JPS5926682Y2 - FM-AM receiver - Google Patents

Description

[Detailed description of the invention] The present invention is an FM-AM communication transmission device that can switch and receive FM radio broadcasts and AM radio broadcasts, and in particular A
This makes it possible to receive M radio broadcasts well.

Generally, FM-AM receivers have been proposed that are capable of receiving FM radio broadcasts and AM radio broadcasts by switching between them.

Conventionally, such FM-AM receivers as shown in FIGS. 1 and 2 have been proposed.

That is, in FIG. 1, 1FM indicates an inter-FMM frequency amplification circuit to which the FM signal from the FM front end circuit is supplied, and the output signal of this FM intermediate open amplification circuit IFM is
The detection circuit 2FM detects the FM and supplies it to one fixed contact of the FM-AMM conversion switch 3, and IAM indicates an inter-AMM frequency amplification circuit to which the AM signal from the AF front end circuit is supplied. The output signal of the frequency amplification circuit 1AM is AM-detected by the AM detection circuit 2AM and converted to FM-A.
It is supplied to the other fixed contact 3AM of the MM switching switch 3, and the movable contact 3a of this FM-AMM switching switch 3 is connected to the input terminal of the multiplex circuit 4.

In this case, when an FM stereo signal is supplied to the input terminal of the multiplex circuit 4, the left signal and right signal of the stereo signal are output to the left signal output terminal 4L and right signal output terminal 4R of the multiplex circuit 4, respectively. Also, when an FM monaural signal and an AM signal are supplied to this input terminal, there is no pilot signal, so the signal supplied to the input terminal is amplified and sent directly to the left signal output terminal 4L and the left signal output terminal 4L of this multiplex circuit 4. They are obtained at the right signal output end 4R.

The left signal output terminal 4L of this multiplex circuit 4 is grounded through a series circuit of a resistor 5a and a capacitor 5b that constitute a de-emphasis circuit 5L, and the connection point of this resistor 5a and capacitor 5b is connected to a semi-fixed resistor 6L. The movable element of this semi-fixed resistor 6L is connected to the audio amplification circuit 7.
The right signal output terminal 4R of the multiplex circuit 4 is connected to a resistor 5C and a capacitor 5d which constitute a de-emphasis circuit 5R. It is grounded through a series circuit, and the connection point of this resistor 5C and capacitor 5d is grounded through a semi-fixed resistor 6R.
The R movable element is connected to the right signal output terminal 8R from which the right signal to be supplied to the right speaker is obtained via the audio amplification circuit 7R.

In this case, the de-emphasis circuits 5L and 5R are each used to compensate for the pre-emphasis of the FM broadcast signal, and their frequency characteristics are, for example, as shown by the solid line in FIG.
It has a characteristic that it decreases by 10 dB at 5 dB and IOK le,
Also, semi-fixed resistors 6L and 6R are multiplex circuit 4.
This is for correcting the level difference between the signals obtained at the left signal output terminal 4L and the right signal output terminal 4R due to variations in circuit components, etc.

In Fig. 1, if you want to receive an FM radio broadcast, connect the movable contact 3a of the FM-AM changeover switch 3 to one fixed contact 3FM, and the FM radio broadcast will be sent to the left signal output terminal 8L and right signal output terminal 8R. A playback signal of
Also, if you want to receive AM radio broadcasts, use this FM-AM
Connect the movable contact 3a of the changeover switch 3 to the other fixed contact 3AM.
If connected to the left signal output terminal 8L and right signal output terminal 8
A reproduced signal of AM radio broadcasting is obtained on R.

In Figure 1, there is no problem when receiving FM radio broadcasts, but when receiving AM radio broadcasts, the AM radio broadcast signal is not pre-emphasized like the FM radio broadcast signal, so there is no de-emphasis. As shown by the solid line in FIG. 3, the frequency characteristics of 5L and 5R are lowered by, for example, 4 to 5 dB at 4 KHz and about 10 dB at 10 KHz, which has the drawback of deteriorating the frequency characteristics of the reproduced signal and impairing the sound quality.

Therefore, a system as shown in FIG. 2 has been proposed to eliminate the decrease in frequency characteristics when receiving AM radio broadcasts.

That is, in FIG. 2, the output end of the FM detection circuit 2FM is connected to the input end of the multiplex circuit 4, and the left signal output end 4L and right signal output end 4 of this multiplex circuit 4 are connected.
R to the first and second FM-AM changeover switches 9 and 1, respectively, via the emphasis circuits 5L and 5R, respectively.
0 to fixed contacts 9FM and 10FM, and the output terminal of the AM detection circuit 2AM to the first and second F.
Connected to the other fixed contacts 9AM and 10aM of the M-AM changeover switches 9 and 10, respectively, and
- The movable contacts 9a and 10a of the AM changeover switches 9 and 10 are grounded via the semi-fixed resistors 6L and 6R, respectively, and the movable elements of the semi-fixed resistors 6L and 6R are respectively connected to the audio amplification circuit 7L. and 7R to the left and right signal output terminals 8L and 8R, respectively.

In FIG. 2, when receiving an FM radio broadcast, the movable contacts 9a and 10a of the first and second FM-AM changeover switches 9 and 10 are connected to one fixed contact 9, respectively.
When connecting to FM and IOFM and receiving AM radio broadcasts, the movable contacts 9a and 10a of the first and second FM-AM changeover switches 9 and 10 are connected to the other fixed contacts 9AM and 1QAM, respectively.

In Fig. 2, when receiving AM radio broadcasting, the de-emphasis circuits 5L and 5R are not used, so the first
As shown in the figure, the frequency characteristics of this AM radio broadcast signal are not deteriorated.

However, the left signal output terminal 4L of the multiplex circuit 4
When the semi-fixed resistors 6L and 6R are adjusted to adjust the imbalance of the signal at the right signal output terminal 4R, the presence of the semi-fixed resistors 6L and 6R causes the left signal and Right signal output terminal 8L and 8
There was a drawback that the signal level obtained for R was unbalanced.

In view of this, an FMAM receiver as shown in FIG. 4 can be considered as an FMAM receiver designed to eliminate the above-mentioned drawbacks.

In Figure 4, the output end of the FM detection circuit 1 is connected to the FM-AM
Connect to one fixed contact 3FM of changeover switch 3, and connect to A
The output end of the M detection circuit 2 is connected to the other fixed contact 3AM of the FMAM changeover switch 3, and the movable contact 3a of this FM-AM changeover switch 3 is connected to the input end of the multiplex circuit 4. The left signal output terminal 4L of the de-emphasis circuit 5L is connected to the collector of the n-type transistor 11 which constitutes the switching element through a series circuit of a resistor 5a and a capacitor 5b which constitutes the de-emphasis circuit 5L, and the right signal output terminal of the multiplex circuit 4. End 4R
is connected to the collector of a transistor 11 through a series circuit of a resistor 5C and a capacitor 5d constituting a de-emphasis circuit 5R, and the emitter of the transistor 11 is grounded.

In this case, the resistance values of resistors 5a and 5C are set to 5Ω,
The capacitance value of each of capacitors 5b and 5d is set to 0°01μ.
F, and when the transistor 11 is turned on, the frequency characteristics of the de-emphasis circuits 5L and 5R are as shown by the solid lines in Figure 3.
The characteristic is that it decreases by 10 dB at Hz.

Reference numeral 12 indicates an FM-AM switching control signal input terminal, and the control signal supplied to this FM-AM switching control signal input terminal 12 controls the switching of the movable contact 3a of the FM-AM changeover switch 3, and also controls the switching of the movable contact 3a of the FM-AM changeover switch 3. The signal is supplied to the base of the transistor 11.

In this case, when there is a control signal at this FM-AM switching control signal input terminal 12, the movable contact 3a of the FM-AM changeover switch 3 is connected to one fixed contact 3FM, the transistor 11 is turned on, and this FM-AM When there is no control signal at the switching control signal input terminal 12, the movable contact 3a of the FM-AM changeover switch 3 is connected to the other fixed contact 3AM, and the transistor 11 is turned off.

In FIG. 4, when receiving an FM radio broadcast, a control signal is supplied to the FM-AM switching control signal input terminal 12, and the movable contact 3a of the FM-AM switching switch 3 is connected to one fixed contact 3FM. At the same time, the transistor 11 is turned on.

At this time, the FM detection signal from the FM detection circuit 2FM is supplied to the multiplex circuit 4, and the transistor 11 is turned on to connect the resistors 5a of the capacitors 5b and 5d.
And the side not connected to 5C is grounded, and de-emphasis circuits 5L and 5R perform de-emphasis operation.

At this time, the reproduction signal of the FM radio broadcast can be obtained at the left signal output terminal 8L and the right signal output terminal 8R, respectively, as in FIG.

Also, when receiving AM radio broadcasting, no control signal is supplied to the FM-AM switching control signal input terminal 12. In this case, the movable contact 3a of the FM-AM switching switch 3 is connected to the other fixed contact 3AM, and the transistor 11 is off.

At this time, the AM detection signal from the AM detection circuit 2AM is supplied to the multiplex circuit 4 and the transistor 11 is turned off, so that the de-emphasis circuits 5L and 5
R no longer constitutes an emphasis circuit.

Therefore, when AM radio broadcasting is being received in FIG. 4, the de-emphasis circuits 5L and 5R are inactive, so the left signal output terminal 8L and the right signal output terminal 8R are connected to the left signal output terminal 8L and the right signal output terminal 8R, which are not affected by the de-emphasis circuit. A good reproduced signal of AM radio broadcasting having a flat frequency characteristic as shown by the broken line in FIG. 3 can be obtained.

However, in Figure 4, when receiving an AM radio broadcast, the electric field is weak, and when the level of the AM radio broadcast signal is low, the noise increases, and especially the high frequency noise becomes harsh. There is a drawback.

In view of this point, the present invention is designed to eliminate the above-mentioned drawbacks in FIG.

Hereinafter, the present invention will be explained with reference to FIG. 5 for an embodiment of an FM-AM receiver.

In FIG. 5, parts corresponding to those in FIG. 4 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 5, the FM-AM switching control signal input terminal 12 is connected to the diode 1 constituting the OR circuit 13 in FIG.
3a to the base of the transistor 11, and A
The output signal of the M intermediate frequency amplification circuit IAM is supplied to the level detection circuit 14.

In this case, the level detection circuit 14 obtains a bi-level signal, for example, a power supply voltage, at the output terminal when the input signal becomes below a predetermined level, and at other times, the output terminal is set to zero voltage or voltage.

The output terminal of this level detection circuit 14 is connected to the base of the transistor 11 via a diode 13b forming an OR circuit 13.

The rest of the structure is the same as that shown in FIG.

In the present invention, a control signal is supplied to the FM-AM switching control signal input terminal 12 when receiving an FM radio broadcast.

At this time, the movable contact 3a of the FM-AM changeover switch 3 is connected to one fixed contact 3FM, the transistor 11 is turned on, and the de-emphasis circuits 5L and 5R perform a de-emphasis operation, respectively.

Therefore, at this time, the FM detection signal from the FM detection circuit 2FM is supplied to the multiplex circuit 4, and as in FIG.
It is possible to obtain reproduction signals of M radio broadcasts.

Further, when receiving AM radio broadcasting, no control signal is supplied to the FM-AM switching control signal input terminal 12.

At this time, the movable contact 3a of the FM-AM changeover switch 3 is connected to the other fixed contact 3AM, the transistor 11 is turned off, and the de-emphasis circuits 5L and 5R do not perform the emphasis operation.

At this time, the AM detection signal from the AM detection circuit 2AM is supplied to the multiplex circuit 4, and since the emphasis circuits 5L and 5R are inactive, the left signal output terminal 8L and right signal output terminal 8R are free from the influence of the de-emphasis circuit. It is possible to obtain a good reproduction signal of AM radio broadcasting having a flat frequency characteristic as shown by the broken line in FIG.

In this invention, in this case, the AM
When radio waves have a weak electric field, the level detection circuit 14
The output side becomes a bi-level signal, which turns on the transistor 11, so the de-emphasis circuits 5L and 5R perform an emphasis operation, respectively, and work as low-pass filters that remove high-frequency signals, thereby eliminating high-frequency noise. is removed, resulting in an easy-to-hear audio signal.

As described above, according to the present invention, it is possible to receive FM radio broadcasts well, and when receiving AM radio broadcasts, when the broadcast signal level of the desired station is above a predetermined level, the receiving frequency characteristics are extended to reproduce the AM radio broadcasts. This has the advantage that the sound quality of the signal is not impaired, and the high frequency part is removed when the broadcast signal level of the desired station is below a predetermined level, making it easier to hear the sound.

In the above embodiment, the AM intermediate frequency amplifier circuit 1AM
The level of the output signal is detected, and when the level is below a predetermined level, the transistor 11 is turned on.For example, when the broadcast signal is below a predetermined level, the muting circuit is operated to perform muting. In such a receiver, if transistor 11 is turned on by a signal that disables the muting circuit, it is possible to listen to weak electric field broadcasts in which the muting circuit is activated, and the circuit configuration becomes simpler. .

In this case, in a receiver that uses a processor in the microphone to configure a synthesizer tuner, muting is turned off in this weak electric field when trying to receive a desired station. The off signal can be used as it is as a signal to turn on the transistor 11.

Furthermore, it goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations can be adopted without departing from the gist of the present invention.

[Brief explanation of drawings]

1 and 2 are block diagrams showing examples of conventional FM-AM receivers, FIG. 3 is a diagram for explaining the present invention, and FIG.
The figure is a block diagram showing an example of an FM-AM receiver, and FIG. 5 is a block diagram showing an embodiment of the FM-AM receiver of the present invention. IFM is an FM intermediate frequency amplification circuit, IAM is an AM intermediate frequency amplification circuit, 2FM is an FM detection circuit, 2AM is an AM detection circuit, 3 is an FM-AM changeover switch, 4 is a multiplex circuit, 5L and 5R are de-emphasis circuits, respectively. , 8L
and 8R are the left signal output terminal and right signal output terminal, respectively.
1 is a transistor constituting a switching element, 12 is an FM-AM switching control signal input terminal, 13 is an OR circuit, 1
4 is a level detection circuit.

Claims (1)

[Scope of utility model registration request] The output signal of the FM detection circuit is supplied to one fixed contact of the changeover switch, and the output signal of the AM detection circuit is supplied to the other fixed contact of the changeover switch, and the movable contact of the changeover switch is connected to the input terminal of the multiplex circuit. connect to,
first and second capacitors, respectively, from the left and right signal output ends of the multiplex circuit;
A left signal output terminal and a right signal output terminal are derived through first and second resistors constituting a de-emphasis circuit,
The sides of the first and second capacitors that are not connected to the first and second resistors are connected to one controlled electrode of the switching element, and the other controlled electrode of the switching element is grounded. FM-A characterized in that the element is turned on when the broadcasting signal level is below a predetermined level when receiving FM broadcasting or AM broadcasting.
M receiver.