JPS58127441A - Receiver - Google Patents

Abstract

PURPOSE:To improve the demodulation distortion at a forced monaural reception mode, by preventing a pilot signal from appearing at a monaural demodulation output when the forced monaural reception function is executed. CONSTITUTION:When a voltage for the forced monarual reception is applied to a terminal 8, a changeover switch 20 is made nonconductive by operating monaural operation for a changeover switch circuit 18 with a changeover switch controlling circuit 26. A changeover switch circuit 24 outputs a signal for making an amplifier 23 nonconductive. But this signal is blocked with a signal transmission controlling circuit 20. Thus, the amplifier 23 and a pilot canceller signal conversion circuit performs a normal operaion and a pilot cancellation signal is given to a demodulator 21. Thus, the pilot signal in an FM composite signal component is canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM receiver having a forced monaural reception function that allows a listener to forcibly stop stereo reception and receive monaural reception even when receiving stereo signals. It is.

First, the reception mode of the F)k'M receiver will be explained with reference to FIG. The horizontal axis in FIG. 1 represents the electric field strength at the antenna of the upper M receiver, and the vertical axis represents the signal-to-noise ratio and the rear leg output. As shown in FIG. 1, the demodulation level of the JN receiver is constant above a certain input level, but below that input level it exhibits attenuation characteristics determined by the detection method. Further, the signal-to-noise ratio (8/N) characteristic gradually improves from a weak electric field to a medium electric field, and shows a saturation characteristic when a strong input is applied. The receiver has two reception modes: stereo reception □ mode and monaural reception mode.
The input level of the 87N degradation in stereo receive mode occurs from an input level about 20 dB higher than that in monaural receive mode. On the other hand, the S/N sensing characteristic of Iruma's ear is S/h
It is a well-known fact that the absolute amount of convergence cannot be identified when the value is 45 dB or more, but it can be easily determined when it is less than 45 dB. Therefore, even if the broadcast transmission signal is in stereo mode, listeners often select mono 2 reception mode from the point of 8/N when the electric field is below medium (antenna input 40 dB/4 V or below). In this way, even if the transmitting side transmits in stereo, the listener switches to monaural reception mode (◆), which is called forced monaural reception.

A conventional FM receiver having such a forced monaural reception function will be explained with reference to FIGS. 2 and 3. First, FIG. 2 will be explained. 1M input from antenna 1
The broadcast wave is mixed with the local oscillation signal at the I''M7H end 2 to become an intermediate frequency of 10.7MHz, which signal is amplified by the FM intermediate frequency amplification circuit IF amplifier 3, and then demodulated by the FRd detector 4. FN detector 4
Since the output of is a monaural demodulation output signal, the first and second channel outputs are FM-q for stereo demodulation.
A stereo first channel output and a stereo second channel output are each output terminal 6 through the multiplex circuit 5.
7. To switch the FM reception mode, use this PI11.
This is done by controlling the control terminal 8 provided in the 4Y lute plex circuit 5.

The FM multiplex circuit 5 will be explained using FIG. The signal demodulated by the FM detector 4 is called a PjJ composite signal, and the signal is demodulated by the FM detector 4.
is applied to the input terminal 10 of.

This PM composite signal is supplied to three paths.

One of them is k'LL (7 aids locked loop)
The second is a stereo signal demodulation system, and the third is a stereo/monaural control system.

First, the first F))', L, L control system will be explained.

The FM composite signal supplied to the input terminal 10 is sent to the first phase comparator 11. First low-pass filter 12 Voltage controlled star oscillator 13, First frequency divider 14 and Second frequency divider 1
j) k'M composite by P, L, L, (7 aids locked loop) control in which 5 are connected in cascade and the output of the second frequency divider 15 is returned to the first phase comparator 11. 19 included in the signal 'J4z pilot signal and 90°
Used to obtain signals with different phases. In other words, the oscillation frequency of the voltage-controlled oscillator 13 is around 76 KHz, and this oscillation frequency is converted to 38 KHz by the first frequency divider 14.
Divide the frequency into Furthermore, in the second branching unit 15, the pilot signal (x9kHz,) in the input FM composite signal and
19kHz with a 0° phase difference is obtained.

Next, I will explain the stereo/monaural control system.
The FM composite signal is fed to a second phase comparator 16 and further passes through a second low-pass filter 17 to provide a stereo signal.
The signal is led to a monaural changeover switch circuit 18. The 14038 KHz frequency divided signal from the first frequency divider is input to the third divider 19 to obtain a 19 KHz signal that is in phase with the pilot signal in the input FIV composite signal, and this signal is sent to the second phase comparator 16. It performs synchronous detection with the pilot signal in the FM composite signal and outputs a signal proportional to the pilot signal level at the output of the second low-pass filter 17.

This signal is input to the stereo/monaural switching circuit 18. If the input signal exceeds the switching threshold level of the stereo/monaural switching circuit 18,
This switching circuit 18 operates the first switching circuit 20 to inject the output of the first branching unit 14 into the demodulator 21,
As a result, 4
The input signals are multiplied to produce a stereo demodulated output at the first channel output 6 and the second channel output cuff of the demodulator. Further, in this state, the switching circuit 18 operates the second switch circuit 24 to activate the second amplifier 23. The output of the @20 branch divider is applied to one input of the amplifier 23 of the filter 2, and the output of the @20 branch divider is applied to the other input, and the output of the second low-pass filter 17 is proportional to the pilot signal in the input composite signal. Therefore, the output of the second amplifier 23 is the output of the second frequency divider 15 proportional to the pilot signal level in the input FM composite signal.
9KHz square technique can be obtained. This signal passes through the 19 sum i pilot can 2 signal conversion circuit 25 and is input to the 'M
It is applied to the demodulation circuit 21 as a signal that follows the same phase and level as the pilot signal in the composite signal, and the demodulation circuit 21 cancels the pilot signal of the input PM composite signal with the input signal.

When a voltage is applied to the control circuit 8 for switching the receiving mode for the forced monaural signal mode, the second switch control circuit 26 makes the second switch circuit 24 non-conducting and switches the second amplifier 23 inactivate.

Further, the stereo/monaural switching circuit 18 is set to the monaural side, and the first switch switching circuit 2o is made non-conductive. As a result, a 38 KHz switching signal is not injected into the demodulator 21, so that monaural signals are output from the first and second channel outputs 6.7.

When the pilot signal is not included in the □M composite signal supplied to the input terminal IO, that is, when in monaural signal mode, the stereo-monaural switching circuit 18 switches to the monaural side, and the output of the demodulator 21 is It becomes a monaural signal.

According to the above explanation, the FM receiver shown in FIG. 3 is in the operating state as shown in Table 1 in each reception mode.

By the way, the input FN composite signal Vcomp is (
1) Expressed by the formula, 1 of the total FN composite signal level
It accounts for 0%.

Vcomp= (L+R)+(L-R) sina+
s t +Pcos -4) s t... (1) However, L+R: Sum component 1 of L channel and R channel, -R,: Difference component P between L channel and R channel: Pilot signal component ωst: Suppressing the difference component between the L channel and the R channel Angular frequency of the carrier wave Normally, to remove the pilot signal component at the input level of the post-tuner 21, a: add the opposite sign component of the third term in equation (1) (or , by subtracting the components of the same sign), for this 19K) 1! The demodulator 2 converts the signal at the third block component level of equation (1) from the canceller-signal conversion circuit 25 to the demodulator 2.
1 and calculate the 19KHz pilot signal component to -60dB to -8 to the composite signal demodulation level.
Enables 0 dB attenuation and further reduces demodulation distortion to 0.0 dB.
A stereo signal demodulation distortion of 1% is obtained. When the control voltage at the control terminal 8 is applied to select the forced monaural reception mode, the stereo/monaural switching circuit 1
8 is in monaural operation and the first changeover switch circuit 2 is non-conductive), and the switching signal output from the first frequency divider 14 for performing stereo tuning is injected into the post-tuner 21. Not done. For this reason, the first . In the second channel output 6.7, the (1, +R) component of equation (1) is not ahed and becomes monaural demodulation, and as mentioned above, the S/
Deterioration of N can be prevented.

However, in the forced monaural reception mode, the second changeover switch circuit 24 also becomes non-conductive, so the 19KHz pint
There is also no output supplied from the two-signal conversion circuit 25 on the can. Therefore, the pilot component in the input composite signal cannot be canceled, and this component is directly transmitted to the first . It appears on the second channel output 6.7 and worsens demodulation distortion. Usually, revenge! 1st of 4 vessels 21. The butterfly on the second channel output 6.7 has a de-emphasis characteristic to correct the pre-emphasis performed on the broadcasting station side, and a low-pass filter with a time constant of 50 μs (or 75 μs). Pass through.

Since the pilot signal component ratio of this de-enassist characteristic and the FM composite signal is 9:1, the first. 1st in forced monaural reception mode for demodulation level of 2nd channel output 6.7. The pilot signal component ratio appearing in the second channel output 6.7 is -40 to -50 dB, and when expressed in terms of demodulation distortion, the distortion is 0.3% to 1%. In other words, 0.01 in the stereo reception mode mentioned above.
The demodulation distortion was 30 to 100 times worse than the demodulation distortion of %.

An object of the present invention is to provide an FM receiver with improved demodulation distortion in forced monaural reception mode.

In the receiver line according to the present invention, a signal is injected to operate the 19 KHz pilot canceller signal conversion circuit without making it non-conductive to cancel the biput signal component to supply a signal voltage for forced monaural reception mode. Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 4 is a block diagram of an FM multiplex circuit according to an embodiment of the present invention, and the same functional parts as in FIG. 3 are denoted by the same numbers and their explanations will be omitted. In FIG. 4, a signal transmission control circuit 30 is inserted between the first changeover switch circuit 24 and the second amplifier 23, and this signal transmission control circuit 30 is controlled by the changeover switch control circuit 26. That is, when a voltage is applied to the terminal 8 for the forced monaural reception mode, the signal transmission control circuit 30 is operated by the signal from the changeover switch control circuit 26, and the signal is transmitted from the second changeover switch (b) path 24 to the This prevents the signal from being supplied to the amplifier 23 of No. 2. Therefore, in the forced monaural reception mode, the second amplifier 23 is conductive and the 19
The KHz pilot canceller signal conversion circuit 25 operates. When no control voltage is supplied to the terminal 8, the signal from the second changeover switch circuit 24 is supplied directly to the second amplifier 23.

Now, when a high-level FM composite signal is supplied to the receiver, in the stereo reception mode, the butterfly 19KHz pilot canceller signal conversion circuit 25 and the first changeover switch circuit 20 are conductive, and the control switch 21 is in the stereo reception mode. Perform demodulation.

Next, for weak FN composite signal input, terminal 8
When a voltage for forced monaural reception is applied to the switch control circuit 26, the stereo/mono switch circuit 18 is set to monaural operation, thereby rendering the first switch circuit 20t'i non-conducting. Further, the second changeover switch circuit 24 also outputs the signal (B) for making the second amplifier 23 non-conductive. However, this signal is blocked by the signal transmission control circuit 20. Therefore,
The second amplifier 23 and the 19 KHz pilot canceller signal conversion circuit operate normally, and the pilot cancel signal is injected into the demodulator 21.

By doing this, in the conventional example, when in forced monaural reception mode, the input )'! '14:=I The pilot signal in the invosite signal component is not removed and the first . The portion appearing in the second channel output 6.7 can be canceled in the same manner as in the stereo reception mode, and no pilot signal is generated in the first and second channel outputs 6.7.

Therefore, the cause of deterioration of demodulation distortion in forced monaural mode is removed, and the level of demodulation distortion becomes the same as that in stereo reception mode.

Furthermore, removal of the pilot signal also improves 8/N.

Actually, since the forced monaural reception mode has j5 S/N degradation compared to the stereo reception mode, the demodulation distortion is reduced by that amount.

Next, during monaural reception, the stereo/monaural changeover switch circuit 18 does not operate in monaural mode without the changeover switch control circuit 26 working, and the second changeover switch circuit 24 causes the second amplifier 23a to become non-conductive. Therefore, a monaural signal is output.

From the above, the receiver of FIG. 4 according to this embodiment has a second
The operating state shown in the table will be reached.

FIG. 5 shows another embodiment. The configuration of Figure 5 is con) 1-
- has an oscillation control circuit 27 that controls the oscillation of the voltage-controlled excavation circuit 13 connected to the voltage control terminal 8. Others are the same as in Figure 4. The oscillation control circuit 27 is activated when a voltage higher than the voltage for forced monaural reception mode is supplied to the control terminal 8, and stops the oscillation of the voltage-controlled oscillation circuit 13. When the oscillation of the oscillator 13 stops, the loop of the P, L, L system is interrupted, and the output of the second low-pass filter 17 is not output. Therefore, the stereo/monaural switching circuit 18 does not operate, the 1g1 selector switch circuit 20 is non-conductive, and the 19 KHz pilot canceller signal conversion circuit 25 is also non-conductive. Therefore, the demodulator 21 performs monaural demodulation because neither the output of the 10th frequency divider 14 nor the 1 gKHz biput cancellation signal for stereo demodulation is injected into the demodulator 21. In addition, when there is no pilot signal in the input FM composite signal, by performing this operation during monophonic reception, the voltage controlled oscillator 13 is not operating at the same time as the seven-channel demodulation, so the amplitude of the oscillator can be demodulated. This also helps improve the S/N ratio of the demodulator output since there is no distortion in the output of the demodulator. Also, if the k''M receiver also has an AM reception function, by controlling this control terminal 8 to stop the oscillator 13 when receiving AI'V, the PM multiplex oscillator output will be on when receiving AM. In addition, a sine wave and a triangular wave can be used as the pilot cancellation signal of the present invention, but in the case of a square wave, the signal of the second changeover switch 24 is used as the signal of the third frequency divider 19. This can be easily done by using the output.

As described above, according to the present invention, it is possible to provide a receiver that does not deteriorate demodulation distortion or signal-to-noise ratio c 8/N > not only in forced monaural reception mode but also in monaural reception mode and AM reception.

Note that the voltage may be supplied to the terminal 8 automatically by detecting the electric field strength, or may be supplied manually using an external switch.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram explaining the difference in signal-to-noise ratio depending on the reception mode of an FM receiver, Figure 2 is a block diagram of the FM receiver, and Figure 3 is a block diagram of a conventional FM multiplex circuit. , FIG. 4 is a block diagram showing an embodiment of the present invention,
FIG. 5 is a block diagram showing another embodiment.

Claims (2)

[Claims] (1) In a receiver having a forced monaural reception function that forcibly generates a monaural demodulated output even when a stereo broadcast is being received, when the forced monaural receiver syndrome is being executed, 1. A receiver comprising means for preventing a pilot signal from appearing in said monaural demodulated output. (2) The means includes a circuit that generates a signal to cancel the pilot signal, and a control circuit that operates the circuit when the forced monaural reception function is executed and stops the operation of the circuit when monaural broadcasting is being received. A receiver according to claim 1, characterized in that it has: