inverter.
a first phase compensation means for substantially matching the phase of a main signal in a composite signal supplied to a synthesis circuit with the output of the multiplier; and a main signal in a composite signal supplied to a second synthesis circuit. A stereo demodulator comprising second phase compensation means for substantially matching the phase with the output of the phase inverter. (5) Stereo demodulation according to claim 4, wherein the first phase compensation means is a phase delay circuit that delays the phase of the composite signal supplied to the first and second combining circuits. vessel. (6) The stereo demodulator according to claim 4, wherein the first phase compensation means is a phase advance circuit that advances the phase of the multiplier output supplied to the first synthesis circuit. (7) The stereo demodulator according to claim 4, wherein the second phase compensation means is a phase advance circuit that advances the phase of the multiplier output supplied to the phase inverter. (8) The stereo demodulator according to claim 4, wherein the second phase compensation means is a phase advance circuit that advances the phase of the multiplier output supplied to the first synthesis circuit.