JPS636905Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to an improvement of a receiving device capable of receiving an FM reception band and a plurality of AM reception bands.

[Technical background of the invention]

Conventionally, a receiving device capable of selectively receiving an FM reception band and a plurality of AM reception bands has an FM front end 1 as shown in FIG.
1 and a radio unit 12. This radio unit 12 is made of, for example, an IC, and includes an intermediate frequency amplifier and a detector for FM.
It has an AM mixer, a local oscillator, an intermediate frequency amplifier, and a detector, and the outputs of the FM and AM detectors are amplified by an amplifier (not shown) to drive a speaker.

Then, the radio unit 12 is
LW selected by band changeover switch S ₁ to S ₄
antenna parts 131, 13 for use, MW, and SW
2, 133 and local oscillation signal generation units 141, 142, and 143 for generating local oscillation frequency signals, AM reception bands for long waves, medium waves, and short waves are respectively determined. Furthermore, the radio unit 12 is configured to selectively supply FM and AM detection outputs to an amplifier for driving a speaker (not shown) by means of an FA/AM reception band switching switch (not shown).

Note that of the variable capacitors VC ₁ and VC ₂ connected to the FM front end 11, VC ₁ constitutes a resonant circuit for the antenna input section, and VC ₂ constitutes a resonant circuit for the local oscillation circuit. . Also,
AM variable capacitors VC ₃ and VC ₄ are connected to the radio unit 12, with VC ₃ connected to each antenna section 131, 1
The resonant circuit of the antenna input section is configured together with either one of the local oscillation signal generating sections 141, 142, 143, and the resonant circuit of the local oscillation circuit is configured with the _VC4 .

The terminal STB of the radio unit 12 is commonly connected to one end of each of the local oscillation coils of the local oscillation signal generating sections 141, 142, and 143, for example.

[Problems with background technology]

However, in such a receiving device, the variable capacitors VC ₁ to VC ₄ are integrally formed, for example, like a well-known polyvaricon, and are used for FM and
Coupling capacitance is generated between the AM variable capacitors VC ₂ and VC ₃ for oscillation. Therefore, the capacitance of variable capacitor VC ₄ as well _as switch S ₃ ,
The capacitive component of any one of the LW, MW, and SW local oscillation signal generation sections 141, 142, and 143 selected for _S4 is added.

As a result, for example, in the FM reception state,
When the AM band switching switches S ₁ to S ₄ are operated, the capacitance between the _two electrodes of the variable capacitor VC changes, which changes the local oscillation frequency of the FM front end 11 and causes a significant shift in the receiving frequency. Become.

For this reason, conventionally, as _shown in FIG. Even if the band changeover switches _S1 to _S4 are switched, the change in capacitance added to both ends of the electrodes of the variable capacitor _VC2 is made small.

However, each local oscillation signal generation section 141, 142,
143 are, for example, two capacitors and one
141 is the capacitor C ₁₁ , C ₁₂ and the coil L ₁
142 is composed of capacitors C ₂₁ , C ₂₂ and coil L ₂ , and 143 is composed of capacitors C ₃₁ , C ₃₂ and coil L ₃ . Note that the same parts in FIG. 2 as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

From the above, as shown in Fig. 3, the capacitances added between both electrodes of variable capacitor VC ₂ are: coupling capacitance C _n between variable capacitors VC ₂ and VC ₄ , variable capacitor VC ₄ , capacitor C ₀ and This is the combined capacitance of any one of the capacitors _C1 to _C3 selected by the switch _S3 .

However, capacitor C ₁ in Figure 3 is a capacitor
This is due to the combined capacitance of C ₁₁ and C ₁₂ , and when the capacitance is expressed using their signs, it becomes C ₁ =C ₁₁ C ₁₂ /(C ₁₁ +C ₁₂ ). Similarly, C ₂ = C ₂₁ C ₂₂ / (C ₂₁ + C ₂₂ ), C ₃ = C ₃₁ C ₃₂ / (C ₃₁ +
C ₃₂ ).

However, as is clear from Fig. 3, even with the above means, the AM band selection switch
When switching S ₁ to S ₃ , it is inevitable that the capacitance added to variable capacitor VC ₂ will change.
For example, when switching to a distant reception band, such as from LW to SW, the change in the additional capacitance of variable capacitor VC ₂ is still large, making it difficult to sufficiently prevent fluctuations in reception frequency in FM reception conditions. I had a problem.

Note that the same parts in FIG. 3 as in FIGS. 1 and 2 are designated by the same reference numerals, and their explanations will be omitted.

[Purpose of invention]

This idea was made in view of the above points,
It is an object of the present invention to provide a good receiving device in which the FM reception frequency does not shift even if an AM band changeover switch is changed in an FM reception state.

[Summary of the idea]

First and second variable capacitors for varying the local oscillation frequency are provided correspondingly for each FM and AM reception band, and the second variable capacitors are selectively connected via an AM band selection switch. In the receiving device having a plurality of local oscillation signal generation units for generating local oscillation frequency signals corresponding to each AM reception band, there is a connection between the second variable capacitor and the AM band switching switch. , due to the coupling capacitance of the first and second variable capacitors.
By interposing an inductance element that prevents the capacitance components of the plurality of local oscillation signal generators selected by the AM band selection switch from being added to the first variable capacitor, the local oscillation frequency for FM reception is This feature is characterized in that it prevents changes in the

[Example of idea]

An embodiment of this invention will be described in detail below with reference to the drawings.

FIG. 4 shows the main parts of the receiving device according to this invention. However, parts in FIG. 4 that are the same as those in FIG. 2 are designated by the same reference numerals and their explanations will be omitted.

That is, the movable section of the switch _S3 constituting the AM band changeover switch is connected to the variable capacitor _VC4.
is connected to one end of the electrode via a coil L ₀ serving as an inductance element. Above coil L ₀
Although it has a small inductance, it is designed to provide a sufficiently high impedance for the FM reception band.

As a result, as shown in Figure 5, the variable capacitor
One end of VC ₄ will be connected to one end of the capacitors C ₁ to C ₃ via the coil L ₀ ,
The coil L ₀ has a sufficiently high impedance for the FM reception band, and the capacitors C ₁ to C ₃
The capacitance of the variable capacitor VC ₂ is connected through the coupling capacitance C _n
It is never added to. Therefore,
In the FM reception state, the AM band selection switch S ₁
Even if _S4 is switched, it is possible to prevent the capacitance between both electrodes of the variable capacitor _VC2 from changing and the FM reception frequency from changing.

However, parts in FIG. 5 that are the same as those in FIGS. 3 and 4 are designated by the same reference numerals and their explanations will be omitted.

It goes without saying that this invention is not limited to the above embodiments, and that various modifications and applications are possible without departing from the gist of this invention.

[Effect of idea]

As explained in detail above, according to this invention, even if the AM band selection switch is switched during FM reception,
It is possible to provide a good receiving device in which the FM reception frequency does not shift.

[Brief explanation of the drawing]

1 to 3 are diagrams used to explain conventional receiving devices, respectively. FIG. 4 is a circuit diagram showing a main part of an embodiment of the receiving device according to this invention, and FIG.
The figure is a diagram used to explain the operation of the circuit of FIG. 4. 11...FM front end, 12...Radio unit, 131, 132, 133...Antenna section, 141, 142, 143...Local oscillation signal generation section, _S1 to _S4 ...AM band switching switch,
VC ₁ to VC ₄ ... Variable capacitor, C ₀ ... Compensation capacitor, C _n ... Coupling capacitance, L ₀ ... Coil.

Claims (1)

[Scope of utility model registration request] First and second variable capacitors for varying the local oscillation frequency are provided correspondingly for each FM and AM reception band, and the second variable capacitors are selectively connected via an AM band selection switch. In a receiving device having a plurality of local oscillation signal generation units for generating local oscillation frequency signals corresponding to each AM reception band,
The plurality of local oscillation signals are generated between the second variable capacitance capacitor and the AM band switching switch, which are selected by the AM band switching switch based on the coupling capacitance of the first and second variable capacitors. A receiving device characterized in that an inductance element is interposed to prevent a capacitance component from being added to the first variable capacitor to prevent a change in a local oscillation frequency for FM reception.