JP3292956B2 - Radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver corresponding to a strong electric field input.

Conventionally, as shown in Figure 3, the tuning coil 20 via the input capacitor _{C 20} to the ANT input, a variable capacitance diode 21a, 21b and the adjustment capacitor 2
2 and a damping circuit 24 composed of a pair of pin diodes, and a capacitor C for dropping a high-frequency current to the ground.
₂₁ and C ₂₂ are connected in parallel to the damping circuit 25 of the antenna tuning circuit 23, and the antenna tuning circuit 23
The via capacitor _{C 23} subsequent high-frequency amplifying device 26
Of the attenuating circuit 24, for example, by an AGC signal obtained from an intermediate frequency signal after frequency conversion.
To reduce the impedance at the time of inputting a strong electric field to lower the resonance impedance characteristic, that is, the selectivity characteristic of the antenna tuning circuit 23, thereby attenuating the antenna input signal, thereby reducing the occurrence of intermodulation distortion and the like. Preventing radio receivers are known.

[0003]

[SUMMARY OF THE INVENTION However, according to the conventional configuration described above, the damping circuit 25, the presence of the capacitor C ₂₁ connected in series to the attenuation circuit 24, the voltage drop height attenuation restricted has the disadvantage that, therefore in order to obtain a large attenuation in the input signal of strong electric field strength, it is necessary to amplify the drive current of the attenuator 24, also the damping effect by increasing the capacitance of the capacitor C ₂₁ However, there is a problem that when trying to increase the frequency, a tuning deviation is induced and the wiring board becomes large.

[0004]

SUMMARY OF THE INVENTION In order to improve the above-mentioned deficiencies of the prior art, the present invention provides an antenna tuning circuit to which a high-frequency amplifier circuit is connected in a subsequent stage, and a damping capacitor and an AGC which reduce selectivity characteristics. A series circuit with a first attenuating circuit consisting of a pin diode driven by a voltage is connected in parallel, and an antenna input terminal is connected to a connection point between the attenuating circuit and the capacitor via an input capacitor. In the above, a second antenna is provided between the antenna input terminal and the input capacitor.
Are connected in series, and A
A second attenuation circuit composed of a pin diode operated by the GC voltage is connected, and the second attenuation circuit is connected in series to the first attenuation circuit.

[0005]

When the electric field strength of the signal input to the antenna input terminal is weak, the impedance of the attenuating circuit is high because the AGC voltage is low. Therefore, the input signal is transmitted to the antenna via the input capacitor and the damping capacitor. After being input to a tuning circuit and selected for tuning, the signal is input to a high-frequency amplifier at a subsequent stage via a coupling capacitor and amplified. In the above description, when the electric field strength of the antenna input signal increases, the AGC voltage also increases, so that the attenuation circuit is driven to lower the impedance of the circuit, and the signal input to the antenna input terminal becomes the impedance between the attenuation circuit and the input capacitor. In addition to the attenuation corresponding to the ratio, the impedance of the attenuating circuit lowers the selectivity characteristic due to the damping capacitor of the antenna tuning circuit, so that a great attenuating effect can be obtained.

[0006]

EXAMPLES based on the following drawings and detailed embodiments of the present application, in FIG. 1, an antenna input terminal P, the capacitor C ₂ and a pair for the damping to reduce the selectivity characteristic via the input capacitor C ₁ It is connected to a series connection point with the attenuation circuit 1 composed of the pin diodes 1a and 1b. A series circuit of the capacitor C ₂ and the attenuation circuit 1 is connected in parallel with a band-pass type antenna tuning circuit 5 including a tuning coil 2, a pair of variable capacitance diodes 3 a and 3 b, and an adjusting capacitor 4. this output terminal of the antenna tuning circuit 5, coupling the first gate g ₁ of the high-frequency amplifying device 6 consisting of MOSFET through the capacitor C ₃ is connected, the drain d is tuning coil 7 via a coupling capacitor C ₄ And a π-type high-frequency tuning circuit 9 composed of a pair of variable capacitance diodes 8a and 8b. The source S of the impedance conversion element 10
Frequency converting circuit 11 through the capacitor C ₅ is, FM consisting of the intermediate frequency amplifier circuit 13 and the gain control signal circuit 12
Front-end IC 14 (for example, LA117 manufactured by Sanyo Electric Co., Ltd.)
The fifth terminal, which is the input terminal of the frequency conversion circuit 11 of 5), and the sixth terminal, which is the output terminal of the AGC voltage of the FM front-end IC 14, are connected to the attenuation circuit 1.

However, if the electric field strength of the signal input to the antenna input terminal is weak, the FM front-end IC
Since the AGC voltage is low output from 14 the sixth terminal of the impedance of the attenuation circuit 1 is high, so that the input signal is tuned selected input to the antenna tuning circuit 5 via the input capacitor C ₁ and the damping capacitor C ₂ and then, coupling capacitor C ₃ via amplified is input to the first gate g ₁ of the high-frequency amplifying device 6, the signal is input to the high frequency tuning circuit 9 of π type via a coupling capacitor C _4, the After the resonance is selected again by the circuit 9, the drain is input to the gate g of the impedance conversion element 10 which is grounded. Here, the π-type high-frequency tuning circuit 9 has a high impedance. Therefore, the output of the circuit 9 is input to the gate g of the impedance conversion element 10 with a high input impedance, so that a high selectivity can be obtained. Signal input to the impedance conversion element 10 is inputted to the frequency converting circuit 11 of the FM front end IC14 via a bonding capacitor C ₅ from the source S is converted into a low output impedance from the fifth terminal, the intermediate frequency signal after being converted, the eighth terminal and to respective outputs from the ninth terminal, an intermediate frequency amplifier circuit 1 than the 12 terminal and its output via a series circuit of an intermediate frequency transformer T and the resistor R ₁ and the ceramic filter F
3 and amplified, and the amplified output is output from the fifteenth terminal to the detection stage.

[0008] Some of the intermediate-frequency broadband intermediate frequency signal passing through the transformer T via a series circuit of a resistor R ₂ and capacitor C ₆ type than the 10 terminal to the gain control circuit 12, from the circuit 12 AGC voltage for driving the pin diode of the attenuation circuit 1 and an AGC voltage for controlling the high-frequency amplification element 6
And these AGC voltages are output from the sixth terminal and the thirteenth terminal, respectively.

In the above, when the electric field strength of the antenna input signal is increased, the pin diode driving AGC output from the gain control circuit 12 of the FM front end IC 14 is output.
The voltage becomes higher, the attenuation circuit 1 decreases the impedance of the driven the circuit, the input signal to the antenna input terminal attenuated corresponds to an impedance ratio of the attenuation circuit 1 and the input capacitor C _1, the attenuation Due to the decrease in the impedance of the circuit 1, the selectivity characteristics of the antenna tuning circuit 4 are also reduced, and a great attenuation effect can be obtained.

[0010] Then further electric field intensity increases, in addition to the damping action by the attenuating circuit 1, a second gate g ₂ a control voltage of the high-frequency amplifying device 6 is applied from the thirteenth terminal of the FM front end IC14 high-frequency amplifying device 6 is controlled.

[0011] Figure 2 in FIG. 1, between the antenna input terminal P and the input capacitor C _1, further input capacitor C
₆ and a pair of pin diodes 15a and 15b
Another embodiment comprising an attenuation circuit 15 is shown. After signal input to the antenna input terminal P is that is first decompressed by the input capacitor C ₆ of the previous stage and the impedance ratio between the second damping circuit 15, a further impedance ratio of the subsequent input capacitor C ₁ and the first attenuation circuit While the pressure is reduced, a significant damping effect can be obtained due to a decrease in selectivity characteristics.

[0012]

As described above, according to the present invention, the antenna tuning circuit is connected in parallel with the series circuit of the diping capacitor and the attenuating circuit composed of the pin diode driven by the AGC voltage, so that a large attenuation is obtained. The effect is obtained, and the variable capacitance diode constituting the antenna tuning circuit can be protected from an input signal having a strong electric field strength.
According to the second aspect of the present invention, the input signal is attenuated at the antenna input end, so that the input signal is attenuated at the antenna input end. It has advantages such as being effective for elimination.

[Brief description of the drawings]

FIG. 1 is a circuit diagram

FIG. 2 is a circuit diagram according to another embodiment.

FIG. 3 is a circuit diagram of a conventional configuration.

[Explanation of symbols]

P Antenna input terminals C ₁ , C ₆ Input capacitors C ₂ Damping capacitors 1, 15 Attenuation circuit 2, 7 Tuning coil 3 a, 3 b, 8 a, 8 b Variable capacitance diode 5 Antenna tuning circuit 6 High frequency amplifier

Claims (2)

(57) [Claims] 1. A series circuit comprising a damping capacitor for reducing selectivity characteristics and a first attenuating circuit comprising a pin diode driven by an AGC voltage is connected in parallel to an antenna tuning circuit to which a high-frequency amplifier circuit is connected in a subsequent stage. ,
A radio receiver, wherein an antenna input terminal is connected to a connection point between the attenuation circuit and the capacitor via an input capacitor. 2. A second input capacitor is connected in series between an antenna input terminal and an input capacitor, and a second attenuating circuit comprising a pin diode operated by an AGC voltage is connected to the series connection point. The radio receiver according to claim 1, wherein the second attenuation circuit is connected in series to the first attenuation circuit.