JPH07143018A - Am radio receiver - Google Patents

Abstract

PURPOSE:To always receive a desired signal stably in an AM radio receiver with an untuned antenna. CONSTITUTION:A wideband level detection circuit 13 is provided at the output stage of a wideband amplifier circuit 2, and a medium band level detection circuit 14 at the input stage of a frequency conversion circuit 5, and a narrow band (intermediate frequency) level detection circuit 11 at the output stage of an intermediate frequency amplifier circuit 6, respectively. The level detection of each stage is performed by the use of level detection circuits 11, 13, and 14. The detection results of medium band level detection circuit 14 and the narrow band level detection circuit 11 are fed back to a wideband level detection sensitivity control circuit 15, optimization control is performed to change wideband level detection sensitivity according to conditions, and a reception defect under the input of intense interference can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuning type AM radio receiver for vehicles, homes, portables and the like.

[0002]

2. Description of the Related Art In recent years, an electronic tuning type AM radio receiver has been widely used in the market regardless of whether it is mounted on a vehicle, for home use, or for portable use, and it is required to always receive desired radio waves stably. .

In an AM radio receiver of an electronic tuning type, when a capacitive antenna is used as an antenna, an antenna non-tuning in which a signal amplified by a wide band amplification circuit which makes the antenna input non-tuning is tuned by a high frequency tuning circuit The method is generally adopted.

FIG. 2 shows the configuration of the signal system of a conventional AM non-tuned antenna radio receiver. In FIG. 2, 1 is an antenna, 2 is a wide band amplifier circuit, 3 is a wide band amplifier circuit 2.
An antenna attenuator circuit for attenuating the level of the signal input to the circuit 4, a high frequency tuning circuit, a frequency converter circuit 5, an intermediate frequency amplifier circuit 6, and an intermediate frequency output signal 7.

Further, 8 is a high frequency level detection circuit for detecting the output level of the wide band amplification circuit 2 and the frequency conversion circuit 5, 5 is an input level of the high frequency level detection circuit, 9 is an antenna attenuation control circuit for controlling the antenna attenuation circuit 3, and 10 is wide band amplification. A wideband amplification gain control circuit for controlling the gain of the circuit 2, 11 is an intermediate frequency level detection circuit for detecting the level of the intermediate frequency output signal 7, and 12 is an intermediate frequency amplification gain control circuit for controlling the gain of the intermediate frequency amplification circuit 6. is there.

Next, the operation of the above conventional example will be described.
The high frequency signal input from the antenna 1 passes through the antenna attenuating circuit 3, is amplified by the wide band amplifying circuit 2, and is output to the high frequency tuning circuit 4. In the high frequency tuning circuit 4, the desired signal is passed in synchronization with the desired signal, and the undesired signal, that is, the interfering signal is excluded. The desired high frequency signal that has passed through the high frequency tuning circuit 4 is input to the frequency conversion circuit 5 and converted into an intermediate frequency signal. This intermediate frequency signal is
After being amplified by the intermediate frequency amplifier circuit 6, it is output as an intermediate frequency output signal 7. The intermediate frequency output signal 7 is detected and becomes an audio signal.

Further, the antenna attenuation control circuit 9 and the gain control circuit 10 are operated in accordance with the signal level detected by the high frequency level detection circuit 8 to control the antenna attenuation circuit 3 and the gain of the wide band amplification circuit 2. Further, the gain control circuit 12 is operated in accordance with the signal level detected by the intermediate frequency level detection circuit 11 to control the gain of the intermediate frequency amplification circuit 6 so that the output level of the audio signal becomes constant.

As described above, the conventional AM radio receiver can also be tuned to and received by the desired signal to be received.

[0009]

However, in the above conventional AM receiver, since the antenna is a non-tuning type, both the desired signal and the interfering signal are directly input to the wide band amplifier circuit 2 and are amplified and output to the subsequent stage. It Then, in the high frequency level detection circuit 8, the antenna attenuation amount control circuit 9 and the wide band amplification gain control circuit 10 are operated so that the input level becomes constant when an excessive signal is input. Also,
Since the high-frequency level detection circuit 8 cannot distinguish between the desired signal and the interfering signal, in a strong electric field region directly below the interfering signal antenna, the so-called sensitivity suppression in which the interfering signal interferes with the desired signal due to the preset detection sensitivity. However, there is a problem that the desired signal cannot be received in the worst case.

The present invention solves such a conventional problem, and an object thereof is to provide an excellent AM radio receiver which can always stably receive a desired signal.

[0011]

In order to achieve the above object, the present invention is provided with wide band, medium band, and narrow band level detection circuits, whereby the input condition of a desired signal is always grasped and grasped. The detection sensitivity of the high frequency level detection circuit for detecting the interfering signal is controlled according to the condition of the desired signal.

[0012]

With the above structure, the present invention detects the input level of the desired signal mainly in the level detection circuit of the middle band and the narrow band, and detects the input level of the interfering signal in the level detection circuit of the wide band. It is possible to grasp the input conditions of the desired signal and the soundproof signal. Then, by changing the sensitivity of the wideband level detection circuit according to the condition of the desired signal, the level detection sensitivity of the wideband is lowered when the desired signal is weakly input, and to some extent the automatic gain control by the interfering signal is eliminated. To prevent sensitivity suppression interference, and when the desired signal is a medium or strong input, raise the level detection sensitivity of the wide band, detect the interference signal and apply automatic gain control to prevent distortion when passing through non-linear elements It is possible to prevent generation and always receive the desired signal in a stable state without any interference.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, the same components as those in FIG. 2 are designated by the same reference numerals, the description of the components will be omitted, and portions different from those in FIG. 2 will be mainly described.

That is, as is apparent from FIG. 1, the output levels of the narrow band level detection circuit 11 and the wide band amplification circuit 2 for detecting the output level of the intermediate frequency amplification circuit 5 are detected, and this detection signal is used as the antenna attenuation amount. Wideband level detection circuit 1 for outputting to control circuit 9 and wideband amplification gain control circuit 10
3. A medium band level detection circuit 14, a narrow band level detection circuit 11 and a medium band level which detect the input level of the frequency conversion circuit 5 and output the detection signal to the antenna attenuation control circuit 9 and the wide band amplification gain control circuit 10. Detection circuit 1
Narrow band level detection circuit 1 based on the detection signal detected in 4.
1. The feature is that a wide band level detection sensitivity control circuit 15 for controlling the sensitivity of the wide band level detection circuit 13 is newly added.

Next, the operation of the above embodiment will be described. Similar to the configuration shown in FIG. 2, the high frequency signal input from the antenna 1 passes through the antenna attenuation circuit 3, is amplified by the wide band amplification circuit 2, and is output to the high frequency tuning circuit 4. In the high frequency tuning circuit 4, the desired signal is passed in synchronization with the desired signal, and the undesired signal, that is, the interfering signal is excluded. The desired high frequency signal that has passed through the high frequency tuning circuit 4 is input to the frequency conversion circuit 5 and converted into an intermediate frequency signal. This intermediate frequency signal is amplified by an intermediate frequency amplifier circuit and then output as an intermediate frequency output signal 7. The intermediate frequency output signal 7 is detected and becomes an audio signal.

Further, the attenuation control circuit 9 and the gain control circuits 10 and 12 are operated in accordance with the levels detected by the level detection circuits 13, 14 and 11 of each stage so that the output level of the audio signal becomes constant. ing.

Generally, in a strong electric field region such as directly below an interference signal antenna, when a weak input electric field of a desired signal is received, an automatic gain control circuit (hereinafter referred to as AGC) operates due to the interference signal to suppress sensitivity. In this case, it is desirable that AGC is not applied even if an interfering signal is detected.

Similarly, in a strong electric field region directly below the disturbing signal antenna, when the electric field of the desired signal is higher than the normal state and the medium strong input is received, distortion is caused when the non-linear element passes due to the mutual relationship between the disturbing signal input and the desired signal input. It causes interference. In this case, it is desirable to detect the interfering signal early and apply AGC in a region where distortion does not occur when passing through the nonlinear element.

Therefore, in this embodiment, the antenna 1
If there is an interfering signal other than the desired signal, the medium band level detection circuit 14 and the narrow band level detection circuit 11 grasp the input condition of the desired signal and the wide band level detection sensitivity control circuit 15 is activated. It is operated to change the detection sensitivity of wide band level.

When the desired signal is weakly input, the level detection sensitivity of the wide band is lowered to reduce the signal input to the wide band level detection circuit 13 to prevent the AGC from being caused by the interfering signal and prevent the sensitivity suppression interference. .

When the desired signal is a medium strong input, the level detection sensitivity of the wide band is increased to increase the number of signals input to the wide band level detection circuit 13, the interfering signal is detected and the AGC is applied, and when the non-linear element passes. Prevents interference by preventing distortion.

As described above, according to the above-described embodiment, the electric field condition of the desired signal can be detected by the medium band level detection circuit 14 and the narrow band level detection circuit 11, so that the wide band level can be adjusted according to the condition of the desired signal. Change the detection sensitivity,
The detection level of the interfering signal can be changed, sensitivity suppression and occurrence of interference can be prevented, and the desired signal can always be received in a stable state without various types of interference.

[0024]

As is apparent from the above embodiment, the present invention includes wide band, middle band and narrow band level detection circuits. Therefore, the desired signal is mainly used in the middle band and narrow band level detection circuits. By detecting the input level of, and by detecting the input level of the interfering signal in the wideband level detection circuit,
It is possible to grasp the input conditions of the desired signal and the disturbing signal.

Further, the present invention has a circuit for changing the sensitivity of the wide band level detecting circuit for detecting the level of the interfering signal according to the condition of the desired signal, so that it is possible to operate under the following strong electric field. Optimal control is possible.

Since the electric field condition of the desired signal can be detected by the medium band and narrow band level detection circuit, the detection sensitivity of the interfering signal in the wide band level detection is changed according to the condition of the desired signal.

When the desired signal is weakly input, the level detection sensitivity of the wide band is lowered to prevent AGC from being applied by the interfering signal to some extent to prevent sensitivity suppression interference. It has the effect of increasing the detection sensitivity, detecting an interfering signal, applying AGC, and preventing distortion when passing through a non-linear element to prevent interference.
The desired signal can always be received in a stable state without any interference.

[Brief description of drawings]

FIG. 1 is a block diagram of an AM radio receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional AM radio receiver.

[Explanation of symbols]

 1 antenna 2 wide band amplification circuit 3 antenna attenuation circuit 4 high frequency tuning circuit 5 frequency conversion circuit 6 intermediate frequency amplification circuit 7 intermediate frequency signal output 8 high frequency level detection circuit 9 antenna attenuation control circuit 10 wide band amplification gain adjustment circuit 11 intermediate frequency level detection Circuit 12 Intermediate frequency amplification gain adjustment circuit 13 Wide band level detection circuit 14 Medium band level detection circuit 15 Wide band level detection sensitivity control circuit

Front page continued (72) Inventor Koichi Ouchi 4-3 Tsunashima Higashi 4-chome, Kohoku Ward, Yokohama City, Kanagawa Matsushita Communication Industrial Co., Ltd.

Claims (1)

[Claims] 1. A wide-band amplifier circuit in which an antenna is a non-tuning type, a high-frequency tuning circuit that tunes to a desired signal, a frequency conversion circuit that generates an intermediate-frequency signal, and an intermediate-frequency amplifier circuit that amplifies the intermediate-frequency signal, A wideband level detecting circuit for detecting an input level of the high frequency tuning circuit; a middle band level detecting circuit for detecting an output level of the high frequency tuning circuit; and a narrow band level detecting circuit for detecting an output level of the intermediate frequency amplifying circuit. A gain control circuit for controlling the gain of the wide band amplification circuit according to the levels detected by the wide band and middle band level detection circuits, and a gain of the intermediate frequency amplification circuit according to the levels detected by the narrow band level detection circuit Of the wide band level detection circuit according to the level detected by the gain control circuit for controlling An AM radio receiver including a detection sensitivity control circuit that changes detection sensitivity.