JPS631463Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an antenna coil switching circuit particularly suitable for a multi-band receiving device.

As is well known, band switching in a multi-band receiver is performed by switching a large number of LC tuning circuits, ie tank circuits, corresponding to each band.
By the way, in this case, there is no particular problem when switching between relatively close bands, where L is shared and C is switched, but when switching between relatively distant bands, an independent antenna coil (tuning circuit) is switched for each band. So there are many problems.

In other words, in such switching, other antenna coils (tuned circuits) adjacent to the band actually used are directly grounded, but the antenna coils (tuned circuits) that are actually used are This is because when viewed from the circuit, it may become anti-resonant (trapped) or resonate within its tuned frequency, causing an adverse effect.

Therefore, this idea was made in view of the above points, and the antenna coil adjacent to the antenna coil actually used is connected to a reference potential point (for example, ground) through a resistor that acts as a damping resistance for the quasi-resonant circuit. It is an object of the present invention to provide an extremely good antenna coil switching circuit that prevents the occurrence of anti-resonance and resonance points by connecting the antenna coils to the antenna coil and enables effective antenna coil switching.

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

That is, FIG. 1 shows a case in which the circuit is applied to a band switching circuit of a multi-band receiver including at least a plurality of shortwave bands. This is circuit 12. The antenna coil switching circuit 11 and the (local) oscillation coil switching circuit 12 are provided with band switching switches S _A , S _B , S _C , _SD and S _E , S _F , S _G , which are interlocked with each other.
It has S _H. First, the former switch S _A has its movable contact A5 connected to the antenna terminal AT, and its first, second, third fixed contacts A1, A2,
A3 is connected to one end of the primary side of each of the antenna coils _T1 , _T2 , _T3 for short wave bands _SW3 , _SW2 , _SW1, respectively, and the remaining fourth fixed contact A4 is used as an idle contact. . Similarly, the movable contact B5 of S _B is grounded via a variable capacitor (VC ₁ ), and the first, second, and third fixed contacts B1,
B2 and B3 are the antenna coils T _{1 and} B3, respectively.
The fourth fixed contact B4 is connected to one end of the primary side of each of T ₂ and T ₃ , and the remaining fourth fixed contact B4 is connected to one end of the primary side of the antenna coil _T4 for medium wave band MW. Similarly, S _C has a movable contact C5 that is grounded directly or via a resistor _R1 that serves as a damping resistance for a pseudo-tuned circuit to be described later, and has first, second, and third fixed contacts C1, C2, C3 are resistors R ₂ , R ₃ , which serve as damping resistances for the quasi-resonant circuits described later, respectively.
It is connected to one end of each primary side of the antennas T ₂ , T ₃ , and T ₄ via R ₄ , and the remaining fourth fixed contact C 4 serves as an idle contact. Similarly, S _D has a movable contact D5 connected to one input end of the mixer 13, and first, second, third, and fourth fixed contacts D1, D2, and D.
3, D4 are the antenna coils T ₁ , T ₂ ,
It is connected to one end of each secondary side of T ₃ and T ₄ .
Here, the primary antenna coils T ₁ , T ₂ , T ₃ , T ₄ are
Each other end of the secondary side is grounded.

In addition, the latter switch S _E has a variable capacitor (variable capacitor) (VC ₂ ) whose movable contact E5 is interlocked with the aforementioned variable capacitor (variable capacitor) (VC ₁ ).
and the first, second, third,
The fourth fixed contacts E1, E2, E3, and E4 are connected to one end of each primary side of local oscillation coils _T5 , _T6 , _T7 , _and T8 for shortwave bands _SW3 , _SW2 , and _SW1, respectively, and for medium wave band MW. are correspondingly connected to via capacitors C ₀₁ , C ₀₂ , C ₀₃ , and C ₀₄ . Similarly, the SF has a movable contact F5 that is grounded directly or via a resistor _R5 that serves as a damping resistance for the pseudo-resonant circuit described later, and the first, second, and third fixed contacts F1,
F2 and F3 connect to the local oscillation coils T ₆ , T ₇ , and T ₈ correspondingly through resistors R ₆ , R ₇ , and R ₈ which serve as damping resistances for the quasi-resonant circuits to be described later, respectively.
The remaining fourth fixed contact F4 serves as an idle contact. Similarly, S _G has its movable contact G5 connected to the output terminal of the local oscillator 14,
and first, second, third, and fourth fixed contacts G1, G
2, G3, and G4 are the local oscillation coils, respectively.
Connected to one end of each primary side of T ₅ , T ₆ , T ₇ , and T ₈ .
Similarly, S _H has its movable contact H5 connected to the mixer 13.
The first, second, third, and fourth fixed contacts H1, H2, H3, and H4 are connected to the other input terminal of the local oscillation coils _T5 , _T6 , _T7 , and _T8 , respectively. Connected to one end of the secondary side. Here the local oscillator coil
The other ends of the primary and secondary sides of T ₅ , T ₆ , T ₇ , and T ₈ are grounded.

The output end of the mixer 13 is connected to an audio stage (not shown) via an intermediate frequency amplifier 15 and a wave detector 16.

In the above configuration, the band switching switches S _A and S _D of the antenna coil switching circuit 11 select one of the antenna coils T ₁ to _{T 4} of the desired band, and S _B selects the corresponding receiving frequency. The antenna coils set and adjacent to the antenna coil selected above by S _C , that is, T ₂ when T ₁ is selected, T ₃ when T ₂ is selected, and T ₄ when T ₃ is selected, are respectively connected to the quasi-resonant circuit. and is grounded via a resistor that serves as a damping resistor.

On the other hand, in conjunction with this, one of the local oscillation coils T ₅ to T ₈ corresponding to the band selected by the band switching switches S _E , S _G , S _H of the local oscillation switching circuit 12 is selected, and Other local oscillator coils not selected above by S _F i.e. T ₅
When selected, T _{6 is} grounded, when T ₆ is selected, T ₇ is grounded, and when T ₇ is selected, T ₈ is grounded.

The received signal obtained by the former is mixed with the local oscillation signal obtained by the latter in the mixer 13 to be converted into a predetermined intermediate frequency signal, and then the intermediate frequency amplifier 15 and the wave detector 16
The signal is then converted into an audio signal and reproduced from a speaker (not shown) or the like.

By the way, with the band switching in the above, other antenna coils T ₂ to T ₄ and local oscillation coils T ₆ to _{T 8} adjacent to the selected band, especially on the low frequency side,
will be grounded selectively through resistors R ₁ to R ₈ , but the impedance of each of these resistance values should be sufficiently low for the selected coil, and the lead wire (printed wiring) in the grounding path should be If you select a value that acts as a damping resistance against pseudo-resonant circuit components consisting of other elements such as conductor patterns (in the case of a board), you can eliminate the problem by directly grounding as in the conventional method. To maintain good sensitivity characteristics, etc. of an antenna coil switching circuit 11 and a (local) oscillation coil switching circuit 12 by preventing undesired resonance and anti-resonance phenomena occurring in a selected antenna coil (tuning circuit). The characteristic of the idea is that it allows you to do the following. In other words, the resistance R ₁ ~
_R8 acts as a damping resistor that lowers the Q value of resonance for the quasi-resonant circuit created by the ground circuit, and its value R is, for example, the resistance of the aforementioned conductor pattern r (≒0.1Ω or less). In addition, the resistance of the tank circuit due to the selected coil is Z (≒
several tens of kΩ, however, Q100), r≪R≪
It is sufficient to select R≒10 to 400Ω so as to satisfy the relationship Z. As a result, as is clear from the circuit analysis described later, the antenna coil switching circuit 11 and the (local) oscillation coil switching circuit 12 are free from undesirable traps and resonance points.
This makes it possible to improve the characteristics of the antenna circuit and local oscillation circuit.

FIG. 2 shows a simplified equivalent circuit of the antenna coil switching circuit 11 when a certain shortwave band is selected in FIG. 1. In this figure, () is the antenna coil section to be selected, () is the quasi-resonant circuit section including the adjacent antenna coil section, and _S is the constant current to see the impedance at the point in ().
R ₁₁ is the resistance that determines the Q of the selected antenna coil section, C ₁₁ is a variable capacitor (varicondenser), L ₁ is the inductance of the selected antenna coil, R ₁₂
is the resistance that determines the Q of the adjacent antenna coil,
C ₁₂ is the stray capacitance, L ₂ is the inductance of the adjacent antenna coil, L ₃ is the inductance of the lead wire as a conductive pattern, C ₁₃ is the coupling stray capacitance, and R ₁₃ is the damping resistance for the quasi-resonant circuit. .

In this figure, to see the impedance (Z _inp ) at point (), we need to look at the voltage characteristics directly from V ₍ 〓 ₎ = _S・Z _inp = Z _inp (∵ _S = 1).

And in this diagram, a variable capacitor (varicon)
The impedance (voltage) characteristics at the point () when C ₁₁ is varied are shown when the above damping resistor (R ₁₃ ) (≒400Ω) is included, and when the quasi-resonant circuit is simply shot without a damping resistor (≒0.1Ω). The tuning characteristic curve diagrams in FIGS. 3 to 8 show the results of circuit analysis (however, the frequency band is 10 to 100 MHz) in three configurations: ) and simply open state (≈1 MΩ). In addition, Figures 3 to 5 show when the value of the variable capacitor _C11 is 15 pF on the minimum side (high frequency side), and Figures 6 to 8 show the value when it is on the maximum side (low frequency side). ) at 60pF. Other parameters R ₁ = 50kΩ, L ₁ = 1.23μH, C ₂ =
0.1 pF, L ₂ = 14.2 μH, L ₃ = 1 μH, C ₃ = 7 pF are common to all figures.

That is, as can be seen from Figures 4, 5, 7, and 8, in the above case where there is no damping resistor for the quasi-resonant circuit, there is an undesired phenomenon before and after the resonance point A due to the original tuning characteristic. Since anti-resonance point B and resonance point C exist, they are adversely affected. However, as can be seen from Figures 3 and 6, when a damping resistor is included for the quasi-resonant circuit, undesired anti-resonance and resonance are suppressed and do not exist, due to the original tuning characteristics. There is only resonance point A.

It should be noted that this invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications and applications can be made without departing from the gist of this invention.

Therefore, as detailed above, according to this invention, the antenna coil adjacent to the antenna coil actually used is connected to a reference potential point (for example, ground) via a resistor that serves as a damping resistor for the quasi-resonant circuit.
It is possible to provide an extremely good antenna coil switching circuit that prevents anti-resonance and resonance states from occurring by connecting the antenna to the antenna coil and performs effective antenna coil switching.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing an embodiment of the antenna coil switching circuit according to this invention, Fig. 2 is an equivalent circuit including a quasi-resonant circuit when the one shown in Fig. 1 is selected, and Figs. FIG. 4 is a curve diagram showing the tuning characteristics of the equivalent circuit shown in the figure with and without damping resistance for the quasi-resonant circuit; 11... Antenna coil switching circuit, 12... Local oscillation coil switching circuit, S _A to S _H ... Band switching switch, AT... Antenna terminal, T ₁ to _{T 4} ...
...Antenna coil, T ₅ - _{T 8} ... (local) oscillation coil, VC ₁ , VC ₂ ... Variable capacitor (varicon), R ₁ - _{R 6} ... Resistor, 13 ... Mixer, 14
... Local oscillator, 15 ... Intermediate frequency amplification section, 16
...Detector.

Claims (1)

[Scope of utility model registration request] A plurality of antenna coils including at least a plurality of antenna coils for short wave bands, respective fixed contacts correspondingly connected to respective input ends of the plurality of antenna coils, and a first movable contact connected to the antenna terminal. Each fixed contact is connected correspondingly to the band switching switch and each input terminal of the plurality of antenna coils, and the movable contact is connected to the reference potential point via a variable capacitor, and the first a second band switching switch that is in an interlocking relationship with the band switching switch; Each fixed contact is connected to the input end of the antenna coil through a resistor of approximately 10 to 400Ω, which serves as a damping resistance for the quasi-resonant circuit, and the movable contact is connected to the reference potential point. An antenna coil switching circuit comprising a third band switching switch that is connected to the first and second band switching switches and is in an interlocking relationship with the first and second band switching switches.