JPS607222A - Fm receiver - Google Patents

Abstract

PURPOSE:To reduce sound interruption because of a component of a large amplitude at a low frequency in a modulation signal by providing hysteresis to a tuning state detecting circuit to detect at a relatively narrow band when a frequency of an intermediate frequency signal is changed in a direction to be brought close to a specified intermediate frequency. CONSTITUTION:Voltage comparator circuits 65' and 66' of the tuning state detecting circuit 60' have respectively hysteresis. That is, an output terminal of an operational amplifier circuit is connected to a non-inverting input terminal via a resistor R2, the non-inverting input terminal is connected to a terminal 69 to which a reference voltage VRO is given via a resistor R3, and detected voltages SX, SY through low-pass filters 63, 64 are given to an inverting input terminal. The state of outputs signals SA, SB of voltage comparators 65', 66' is changed depending on whether the detected voltages SX and SY are respectively a voltage VR2 or not and the state of a synthesized signal SC is changed depending whether a frequency f1 of an intermediate frequency signal is within a range of a relatively wide prescribed band B2 before and after a specified intermediate frequency f10. That is, whether or not the tuning is attained when once tuned is detected by the wide band B2.

Description

DETAILED DESCRIPTION OF THE INVENTION In the field of industrial application, the present invention employs a so-called frequency synthesizer type in which a local oscillation circuit receives all external input signals and changes the local oscillation frequency at regular intervals. An FM in which the frequency is automatically changed at regular intervals by a tuning signal from an automatic tuning circuit, and the change in the local oscillation frequency is automatically stopped when tuned to a broadcast wave at a predetermined level or higher. This invention relates to a receiving device.

BACKGROUND TECHNOLOGY AND PROBLEMS A so-called frequency oscillator is used, in which a local oscillation circuit receives an external input and changes its local oscillation frequency at regular intervals. An FM receiver has been proposed in which the local oscillation frequency is automatically changed at regular intervals, and the change in the local oscillation frequency is automatically stopped when the frequency is tuned to a broadcast wave at a predetermined level or higher.

In such an FM receiving device, whether the received signal level is above a predetermined level or not is in tune with the detected received signal level detection signal and the broadcast wave, the FM detection signal is completely cut off or detected. The muting open side I signal that causes conduction is simultaneously used as an automatic stop signal that automatically stops the change in the local oscillation frequency.

Figure 1 shows an example of a conventional FM receiver using this type of system.
The FM broadcast wave received by the antenna // is supplied to the front end, 20, to a high frequency amplification circuit, 2l, all the way to a mixing circuit 22, and a local oscillation circuit, 23, which converts the local oscillation signal into 9 intermediate frequency words. The intermediate frequency signal is passed through the intermediate frequency amplification circuit 37 to the FM detection circuit 32.
The FM detection signal is supplied to the stereo demodulation circuit 33, where the left and right signals, R, are demodulated, and the demodulated signal, R, is muted (i, iJ
The local oscillation circuit 23, which is not shown, divides the oscillation signal of the voltage controlled oscillator into A by a frequency dividing circuit, and outputs the frequency-divided signal to the output terminal 3. It consists of a phase-locked loop (PLL) in which the signal is phase-compared with a constant frequency signal from a reference oscillator, and the comparison output voltage controls the oscillation frequency of the voltage-controlled oscillator. It is used as a signal, but the frequency dividing circuit consists of a programmable counter whose frequency dividing ratio N is determined by a preset program σ corresponding to the received frequency at regular intervals, and the automatic tuning circuit θ is shown in the diagram. By inputting the count output of the scanning counter that counts clock pulses as a preset input to this programmable counter, the division ratio N is automatically changed and the local oscillation frequency is automatically changed at regular intervals. et t7. Ru. The automatic tuning circuit 0 automatically stops changes in the local oscillation frequency by completely stopping the counting of the scanning counter in response to the automatic stop signal SM, which will be described later, and by fixing the preset input of the programmable counter. Has a function.

Then, the intermediate frequency signal amplified by the intermediate frequency amplification circuit 3 is supplied to the received signal level detection circuit so, and it is detected whether the level of the received signal is higher than a predetermined level.
The FM detection voltage output from the FM detection circuit 3.2 is supplied to the tuning state detection circuit 00, which detects whether it is tuned to the broadcast wave or not, and outputs the detection signal SL from the received signal level detection circuit 00. and the detection signal Sc of the output of the tuning state detection circuit Otsu0.
are synthesized by the synthesis circuit 70, and the synthesized signal SM is supplied to the muting circuit 3 as a muting control signal, and is also supplied to the automatic tuning circuit 11 as an automatic stop signal.
．． 0, and when the muting circuit 3+! is not in tune, or even if it is in tune but the level of the received 1 word signal is not above a predetermined level, the composite signal SM becomes, for example, a low level, and the muting circuit 3+! When the demodulated signal and R are cut off, the local oscillation frequency continues to change, and when the received signal level is tuned to a predetermined level or higher, the composite signal SM changes from a low level to a high level, causing muting. is canceled and the demodulated signal is output, R appears at the output terminal 35°3, and the local oscillation frequency stops changing as described above.

Specifically, the received signal level detection circuit 30 consists of an AM detection circuit (left) which detects the intermediate frequency signal 'tAM, and a voltage comparison circuit 5.2 which compares the detected voltage with the total reference voltage.
The voltage comparator circuit S2 has full hysteresis, and when the level of the received signal changes in the direction of increasing, the reference voltage is made relatively high, and the detected first word S■ becomes the signal SL/ in FIG.
As shown in , the state changes depending on whether the level of the received f signal is at a relatively large predetermined level L/2 or less,
When the level of the received signal is at this relatively high predetermined level L/
When the reference voltage changes in the direction of decreasing after becoming above, the reference voltage is made relatively low, and the level of the received signal is set to a relatively low predetermined level as shown by signal SL2 in the same figure. The state changes depending on whether the level is 52 or higher.

In the tuning state detection circuit Otsu 0, the FM detection voltage is taken out through the buffer amplifier circuit Otsu, and the detected E voltage Sx is inverted in the inverting amplifier circuit 4. Detection 1 [Pressure Sy is low-pass filter Otsu 3 and Otsu 4 consisting of resistor R1 and capacitor CI, respectively]
=4- is supplied to the voltage comparison circuits S and 4B and compared with the reference voltage VR/ given from the terminal Otsu 7, respectively, and the output signals SA and SB of the voltage comparison circuits 4 left and 4B
are synthesized in a synthesis circuit Og, and the detected voltages Sx and Sy are respectively set at a specified intermediate station e and a number fIO-70,7 for the frequency fI of one intermediate frequency word, as shown in Fig. 3.
The output signals SA and SB of the voltage comparator circuit 45, Otsu, and 4 change their states depending on whether or not the detection voltages Sx and Sy are respectively higher than the reference voltage VR/. Therefore, the state of the composite signal Sc changes depending on whether the frequency f of the intermediate frequency signal is within a predetermined band B/ around the specified intermediate frequency f'ro. That is, it is detected whether or not they are tuned by the composite signal Sc.

By the way, this tuning state detection circuit Otsu 0 low) (Sfilter Otsu 3 and Otsugu are used to remove the modulation signal component from the detection voltages Sx and Sy so that the detection of the tuning state is not affected by the modulation signal. In this respect, it is desirable to make the time constants of the resistor R/ and the capacitor Ct as large as possible to make the cutoff frequency sound of the low-pass filter Otsu 3 and Otsu as low as possible.However, the tuning state detection signal Sc and the reception Composite signal S of signal level detection signal SL
As mentioned above, M is used not only as a muting control signal, but also as an automatic stop signal that stops all changes in the local oscillation frequency. The condition needs to be detected. Therefore, it is not possible to increase the time constants of the resistance R/ and the capacitance C/, and the cutoff frequency t of the low-pass filters Otsu 3 and Otsu is 50 at most.
It can only be lowered by about Hz.

However, in conventional devices, the modulation signal has a low frequency of 50 Hz or less, and the intermediate frequency signal has a frequency f.
As shown by frx in FIG. 3, if there is a large-amplitude component that changes within the above-mentioned predetermined band B/, the tuning state detection 1 signal Sc and therefore the muting control signal As the state of the SM changes intermittently, the demodulated signal becomes weaker, and the R is intermittently cut off, resulting in sound interruptions. Especially in foreign countries, there are places where the frequency interval between adjacent channels of FM broadcasting is set as narrow as 3 (7 kHz), and in that case, the above-mentioned band B/ is originally the intermediate frequency f.
ro' is set in a narrow range of 10 θkHz to ±30 kHz, and furthermore, it may deviate significantly back and forth due to changes in circuit constants due to temperature, humidity, or time, or initial adjustment deviations, etc. Sound breakage appears prominently due to large amplitude components at low frequencies of the modulation signal.

Purpose of the Invention In view of this point, the present invention provides an FM receiver of the above-mentioned type in which a muting control signal is simultaneously used as an automatic stop signal to automatically stop changes in the local oscillation frequency. This is designed to reduce sound breakage caused by components with large amplitudes in frequency.

Summary of the Invention In the present invention, a tuning state detection circuit that completely detects whether or not the tuning is performed from the FM detection voltage is provided with hysteresis, and when the frequency f of the intermediate frequency signal changes in the direction approaching the specified intermediate layer wave number flo, L2 is detected in a relatively narrow band B, and conversely when it changes in a direction away from the specified intermediate frequency flo after rt, it is detected in a relatively wide band Bs. to be done.

Embodiment FIG. 7 shows an example of the FM receiving device of the present invention, in which the voltage comparator circuits Otsu 5' and 6 Otsu' of the tuning state detection circuit Otsu θ' each have full hysteresis. .

Specifically, the output terminals of the operational amplifier circuits of the voltage comparison circuits Otori' and 6Otsu' are connected to the non-inverting input terminals through the resistors R and 2, and the non-inverting input terminals are connected to the resistors R and 6, respectively. 3
' is connected to the terminal Otsuwa to which the reference voltage VRO is applied, and low-pass filters Otsu3 and Otsu11 are connected to the inverting input terminal.
．． With a configuration in which the detected voltages Sx and Sy are given through the
When the frequency fl of one intermediate frequency word changes in the direction approaching the specified intermediate frequency flo as shown by the arrow a in Fig. The reference voltage VR applied to the non-inverting input terminal of the constituent operational amplifier circuit becomes a relatively high voltage VR/, and as shown in FIG. The states of SA and SB change depending on whether or not the detection voltages Sx and Sy are respectively higher than the voltage VR/, and therefore the composite signal S
c is the frequency f of the intermediate frequency signal I is the specified intermediate frequency f
The shape changes depending on whether or not it is within a relatively narrow predetermined band B/ before and after Io. Therefore, when tuning, whether or not tuning is achieved can be detected using the narrow band B/.

Once tuned, that is, the frequency f of the intermediate frequency signal
Once r falls within the narrow band B/, the voltage comparator circuit S'
and 6 O' output signals SA and SB become low level,
That is, the voltage at the output terminal of the operational amplifier circuit constituting the voltage comparison circuits S' and 6' decreases, and the reference voltage vR applied to its non-inverting input terminal becomes a relatively low voltage VR,2. Therefore, when the frequency f of the intermediate frequency signal changes in a direction away from the specified intermediate frequency fIo, as shown by the arrow, the outputs of the voltage comparison circuits 6' and 6', as shown in FIG. Signals SA and sB are detection voltage S
The state changes depending on whether x and Sy are respectively higher than or equal to the voltage VR, 2, and the composite signal Sc has a frequency fl of the intermediate frequency signal in a relatively wide predetermined band B2 before and after the specified intermediate frequency f o. The state changes depending on whether it is within the range or not. That is, once tuned, whether or not it is tuned is detected in the wide bands B and 2. The width of band B2 is selected to be approximately S times the width of band B/ or more, and when band B/ is set to a width of 1000kH2 centered on the intermediate frequency flo, band B2 is The frequency is set to a width of 2 to 70 kHz.

Therefore, once tuned, the modulation signal
At a low frequency as below, and the frequency f■ of the intermediate frequency signal has a large amplitude component that changes outside the y range Bl as shown by flX in Figure S, the detected voltage SX
This component that is shaded by and SYK is the low-pass filter Otsu 3.
and i-pressure comparison circuit Otsu S' and Otsu 6' without being removed by Otsugu.
Even if the frequency f of the intermediate frequency signal is not large enough to change the frequency f of the intermediate frequency signal out of band B, the state of the tuning state detection signal SC and therefore the muting control signal SM will be intermittently due to its component. The demodulated signal changes,
R is intermittently cut off and no sound breaks occur.

Effects of the Invention In the present invention, whether the level of the received signal is equal to or higher than a predetermined level is determined by the synchronization state in which it is detected whether the level of the received signal is at least a predetermined level or not. In the case of a method in which the muting open side J signal obtained by fully synthesizing the detection signal is used as an automatic stop signal that simultaneously stops the change in the local oscillation frequency (with a power tuned from the 2M detection voltage) If the circuit has hysteresis and the frequency of the intermediate frequency signal changes in the direction approaching the specified intermediate frequency, a relatively narrow predetermined value is applied. If the frequency of the intermediate frequency signal is within the f+ range B/, then it is detected in the narrow band B, and when the frequency of the intermediate frequency signal is -, it is detected in the narrow band B. On the other hand, when the intermediate frequency changes in the direction away from the specified intermediate frequency after entering the specified intermediate frequency, it is detected whether or not it is within the relatively wide predetermined band B2. Since the detection is performed in the wide band B2, it is possible to significantly reduce sound breakage due to low frequency and large amplitude components of the modulation signal.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of an example of a conventional FM receiver, FIGS. 2 and 3 are diagrams for explaining the operation of its main parts, and FIG. 7 is a connection diagram of an example of an FM receiver of the present invention. FIG. S is a diagram for explaining the operation of its main parts.

Claims (1)

[Claims] A front end that has a local oscillation circuit whose local oscillation frequency can be changed at regular intervals in response to external input, and an FM that detects the intermediate frequency signal 'kFM of the output of this front end.
A detection circuit, a muting circuit that disconnects or conducts the FM detection signal kA of the output of this FM detection circuit according to the IJ An automatic tuning circuit that has a function of automatically changing the channel at intervals and automatically stopping the change in response to an automatic stop signal;
From the intermediate frequency signal, when the level of the received one-word signal changes in the direction of increasing, it is determined whether or not the level is at least the relatively large predetermined level. a received signal level detection circuit for detecting whether or not the received signal level is above a relatively small predetermined level U when the signal changes in the direction of vomiting after becoming vomiting;
From the FM detection voltage output from the detection circuit, it is determined whether the frequency of the intermediate frequency signal is within a relatively narrow predetermined band before and after the specified intermediate frequency when the frequency changes in a direction approaching the specified intermediate frequency. If the frequency changes in a direction away from the specified intermediate frequency after entering the relatively narrow predetermined band, does it fall within the relatively wide predetermined band before and after the specified intermediate frequency? A tuning state detection circuit for all detections, a detection signal k of the output of the received signal level detection circuit, and a detection signal k of the output of the tuning state detection circuit.
gi, and obtain a signal whose state changes depending on when the level of the received signal is above the predetermined level and the frequency of the intermediate frequency signal is within the predetermined band and when it is not,
Muting that signal above flill 1111
An FM receiving device comprising a combining circuit which supplies the multiplication signal and the automatic stop signal to the muting circuit and the automatic tuning circuit.