JPS597782Y2 - Band switching circuit of multi-band receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a band switching circuit for a multiband receiver having an FM band and a plurality of AM bands.

In the converter circuit of AM multi-band radio, when the oscillation coil of one band is used, if the oscillation coil of another band is connected, the M coupling between the oscillation coils or the oscillation coil and the intermediate frequency Since interference with the transformer usually causes the oscillation frequency to be pulled in or abnormal oscillations to occur, conventionally, as shown in Figure 1, the oscillation coils of other bands that are not being used are grounded, or It was necessary to use a switch circuit that switches the collector side of the oscillation coil and disconnects the oscillation coils of other bands from the transistor Q, as shown in FIG.

In Figures 1 and 2, 1 is the FM front end, Q is the AM converter transistor, R1 is the base bias resistance of Q, R2 is the emitter resistance of Q, C1 is the coupling capacitance with the antenna coil, C2 is a variable capacitor as a variable reactance element for channel selection on the AM oscillation side, C3, C6
is a padding capacitor connected to variable capacitor C2 in order to keep the frequency difference between the local oscillation frequency and the receiving frequency approximately constant; C4 and C7 are trimmer capacitors for cover adjustment; C5 and C8 are injection capacitors; L1 and L2 are oscillation coils for medium wave MW and long wave LW, IFT is AM
intermediate frequency transformer, S1 to S5 are band switching switches, S is for injection switching, S2 is for oscillation coil grounding, S
3 is for VC switching, S4 is for FM and AM power switching, S5
indicates the oscillation coil switching.

However, the circuits shown in Figures 1 and 2 require many switch circuits to switch the oscillation coil of the AM converter.
This resulted in circuit instability and was disadvantageous in terms of miniaturization and cost reduction of the switch.

In view of this, the present invention aims to reduce the number of switch circuits that change over the oscillation coil of the AM converter by using the FM front end and the power switch for the AM converter. An example will be explained according to FIG.

Also, are the parts in Figure 3 the same as those in Figures 1 and 2? Therefore, the same figure numbers as in FIGS. 1 and 2 will be used.

In the circuit shown in FIG. 3, the secondary windings 11-2 and 12-2 of the oscillation coils L1 and L2 are set to AM by switches S1 and S3.
The emitter of the converter transistor Q and the variable capacitor C2 are selectively connected to each other as in FIG. 2.

However, in the circuit shown in Figure 3, the output. The FM front end 1 and the FM front end 1 can selectively connect the primary windings l1-1 and 1-1 of the oscillating coils L and L2 to the collector of the AM converter transistor Q without using a dedicated switch. AM converter transistor Q power supply selection switch S4'
It is characterized by the use of

That is, the FM-AM power supply selector switch S4' has a common terminal CO connected to the primary side terminal 2 of the AM intermediate frequency transformer IFT.
, the power supply line 3 of the FM front end 1 is connected to the FM side fixed terminal FM, the primary winding 1-1 of the medium wave oscillation coil L1 is connected to the AM medium wave side terminal MW, and the primary winding 1-1 of the medium wave oscillation coil L1 is connected to the AM long wave side terminal LW. The primary windings l2-1 of the long wave oscillation coil L2 are connected to each other.

In a circuit constructed in this manner, when the band selection switches S1, S3, and S4' are on the FM side during FM reception, the FM front is connected from the power supply 1B through the primary coil 4 of the AM intermediate frequency transformer IFT. Since power is supplied to end 1, the operation of the FM remains the same as before.

The collector side of transistor Q for AM converter is A.
Primary winding 1-1.1 of each oscillation coil L1, L2 for M
2-1, but is separated from the AM intermediate frequency transformer IFT and the power supply 1B by the switch S4', so even if the base bias resistor R1 is connected to the power supply 1B, the transistor Q doesn't work.

When receiving medium wave MW, band selection switch St, S3, S4
When ' is set to the MW side, the power supply line 3 of the FM front end 1 is cut off by the switch S4', so the FM front end 1 does not operate.

Also, in the long wave oscillation coil L2, the primary winding l2- is connected to the intermediate frequency transformer IFT, and the secondary winding l2-2 is connected to the AM transformer. The primary winding l1-1 and the secondary winding 1-2 of the medium wave oscillation coil L1 are separated from the inverter transistor Q.
Since only the intermediate frequency transformer IFT and the AM converter transistor Q are connected to the intermediate frequency transformer IFT and the AM converter transistor Q, broadcasting in the medium wave band can be received without being affected by the long wave oscillation coil L2.

Similarly, when receiving long wave LW, [band selector switch S1, S
3, when S4' is set to the LW side], the FM front end 1 does not operate, and long wave band broadcasting can be received without being affected by the medium wave oscillation coil L1.

Therefore, the power supply switching of the FM front end 1 and the AM converter transistor Q, and the AM oscillation coils L1 and L
The two switching connections can be achieved by first, second and third band changeover switches S1, S3 and S4'.

As described above, the present invention utilizes the power switch of the FM front end and the AM converter in a multi-band receiver equipped with an FM band and multiple AM bands.
Since I changed the oscillation coil of the converter,
There are advantages such as the number of switch circuits can be reduced and the board space can be used more effectively due to the miniaturization of the switch.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing a band switching circuit of a conventional multi-band receiver, and FIG. 3 is a circuit diagram showing a band switching circuit of a multi-band receiver according to the present invention. 1... FM front end, 3... FM front end power supply line, L1, L2... AM band oscillation coil, 11-1. 12-1. 1-2, 1-
2... Primary winding and secondary winding of the oscillation coil, C
2... Variable capacitor, Q... AM converter transistor, IFT... AM intermediate frequency transformer, Sl
5 S3, 84'...First, second, third band changeover switch.

Claims (2)

[Scope of utility model registration request] (1) A first band changeover switch that is equipped with FM and a plurality of AM bands and selectively connects the secondary winding of the oscillation coil for each AM band to a variable reactance element for channel selection, and each of the AM bands. AM the secondary winding of the band oscillation coil.
In a multi-band receiver equipped with a second band changeover switch selectively connected to the first predetermined electrode of the converter transistor, one end of the primary winding of each AM band oscillation coil is connected to the AM The second converter transistor
At the same time, connect the FM side fixed terminal to the specified electrode of the FM
A third band changeover switch is connected to the power supply line of the front end, and the common terminal is connected to the AM intermediate frequency transformer and the power supply, and each fixed terminal on the AM side is connected to the primary winding of the oscillation coil for each AM band. A band switching circuit for a multi-band receiver. (2) A band switching circuit for a multi-band receiver according to claim 1, wherein the first predetermined electrode of the AM converter transistor is an emitter and the second predetermined electrode is a collector.