JPH03297227A - wireless receiving device - Google Patents

Abstract

PURPOSE:To vary the attenuation of an input signal level at every reception frequency by providing a resonance circuit tuned to a specific frequency on an automatic gain control circuit so as to control the input signal level to a high frequency amplifier in response to the reception frequency. CONSTITUTION:When the impedance of a variable impedance circuit 21 is decreased, the input signal is attenuated through a resonance circuit 23 and an AGC circuit 2 is operated. Since the impedance of the circuit 23 is decreased at a band width around the resonance frequency as a center, a large attenuation is obtained as the operation of the circuit 2 with respect to a resonance frequency f0 as shown in figure. Since the attenuation is decreased as the frequency is parted from the frequency f0, a disturbing wave is suppressed as shown in figure. Thus, the attenuation of the desired input signal to an RF amplifier 3 among the received frequencies is less and the attenuation in the disturbing wave is increased. Assuming the frequency of the disturbing wave is the frequency f0, the attenuation is increased and since the attenuation is less with respect to the desired wave apart from the frequency f0, even when the disturbing wave is close to the desired wave, the desired wave is clearly received.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an AM receiver or an FM receiver equipped with an automatic gain control circuit (hereinafter referred to as an AGC circuit) that controls the input signal level from an antenna to a high frequency amplifier. The present invention relates to a wireless receiving device such as the above.

BACKGROUND ART FIGS. 4 and 5 show the configuration of a conventional radio receiving apparatus.

In FIGS. 4 and 5, the received signal received by the antenna 1 is transmitted to the AGC circuit 2. The signal is input to a frequency mixer 5 via a high frequency amplifier (hereinafter referred to as an RF amplifier) 3.

At this time, the input (Fig. 5) or output (
The signal level of FIG. 4) is detected by a level detector 4, and the detected signal is supplied to the AGC circuit 2 to control the input signal level from the antenna 1 to the RF amplifier 3.

Note that 6 is a local oscillator, which supplies a frequency to the frequency mixer 5 for converting the frequency supplied from the RF amplifier 3 to the frequency mixer 5 into an intermediate frequency.

FIG. 6 shows the configuration of the AGC circuit 2.

In FIG. 6, when the input to the antenna 1 is large, that is, when the detected signal of the level detector 4 is large, the impedance of the variable impedance circuit 21 made up of variable impedance elements such as transistors and diodes becomes small. , when the detected signal from the level detector 4 is small, the impedance of the variable impedance circuit 21 becomes large.
A load 22, such as a large-capacity fixed capacitor or a fixed resistor that does not depend on frequency characteristics, is connected in series with 1.
The combined impedance of the level detector 4 automatically changes depending on the magnitude of the detection signal of the level detector 4.

Therefore, the input signal level to the RF amplifier 3 can be controlled to be constant.

Problems to be Solved by the Invention However, in the conventional radio receiving device described above, the input signal level of the RF amplifier 3 is uniformly controlled regardless of the receiving frequency. radio waves (hereinafter referred to as waves) and strong electric field radio waves (hereinafter referred to as
This is called an interference wave. ) are close to each other, the gain of the AGC circuit 2 decreases depending on the input signal level of the interference wave.

Therefore, since the input signal level of the desired wave is attenuated at the same time and the input signal level to the RF amplifier 3 is also reduced, there is a problem that it becomes impossible to receive the desired wave with a weak electric field.

The present invention solves these conventional problems, and provides an excellent radio receiving device that can clearly receive a desired signal even if the frequency of the interference wave in a strong electric field is close to that of the desired wave in a weak electric field. The purpose is to provide

Means for Solving the Problems In order to achieve the above object, the present invention has a configuration in which the AGC circuit is provided with a resonant circuit tuned to a specific frequency, and the input signal level to the RF amplifier is controlled according to the receiving frequency. This is what I did.

Therefore, according to the present invention, the level of the input signal to the RF amplifier at the reception frequency corresponding to a specific frequency is greatly attenuated by the AGC circuit, and the amount of attenuation for other reception frequencies can be reduced, thereby reducing the interference wave. This has the effect that the interference wave can be received by setting the gain to be small and the gain of the desired wave to be large.

Example FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, 1 is an antenna, 2 is an AGC circuit, a variable impedance circuit 21 consisting of diodes D+ and Dz, and a resonant circuit 2 consisting of a capacitor C and a coil L.
It consists of 3.

3 is an RF amplifier; 4 is a level detector for detecting the level of the output of the RF amplifier 3; the detected signal is supplied to the diode D1 of the variable impedance circuit 21;

5 is a frequency mixer to which the output of the RF amplifier 3 is supplied; 6
is a local oscillator, which is connected from the RF amplifier 3 to the frequency mixer 5
The frequency mixer 5 supplies a frequency for converting the frequency supplied to the intermediate frequency to an intermediate frequency.

Next, the operation of the above embodiment will be explained.

In FIG. 1, when the impedance of variable impedance circuit 21 decreases, the input signal is attenuated through resonance circuit 23, and AGC circuit 2 operates.

However, since the impedance of the resonant circuit 23 decreases in a certain bandwidth around the resonant frequency, the operation of the AGC circuit 2 is to obtain a large amount of attenuation with respect to the resonant frequency f0, as shown in FIG. Since the amount of attenuation decreases as the distance from the resonant frequency f0 increases, interference waves can be suppressed as shown in FIG.

Therefore, the RF amplifier 3 of the desired wave among the receiving frequencies
The amount of attenuation of the human input signal level is small, and the amount of attenuation of the interference wave is large.

In this way, according to the above embodiment, by providing the resonant circuit 23 in the AGC circuit 2, the gain changes depending on the reception frequency, and the amount of attenuation of the human input signal level to the RF amplifier 3 for each reception frequency is changed. It has the advantage of being able to

Therefore, if the resonance frequency f0 is used as a disturbance wave, the amount of attenuation of the interference wave can be increased, and the amount of attenuation can be reduced for the desired wave far from the resonance frequency f0. This has the effect that the desired wave can be clearly received even if the waves are close to each other.

In the above embodiment, one resonant circuit 23 is provided, but it is also possible to provide a resonant circuit corresponding to a plurality of interference waves and switch when receiving a desired wave that is close to the interference wave. good.

Furthermore, the resonant circuit 23 may be a series resonant circuit or a parallel resonant circuit, and the input of the level detector 4 may be the input or output of the RF amplifier 3.

Effects of the Invention As is clear from the above embodiments, the present invention has a configuration in which the automatic gain control circuit is provided with a resonant circuit tuned to a specific frequency, and the input signal level to the high frequency amplifier is controlled according to the receiving frequency. Therefore, there is an advantage that the gain changes depending on the reception frequency, and the amount of attenuation of the input signal level to the high frequency amplifier can be changed for each reception frequency.

Therefore, if the resonant frequency is used as an interfering wave, the amount of attenuation of the interfering wave can be increased, and the amount of attenuation can be reduced for the desired wave far from the resonant frequency.
This has the effect that the desired wave can be clearly received even if the interfering wave is close to the desired wave.

[Brief explanation of the drawing]

Part 1 is a block diagram of the configuration of a radio receiving device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of the automatic gain control amount in the embodiment, Fig. 3 is a characteristic diagram of the suppression amount in the embodiment, and Fig. 4 is a characteristic diagram of the amount of suppression in the embodiment.
5 is a block diagram of a conventional radio receiving apparatus, and FIG. 6 is a block diagram of a conventional automatic gain control circuit. ■...Antenna, 2...Automatic gain control circuit, 3...High frequency amplifier, 4...Level detector, 21...Variable Impedance circuit, 23... Resonance circuit, DD2... Diode, C... Capacitor, L... Coil.

Claims (1)

[Claims] A resonant circuit that resonates at a specific frequency and a variable impedance circuit whose impedance changes depending on the magnitude of the detected signal that is supplied are connected in series, and the automatic attenuator that attenuates the signal received by the antenna according to the magnitude of the detected signal. A gain control circuit, a high frequency amplifier that amplifies the output of the automatic gain control circuit, and a level detector that detects the signal level of either the input or output of the high frequency amplifier and outputs the detected signal. Wireless receiving device.