JPH0724828Y2 - Local oscillator circuit of multiband receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a local oscillation circuit of a multiband receiver.

(B) Conventional Technology A multi-band receiver capable of receiving a medium wave band and a short wave band has been conventionally known [see, for example, Japanese Utility Model Publication No. 58-34827 (H03J5 / 00)].

In this kind of multi-band receiver, a resonance circuit that constitutes a local oscillation circuit is provided corresponding to each band, and a variable capacitance element (varicon) is connected to the resonance circuit according to band switching, so that a desired band is obtained in each band. The local oscillation frequency is obtained.

Recently, multi-band receivers that perform electronic tuning using a phase-locked loop (PLL) have become the mainstream. In such receivers, variable capacitance diodes are used as variable capacitance elements and variable resistors are used. L that configures the set voltage or PLL
Supply the DC output from PF to the variable capacitance diode,
It is designed to obtain a desired local oscillation frequency.

(C) Problems to be solved by the invention When a variable capacitance diode is used as the variable capacitance element,
Generally, the variable capacitance diode is arranged in each local oscillation circuit provided corresponding to each band, and the output from each circuit is selected according to band switching, so that the number of parts is large, This has caused an increase in cost and a complicated circuit configuration.

Further, Japanese Patent Laid-Open No. 63-18806 discloses a circuit in which a single variable capacitance diode can obtain resonance frequencies of a plurality of bands. However, in this circuit, the coils of the resonance circuits of the respective bands are connected to one end side of the variable capacitance diode. Therefore, the stray capacitance of the coil for one band may adversely affect the resonance circuit for another band.

(D) Means for Solving the Problems In view of the above problems, the present invention relates to a variable capacitance diode whose capacitance value is variable by a tuning voltage, and a medium-wave band resonance circuit connected to one end of the variable capacitance diode. A short-wave band first and second resonance circuit connected in series to the other end side of the variable capacitance diode, and a switching circuit for selectively short-circuiting the resonance circuits according to the power supply voltage of each band. It is intended to provide a local oscillation circuit of a multiband receiver characterized by the above.

(E) Operation According to the present invention, for example, when receiving the medium wave band, the first and second resonance circuits for the short wave band are short-circuited by the switching circuit so that the medium wave band resonance circuit and the variable capacitance diode are used. A local oscillation circuit is configured to obtain a local oscillation output according to the tuning voltage.

Further, when receiving a short wave band, the switching circuit short-circuits the medium-wave band resonance circuit and selectively short-circuits the first resonance circuit to connect the first and second resonance circuits to the variable capacitance diode or the second resonance circuit. A local oscillation circuit is composed of variable capacitance diodes, and a local oscillation output according to the tuning voltage is obtained.

Further, since the resonance circuit for the medium wave band and the resonance circuit for the short wave band are connected to the opposite side of the variable capacitance diode, the coil for one band, for example, the medium wave band, is used for the other band, for example, the short wave band. It is possible to prevent the resonant circuit from being adversely affected.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, (1) is a variable capacitance diode whose capacitance value is variable by a tuning voltage, (2) is a resonance circuit for a medium wave band connected to the cathode of the variable capacitance diode (1), and a resonance coil (3), It is composed of a trimmer capacitor (4) and a pattern capacitor (5). (6) (7) are first and second resonance circuits for the short wave band connected to the anode of the variable capacitance diode (1), and the first and second resonance circuits for the first short wave band
The resonance circuit (6) is composed of a resonance coil (8) and a trimmer capacitor (9), and the second resonance circuit (7) for the second shortwave band is composed of a resonance coil (10) and a trimmer capacitor (11). It is configured. (12) is a shorting band putting capacitor, (13) is a tuning voltage input terminal, (14)
Is the first power supply input terminal to which the power (+ B) is supplied when receiving the first and second short wave bands, and (15) is the middle wave band receiving,
The second power supply input terminal to which the power supply (+ B) is supplied, (16) is the third power supply input terminal to which the power supply (+ B) is supplied during reception of the medium wave band and the second short wave band, (17) (18) ( 19) (2
0) is a switching transistor, (21) (22) (23)
(24) is a switching transistor (17) (18) (19)
Bias resistance of (20), (25) and (26) are bias resistance of the variable capacitance diode (1), (27) and (28) are capacitors for short-circuiting the resonance coil (3) in an alternating current, (2
9) (30) is a resistor for charging the capacitors (27) (28), (31) is a bypass capacitor, (32) (33) are oscillation terminals of the integrated circuit, terminal (32) is hot side, terminal (3
3) is the ground side.

Next, the operation will be described.

The second and third power input terminals (1
5) Since the power (+ B) is supplied from (16), the resistance (2
3) (24) switching transistor (19) (20)
Is biased on. Therefore, the anode side of the variable capacitance diode (1) is grounded and the first and second resonance circuits (6) and (7) are short-circuited.

Thus, the capacitance is integrated at the resonance frequency determined by the capacitance of the variable capacitance diode (1), the capacitance of the trimmer capacitor (4) and the resonance coil (3) according to the tuning voltage input from the tuning voltage input terminal (13). An oscillator (not shown) provided inside the circuit oscillates.

At the time of receiving the first short wave band, since the power (+ B) is supplied from the first power input terminal (14), the switching transistors (17) and (18) are biased by the resistors (21) and (22) to be turned on, The cathode side of the variable capacitance diode (1) is AC-grounded via the capacitor (27), and the secondary side of the resonance coil (3) is AC-grounded via the capacitor (28).

Thus, the capacitance of the variable capacitance diode (1) according to the tuning voltage input from the tuning voltage input terminal (13), the capacitance of the trimmer capacitors (9) (11) and the resonance coil (8) (1
The oscillator oscillates at the resonance frequency determined by (0).

Further, at the time of receiving the second short-wave band, the power source (+ B) is supplied from the first and third power source input terminals (14) and (16), so the switching transistors (17) are connected to the resistors (21) (22) (24). ) (18) (20) are biased and turned on,
The cathode side of the variable capacitance diode (1) is AC-grounded via the capacitor (27), and the secondary side of the resonance coil (3) is AC-grounded via the capacitor (28). Furthermore, the first resonance circuit (6) is also short-circuited.

Thus, the oscillator oscillates at a resonance frequency determined by the capacitance of the variable capacitance diode (1) corresponding to the tuning voltage input from the tuning voltage input terminal (13) and the second resonance circuit.

(G) Effect of the Invention According to the present invention, a resonant circuit for the medium wave band is provided at one end of the variable capacitance diode, and first and second resonant circuits for the short wave band are provided at the other end of the variable capacitance diode according to the power supply voltage of each band. Since each resonance circuit is selectively short-circuited with each other, it is possible to obtain resonance frequencies of a plurality of bands with one variable capacitance diode.

Since the resonance circuit for the medium wave band and the resonance circuit for the short wave band are connected to the opposite side of the variable capacitance diode, the coil for one band, for example, the medium wave band, is used for the other band, for example, the short wave band. It is possible to prevent the adverse effect on the resonant circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. (1) ... variable capacitance diode, (2) ... medium-wave band resonance circuit, (6) ... first resonance circuit, (7) ... second
Resonance circuit, (17) (18) (19) (20) …… Switching transistor (switching circuit).

Claims (1)

[Scope of utility model registration request] 1. A variable capacitance diode whose capacitance value is varied by a tuning voltage, a medium-wave band resonance circuit connected to one end side of this variable capacitance diode, and a series connection to the other end side of the variable capacitance diode. Local oscillation of a multi-band receiver comprising first and second resonance circuits for short-wave band, and a switching circuit for selectively short-circuiting each resonance circuit according to a power supply voltage of each band. circuit.