JPH0520026Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field The present invention relates to an improvement of a stereo multiplex circuit, and in particular prevents deterioration of stereo separation due to a 57KHz SK signal indicating a traffic information station. This invention relates to a stereo multiplex circuit. (b) Prior art A stereo multiplex circuit for separating left and right stereo signals from a stereo composite signal obtained at the output end of a detection circuit was developed, for example, in 1981.
It is conventionally known as described in "'82 Sanyo Semiconductor Handbook", page 307, published on October 1st. The stereo multiplex circuit is
As shown in Figure 2, from the detection circuit to the input terminal 1
A sum signal circuit 2 for obtaining a stereo sum signal (L+R) in a stereo composite signal applied to
and, in response to the 19KHz stereo pilot signal in the stereo composite signal, to obtain a 38KHz switching signal synchronized with the pilot signal.
PLL (phase locked loop) circuit 3,
a difference signal circuit 4 that demodulates a stereo difference signal (L-R) in a stereo composite signal using the 38KHz switching signal output from the PLL circuit 3;
and a matrix circuit 5 which matrixes the stereo sum signal obtained from the sum signal circuit 2 and the stereo difference signal obtained from the difference signal circuit 4 and separates left and right stereo signals L and R,
A left stereo signal L is generated at the left output terminal 6, and a right stereo signal is generated at the right output terminal 7. Therefore, if the received signal is a signal from a normal stereo broadcasting station, by using the circuit shown in FIG. 2, it is possible to obtain left and right stereo signals having a sufficient degree of separation. (c) Problems that the invention aims to solve: However, the received signal is
If the signal includes an SK signal of 57 KHz, there is a drawback that the degree of stereo separation deteriorates due to the SK signal. In other words, the signal from the traffic information station is 57K so that it can be identified as a traffic information station.
Hz SK signal, but the frequency of the SK signal, 57KHz, is the frequency of the stereo pilot signal.
19KHz, and the phase characteristics from the antenna to the detection circuit are different between the SK signal and the stereo pilot signal, so when it reaches input terminal 1, there is a phase difference between the SK signal and the stereo pilot signal. Causes a phase difference. Then, the voltage controlled oscillator of the PLL circuit 3 is adversely affected by the SK signal, which has a phase different from the stereo pilot signal, and the PLL circuit 3
The phase of the 38KHz switching signal output from circuit 3 is disturbed. As a result, the level of the stereo difference signal becomes lower than the level of the stereo sum signal, and when matrixed by the matrix circuit 5, the degree of stereo separation deteriorates. (d) Means for solving the problem The present invention has been made in view of the above points, and includes a separation degree adjusting resistor, a short circuit that shorts the resistor,
The present invention is characterized by comprising a control circuit that detects a 57KHzSK signal included in the output signal of the detection and controls the short circuit. (E) Effect According to the present invention, the resistance value of the separation adjustment resistor is varied depending on the presence or absence of the 57KHz SK signal, and the levels of the stereo sum signal and the stereo difference signal are matched, so the stereo separation is deteriorated. do not. (F) Embodiment Figure 1 is a circuit diagram showing an embodiment of the present invention.
8 is a reception antenna; 9 is a front end (FE) that converts the high frequency signal received by the antenna 8 into an IF (intermediate frequency) signal; 10 is an IF amplification circuit (IFA) that amplifies the IF signal; 11 1 is a detection circuit (DET) that detects the output signal of the IF amplifier circuit 10;
2 is a stereo multiplex circuit (MPX) that separates the detection output signal into left and right stereo signals, and 13 is a 57KHz SK included in the output signal of the detection circuit 11.
SK signal detection circuit (SKD) that detects the signal, 14
15 is a drive transistor that is turned on according to the output signal of the detection circuit 13, and 15 is the drive transistor 14.
16 and 17 are first and second separation adjustment resistors for adjusting the stereo separation of the stereo multiplex circuit 12, and 18 is a drive coil excited by the second separation adjustment resistor 17. These are normally closed switch contacts that are connected in parallel and operate as a short circuit. Now, if the antenna 8 receives a signal from a normal stereo broadcasting station, an IF signal is generated from the front end 9, and the IF signal is sent to the IF amplifier circuit 10.
The signal is amplified by the detector circuit 11, and the stereo sum signal (L+R) is output to the output terminal of the detector circuit 11.
A detection output signal is generated that includes a stereo difference signal (L-R) and a 19KHz stereo pilot signal. The output signal of the detection circuit 11 is separated by a stereo multiplex circuit 12, and left and right stereo signals L and R are generated at left and right output terminals 19 and 20, respectively. Since the output signal of the detection circuit 11 does not contain the 57KHz SK signal, the PLL circuit for generating the 38KHz switching signal in the stereo multiplex circuit 12 is not interfered with, and the demodulated stereo The difference signal (LR) has a predetermined level. Furthermore, since the 57KHz SK signal is not included, no output signal is generated from the SK signal generation circuit 13, and the drive transistor 14 is not turned on. Therefore, the drive coil 15 is not excited, the normally closed switch contact 18 remains closed, and the second
The degree of separation adjustment resistor 17 is short-circuited, and the level of the stereo sum signal (L+R) is set to the level of the first degree of separation adjustment resistor 16.
Determined only by the value of . Therefore, the first separation degree adjusting resistor 16 is appropriately determined, and the level of the stereo sum signal (L+R) and the stereo difference signal (L-R) are adjusted.
By making the levels equal to each other, it is possible to achieve the best stereo separation. Next, if the antenna 8 receives a signal from a traffic information station, a detection output signal is generated at the output end of the detection circuit 11, as in the case of receiving a signal from a normal stereo broadcasting station. Therefore, the detection output signal includes a stereo sum signal (L+R), a stereo difference signal (L-R), a 19KHz stereo pilot signal, and a stereo sum signal (L+R).
Since it contains a 57KHz SK signal, the 57KHzSK signal interferes with the PLL circuit of the stereo multiplex circuit 12, and the demodulated stereo difference signal (L-
The level of R) decreases. Meanwhile, the 57KHzSK
The signal is detected by the SK signal detection circuit 13 and applied to the base of the drive transistor 14. Therefore, the drive transistor 14 is turned on, the drive coil 15 is excited, the switch contact 18 is opened, and the short circuit of the second separation degree adjustment resistor 17 is released. Therefore, the level of the stereo sum signal (L+R) is determined by the first and second separation adjustment resistors 16 and 1.
If the combined resistance value is determined appropriately, the level of the stereo sum signal (L+R) and the level of the stereo difference signal (L-R) can be made equal, and the stereo separation It is possible to bring the temperature to its best condition. In that case, the level of the stereo sum signal (L+R) will decrease by the addition of the second separation degree adjustment resistor 17, so the level of the stereo sum signal (L+R) will be reduced to 57KHz
The stereo difference signal (L-R) is disturbed by the SK signal, and it is easy to measure the level drop of the stereo sum signal (L+R) by the level drop. FIG. 3 shows a specific circuit example of the stereo multiplex circuit according to the present invention, in which 21 indicates a stereo difference signal (L-
22 is a sum signal circuit for generating a stereo sum signal (L+R), and 23 is a PLL circuit for generating a 38KHz switching signal used in the difference signal circuit 21 . When a signal from a normal stereo broadcasting station is received, as explained earlier in FIG. 1, the drive transistor 14 is off and the drive coil 15 is in a non-excited state, so the switch contact 18 is closed. The second degree of separation adjustment resistor 17 is short-circuited. In this state, the detection output signal applied to the input terminal 24 is AM-detected by the 38KHz switching signal of the PLL circuit 23 in the difference signal circuit 21.
A stereo difference signal (LR) is generated at the collectors of 26, 27 and 28. In addition, the sum signal circuit 22
A stereo sum signal (L+R) is generated at the collectors of the transistors 29 and 30. Therefore, left and right output signals L and R are generated at the left and right output terminals 19 and 20 according to the stereo sum signal (L+R) and the stereo difference signal (L-R). At that time, the level of the stereo difference signal (L-R) is determined according to the 38KHz switching signal, and the level of the stereo sum signal (L+R) is determined by the first Since it is determined according to the degree of separation adjustment resistor 16, the value of the first degree of separation adjustment resistor 16 is adjusted so that the levels of the stereo sum signal (L+R) and the stereo difference signal (L-R) become equal. If so, the stereo separation will be at its best. When a signal from the traffic information bureau is received, the drive transistor 14 is turned on, the drive coil 15 is energized,
The switch contact 18 is opened, and the short circuit of the second degree of separation adjustment resistor 17 is released. At that time, 57KHz
38KHz from PLL circuit 23 due to interference with SK signal
The phase of the switching signal is shifted, and the level of the stereo difference signal (L-R) subjected to AM detection by the difference signal circuit 21 is lowered by the 38 KHz switching signal. On the other hand, since the second degree of separation adjustment resistor 17 is connected in series with the first degree of separation degree adjustment resistor 16, the gains of the transistors 29 and 30 constituting the sum signal circuit 22 are reduced, and the output terminal of the sum signal circuit 22 is The level of the stereo sum signal (L+R) obtained also decreases. Therefore, if the value of the second separation adjustment resistor 17 is determined so that the levels of the stereo difference signal (L-R) and the stereo sum signal (L+R) are equal, the stereo separation can be made in the best state. I can do it. (g) Effect of the invention As stated above, according to the invention, 57KHzSK
When the signal exists, the level of the stereo sum signal (L+R) is lowered by the amount that the stereo difference signal (L-R) is interfered with by the SK signal and the level of the stereo difference signal (L-R) is lowered, and the stereo difference signal (L-R) is Since the levels of the stereo sum signal (L+R) and the stereo sum signal (L+R) can be made equal, there is an advantage that deterioration of the degree of stereo separation caused by the 57KHz SK signal can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional stereo multiplex circuit, and FIG. 3 is a circuit diagram showing a specific example of the circuit shown in FIG. Explanation of main drawing numbers, 11...Detection circuit, 12...
Stereo multiplex circuit, 13... SK signal detection circuit, 16, 17... Separation degree adjustment resistor, 1
8...Switch contact.

Claims (1)

[Scope of utility model registration request] In a stereo multiplex circuit for separating left and right stereo signals from a stereo composite signal obtained at the output end of a detection circuit, a separation degree adjustment resistor for determining a degree of stereo separation, a short circuit for shorting the resistors, and the above-mentioned and a control circuit that detects a 57KHz SK signal included in the output signal of the detection circuit and controls the short circuit, and when the SK signal is detected, the short circuit is inactivated and the short circuit of the separation degree adjustment resistor is released. A stereo multiplex circuit characterized by the following features: