JPS6145657Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a band switching circuit for a receiver for medium waves and short waves, for example.

In a medium wave and short wave receiver, the reception band can be switched as shown in FIG. 1, for example. That is, the antenna tuning circuit 1 for medium waves and the antenna tuning circuit 2 for short waves are selectively connected to the mixer circuit 4 by the band changeover switch 3, and the local oscillation circuit 5 for medium waves and , a shortwave local oscillation circuit 6 is selectively connected to the mixer circuit 4 by a band changeover switch 7.
All you have to do is connect it to .

However, in such band switching, the switches 3 and 7 must switch between received signals and local oscillation signals, that is, high-frequency signals must be switched. Therefore, switch 3,
7, a device with small stray capacitance between contacts is required, and if a device with this consideration is used, the cost will increase.

Further, since the switches 3 and 7 handle high frequency signals, the arrangement of the switches 3 and 7 and the wiring between the switches 3 and 7 and the circuits 1, 2, 5, and 6 must also be considered.

Of course, there are other band switching methods, but they basically involve switching high-frequency signals using a switch, which results in similar problems.

This invention attempts to solve these problems.

An example of this will be explained below. In this example, the medium wave receiving system is a single super system, but the short wave receiving system is a double super system.

In FIG. 2, 11 to 16 indicate medium wave receiving systems, 14 is a mixer circuit, 15 is a local oscillation circuit,
16 is its resonant circuit.

In addition, 21 to 29 indicate short wave receiving systems, and 24
is the first mixer circuit, 25 is the first local oscillation circuit, 2
6 is its resonant circuit, 28 is the second mixer circuit, 29
is the second local oscillation circuit.

Furthermore, 31 to 34 are a common signal system, 41 is a band changeover switch, 42 is a power source, and 43 is a power switch.

The output side of the switch 43 is connected to the amplifier 3.
1 and 33, and is also connected to the parent contact of the switch 41, the medium wave side contact M of the switch 41 is connected to the power line of the circuits 13 and 15, and the short wave side contact S of the switch 41 is connected to the power lines of the circuits 13 and 15. circuit 23
- Connected to power lines 25, 27, and 29.

Furthermore, as the mixer circuit 14, for example, an FET
(Q ₁ ) is provided, and its gate is connected to circuits 13 and 14.
is connected to the output terminal of the intermediate frequency amplifier 3, and is also grounded through the resistor _R11 , and its drain is
1 is connected to the output side of the switch 43 through the input coil of the first stage intermediate frequency transformer _T1 , and
The source of the FET (Q ₁ ) is grounded through resistor R ₁₂ and bypass capacitor C ₁ , and
It is connected to the contact S of the switch 41 through _R13 .

Further, the mixer circuit 28 is similarly configured, and is provided with an FET (Q ₂ ), the gate of which is connected to the circuit 2.
Connected to the output terminals of 7 and 29, and a resistor
Grounded through R ₂₁ and its drain connected to the FET
(Q ₁ ), and its source is grounded through a resistor R ₂₂ and a bypass capacitor C ₂ , and connected to the contact M of the switch 41 through a resistor R ₂₃ .

According to this configuration, when the switch 43 is turned on and the switch 41 is connected to the contact M, medium waves can be received. That is, in this case, the voltage of the power supply 42 is supplied to the amplifiers 31 and 33, and is also supplied to the circuits 13 and 15 through the contact M of the switch 41, so that these are in an operating state.

Also, the FET is connected through the input coil of the transformer _T1 .
Drain voltage is also supplied to (Q ₁ , Q ₂ ). However, since voltage is supplied to the source of the FET (Q ₂ ) through the contact M of the switch 41 and further through the resistor R ₂₃ , the FET (Q ₂ ) is reverse biased and turned off. And since the FET (Q ₁ ) is not supplied with such a reverse bias voltage, the FET
(Q ₁ ) becomes active.

Therefore, the received signal from the antenna 11 is supplied to the tuning circuit 12 to extract only the desired received signal, and this signal is supplied to the gate of the FET (Q ₁ ) through the high frequency amplifier 13, and is also used as a local oscillator. A local oscillation signal is supplied from the circuit 15 to the gate of the FET (Q ₁ ). Therefore, frequency conversion is performed in the FET (Q ₁ ), and the intermediate frequency signal (the intermediate frequency is, for example, 455 kHz) of the target medium wave reception signal is taken out at the drain thereof.

This intermediate frequency signal is then supplied to the detection circuit 32 through the intermediate frequency transformer T ₁ and further through the intermediate frequency amplifier 31 to extract an audio signal, and this signal is supplied to the speaker 34 through the low frequency amplifier 33. Therefore, medium wave reception is possible.

Also, switch 43 is turned on and switch 41 is turned on.
When connected to contact S, short waves can be received. That is, in this case, the voltage of the power supply 42 is supplied to the amplifiers 31 and 33, and the voltage of the power supply 42 is supplied to the circuits 23 to 25, 27, 2 through the contact S of the switch 41.
9 are also supplied, and these become operational.

Furthermore, FET (Q ₁ ) is reverse biased through resistor R ₁₃ and turned off, whereas FET (Q ₂ ) is not reverse biased and becomes active.

Therefore, the received signal from the antenna 21 is supplied to the tuning circuit 22 to extract the target signal, and this signal is supplied to the first mixer circuit 24 through the high frequency amplifier 23 and also to the first local oscillation circuit 25. The first local oscillation signal from the mixer circuit 24
Only the target shortwave reception signal is supplied to the first intermediate frequency signal (the intermediate frequency is, for example, 19.055M).
Hz).

Then, this first intermediate frequency signal is supplied to the gate of FET (Q ₂ ) through the first intermediate frequency amplifier 27, and the second local oscillation signal is supplied from the second local oscillation circuit 29 to the gate of FET (Q ₂ ). The first intermediate frequency signal is frequency-converted into a second intermediate frequency signal having an intermediate frequency equal to the intermediate frequency of the medium wave.

Then, this second intermediate frequency signal is applied to the FET
(Q ₂ ), passed through the intermediate frequency transformer T ₁ and then supplied to the detection circuit 32 through the intermediate frequency amplifier 31 to extract an audio signal.
is supplied to

In this way, it is possible to receive medium waves and short waves. In this case, in this case, a medium wave mixer FET (Q ₁ ) and a short wave mixer FET are used.
(Q ₂ ), the FET (Q ₂ ) is reverse biased and turned off when receiving medium waves, and the FET (Q 2 ) is turned off when receiving short waves.
Since (Q ₁ ) is turned off by reverse biasing, that is, band switching is performed using direct current, a simple switch 41 can be used.
Can reduce costs. Further, there is no need to pay special consideration to the arrangement of the switch 41 or the wiring of the switch 41, and the degree of freedom in design can be increased.

Furthermore, since the mixer circuits 14 and 28 are dedicated to medium waves and short waves, the degree of freedom in design is increased from this point of view as well, and performance can be improved. In addition, band switching can be performed by the switching operation of the mixer transistor.In other words, since the mixer transistor is used for band switching, a separate switching element is required for band switching. No switching circuit is required. In other words, the number of parts can be reduced by eliminating the need for switching elements and associated switching circuits, and costs can be reduced.

Although the above example is a case of a receiver for medium waves and short waves, it can also be applied to a receiver for medium waves and FM, for example. In this case, the intermediate frequency amplifier 31 can be It can be used as an amplifier. Moreover, it can be applied to receivers with three or more bands.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a conventional example, and FIG. 2 is a connection diagram of an example of this invention. 15, 25, 29 are local oscillation circuits, 14, 28
is a mixer circuit, and 31 is an intermediate frequency amplifier.

Claims (1)

[Scope of utility model registration request] In a receiver that receives multiple frequency bands, a mixer transistor is provided for each frequency band, and the output electrodes of these mixer transistors are commonly connected to an intermediate frequency amplifier. A switch is provided to switch bands by selectively supplying an operating voltage to the circuit before the mixer circuit. A receiver that performs reception and also supplies reverse bias voltage to mixer transistors for other frequency bands to turn them off.