JPH0739111U - Double tuning circuit - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Stable high selectivity Q can be obtained even when a strong interfering signal is input, and high frequency distortion, IM with a simple circuit configuration.
Reduce the occurrence. In a double tuning circuit composed of a first tuning circuit 5a and a second tuning circuit 6a, a signal supplied from an antenna 1 is input to an RF amplifier circuit 4 and amplified, and a high frequency transformer RFT3 of the first tuning circuit 5a. Is sent to the primary coil a. Tuning is performed by the varicap VC5 for tuning adjustment and the trimmer capacitor CV3 for fine tuning. Tuning is performed by changing the capacitance of the double tuning circuits 5a and 6a,
The signal component is sent to the mixer circuit 7. Since the tuning capacitance value of the first tuning circuit 5a is half that of the second tuning circuit 6a due to the connection of the varicaps VC5 and VC6, the inductance L of the tuning coil of the first tuning circuit 5a is the second.
It is twice as large as the tuning circuit 6a.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a double tuning circuit, and more particularly, to a high frequency amplitude modulation signal retuning circuit suitable for an AM radio tuner.

[0002]

[Prior art]

 Conventionally, the detuning circuit of the received signal, that is, the high frequency amplitude modulation signal in the receiving block in this type of radio tuner has the configuration shown in FIG. FIG. 2 is a diagram showing a double-tuned circuit of a radio tuner, in which a signal supplied from an antenna 1 is input to an RF amplification circuit 4 via an RF (radio frequency) bandpass filter 3 to be amplified, and a high frequency transformer RFT1 and A first tuning circuit 5 including a varicap VC1 which is used for adjustment for tuning and whose capacitance is changed by voltage, and a trimmer capacitor CV1 which is used for fine adjustment, and a high frequency transformer RFT2 and a varicap. Tuning is performed by varying the capacitances of the double tuning circuits 5 and 6 of the VC2 and the second tuning circuit 6 including the trimmer capacitor CV2, and the signal component thereof is sent to the mixer circuit 7 in the subsequent stage.

The selectability Q of the double tuning circuits 5 and 6 determines whether the characteristics are good or bad. When the selectability Q becomes high, frequencies other than the desired frequency are attenuated. Therefore, it is necessary to design so that the value of normal Q becomes high. At this time, however, the double tuning circuits 5 and 6 are set so that their selectivity Q can be impedance matched with the circuit at the subsequent stage. Also, the mixer circuit 7 is configured to mix the local frequency fb supplied from the local oscillator circuit 8 and the received signal fa to obtain an intermediate frequency difference between the two frequencies and output the intermediate frequency to the circuit in the subsequent stage. A voice signal is extracted from the carrier wave centered on fa received by the antenna 1 through these circuits.

[0004]

[Problems to be solved by the device]

 However, the conventional double-tuned circuit shown in FIG. 2 has the following drawbacks. In the conventional example shown in FIG. 2, one varicap VC1 and one varicap VC2 are used for both the first tuned circuit 5 and the second tuned circuit 6, respectively. However, when a signal is added, high-frequency distortion and IM are generated, so there is a drawback that a large signal input other than the desired reception band adversely affects the reception condition in the desired band. As a countermeasure for this, there is a method of speeding up the operation sensitivity of the RF amplifier circuit 4 by automatic gain control from the AGC control terminal t5 to suppress the signal level applied to the varicaps VC1 and VC2. Malfunctions and the sensitivity of signals in the desired band is suppressed. In addition, in order to solve these problems, there was a problem that the circuit configuration became large and the cost increased, and when it was used in a radio tuner, it was an obstacle to reducing the size and weight, which is the condition. It is an object of the present invention to provide a double tuning circuit which eliminates the above-mentioned conventional problems, obtains a high and stable selectivity Q 2, and is free from high frequency distortion and IM even when a strong received signal fa is input. It is in.

[0005]

[Means for Solving the Problems]

 In order to achieve this object, the present invention inputs a reception signal of a required frequency band input via an antenna, and a high frequency transformer of a first tuning circuit and a high frequency transformer of a second tuning circuit are coupled to each other to provide a predetermined signal. In a double-tuned circuit that outputs a signal tuned to a frequency, the secondary coils of both the high-frequency transformers of the first and second tuning circuits have a two-winding structure, and one end of one of the two windings is a coil. And the other end is directly coupled and connected to a power supply terminal (GRD), one end of the coil is connected to the power supply terminal (GRD) through a resistor, and the other winding Has one end connected to the power supply terminal (GRD) and the other end connected to the power supply terminal (GRD) via a variable capacitor and also connected to the anode of the first varicap. , A cathode thereof is connected to each other through a resistor, a cathode of the first varicap of the first tuning circuit is connected to a cathode thereof, and an anode thereof is connected to the power supply terminal (GRD). It is characterized in that a cap is provided and the cathode of the first varicap of the second tuning circuit is connected to another power supply terminal (VT).

[0006]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a radio tuner including a circuit configuration diagram of a double tuning circuit showing an embodiment of the present invention. In FIG. 1, the same symbols as those in FIG. 2 indicate the same things. Note that t1 to t3 are connection terminals, t4 is a signal output terminal, t5 is an AGC control terminal, t6 is a power supply terminal (Vcc), t7 is a power supply terminal (Vt), t8 is a power supply terminal (GRD), C1 to C1. C4 is a capacitor, R1, R4 and R5 are resistors, L1 is a coil, and VC3 and VC4 to VC7 are varicaps. The RFTs 3 and 4 are high frequency transformers, and the primary coil a has one winding, but the secondary coil has two windings b and c in order to increase the selectivity Q. FIG. 1 is a diagram showing a double-tuned circuit of a radio tuner. A signal supplied from an antenna 1 is input to an RF amplification circuit 4 via an RF (radio frequency) bandpass filter 3 and amplified.

The output of the RF amplifier circuit 4 is connected to the connection terminal t1 of the first tuning circuit 5a, which is connected to the primary coil a of the high frequency transformer RFT3 and connected to the power supply terminal t6 via a resistor. Has been done. Both ends of the secondary coil b of the high frequency transformer RFT3 are coupled to both ends of the primary coil b of the high frequency transformer RFT4 via the coil L1. The connection point between one end of the secondary coil b of the high frequency transformer RFT3 and the coil L1 is connected to the earth through a resistor R4, and the other end is directly connected to the earth. On the other hand, one end of the secondary coil c of the high frequency transformer RFT3 is connected to the anode of the varicap V C5. The cathode is connected to the cathode of the varicap VC6, and the anode of the varicap VC6 is connected to the ground. The other end of the secondary coil c of the high frequency transformer RFT3 is connected to the earth. A trimmer capacitor CV3 is connected in parallel with the secondary coil c.

The secondary coil c of the high frequency transformer RFT4 has one end connected to the anode of the varicap VC7. The cathode is connected to the connection point of the cathodes of the varicaps VC5 and VC6 via the resistor R5. Further, the cathode of the varicap VC7 is connected to the ground through the capacitor C4 and is also connected to the power supply terminal t7 through the resistor R3. The other end of the secondary coil c of the high frequency transformer RFT4 is connected to the earth. A trimmer capacitor CV4 is connected in parallel with the secondary coil c. On the other hand, one end of the primary coil a of the high frequency transformer RFT4 is connected to the connection terminal t3, and the t3 is connected to the mixer circuit 7 via the capacitor C1. The other end is connected to the earth. The cathode of the varicap VC3 is connected from the connection point of the capacitor C4 and the resistor R3, and its anode is connected to the local oscillation circuit 8 via the capacitor C2. The output terminal of the local oscillator circuit 8 is connected to the mixer circuit 7. A parallel circuit of a resistor R2 and a capacitor C3 is inserted between the anode of the varicap VC3 and the ground.

In the double tuning circuit including the first tuning circuit 5 a and the second tuning circuit 6 a shown in FIG. 1, the signal supplied from the antenna 1 passes through the RF (radio frequency) band pass filter 3. Is input to the RF amplifier circuit 4 and amplified. The amplified output is sent to the primary coil a of the high frequency transformer RFT3 of the first modulation circuit 5a and induced in the secondary coils b and c. Then, a varicap VC5, which is used for adjustment to adjust the capacitance and whose capacitance varies with the voltage, and a trimmer capacitor CV3, which is used for the fine adjustment, are tuned to match a predetermined frequency. Similarly, the high-frequency transformer RFT4, the varicap VC7, and the second tuning circuit 6a including the trimmer capacitor CV4 are tuned by changing the capacitances of the double-tuned circuits 5a and 6a, and the signal component thereof is sent to the mixer circuit 7 in the subsequent stage. It

In such a tuning circuit, since the tuning capacitance value of the first tuning circuit 5a becomes half that of the second tuning circuit 6a due to the connection of the varicaps VC5 and VC6, the first tuning circuit 5a has The inductance L of the tuning coil is twice as large as that of the second tuning circuit 6a. With this circuit, the harmonic distortion and the IM level, which have been conventionally generated on the varicap VC1 side of the first tuning circuit 5, are reduced to the level shown in FIG. According to the double-tuned circuit of the present invention shown in (1), it is significantly reduced, and as a result, the following disturbance characteristics are improved. (1) Interference characteristic of interfering wave frequency 1 / 2f0 with respect to tuning frequency f0 (2) Interfering characteristic of interfering wave frequency 2f0 with respect to tuning frequency f0 (3) Interfering wave frequencies f1, f2 (with respect to tuning frequency f0 f1 + f2 = f0) Disturbance characteristics When using four varicaps enclosed in one package, only one varicap VC5-7 of the double tuning circuit and one varicap VC3 of the local oscillation circuit 8 are used. Can be used as

Further, in the mixer circuit 7, when a high frequency signal (RF signal) in which two frequencies are superposed and mixed is input, that is, a reception signal fa transmitted via the antenna 1 and a local oscillation circuit. By mixing the local frequencies fb supplied via 8, the intermediate frequency IF of the difference between both frequencies fa and fb is obtained and output to the subsequent circuit, and finally these circuits are An audio signal is extracted from the carrier centered on fa 1 and received by the antenna 1 via.

[0012]

[Effect of device]

 As is apparent from the above description, the present invention has the secondary coil of the high-frequency transformer of the first and second tuning circuits having a two-winding configuration and the two varicaps of the first tuning circuit having a connection configuration. The advantage is that a stable high selectivity Q can be obtained even when a strong interference signal is input, and a double-tuned circuit with excellent characteristics that can prevent harmonic distortion can be obtained. Further, in the present invention, the circuit configuration for increasing the selectivity Q can be realized in a simple and small size and light weight, so that there is a practical advantage that it is a circuit suitable for a radio tuner that is inexpensive and requires miniaturization. .

[Brief description of drawings]

FIG. 1 is a block diagram of a radio tuner including a circuit configuration diagram of a double tuning circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram of a radio tuner including a circuit configuration diagram showing a conventional double-tuned circuit.

[Explanation of symbols]

 1 antenna 3 RF band pass filter 4 RF amplification circuit 5, 5a first tuning circuit 6, 6a second tuning circuit 7 mixer circuit 8 local oscillation circuit t1 to t3 connection terminal t4 signal output terminal t5 AGC control terminal t6 power supply terminal ( Vcc) t7 power supply terminal (Vt) t8 power supply terminal (GRD) R1 to R6 resistors C1 to C4 capacitors RFT1 to RFT4 high frequency transformers CV1 to CV4 trimmer capacitors VC1 to VC7 varicap L1 coils

Claims (1)

[Scope of utility model registration request] 1. A signal which receives a received signal in a required frequency band input via an antenna and is tuned to a predetermined frequency by coupling a high frequency transformer of a first tuning circuit and a high frequency transformer of a second tuning circuit. In the double tuning circuit for outputting the above, the secondary coils of both the high frequency transformers of the first and second tuning circuits have two windings, and one end of one of the windings is coupled through a wire ring and the other is The ends are directly coupled and connected to a power supply terminal (GRD), one end of the coil is connected to the power supply terminal (GRD) via a resistor, and one end of the other winding is connected to the power supply terminal (GRD). ), And the other end is connected to the power supply terminal (GRD) through a variable capacitor and is also connected to the anode of the first varicap, and the cathode thereof is connected through a resistor. A second varicap, which is connected to each other and has a cathode connected to the cathode of the first varicap of the first tuning circuit and an anode connected to the power supply terminal (GRD), is provided. A double-tuned circuit characterized in that the cathode of the first varicap of the circuit is configured to be connected to another power supply terminal (VT).