JPH0656963B2 - Local oscillator circuit of receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local oscillating circuit of a receiver capable of multiband reception.

Configuration of Conventional Example and its Problems There have been remarkable developments in receivers capable of multiband reception. A local oscillator circuit of a conventional two-band receiver that switches between the medium wave band (first band) and the long wave band (second band) will be described below. FIG. 1 shows a conventional local oscillation circuit of a two-band receiver for switching between a medium wave band (first band) and a long wave band (second band), where 1 is a medium wave band oscillation coil and 2 is a long wave band. Oscillation coil, 1a and 2a are tuning windings for each coil, 1b and 2b are base windings for each coil, 12 is a capacitor connected to one end of the base winding 1b of the medium waveband oscillation coil 1, and 4 is A switching transistor connected to the other end of the base winding 1b, 22 a resistor connected to the base and collector of the switching transistor 4, 21 an emitter of the switching transistor 4 and a tuning winding 1a of the medium-wave band oscillation coil 1 , A resistor connected to one end of the tuning winding 1a, a capacitor connected between one end of the tuning winding 1a and ground, 10 a capacitor connected between the other end of the tuning winding 1a and ground, 3 a switching transistor, 20 a That Over the scan, a resistor connected between the earth, the padding capacitor for medium wave band, which is connected to the collector 9, 17
Is a capacitor connected between one end of the base winding 2b of the long-wave band oscillation coil 2 and the ground, 6 is a switching transistor connected to the other end of the base winding 2b, 26 is a resistor connected to its base, 25 Is its collector and tuning winding 2
a is a resistor connected to one end of a, 16 is a capacitor connected between one end of the tuning winding 2a and ground, 15 is a capacitor connected between the other end of the tuning winding 2a and ground, 5 is a switching transistor, 24 Is a resistor connected between its base and ground, 14 is a long-wave band padding capacitor connected to its collector, and 23 is a padding capacitor 9, 14
A resistor connected between the earth and ground, 7 a switching transistor for controlling the switching transistors 3, 4, 5 and 6, 27 a resistor connected to its base, 19 a coil for applying a DC bias to the terminal 28, 13 a switching A capacitor connected to the collector of the transistor 6, 8 a variable capacitor connected to the padding capacitors 9 and 14,
Reference numeral 18 is a capacitor, 28 is an oscillation terminal, 29 is a power supply terminal to which + B is applied, 30 is a band switching signal input terminal, and 31 is a tuning control signal input terminal.

In the above structure, a band change switch (not shown)
Is operated to switch to the first band (medium wave band) side, the switching signal is input to the input terminal 30 at the "L" level in conjunction with this. Therefore, the transistor 7 is turned off and the transistor 4 is biased by the resistor 22 and turned on. Further, the transistor 3 is turned on because it is biased via the resistor 21 and the tuning winding 1a of the medium-wave band oscillation coil 1. On the other hand, the transistor 6 has its base and the collector of the transistor 7 connected to the resistor 26, but since the transistor 7 is off, it is not biased and is turned off. Also, the transistor 5
The emitter is the tuning winding 2a of the oscillation coil 2 for the long wave band.
Is connected to the collector of the transistor 6 through the resistor 25, and the transistor 6 is off as described above. Therefore, the transistor 5 is not biased and is off. Therefore, the tuning circuit of the oscillator circuit is determined by the tuning coil 1a of the medium-wave band oscillation coil 1, the capacitor 10 connected in parallel with the tuning coil 1a, the medium-wave band padding capacitor 9, and the variable capacitor 8.

On the other hand, when switching to the second band (long-wave band) side, the input terminal 30 becomes "H" level and the transistor 7 is turned on, which turns on the transistors 6 and 5 contrary to the previous time, and the transistor 4 and the transistor 4 are turned on. 3 turns off. Therefore, the tuning circuit of the oscillation circuit is the tuning coil 2a of the oscillation coil 2 for the long wave band.
, The capacitor 15 connected in parallel with this, the long-wave band padding capacitor 14, and the variable capacitor 8.

Here, the capacitors 11, 16, 12, 17, 13, 18 are for cutting only direct current and are connected in an alternating current.

However, the above-mentioned conventional configuration has a problem that the circuit is very complicated, the number of parts is large, and the cost is high.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a local oscillation circuit of a multi-band receiver with a simple circuit configuration and low cost.

According to the present invention, each has a base winding and a tuning winding, these base windings are connected in series, and the tuning windings are connected in series via a first padding capacitor. First and second oscillation coils, a switching element connected to one end of the tuning winding of the first oscillation coil, and a variable capacitor connected in series to the other end of the tuning winding via a second padding capacitor. Be prepared, when selecting the first band,
When the switching element is turned on, a signal having a frequency determined by the tuning winding of the first oscillation coil, the second padding capacitor, and the variable capacitor is applied to the first and second
Is taken out from one end of the series circuit of the base winding of the oscillation coil, the switching element is turned off at the time of selecting the second band, and the tuning winding of each of the first and second oscillation coils and the first, A signal having a frequency determined by the second padding capacitor and the variable capacitor is taken out from one end of the series circuit of the base winding by the first and second oscillation coils, thereby simplifying the circuit configuration. It is possible.

Description of Embodiments FIG. 2 shows an embodiment in which the present invention is applied to a two-band receiver for switching between a medium wave band (first band) and a long wave band (second band).

In FIG. 2, 41 is a medium wave band oscillation coil, 42 is a long wave band oscillation coil, 41a and 42a are respective tuning windings, and 41b and 42 are shown.
Reference numeral b is each base winding, 43 is a first padding capacitor connected to one end of each tuning winding 41a, 42a of the oscillation coils 41, 42, and 44 is another end of the tuning winding 41a of the oscillation coil 41. A second padding capacitor connected, 49 a variable capacitor connected to the second padding capacitor 44,
50 is a capacitor, 47 is a tuning winding of the medium-wave band oscillation coil 41.
A switching transistor connected to one end of 41a, 48
Is a resistor connected to its base, 45 is an additional capacitor connected in parallel to the tuning winding 41a of the medium-wave band oscillation coil 41, and 46 is connected in parallel to the tuning winding 42a of the long-wave band oscillation coil 42. An additional capacitor, 51 is an oscillation terminal, 52 is a power supply terminal for applying a + B power supply, 53 is a tuning control signal input terminal, and 54 is a band switching signal input terminal.

The operation of the local oscillator circuit configured as described above for switching between the medium wave band (first band) and the long wave band (second band) will be described below. When a band changeover switch (not shown) is operated to change over to the first band (medium wave band) side, a "H" level changeover signal is input to the input terminal 54 in conjunction with this. Therefore, the transistor 47 is turned on, the tuning winding 41a of the medium-wave band oscillation coil 41, the additional capacitor 45, the second padding capacitor 44,
The tuning circuit is determined by the variable capacitor 49, and the oscillating terminal 51 at one end of the base windings of the first and second oscillating coils connected in series has a frequency to receive the first band (medium wave band). Oscillate.

On the other hand, when switching to the second band (long wave band) side, an "L" level signal is input to the input terminal 54. Therefore, the transistor 47 is turned off, and the tuning circuit for oscillation has the tuning windings 41a and 42a of the first and second oscillating coils connected in series via the first padding capacitor 43. An additional capacitor 45 for the tuning winding of the second oscillator coil and
46, a second padding capacitor 44, and a variable capacitor 49, and the oscillation terminal 51 oscillates at a frequency to receive the second band (long wave band). At this time, the padding capacitor of the oscillation circuit becomes a combined capacitance in which the first padding capacitor 43 and the second padding capacitor 44 are connected in series, ignoring the stray capacitance. This is extremely effective in tracking because the padding capacitor in the operation of the first band (medium wave band) is only the second padding capacitor 44, but the capacitance is small. Operate.

Thus, according to the present embodiment, the first padding capacitor 43 is connected in series to one end of the tuning winding 41a of the first oscillation coil 41 and one end of the tuning winding 42a of the second oscillation coil 42. The second padding capacitor 44 is connected to the other end of the tuning winding 41a of the first oscillation coil 41 and the variable capacitor 49a.
By connecting the switching transistor 47 to one end of the tuning winding 41a of the first oscillation coil 41 and turning on / off this point, the first band (medium wave band)
In the case of receiving, the only padding capacitor of the tuning circuit of the local oscillation circuit is the second padding capacitor 44, and in the case of receiving the second band (long wave band),
The capacity of the padding capacitor of the tuning circuit at this time is the combined capacity of the first and second padding capacitors 43 and 44, and is smaller than the padding capacitor 44 when receiving the first band (medium wave band). It becomes smaller and can be tracked.

In the above embodiment, switching between the medium wave and the long wave has been described, but it can be applied to other band switching. Further, although the transistor is used as the switching element in the embodiment, other elements such as a field effect transistor may be used.

As described above, according to the present invention, the first padding capacitor is connected in series to one end of the tuning winding of the first oscillating coil and one end of the tuning winding of the second oscillating coil to provide the second padding. A capacitor connected to the other end of the tuning winding of the first oscillation coil;
When connecting to the variable capacitor in series and connecting the switching transistor to one end of the tuning winding of the first oscillation coil, when receiving the first band (medium wave band), the switching transistor turns on and the local oscillation is generated. The pad of the tuning circuit of the circuit is only the second padding capacitor. When receiving the second band (long wave band), the switching transistor is turned off, and the padding capacitor of the tuning circuit of the local oscillator circuit at this time. Is a series combined capacitance of the first and second padding capacitors, which can be made smaller than the padding capacitor when receiving the first band (medium wave band). Since there is a degree of freedom in setting, tracking is easy. Further, the circuit configuration can be simplified and the number of parts can be reduced, so that the cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a local oscillator circuit diagram of a conventional two-band receiver for switching between the medium wave band and the long wave band, and FIG. 2 is a local oscillator circuit diagram of an embodiment according to the present invention. 41 ... Medium-wave band oscillation coil, 41a ... Medium-wave band oscillation coil tuning winding, 41b ... Medium-wave band oscillation coil base winding,
42 ... Long-wave band oscillation coil, 42a ... Long-wave band oscillation coil tuning winding, 42b ... Long-wave band oscillation coil base winding, 43 ... First padding capacitor, 44 ... Second Padding capacitors, 45, 46 ... Additional capacitors, 47
...... Switching transistor, 48 ...... Resistor, 49 ...... Variable capacitor, 50 ...... Capacitor, 51 ...... Oscillation terminal, 52
…… Radio terminal, 53 …… Tuning signal input terminal, 54…
... Switch control signal input terminal.

Claims (1)

[Claims] 1. A base winding and a tuning winding, each of which has a base winding connected in series, the tuning windings being connected in series via a first padding capacitor. A first and a second oscillation coil, a switching element connected to one end of the tuning winding of the first oscillation coil, and a variable capacitor connected in series to the other end of the tuning winding via a second padding capacitor. The switching element is turned on at the time of selecting the first band, the tuning winding of the first oscillation coil, the second padding capacitor,
A signal having a frequency determined by the variable capacitor is supplied to the first,
Taking out from one end of the series circuit of the base winding of the second oscillation coil, the switching element is turned off at the time of selecting the second band, and the tuning windings of each of the first and second oscillation coils and the First and second padding capacitors,
A signal having a frequency determined by the variable capacitor is supplied to the first,
A local oscillator circuit of a receiver, which is taken out from one end of a series circuit of a base winding of a second oscillator coil.