JPH0761026B2 - Band switching circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a band switching circuit for a radio receiver.

[Conventional technology]

Synthesizer receivers can be used in the long-wave band to the short-wave band (for example, 150kHz to 30MH) without band switching.
z) can be continuously received. However, band switching is necessary to receive two bands whose frequencies are not continuous, such as the band from the long wave band to the short wave band and the air band (aviation radio, for example, 116 MHz to 136 MHz).

FIG. 4 shows an example of a band switching circuit in such a case. (10) is a high frequency input circuit for extracting a high frequency signal (broadcast wave signal) from the long wave band to the short wave band, (20)
Is a high frequency input circuit for extracting a high frequency signal of the air band, (3) is a mixer circuit, (4) is a local oscillation circuit,
(5) is a band changeover switch.

When the switch (5) is connected as shown in the figure, the diode Da is turned on, so that the high frequency signal from the high frequency input circuit (10) is supplied to the mixer circuit (3) through the diode Da. It is converted to an intermediate frequency signal and thus in this case long waves to short waves can be received.

Further, when the switch (5) is connected in a state opposite to that shown in the figure, the diode Db is turned on, so that the high frequency signal from the high frequency input circuit (20) is transmitted to the mixer circuit (3) through the diode Db. It is supplied and converted into an intermediate frequency signal, so that in this case, the air band can be received (reference: Japanese Utility Model Laid-Open No. 51-75140).

[Problems to be solved by the invention]

However, in such a circuit, the diode Da causes a problem.

That is, for example, when receiving a medium-wave broadcast, the switch (5) is connected to the state shown in the figure, and the diode Da
A direct current is supplied to the diode Da to turn it on. However, there are some extremely powerful broadcasts in medium-wave broadcasting and short-wave broadcasting, and when such a powerful broadcasting is received, the signal is distorted due to the nonlinearity of the diode Da even if the diode Da is turned on. However, various reception characteristics such as interference characteristics deteriorate.

Of course, if the DC current flowing through the diode Da is increased,
Although the non-linearity of the diode Da is improved and thus the reception characteristic is also improved, a direct current of 20 mA or more is required to make the non-linearity of the diode Da practically unproblematic.

However, such high currents are not desirable, especially when the receiver is battery operated. Further, the diode Da must be a switching diode having a good high-frequency characteristic, which increases the cost.

The present invention seeks to solve these problems.

[Means for solving problems]

Therefore, in the present invention, in a receiver that receives a signal in the first reception band and a signal in the second reception band in a frequency band higher than the first reception band,
A first high-frequency input circuit (10) for receiving and extracting the signal of the first reception band, and a second high-frequency input circuit (10) provided after the first high-frequency input circuit (10) for the signal of the second reception band. Trap circuit with sufficiently high impedance (1
5), a mixer circuit (3) whose input end is connected to the output end of this trap circuit (15), and a second harmonic input circuit (20) for receiving and extracting the signal of the second reception band. , A tuning circuit (22) provided after the second harmonic input circuit (20), and the tuning circuit (22) includes a transistor Q ₂₁
A tuning coil L ₂₁ connected to the output electrode of a smaller impedance than the signal of the first reception band, to the signal of the second reception band, the auxiliary coil L ₂₂ having a predetermined impedance, the bypass capacitor C ₂₁ And D are connected in series and are connected in the forward direction to the connection point between the tuning coil L ₂₁ and the auxiliary coil L ₂₂ and the input end of the mixer circuit (3).
₂₂ and a contact for selecting the signal of the second receiving band of the band changeover switch (5) at the connection point of the auxiliary coil L ₂₂ and the bypass capacitor C ₂₁ and turning off the diode when receiving the first receiving band. As the first high frequency input circuit (1
The output signal of (0) is supplied to the mixer circuit (3) and frequency-converted into an intermediate frequency signal, and the diode D ₂₂ is turned on at the time of reception of the second reception band to generate the second high frequency input circuit (20).
The output signal from the mixer circuit through the diode D ₂₂ (3)
To the intermediate frequency signal for frequency conversion and
The output signal of the high frequency input circuit (10) of the diode D ₂₂
And a band switching circuit configured to be bypassed via an auxiliary coil L ₂₂ and a bypass capacitor C ₂₁ .

[Action]

Therefore, according to the present invention, since band switching is performed by utilizing the difference in impedance with respect to the reception band, the diode Da in the conventional circuit becomes unnecessary, and the reception characteristic such as the interference characteristic due to the nonlinearity of the diode Da is not received. It is possible to eliminate the deterioration of the characteristics.

In addition, since it is not necessary to supply a large on-current to the diode Da, it is possible to save power and prolong the life of the battery. Further, since the diode Da is unnecessary, the cost can be reduced.

〔Example〕

In FIG. 1, a high frequency input circuit (10) is for receiving from a long wave band to a short wave band, and a high frequency input circuit (20) is for receiving an air band. The band changeover switch (5) has a contact point AM when receiving from the long wave band to the short wave band and a contact point AIR when receiving the air band.

Further, (6) is a control circuit for the line station, which is, for example, 4
It consists of a bit microcomputer.
The local oscillator circuit (4) has a PLL and is of a synthesizer type.

Further, in the high frequency input circuit (10), (11) indicates an antenna input circuit mainly for receiving signals in a long wave band and a medium wave band, and this input circuit (11) is a bar antenna (bar antenna coil) ( a main coil L ₁₁ of 11A), and the source-grounded FET (Q _11), by the interstage transformer T ₁₁ with configured asynchronous type, the power line switch of the input circuit (11) (5) Connected to contact AM. Incidentally, a bar antenna (11A) also has a negative feedback coil L _12.

Also, (12) is an external antenna or rod antenna for mainly receiving signals in the shortwave band and the air band, (13) is a trap for mainly blocking signals in the shortwave band and the air band, and Q ₁₂ is a source follower. FET
Then, its drain is connected to the contact AM of the switch (5). Further, (14) is a fifth-order low-pass filter that passes signals in the long-wave band to the short-wave band, and (15) is a trap for blocking signals in the air band.

This trap (15) is provided at the final stage of the harmonic input circuit (10), so the output impedance of the high frequency input circuit (10) is sufficiently high for air band signals. Indicates. The output terminal of this input circuit (10) is connected to the hot side of the input coil L ₃₁ of the interstage transformer T ₃₁ , and the output coil of the transformer T ₃₁ is connected.
L ₃₂ is connected to the input end of the mixer circuit (3).

Furthermore, in the high frequency input circuit (20), (21) is a bandpass filter that passes only signals in the air band,
(22) is a tuning circuit.

The tuning circuit (22) is the final stage of the harmonic input circuit (20), and its output impedance is set to be sufficiently low for signals in the long wave band to the short wave band. Therefore, the tuning circuit (22) is configured as follows.

That is, a FET (Q ₂₁ ) is provided, its gate is connected to the output terminal of the filter (21), its source is grounded,
A series circuit of a tuning coil L ₂₁ , an auxiliary coil L _22, and a bypass capacitor C ₂₁ is connected between the drain and the ground, and a series circuit of a DC cut capacitor C ₂₂ and a variable capacitance diode D _21. Are connected. The coil L ₂₂ is an inductance that has a low impedance for signals in the long-wave band to the short-wave band and has a predetermined impedance for signals in the air band. Further, there may be a transformer coupling between the coil L ₂₁ and the coil L ₂₂ .

Further, the connection point between the coil L ₂₂ and the capacitor C ₂₁ is connected to the contact AIR of the switch (5), and the connection point between the coil L ₂₁ and the coil L ₂₂ is connected to the transformer T through the diode D _22.
It is connected to the hot side of the coil L ₃₁ of _31.

In addition, a bias resistor R is connected between the power supply + V _DD and ground.
₁ and R ₂ are connected in series, and the midpoint of the connection is coil L
_It is connected to the cold side of ₃₁ , and the bypass capacitor C ₁ is connected in parallel to the resistor R ₂ .

Further, a control voltage for tuning is supplied from the control circuit (6) to the variable capacitance diode D ₂₁ and the local oscillation circuit (4). The parent contact of the switch (5) is connected to the power supply + V _DD .

In such a structure, when the switch (5) is connected to the contact AM, the drain voltage of the FET (Q ₁₁ , Q ₁₂ ) is supplied through the contact AM. Therefore, the bar antenna (11
The signal voltage in the long-wave band or medium-wave band induced in the coil L _{11 of} A) is amplified by the FET (Q ₁₁ ), and this amplified output is transformer T ₁₁ → trap (13) → FET (Q ₁₂ ) → filter. (1
4) → trap (15) → supplied to the mixer circuit (3) through the signal line of the transformer T ₃₁ . Also, the antenna (1
The short-wave band signal voltage induced in 2) is also supplied to the FET (Q ₁₂ ), and thereafter is similarly supplied to the mixer circuit (3).

Therefore, in the mixer circuit (3), of the signals from the long-wave band to the short-wave band, only the signal of the frequency corresponding to the local oscillation signal from the local oscillation circuit (4), that is, the signal of the frequency desired to be received, For example, the frequency is converted into the first intermediate frequency signal IF of 55.845 MHz. Although not shown, the signal IF is further frequency-converted into a second intermediate frequency signal and then demodulated. Further, in the input circuit (11), the drain current of the FET (Q ₁₁ ) is negatively fed back by the coil L ₁₂ , so that the coil L ₁₁ and the free capacitance and the input capacitance of the FET (Q ₁₁ ) are within the reception band. A flat frequency characteristic can be obtained even if resonance occurs in the.

At this time, the drain voltage is not supplied to the FET (Q ₂₁ ) by the switch (5). Also, the diode D ₂₂
With the cathode bias voltage is supplied by a resistor R _1, R _2, since the anode of the diode D ₂₂ is grounded through the drain-source of the coil L ₂₁ and FET (Q _21), a diode D ₂₂ is reversed Biased off.

Therefore, when the switch (5) is connected to the contact AM,
It can receive signals from the long wave band to the short wave band.

On the other hand, when the switch (5) is connected to the contact AIR,
The drain voltage is supplied to the FET (Q ₂₁ ) through the contact AIR, and the contact AIR → coil L ₂₂ → diode D ₂₂ →
The diode D ₂₂ is forward biased and turned on by the current line at the connection point between the coil L _{31 and the} resistors R ₁ and R ₂ . Therefore,
The air band signal voltage induced in the antenna (12)
While being supplied to the tuning circuit (22) through the filter (21), the coil L ₂₂ exhibits a predetermined impedance with respect to the air band signal, so that only the signal of the frequency desired to be received is extracted from the coil L ₂₂ . The extracted signal is supplied to the mixer circuit (3) through the diode D ₂₂ and further through the transformer T ₃₁ , and is frequency-converted into the first intermediate frequency signal IF.

Then, at this time, the FET (Q ₁₁ ,
The drain voltage is not supplied to Q ₁₂ ) and it is off. Further, the signal voltage in the short-wave band (and long-wave band, medium-wave band) induced in the antenna (12) leaks from the FET (Q ₁₂ ) that is off, and this leak signal is trapped (15) through the filter (14). This leak signal appears at the output side of the diode D ₂₂ → coil L ₂₂ (which has a low impedance for the short wave band) → bypassed through the line of the capacitor C ₂₁ and supplied to the mixer circuit (3). There is no such thing.

Therefore, when the switch (5) is connected to the contact AIR, the air band can be received.

Thus, according to the present invention, band switching is performed. In this case, in particular, according to the present invention, band switching is performed by utilizing the difference in impedance with respect to the reception band. It is not necessary, and therefore, the deterioration of the reception characteristics such as the interference characteristics due to the nonlinearity of the diode Da can be eliminated.

In addition, since it is not necessary to supply a large on-current to the diode Da, it is possible to save power and prolong the life of the battery. Further, since the diode Da is unnecessary, the cost can be reduced.

By the way, in the above description, the coil L ₂₂ of the tuning circuit (22) is
The number of turns of may be several times in terms of impedance from the long wave band to the short wave band. However, considering the power matching between the output of the FET (Q ₂₁ ) and the mixer circuit (3), the turns ratio of the coils L ₂₁ and L ₂₂ is naturally determined, and in the above example, the coil L ₂₁ is 3 times. Coil in degree L ₂₂
Is optimal about 0.5 times.

However, winding the coil L ₂₂ only 0.5 times around the same bobbin as the coil L ₂₁ is difficult in manufacturing the coil.

Therefore, the coils L ₂₁ and L ₂₂ described above are specifically configured as shown in FIGS. 2 and 3.

That is, in the figure, (70) shows a printed circuit board, (71) is its insulating substrate, (72) to (74) are conductive patterns for wiring, of which the pattern (72) is a ground pattern. . In addition, the bobbin (80) has 3 wires (81).
The coil L ₂₁ is wound and wound, and the bobbin (8
Both ends of the wire (81) are soldered to the patterns (73) and (74) through the through holes of the board (71), respectively, with the lower end of the wire (81) in contact with the component mounting surface of the board (70).

Further, a wire rod (82) having a U shape as a whole and having a pitch of about 3 to 5 mm, that is, a jumper wire (82) is prepared, and both ends of the wire rod (82) through the through holes of the substrate (71) to form the patterns (72), ( 73) soldered to each.

Therefore, the jean wire (82) acts as the coil L ₂₂ .

At this time, the transformer coupling between the coil L ₂₁ and the coil L ₂₂ is unnecessary, and therefore, as shown in the figure, the jumper wire (8
2) can be located on the extension of the diameter of the bobbin (80).

Further, according to such a coil L ₂₂ , manufacturing is simple and it is possible to simultaneously attach other jumper wires at the time of attaching other jumper wires, so that the cost can be reduced.

In the above description, the output impedance of the high frequency input circuit (22) can be lowered by using a source follower FET, for example.

〔The invention's effect〕

According to the present invention, since band switching is performed by utilizing the impedance difference with respect to the reception band, the diode Da in the conventional circuit becomes unnecessary, and therefore, the reception characteristic such as the interference characteristic due to the nonlinearity of the diode Da is not received. It is possible to eliminate the deterioration of the characteristics.

In addition, since it is not necessary to supply a large on-current to the diode Da, it is possible to save power and prolong the life of the battery. Further, since the diode Da is unnecessary, the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a connection diagram of an example of the present invention, and FIGS. 2 to 4 are diagrams for explaining the same. (10) and (20) are high frequency input circuits, and (3) is a mixer circuit.

Claims (1)

[Claims] 1. A receiver for receiving a signal of a first reception band and a signal of a second reception band of a frequency band higher than the first reception band, wherein the signal of the first reception band is A first high-frequency input circuit for receiving and extracting, and a second high-frequency input circuit provided after the first high-frequency input circuit,
A trap circuit exhibiting a sufficiently high impedance with respect to a signal in the reception band, a mixer circuit having an input terminal connected to the output terminal of the trap circuit, and a second circuit for receiving and extracting the signal in the second reception band. A harmonic input circuit, a tuning circuit provided after the second harmonic input circuit, a tuning coil connected to the output electrode of the transistor, and a signal of the first reception band. The impedance is small, and for the signal of the second reception band,
An auxiliary coil having a predetermined impedance and a bypass capacitor are connected in series, a connection point between the tuning coil and the auxiliary coil, a diode forward-connected to the input terminal of the mixer circuit, and a connection between the auxiliary coil and the bypass capacitor. And a contact for selecting a signal of the second reception band of the band changeover switch at a point, and when the first reception band is received, the diode is turned off to output the output signal of the first high frequency input circuit to the mixer. The frequency signal is supplied to a circuit and converted into an intermediate frequency signal, and when the second reception band is received, the diode is turned on and the output signal of the second high frequency input circuit is supplied to the mixer circuit through the diode to generate the intermediate frequency signal. The frequency of the signal is converted into a signal, and the output signal of the first high frequency input circuit is converted to the diode and the auxiliary coil. And a band switching circuit configured to be bypassed via the bypass capacitor.