JPH0149209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a band switching circuit for a multiband receiver.

[Prior Art] A conventional band switching circuit will be described below.

Figure 1 shows a circuit diagram of a conventional band switching circuit, where 1 is a receiving antenna consisting of a rod antenna, 2, 4, 5, 8, 10, 11, and 14 are interlocking band switching switches, and 3 is an antenna. A variable capacitor for tuning; 6 is an antenna tuning circuit for a first frequency band, for example a medium wave band; 7 is an antenna tuning circuit for a second frequency band, for example a short wave band;
9 is a variable capacitor for oscillation tuning that works with the variable capacitor 3; 12 is a medium wave band oscillation tuning circuit; 1
3 is a shortwave band oscillation tuning circuit.

Then, as shown in FIG. 1, when the movable contact a of the band changeover switch 2 is connected to the fixed contact c,
The receiving antenna 1 is an antenna tuning circuit 7 in a short wave band.
It is configured to be connected to the tap of the coil. In addition, the movable contact a of the band changeover switch 2
In other words, the receiving antenna 1 is grounded during medium wave band reception, so that external noise from the receiving antenna 1 does not affect medium wave band reception. and,
Band switching switches 4, 5, 10, and 11 are used to switch and connect the variable capacitors 3 and 9, respectively, and when receiving a short wave band, the medium wave antenna tuning circuit 6
Both input terminals of the coils of the oscillation tuning circuit 12 and the oscillation tuning circuit 12 are grounded so as not to affect shortwave band reception. Both input ends of the coil are grounded so as not to affect medium wave reception.

Further, the band selection switch 8 selects either one of the antenna tuning circuits 6, 7 and connects it to the high frequency amplifier, and the band selection switch 14 selects either one of the oscillation tuning circuits 12, 13 and connects it to the oscillation circuit. Connect to.

[Problems to be Solved by the Invention] However, the above configuration has the problem that the number of circuits for the band changeover switch is large, the switching of the band changeover switch is heavy, and the operability is poor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a band switching circuit which solves the problems of the conventional example and can reduce the number of band switching circuits.

[Means for Solving the Problems] The band switching circuit of the present invention includes a first variable capacitor 3 for antenna tuning, and a first variable capacitor 3 to which the first variable capacitor 3 is connected and which is tuned to a first frequency band. a second antenna tuning circuit 7 to which the first variable capacitor 3 is connected and which tunes to a second frequency band; Reception band switching switches 4 and 5 connected to antenna tuning circuits 6 and 7, reception antenna 1 of a second frequency band connected to said second antenna tuning circuit 7, and said reception band switching a band selector switch 8 for selecting a received signal, which selects one of the outputs of the first and second antenna tuning circuits 6, 7 in conjunction with the switches 4, 5; and a second variable capacitor for oscillation tuning. 9, a first oscillation tuning circuit 12A to which the second variable capacitor 9 is connected and tuned to the first frequency band, and a first oscillation tuning circuit 12A to which the second variable capacitor 9 is connected and tuned to the second frequency band. For oscillation, the second oscillation tuning circuit 13 and the second variable capacitor 9 are connected to the first and second oscillation tuning circuits 12A and 13 in conjunction with the reception band switching switches 4 and 5. and an oscillation signal selection circuit that selects one of the outputs of the first and second oscillation tuning circuits 12A and 13 in conjunction with the reception band selection switches 4 and 5. Band change switch 1
4, a semiconductor switching element 18 connected between the receiving antenna 1 for the second frequency band and the ground, and a tuning circuit whose input terminal is connected to one of the first and second variable capacitors 3 and 9. The connection end is connected to the output end of the semiconductor switching element 18.
a high-frequency cutoff filter 17 connected to the control terminal of the
A DC voltage for making the semiconductor switching element 18 conductive is applied to the variable capacitor connection end of the first antenna tuning circuit 6 and the first oscillation tuning circuit 12A to which the high frequency cutoff filter 17 is connected. It is equipped with a DC voltage applying means 15.

[Function] According to the configuration of the present invention, when the first antenna tuning circuit and the first oscillation tuning circuit that tune to the first frequency band are selected by the band switching switch, the semiconductor switching element is switched from the DC voltage applying means. A DC voltage is applied to the semiconductor switching element, and the semiconductor switching element becomes conductive, thereby grounding the receiving antenna for the second frequency band. Therefore, a band changeover switch for grounding the receiving antenna is not required, and the number of band changeover switch circuits can be reduced.

[Embodiment] FIG. 2 shows an electrical circuit diagram of a band switching circuit in a first embodiment of the present invention. Second
In the figure, the same components as in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted.

In FIG. 2, 12A is a medium wave band oscillation tuning circuit, and 15 is a DC voltage applying means consisting of a resistor connected in parallel to a padding capacitor 16 for tracking correction. 17 is a high-frequency cutoff filter, which is a semiconductor switching element 1 made of a transistor connected between the receiving antenna 1 and the ground.
8 and the variable capacitor 9 are connected.
The ground side terminal of the oscillation coil of the oscillation tuning circuit 12A is connected to the power supply +B.

The operation of the band switching circuit of the embodiment configured as described above will be described below.

When the movable contact a of the band changeover switch 10 is connected to the fixed contact b, the variable capacitor 9 is connected to the medium wave band oscillation tuning circuit 12A, and the power supply +B is connected to the resistor which is the DC voltage applying means 15 and the high frequency cutoff filter. 17 to the base of the transistor which is the semiconductor switching element 18,
The semiconductor switching element 18 becomes conductive and the receiving antenna 1 is grounded.

Other operations are similar to the conventional example.

As described above, in this embodiment, the semiconductor switching element 18 is connected between the receiving antenna 1 and the ground.
is provided, and when the band changeover switch 10 is turned on to the receiving side of the medium wave band, the oscillation tuning circuit 12A
Since the power supply +B is applied to the base of the transistor which is the semiconductor switching element 18, the band switching switch 2 for switching the receiving antenna 1 in the conventional configuration shown in FIG. 1 can be omitted. . As a result, the number of circuits in the band changeover switch can be reduced, and the operability of the band changeover switch can be improved.

FIG. 3 is an electrical circuit diagram of a main part of a band switching circuit showing a second embodiment of the present invention. In the figure, 12B is a medium wave band oscillation tuning circuit, 19 is a DC voltage application means consisting of a resistor connected between the movable contact a of the band changeover switch 10 and the power supply +B, and the DC voltage application means shown in FIG. It functions similarly to means 15.

Note that the receiving antenna 1 in the embodiment may be another type of antenna, or may be an externally connected antenna in the case of a receiver equipped with an external antenna terminal. Further, the medium wave band may be a long wave band, and the short wave band may be a very short wave band. Further, in the above embodiment, a DC voltage is applied from the power supply +B to the variable capacitor connection terminal of the medium wave band oscillation tuning circuit 12A, that is, the movable contact a of the band changeover switch 10, by the resistors 15 and 19, and Semiconductor switching element 18
The base of the was connected to the tuning circuit connection end of the variable capacitor 9 via the high-frequency cutoff filter 17.
If attention is paid to reception sensitivity, the following configuration may be used instead of the configuration described above. That is, the variable capacitor connection end of the medium wave band antenna tuning circuit 6, that is, the movable contact a of the band switching switch 4.
A DC voltage is applied from power supply +B to
It may also be connected to the tuning circuit connection end of the variable capacitor 3 via.

[Effects of the Invention] According to the band switching circuit of the present invention, since the receiving antenna for the second frequency band is grounded by the semiconductor switching element when receiving the first frequency band, the number of circuits for the band switching switch is reduced. can be reduced, and the operability of the band changeover switch can be improved. Further, by reducing restrictions on wiring to the band switching switch, etc., it is possible to obtain the effect that the degree of freedom in designing the printed wiring board on which the band switching circuit is mounted is improved.

[Brief explanation of drawings]

Figure 1 is an electric circuit diagram of a conventional band switching circuit.
FIG. 2 is an electric circuit diagram of the band switching circuit in the first embodiment of the invention, and FIG. 3 is the electrical circuit diagram of the band switching circuit in the first embodiment of the invention.
FIG. 2 is an electrical circuit diagram of a main part of a band switching circuit in an embodiment of the present invention. 1... Receiving antenna, 4, 5, 8, 10, 1
1, 14... Band selection switch, 3, 9... Variable capacitor, 6, 7... Antenna tuning circuit, 1
7...High frequency cutoff filter, 18...Semiconductor switching element, 12A, 13...Oscillation tuning circuit, 1
5, 19...DC voltage application means.

Claims (1)

[Claims] 1 a first variable capacitor for antenna tuning;
a first antenna tuning circuit to which the first variable capacitor is connected and tuned to a first frequency band; and a second antenna tuning circuit to which the first variable capacitor is connected and tuned to a second frequency band. a receiving band switching switch for selectively connecting the first variable capacitor to the first and second antenna tuning circuits; and a receiving antenna for a second frequency band connected to the second antenna tuning circuit. and the first band changeover switch in conjunction with the reception band changeover switch.
and a band selector switch for selecting a received signal that selects one of the outputs of the second antenna tuning circuit, a second variable capacitor for oscillation tuning, and a second variable capacitor connected to the first one. a first oscillation tuning circuit tuned to a frequency band; and the second oscillation tuning circuit.
a second oscillation tuning circuit to which a variable capacitor is connected and tunes to a second frequency band; An oscillation band changeover switch connected to the circuit and a reception band changeover switch interlocked with the first
and a band switching switch for selecting an oscillation signal that selects one of the outputs of the second oscillation tuning circuit, and a semiconductor switching element connected between the receiving antenna of the second frequency band and the ground;
a high-frequency cutoff filter having an input end connected to a tuning circuit connection end of one of the first and second variable capacitors and an output end connected to a control terminal of the semiconductor switching element; and the first antenna tuning circuit. and a band switching circuit comprising a DC voltage applying means for applying a DC voltage for making the semiconductor switching element conductive to the variable capacitor connection end of the first oscillation tuning circuit to which the high-frequency cutoff filter is connected. .