JPH0113462Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a band switching device for a tuning circuit in a radio receiver.

The high frequency tuning circuit in a radio receiver is generally configured as shown in FIG.
1. Connect the tuning variable capacitor VC to the tuning coil L1,
switch S2 for switching to L2 and L3;
A switch S3 and a tuning coil L1 for AC-shutting unnecessary tuning coils other than a specific tuning coil,
Tuning output switching switches S4 for the secondary coils L2 and L3 are provided so as to be interlocked with each other. In response to this, there has been a demand to reduce the number of band switching switches in order to reduce the number of mechanical contacts to reduce noise and causes of failure, or to reduce the number of parts as much as possible.

Therefore, this invention focuses on the above points, reduces the number of band switching switches in the tuning circuit of a multiband radio receiver, reduces the number of parts, and also reduces the number of mechanical contacts. An object of the present invention is to provide a band switching device for a radio receiver that can reduce noise and causes of failure.

Therefore, the present invention connects the secondary sides of a plurality of tuned coils in series in order of frequency, connects the secondary side end of the tuned coil in the lowest frequency band to a power supply, and connects an impedance conversion element to the antenna circuit. At the same time, the output side of the element is connected to the secondary side end of the tuning coil of the highest frequency band, and a variable tuning capacitor is switchably connected to the primary side of each tuning coil via the first switch. The connection point between the secondary side of a tuning coil and another tuning coil is grounded by a capacitor via a second switch.

Hereinafter, embodiments of this invention will be described based on the drawings.

FIG. 2 shows a high frequency tuning circuit in a multi-band radio receiver, in which an impedance conversion element 2 is connected to an antenna circuit 1. For example, an FET is used as this impedance conversion element 2,
The gate on the FET input side is connected to the antenna circuit 1 through a capacitor, and the drain on the output side is connected to the mixer circuit 5 through a reactor 3 for a filter and a coupling capacitor 4. 6 is a tuning coil for the highest frequency band, 7 is a tuning coil for an intermediate frequency band, 8
are tuning coils for the lowest frequency band, and the primary ends of each of the tuning coils 6, 7, and 8 are connected to a tuning variable capacitor 1 which can be switched via a first switch 9.
Connected to 0. In addition, each tuning coil 6, 7, 8
are connected in series in order of frequency, the secondary end of the tuned coil 8 in the lowest frequency band is connected to the power supply, and the secondary end of the tuned coil 6 in the highest frequency band is connected to the filter reactor 3. It is connected to the output side of the impedance conversion element 2 via. Furthermore, the connection points between the secondary coils of each of the tuned coils 6, 7, and 8 with other tuned coils and the connection between the secondary coil of the tuned coil 8 and the power source can be switched via the second switch 11. is grounded through the capacitor 12. Therefore, the tuning coil in the frequency band lower than the grounded tuning coil, that is, the second
In the figure, the secondary side coils of tuning coils 7 and 8 are short-circuited in an alternating current manner via a capacitor 12 and an electrolytic capacitor 13 on the power supply side, so that unnecessary tuning coils are shot on the secondary side. next,
The operation of the above tuning circuit will be explained.

First, a high impedance signal induced in the antenna is changed to a low impedance signal by the impedance conversion element 2, and a frequency signal that resonates with the grounded tuning coil appears on the output side of the impedance conversion element 2. Note that the conversion element 2
If is a FET, the signal is also amplified, and the amplified relatively low impedance tuning frequency signal is outputted to the next stage mixer circuit 5 via the reactor 3 and the coupling capacitor 4.

At this time, if the band switching switch is set to the tuning coil 6 of the highest frequency band as shown in Fig. 2, the tuning coils 7 and 8 of the frequency band lower than this tuning coil 6 are Since the side coils are connected in series and are switched in alternating current via the second switch 11, the tuning function is canceled and only the tuning coil 6 functions. In addition, the unnecessary tuning coil 2
Although the secondary side is shot in an alternating current manner, since the coupling between the primary side and the secondary side is tight, the same effect as when the primary side coil is shot can be obtained.

Next, when the band switching switch is switched to an intermediate frequency band, the switching connection of the first switch 9 connects the tuning variable capacitor 10 to the primary side end of the tuning coil 7 of the intermediate frequency. On the other hand, by switching and connecting the second switch 11, only the secondary coil of the tuning coil 8 in the lowest frequency band is switched in an alternating current manner. Therefore, a frequency signal tuned to the tuning coil 7 in the intermediate frequency band to which the variable tuning capacitor 10 is connected appears on the output side of the impedance conversion element 2 via the secondary coil. Note that at this time, the secondary side of the tuning coil 6 in the highest frequency band is not AC shot, but the self-resonance frequency of the secondary side of the tuning coil on the higher frequency side than the tuning frequency is considerably higher than the tuning frequency. There is no effect on the low frequency tuning signal, and there is no problem simply by shooting the tuning coil 8 in the lowest frequency band. This also applies when the band switching switch is switched to the lowest frequency band and the secondary sides of the higher frequency tuning coils 6 and 7 are left unshot in alternating current.

In the above embodiment, the tuning output signal is output from the secondary end of the tuning coil to the mixer circuit 5 via the capacitor 4, but the tuning signal is output from the tuning variable capacitor 10 via the FET and the capacitor. It can also be output. Furthermore, even if there are three or more tuning coils, the same implementation can be achieved by increasing the number of contacts of each switch.

As explained above, the band switching device of this invention uses a first switch that switches the variable tuning capacitor, and a second switch that has the functions of shooting an unnecessary tuning coil, switching the antenna, and switching the output signal. Since the band switching in the tuning circuit can be performed by using the switch, the number of switches can be reduced compared to the conventional one, simplifying the circuit configuration, and the number of mechanical contacts can be reduced, thereby reducing the causes of noise and failure. Furthermore, since an impedance conversion element is inserted into the antenna circuit, even if the antenna is touched with a hand, the tuning frequency will not be affected, and an amplification effect can be expected.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional high frequency tuning circuit, Figure 2 is a circuit diagram of a conventional high frequency tuning circuit.
The figure is a circuit diagram showing an embodiment of this invention. 1... Antenna circuit, 2... Impedance conversion element, 6, 7, 8... Tuning coil, 9... First
Switch, 10... Tuning variable capacitor, 11
...Second switch.

Claims (1)

[Scope of utility model registration request] The secondary sides of a plurality of tuned coils are connected in series in order of frequency, the secondary side end of the tuned coil in the lowest frequency band is connected to a power supply, and an impedance conversion element is connected to the antenna circuit, and the impedance conversion element The output side of the tuning coil is connected to the secondary side end of the tuning coil of the highest frequency band, and a tuning variable capacitor is switchably connected to the primary side of each of the tuning coils via a first switch, and coil 2
1. A band switching device for a radio receiver, characterized in that a connection point with another tuning coil on the next side is grounded by a capacitor via a second switch.