JPH05206885A - Radio receiver - Google Patents

Abstract

PURPOSE:To obtain the radio receiver in which an amplification factor of a high frequency amplifier circuit is not fluctuated even when a level fluctuation of a frequency signal other than a reception desired frequency signal takes place. CONSTITUTION:An amplification factor of a high frequency amplifier circuit is controlled by a signal from a narrow band AGC drive circuit 62 and an attenuation of an antenna attenuation circuit is controlled by a signal from a narrow band AGC drive circuit 62 and a broad band AGC drive circuit 74. Thus, a broad band AGC signal from the broad band AGC drive circuit 74 does not give any effect onto the amplification factor of the high frequency amplifier circuit. Thus, even when a level fluctuation takes place in the frequency signal other than the reception desired frequency, the amplification factor of the high frequency amplifier circuit is not fluctuated and the radio receiver realizing stable reception is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC circuit of a radio receiver for receiving AM broadcast and FM broadcast.

[0002]

2. Description of the Related Art Conventionally, a general radio receiver is provided with a so-called AGC (auto gain control) circuit. This circuit is provided to adjust the reception sensitivity according to the strength of the received signal and achieve stable reception. For example, in an AM radio receiver, the receiving sensitivity is adjusted by setting the amplification factor in the high frequency amplification and adjusting the attenuation amount of the received signal based on the RF signal or the IF signal after the high frequency amplification.

A part of the circuit of a conventional radio receiver is shown in FIG. The signal received by the antenna 10 is applied to the gate of the FET 14 via the capacitor 12. FET
After being amplified by 14, it is applied to the tuning circuit 18 through the emitter / collector of the AGC transistor 16. The signal including only the desired reception frequency output from the tuning circuit 18 is supplied to the mixing circuit 20 and the diode detection circuit 22.

The signal extracted from the connection point between the primary tuning coil 24 of the tuning circuit 18 and the small resistor 26 is supplied to the diode detection circuit 28. This diode detection circuit 28
Since the signal supplied to (1) is not subjected to band limitation by the tuning circuit 18, it becomes a signal of a wide frequency band (wide band), unlike the signal (narrow band) supplied to the diode detection circuit 221 described above.

The signals of the diode detection circuits 22 and 28 are supplied to an AGC drive circuit 32 via an adder 30.
The AGC signal which is the output signal of the AGC drive circuit 32 is A
It is supplied to the base of the GC transistor 16. Therefore, the transconductance of the FET 14 changes according to the AGC signal, and the level of the output signal is adjusted. On the other hand, the AGC signal is also supplied to the comparator 34. The comparison output is the antenna attenuation drive circuit 36.
Is supplied to the antenna attenuation circuit 38 via. Therefore, the amount of attenuation in the antenna attenuation circuit 38 is controlled according to the level of the output signal of the FET 14, and the level of the input signal of the FET 14 will not exceed a predetermined value.

As described above, in the conventional radio receiver, the AGC based on the signal in the wide frequency band before passing through the tuning circuit 18 and the AGC based on the desired frequency signal to be received after passing through the tuning circuit 18 are provided. Two AGCs are used. Then, in the conventional radio receiver shown in FIG. 2, the attenuation amount of the antenna attenuation circuit 38 and the amplification factor of the FET 14 are obtained by the AGC signal obtained by adding the wide band AGC signal and the narrow band AGC signal by the adder 30. Was under control.

[0007]

As described above, in the conventional radio receiver, wide band and narrow band AGC are realized by one AGC signal. However, the broadband AGC is an AGC according to the output signal of the FET of the high frequency amplification stage,
Its purpose is primarily to prevent excessive input to the FET.

In the conventional radio receiver, the amplification factor of the FET in the high frequency amplification stage is also controlled by this wide band AGC. Therefore, there is a problem in that the amplification factor of the FET fluctuates due to the level fluctuations of frequency signals other than the desired reception frequency.

The present invention has been made in view of the above problems, and an object thereof is to obtain an AGC circuit for a radio receiver in which the amplification factor of a high frequency amplification stage is not affected by a wide band AGC.

[0010]

In order to solve the above problems, the present invention provides an attenuating circuit for attenuating a high frequency signal received by an antenna, and a high frequency for amplifying a high frequency signal attenuated by the attenuating means. An amplifier circuit, a tuning circuit for extracting a signal of a desired frequency from the output signal of the high frequency amplifier circuit, a wideband signal detection circuit for detecting a wideband received signal strength according to the magnitude of the output signal of the high frequency amplifier circuit, A narrowband signal detection circuit for detecting the received signal strength of a narrowband according to the magnitude of the output signal of the tuning circuit, and based on the detection results of both the narrowband signal detection circuit and the wideband signal detection circuit An attenuation amount control circuit for controlling the attenuation amount of the attenuation circuit, and an amplification factor control circuit for controlling the amplification factor of the high frequency amplification circuit based only on the detection result of the narrow band signal detection circuit. When a radio receiver, characterized in that it comprises a.

[0011]

The wide band AGC signal by the wide band AGC drive circuit in the present invention is supplied only to the attenuation amount control circuit. Further, the amplification factor control means in the present invention is a narrow band AG.
The amplification factor of the high frequency amplifier circuit is controlled based on only the narrow band AGC signal from the C drive circuit.

Therefore, the amplification factor of the high frequency amplifier circuit is not affected by the level fluctuations of frequency signals other than the desired reception frequency.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a radio AGC circuit according to a preferred embodiment of the present invention. Antenna 5
The signal received at 0 is FET through the capacitor 52
It is supplied to the gate of 54. The FET 54 constitutes a high frequency amplifier circuit, and the output of this circuit is applied to the tuning circuit 58 via the AGC transistor 56. The output signal of the tuning circuit 58 is supplied to the mixing circuit 60, and
It is supplied to the narrow band AGC drive circuit 62. further,
The narrow band AGC signal which is the output signal of the narrow band AGC drive circuit 62 is supplied to the diode detection circuit 64 and the RF-AG.
It is supplied to the adder 68 through the C circuit 66.
Further, the output signal of the RF-AGC circuit 66 is the above-mentioned AG.
It is also supplied to the base of the C transistor 56. Therefore, the AGC transistor 56 is controlled according to the AGC signal, and the gm (transconductance) of the FET 54 is adjusted. Therefore, the narrow band A in which the amplification factor of the high frequency amplifier circuit is controlled according to the output signal strength of the tuning circuit 58.
GC has been realized.

The characteristic feature of the present invention is that the amplification factor of the high frequency circuit is controlled only by the narrow band AGC by the output signal of the tuning circuit 58, and the wide band AGC by the signal before being selected by the tuning circuit 58 as described above. Is not affected by.

The primary tuning coil 70 of the tuning circuit 58 is also used.
A part of the output signal of the high frequency amplifier circuit taken out from the connection point between the low resistance 72 and the small resistor 72 is supplied to the wide band AGC drive circuit 74. Further, the wide band AGC signal which is the output signal of the wide band AGC drive circuit 74 is supplied to the adder 68 through the diode detection circuit 76.

Then, in the adder 68, the narrow band AG
The C signal is added, and the comparator 78 compares it with the reference signal. The signal of this comparison result is the attenuation control circuit 8
0 to the antenna attenuation circuit 82.
The antenna attenuation circuit 82 is provided between the signal line from the antenna 50 and the ground line, and is composed of pin diodes 84 and 85 for adjusting the resistance value therebetween. In this way, the attenuation amount of the antenna attenuation circuit 82 is controlled based on the sum signal of the wide band AGC signal and the narrow band AGC signal.

A characteristic of the present invention is that the broadband A
That is, the GC signal is used only to control the amount of attenuation for the received signal from the antenna. Therefore, as in the conventional case, the level of the signal input to the high frequency amplification circuit can be set to a certain value or less, while the wide band AGC signal does not affect the amplification factor of the high frequency amplification circuit.

As described above, according to this embodiment, only the attenuation amount of the received signal from the antenna 50 is adjusted by the wide band AGC based on the output signal of the high frequency amplifier circuit. The amplification factor is not affected at all. Therefore, even if the level of the frequency other than the desired frequency fluctuates, the amplification factor of the high-frequency amplifier circuit does not change, which does not unnecessarily reduce the sensitivity of the desired station.

[0020]

As described above, according to the present invention, the wide band AGC signal based on the output signal of the high frequency circuit adjusts only the amount of attenuation from the antenna. Therefore, even if the level fluctuation occurs in the signal of the interfering station that is sufficiently distant from the desired station and can be sufficiently attenuated by the RF tuning circuit, the amplification factor of the high frequency amplifier circuit does not change, and stable reception can be achieved. Have an effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a part of a circuit of a radio receiver according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a part of a circuit of a conventional radio receiver.

[Explanation of symbols]

 54 FET 56 AGC transistor 58 Tuning circuit 62 Narrow band AGC drive circuit 74 Wide band AGC drive circuit 82 Antenna attenuation circuit

Claims (1)

[Claims] 1. An attenuator circuit for attenuating a high frequency signal received by an antenna, a high frequency amplifier circuit for amplifying a high frequency signal attenuated by said attenuating means, and a signal of a desired frequency from an output signal of said high frequency amplifier circuit. A tuning circuit to be taken out, a wideband signal detection circuit for detecting a wideband received signal strength according to the magnitude of the output signal of the high frequency amplifier circuit, and a narrowband received signal strength according to the magnitude of the output signal of the tuning circuit. A narrowband signal detection circuit for detecting, a attenuation amount control circuit for controlling the attenuation amount of the attenuation circuit based on the detection results of both the narrowband signal detection circuit and the wideband signal detection circuit, the narrowband signal detection A radio receiver comprising: an amplification factor control circuit that controls the amplification factor of the high frequency amplification circuit based only on the detection result of the circuit.