JPH0666709B2 - 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.

2. Description of the Related Art The development of receivers capable of multiband reception has been remarkable from the past. An example of a local oscillation circuit of a two-band receiver for switching the above-mentioned conventional medium wave band (first band) and long wave band (second band) will be described below with reference to the drawings.

Figure 2 shows the conventional medium wave band (first band) and long wave band (second band).
Is a local oscillation circuit of a two-band receiver for switching the band), 1 is an oscillation coil for medium-wave band, 2 is an oscillation coil for long-wave band, 1a and 2a are respective tuning windings, and 1b and 2b are respective bases. A winding 3 is a first padding capacitor connected to one end of each of the tuning windings 1a and 2a of the oscillation coils 1 and 2, and a second padding capacitor 4 is connected to the other end of the tuning winding 1a of the oscillation coil 1. Padding capacitor, 9 is a variable capacitor connected to the second padding capacitor 4, 10 is a capacitor, 11 is a resistor, 7
Is a first switching transistor connected to one end of the tuning winding 1a of the medium-wave band oscillation coil 1, 8 is a resistor connected to the base thereof, and 5 is a tuning winding of the medium-wave band oscillation coil 1.
1a is an additional capacitor connected in parallel, 6 is an additional capacitor connected in parallel to the tuning winding 2a of the long-wave band oscillation coil 2, and 12 is connected to the first switching transistor 7 via the resistor 8. Second switching transistor, 13 is a resistor connected to its base, 14 is a resistor connected to its collector, 15 is an oscillation terminal, 16 is a power source terminal for a local oscillator circuit for applying + B power, and 17 is a tuning A control signal input terminal, 18 is a local oscillation circuit switching power supply terminal for applying a + B power supply, and 19 is a band switching signal input terminal.

Conventional medium-wave band (first band) configured in this way
The operation of the local oscillation circuit for switching 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, an "L" level changeover signal is input to the input terminal 19 in conjunction with this. Therefore, the transistor 12 is turned off and the transistor 7 is turned on. Therefore, the tuning winding 1a of the medium-wave band oscillation coil 1, the additional capacitor 5, and the second
The tuning circuit is determined by the padding capacitor 4 and the variable capacitor 9, and the oscillation terminal 15 at one end of the base windings 1b and 2b connected in series with the first and second oscillation coils
Oscillates at a frequency to receive the first band (medium wave band).

On the other hand, when switching to the second band (long wave band) side, the "H" level signal is input to the input terminal 19. Therefore, the transistor 12 is turned on and the transistor 7 is turned off. Therefore, in the oscillation tuning circuit, since the tuning windings 1a and 2a of the first and second oscillation coils are connected in series via the first padding capacitor 3, tuning of the first and second oscillation coils is performed. It is composed of additional capacitors 5 and 6 of the winding, the second padding capacitor 4, and the variable capacitor 9. The oscillation terminal 15 oscillates at a frequency to receive the second band (long wave band) (at this time, When the stray capacitance is ignored, the padding capacitor of the oscillating circuit becomes a synthetic capacitance in which the first padding capacitor 3 and the second padding capacitor 4 are connected in series. The second padding capacitor 4 is the only padding capacitor in the operation of (wave band), but the capacitance is small, so it is extremely necessary for tracking. Works effectively.).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above configuration, when the band change switch (not shown) is changed from the second band (long wave band) to the first band (medium wave band), the input The terminal 19 changes from the “H” level to the “L” level, the transistor 12 turns from on to off, and the transistor 7 turns from off to on. As described above, the oscillation tuning circuit is the tuning of the medium-wave band oscillation coil 1. Winding
1a, the additional capacitor 5, the second padding capacitor 4, and the variable capacitor 9, while the switching transistor 7 is on, the tuning winding 2a of the long-wave band oscillation coil 2 The tuning circuit is also determined by the additional capacitor 6 and the first padding capacitor 3, and the desired end of the oscillating end 15 at one end of the base windings of the first and the second oscillating coils connected in series. There is a problem in that it may not oscillate at a frequency in order to receive the first band (medium wave band).

In view of the above problems, the present invention provides a local oscillation circuit of a multi-band receiver which is low in cost, stable in operation, and capable of reliably obtaining a local oscillation frequency corresponding to a desired reception frequency.

Means for Solving the Problems In order to solve the above problems, a local oscillation circuit of a receiver capable of multiband reception according to the present invention has a base winding and a tuning winding, and One ends of the base windings are connected in series, and one end of each of the tuning windings is connected to the first
First and second oscillation coils connected in series via a padding capacitor, a first switching element connected between one end of a tuning winding of the first oscillation coil and a ground point, and 2nd at the other end of the tuning winding of the 1st oscillation coil
And a variable capacitor connected in series via a padding capacitor, the other end of the tuning winding of the second oscillation coil is grounded when turned on, the first switching element is turned off, and the second switching device is turned off when turned off. The second switching element is configured to connect the other end of the tuning winding of the oscillation coil to a high impedance and to turn on the first switching element.

Operation The present invention has the above-described configuration, when the first band is selected, the second switching element is turned off, the first switching element is turned on, and the tuning winding of the first oscillation coil is 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 windings of the first and second oscillation coils, and the second switching element is selected when the second band is selected. Is turned on, the first switching element is turned off, and the tuning windings of the first and second oscillation coils, the first and second padding capacitors, and the variable capacitor A local oscillating circuit of a receiver adapted to take out a signal from one end of a series circuit of base windings of the first and second oscillating coils, the other end of a tuning winding of the second oscillating coil being a second Sui By connecting to the
The tuning winding of the second oscillator coil when selecting the first band,
This prevents the tuning circuit from being formed by the first padding capacitor.

Embodiment A local oscillation circuit of a multiband receiver according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a local oscillation circuit of a two-band receiver for switching between a medium wave band (first band) and a long wave band (second band) in the embodiment of the present invention. In FIG. 1, reference numeral 21 is a medium wave band oscillation coil, 22 is a long wave band oscillation coil, and 21a and 22a.
Is a tuning winding, 21b and 22b are base windings, 23 is a first padding capacitor connected to one end of the tuning coils 21a and 22a of the oscillation coils 21 and 22, and 24 is an oscillation coil 21.
Second padding capacitor connected to the other end of the tuning winding 21a, 29 is a variable capacitor connected to the second padding capacitor 24, 30 is a capacitor, 31 is a resistor, and 27 is a medium-wave band oscillation coil 21. Of the tuning winding 21a of the first switching transistor, 28 is a resistor connected to its base, 25 is the tuning winding of the mid-wave band oscillation coil 21
21a is an additional capacitor connected in parallel, 26 is an additional capacitor connected in parallel to the tuning winding 22a of the long-wave band oscillation coil 22, and 32 is the first switching transistor 27.
Is connected via the resistor 28 to the second switching transistor connected to the other end of the tuning winding 22a of the long-wave band oscillation coil 22, and 33 is a resistor connected to its base,
34 is a resistor connected to its collector, 35 is an oscillation terminal, 36
Is a power supply terminal for the local oscillator circuit that applies + B power supply, 37
Is a tuning control signal input terminal, 38 is a power source terminal for switching a local oscillation circuit for applying a + B power source, and 39 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 "L" level changeover signal is input to the input terminal 39 in conjunction with this. Therefore, the transistor 32 is turned off and the transistor 27 is turned on. Therefore, the tuning circuit is determined by the tuning winding 21a of the medium-wave band oscillation coil 21, the additional capacitor 25, the second padding capacitor 24, and the variable capacitor 29, and the first and second oscillation coils are connected in series. The oscillation terminal 35 at one end of the connected base winding is
It oscillates at a frequency to receive the first band (medium wave band). On the other hand, the other end of the tuning winding 22a of the long-wave band oscillation coil 22 is connected to the second switching transistor 32,
Since the second switching transistor 32 is off, the first switching transistor 27 is on, so that the tuning winding 22a of the long-wave band oscillation coil 22, the additional capacitor 26 thereof, and the first The tuning circuit constituted by the padding capacitor 23 prevents the oscillation.

On the other hand, if you switch to the first band (long wave band) side, the input terminal
The “H” level signal is input to 39. Therefore, the transistor 32 is turned on and the transistor 27 is turned off. Therefore, in the oscillation tuning circuit, the tuning windings 21a and 22a of the first and second oscillation coils are connected in series via the first padding capacitor 23, and the tuning winding 22 of the second oscillation coil 22 is connected.
Since the other end of a is connected to the ground via the second switching transistor 32, the tuning windings 21a and 22a of the first and second oscillation coils and the tuning windings of the first and second oscillation coils are connected. Line additional capacitors 25 and 26, first and second padding capacitors 23 and 24, and variable capacitor 2
The oscillation terminal 35 oscillates at a frequency for receiving the second band (long wave band).

Thus, according to this embodiment, the other end of the tuning winding 22a of the second oscillation coil 22 is connected to the second switching transistor 3
When the band changeover switch (not shown) is switched from the second band (long wave band) side to the first band (medium wave band) side by connecting to 2, the tuning winding of the second oscillation coil It is desired to prevent the tuning circuit from being constituted by 22a, the additional capacitor 26 thereof, and the first padding capacitor 23. First oscillation coil 21a and its additional capacitor 2
5, the second padding capacitor 24, and the variable frequency capacitor 29, which have a tuning frequency,
It is stably obtained from the oscillation terminal 35 at one end of the base winding of the oscillation coil connected in series.

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.

Effects of the Invention According to the local oscillator circuit of the receiver capable of multi-band reception of the present invention, each has a base winding and a tuning winding, and one end of each base winding is connected in series. One end of each of the tuning windings is in contact with the first and second oscillation coils connected in series via the first padding capacitor, and one end of the tuning winding of the first oscillation coil. A first switching element connected between the points, a variable capacitor connected in series to the other end of the tuning winding of the first oscillation coil via a second padding capacitor, and the second oscillation when turned on The other end of the tuning winding of the coil is grounded, the first switching element is turned off, and when turned off, the other end of the tuning winding of the second oscillation coil is connected to high impedance and the first switching element is connected. Turn on the element A second switching element configured to turn on, the second switching transistor is turned off and the first switching transistor is turned on when receiving the first band (medium wave band). The tuning winding of the second oscillating coil and the first padding capacitor are prevented from forming a tuning circuit, and the desired tuning coil of the first oscillating coil, the second padding capacitor, and the variable capacitor are used. Since it is possible to stably and reliably obtain the signal of the configured tuning frequency and the number of parts is small, the cost can be reduced.

On the other hand, when receiving the second band (long wave band), the second switching transistor is turned on and the first switching transistor is turned off, and the tuning circuit of the local oscillation circuit at this time is The tuning winding of the second oscillation coil, the first and second padding capacitors, and the variable capacitor.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a local oscillator circuit of a two-band receiver that switches between a medium wave band and a long wave band according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional local oscillator circuit. 21 ... Medium-wave band oscillation coil, 21a ... Medium-wave band oscillation coil tuning winding, 21b ... Medium-wave band oscillation coil base winding, 2
2 ... Long-wave band oscillation coil, 22a ... Long-wave band oscillation coil tuning winding, 22b ... Long-wave band oscillation coil base winding, 23 ... First padding capacitor, 24 ... Second Padding capacitor, 27 ... first switching transistor, 29 ... variable capacitor, 32 ... second switching transistor, 37 ... tuning control signal input terminal, 39 ... switching control signal input terminal.

Claims (1)

[Claims] 1. A base winding and a tuning winding are respectively provided, and one end of each of the base windings is connected in series, and one end of each of the tuning windings has a first padding capacitor. First and second oscillating coils connected in series via the first oscillating coil, a first switching element connected between one end of a tuning winding of the first oscillating coil and a ground point, and the first oscillating coil Of the tuning winding of the second oscillation coil is connected to the other end of the tuning winding of the second oscillation coil in series, and the first switching element is connected to the other end of the tuning winding of the second oscillation coil. A first band, which is turned off, and includes a second switching element configured to connect the other end of the tuning winding of the second oscillation coil to a high impedance and turn on the first switching element when the first band is turned off. Election Sometimes the second switching element is turned off and the first switching element is turned on, and a signal having a frequency determined by the tuning winding of the first oscillating coil, the second padding capacitor, and the variable capacitor is output. It is taken out from one end of the series circuit of the base windings of the first and second oscillating coils, and when the second band is selected, the second
Switching element is turned on, the first switching element is turned off, and each of the tuning windings of the first and second oscillation coils, the first and second padding capacitors, and the variable capacitor The signal of the determined frequency is applied to the first and second signals.
The local oscillator circuit of the receiver, which is taken out from one end of the series circuit of the base winding of the oscillator coil.