JPH0136359Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention relates to a tuning switching circuit used in a multi-band receiver.
This is intended to prevent problems such as a decrease in image sensitivity or abnormal oscillation, and to reduce the number of parts and production man-hours.

Conventional configuration and its problems FIGS. 1, 2, and 3 show tuning switching circuits used in conventional multiband receivers. 1st
In Figures to Figure 3, T ₁ and T ₂ are transformers (frequency band coils) corresponding to each of the two frequency bands,
L ₁ and L ₂ are their tuning coils, L ₁ ′ and L ₂ ′ are their output coils, C ₁ and C ₂ are capacitors connected in parallel to each tuning coil L ₁ and L ₂ , and CT ₁ and CT ₂ are The antenna trimmer is also connected in parallel to the tuning coils L ₁ and L ₂ , CV ₁ is a variable capacitor, _S1-1 ,
_S1-2 are interconnected switches, _Q1 is a transistor, and _R1 is its base resistor.

Figure 1 shows the tuning coils L ₁ , L ₂ and the output coil L ₁ ′,
This circuit switches L ₂ ' using switches _S1-1 and _S1-2 . Switch _S1-1 is now transformer
The switch S1-2 is connected to the tuning coil _L1 of _T1 , and the switch _S1-2 is connected to the output coil _L1 ', and in this state,
Transformer _T1 becomes tuned. Next, switch
By connecting _S1-1 to the tuning coil _L2 of the transformer _T2 and connecting the switch _S1-2 to the output coil _L2 ', the transformer _T2 becomes tuned.

FIG. 2 shows a conventional tuning switching circuit in which switches _S1-2 are removed from FIG. 1. That is, remove _S1-2 , connect the output coils L ₂ ′ and L ₂ ′ of transformers T ₁ and T ₂ in series, and connect the transistor
The switching operation of Q ₁ is used to short-circuit the output coil L ₂ ' of transformer T ₂ to prevent a decrease in sensitivity. Now transform the switch _S1-1
If the output coil L _{2 '} of the transformer T ₂ is connected to the tuned coil L 1 of the transformer T ₁ and a bias is applied to the base of the transistor Q 1 through the resistor R ₁ to short-circuit the output coil L ₂ ' of the transformer T ₁ , then the output coil L of the transformer T ₁ From ₁ ', the tuned output can be obtained without any problem. Next is the switch
Connect S1 _- 1 to the tuning coil L ₂ of the transformer T ₂ ,
When the transistor Q ₁ is turned off, the output of the transformer T ₂ can be taken out from the output coil L ₂ ′ via the output coil L _{1 ′} of the transformer T 1 .

Figure 3 shows the transistor Q ₁ in Figure 2 connected in parallel to the tuning coil L ₂ of the transformer T _2. In this case, the same principle as in Figure 2 is used to calculate the tuned output for each frequency band. can be taken out.

However, in the configuration shown in Figure 1, the number of switches increases, which is disadvantageous in terms of the number of parts, production man-hours, and cost.On the other hand, in the configurations shown in Figures 2 and 3, the output of transformer _T2 is transferred to When taking out from L ₂ ′,
Since the output coil L ₁ of the transformer T ₁ is connected in series, this may cause a decrease in sensitivity and image sensitivity, abnormal oscillation, etc. Almost the same problem occurs in FIG. 3 as well.

Purpose of the invention The present invention prevents various troubles such as a decrease in sensitivity and image sensitivity, and abnormal oscillation, and also eliminates switches _S1-2 , reduces the number of parts and production man-hours, and simplifies the process. A tuning switching circuit is provided.

Structure of the invention This invention connects each tuning coil of two or more tuning circuits in series, connects the output coil in series, and connects a variable capacitor to both ends of the tuning coils connected in series. By short-circuiting all the tuning coils other than the frequency band using a switch, only the desired frequency band can be selected.

DESCRIPTION OF EMBODIMENTS FIG. 4, which is an embodiment of the present invention, will be described below. In Fig. 4, the tuning coils L ₁ and L ₂ of the transformers T ₁ and T ₂ are connected in series, and the output coils L ₁ ',
L ₂ ′ are connected in series, and the variable capacitor
CV ₁ is connected to both ends of tuning coils L ₁ and L ₂ connected in series. Also, the tuning switch
_S1-1 is unnecessary when using the tuning coil _L1 of one transformer _T1 , the other transformer _T2
short-circuit the tuning coil L ₂ of the tuning coil L ₂ of the other tuning coil L 2
One tuning coil is not required when using
It is designed to short-circuit _L1 . In this way, even though the unused and unnecessary tuning coil and output coil are connected in series, the impedance of the short-circuited coil becomes extremely low, so the transformers T ₁ and T Mutual interference between _{the two} is eliminated, and the above-mentioned trouble can be prevented. Note that the switch _S1-1 may be constructed of a semiconductor switch such as a transistor.

Effects of the invention As described above, the present invention connects the tuning coils and output coils of each tuning circuit in series, and short-circuits all the tuning coils other than the frequency band to be used with a switch to tune only the desired frequency band. To provide an inexpensive tuning switching circuit that prevents troubles such as a decrease in sensitivity and image sensitivity or abnormal oscillation, and also reduces the number of switches, the number of parts, and the number of production steps. I can do it.

[Brief explanation of the drawing]

1, 2, and 3 are circuit diagrams showing essential parts of a conventional tuning switching circuit, and FIG. 4 is a circuit diagram showing an embodiment of the present invention. CV ₁ ...Variable capacitor, CT ₁ , CT ₂ ...
Antenna trimmer, T ₁ , T ₂ ...Transformer (frequency band coil), L ₁ , L ₂ ' ... Output coil, L ₁ ,
L ₂ ... Tuning coil, S1 _- 1, S1 _- 2 ... Switch, Q ₁ ... Transistor, R ₁ ... Transistor
Bias resistance for Q ₁ .

Claims (1)

[Scope of utility model registration request] Two or more frequency band coils and variable capacitance capacitors form two or more tuned circuits, each tuned circuit is configured to tune two or more frequency bands, and each frequency band coil is Tuning coils are connected in series, an output coil coupled and wound around each tuning coil is connected in series, and a variable capacitor is connected to both ends of the tuning coils connected in series, and tuning for frequencies other than the frequency band used is performed. By shorting all the coils with a switch,
A tuning switching circuit characterized by allowing only a desired frequency band to be selected.