JP2002368631A - Fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver that avoids radio waves of a desired station from becoming unable to be received properly, due to suppression of an AGC circuit, on the basis of a disturbance noise of a station adjacent to a desired station. SOLUTION: The FM receiver is provided with an adjacent noise detector 11, that detects a spectrum (adjacent noise) 24 of an adjacent disturbing wave included in a detection output signal from an FM detector 10, and when the adjacent noise exceeds a prescribed level, an output of the adjacent noise detector 11 selects AGC sensitivity of the AGC circuit 19. The adjacent noise detector 11 comprises a band-pass filter 12, a level detector 13, a comparator 14 and a reference DC level unit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver, for example, an FM receiver having an AGC (Automatic Gain Control) circuit.

[0002]

2. Description of the Related Art FM (Frequency Modulation) broadcasting is widely used for broadcasting programs requiring high sound quality while minimizing the influence of noise such as music programs. The FM system is also used for transmitting and receiving audio signals of TV (television) broadcasting. Since FM broadcasting requires a relatively wide frequency band and the frequency range is relatively narrow, noise (interference) between a desired station and an adjacent station as the number of FM broadcasting stations increases.
And the like. The prior art relating to the transmission and reception of the FM system is disclosed in, for example, Japanese Unexamined Patent Application Publication No. HEI 5-221175, "In-Vehicle Antenna Amplifier Device" and Japanese Unexamined Patent Publication No. HEI 8-111648.
No. 6,098,098, which is incorporated herein by reference.

FIG. 3 is a block diagram showing a configuration of a conventional FM receiver. This FM receiver comprises an antenna 1, a tuning circuit 2, an RF (radio frequency) amplifier 3, a mixer 4, an IF
It comprises T (intermediate frequency transformer) 5, filters 6, 8, IF amplifier 7, limiter amplifier (amplitude limiter) 9, FM detector 10, level detector 15, and AGC circuit 19. The AGC circuit 19 includes an AGC amplifier 17 and a level detector 18.

In the FM receiver shown in FIG. 3, antennas 1 to FM detector 10 are sequentially connected in cascade.
The input terminal of the level detector 15 is connected to the limiter amplifier 9, and the output is input to the AGC amplifier 17 of the AGC circuit 19. The output of the mixer 4 is also supplied to the AGC amplifier 17.
Is input to The output of the AGC amplifier 17 is input to the level detector 18. The output of the level detector 18 is input to the tuning circuit 2 and the RF amplifier 3.

[0005] An antenna 1 selects a plurality of FM signals included in a received FM radio wave via a tuning circuit 2, inputs a desired FM signal to an RF amplifier 3, and amplifies the signal to a predetermined level. Here, the RF amplifier 3 generally has a dual gate MOSFET (MOS type field effect transistor).
Is used. The FM signal output from the RF amplifier 3 is input to the mixer 4 and mixed (mixed) with a local oscillation signal from a local oscillator (not shown) to obtain an IF signal having a predetermined IF frequency (for example, 10.7 MHz). Generate a signal. This IF signal is amplified by an IF amplifier 7 via an IFT 5 and a filter 6 which is, for example, a ceramic filter. The amplified IF signal is input to a limiter amplifier 9 via another filter 8 which is, for example, a ceramic filter. An output signal having a constant amplitude output from the limiter amplifier 9 is subjected to FM detection by an FM detector 10, and an audio signal is extracted from the IF signal.

[0006] As described above, the output signal of the mixer 4 is AG
The output signal is also input to the C amplifier 17, and the output signal is input to the tuning circuit 2 including, for example, a PIN diode and the RF amplifier 3 via the level detector 18. Level detector 1
The output 8 drives the PIN diode of the tuning circuit 2 and is input to the gate of the dual gate MOSFET of the RF amplifier 3. In addition, the level detector 15 connected to the limiter amplifier 9 outputs a DC signal (that is, a DC signal) corresponding to the intensity (reception intensity) of the FM signal input to the limiter amplifier 9.
Level meter output). The level meter output is used for various controls of the FM receiver, and one of them is used for gain control of the AGC amplifier 17.

A case where the antenna 1 simultaneously receives a desired wave (FM signal) and an interfering wave (including signals other than the desired wave) in a conventional FM receiver having the configuration shown in FIG. 3 will be described. In this case, these wanted and disturbing waves are
From the output of the mixer 4, the AGC amplifier 17 of the AGC circuit 19
Is input to the level detector 18 via the. When the signal strength of any one of the amplified desired wave and the interfering wave exceeds the level set in advance by the level detector 18, the two direct current signals (DC signals) are output from the level detector 18.
Is output. One DC signal is the tuning circuit 2 described above.
, And attenuates the signal input from the antenna 1. The other DC signal lowers the gain of the RF amplifier 3 and suppresses and controls the sensitivity.

Here, if the received desired wave is significantly smaller than the interfering wave, the desired wave cannot be received due to sensitivity suppression. In order to improve this situation, the level detector 15
The gain of the AGC amplifier 17 is controlled using the level meter output according to the intensity of the desired wave from the AGC amplifier 17. The gain control of the AGC amplifier 17 will be described with reference to FIG. FIG.
(A) shows the AGC sensitivity of A when the desired wave is small and B when the desired wave is large. If the desired signal is small, the gain of the AGC amplifier 17 is lowered and the level detector 18
Signal level (AGC sensitivity) of DC signal output from
Is smaller than the AGC sensitivity of B when the desired wave is large.

[0009]

The conventional FM shown in FIG.
In the receiver, the band characteristics of the level meter output are determined by the filters 6 and 8. FIG. 4 (B) shows the filter 6,
8 and the desired wave 2 in this band characteristic 23
1 and an interference wave 22 are shown. That is, when the desired wave 21 and the interference wave 22 are present in the band characteristic 23, the output of the level meter, which should originally respond to only the desired wave 21, becomes the interference wave 2
2 As a result, although the desired wave is small, the AGC sensitivity is set to be large by the larger interference wave 22, the sensitivity is suppressed excessively, and it becomes difficult to receive the desired wave 21 properly. there were.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the prior art, and has as its object to provide an FM receiver capable of obtaining a good reception state even when a desired wave and an interfering wave are present. I do.

[0011]

In order to solve the above-mentioned problems, an FM receiver according to the present invention employs the following characteristic configuration.

(1) An FM receiver including a tuning circuit and an RF amplifier for selecting and amplifying a signal received from an antenna, and detecting the FM detector and controlling the tuning circuit and the RF amplifier via an AGC circuit. , An FM receiver including an adjacent noise detector that detects adjacent noise included in an output signal of the FM detector and controls the AGC circuit.

(2) The adjacent noise detector includes a bandpass filter for detecting the adjacent noise, a level detector for converting an output of the bandpass filter into a DC signal, and a DC signal output from the level detector. The FM receiver according to (1), further including a comparator for comparing with a reference DC level.

(3) The FM receiver according to (2), wherein the AGC circuit sets a maximum gain when a DC signal to the comparator of the adjacent noise detector exceeds the DC level.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a preferred embodiment of an FM receiver according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a preferred embodiment of an FM receiver according to the present invention. Note that, for convenience of description, the same reference numerals are used for components corresponding to the above-described components of the related art. In addition, detailed description of the same components will be omitted, and the description will focus on the differences.

This FM receiver comprises an antenna 1, a tuning circuit 2, an RF amplifier 3, a mixer 4, an IFT 5, a filter 6,
8, IF amplifier 7, limiter amplifier 9, FM detector 1
0, the level detector 15 and the AGC circuit 19 are provided, and the AGC circuit 19 is the same as the conventional FM receiver shown in FIG. 3 by including the AGC amplifier 17 and the level detector 18. However, the FM receiver of the present invention
The difference is that an adjacent noise detector 11 connected between the detector 10 and the AGC circuit 19 is provided.

The above-described adjacent noise detector 11 includes a band-pass (band-pass) filter 12, a level detector 13, a comparator 14, and a reference DC level (DC level) for inputting a reference voltage to a reference input terminal of the comparator 14. Generator) 16
It consists of. The bandpass filter 12 receives the output signal of the FM detector 10 as an input, and inputs the output signal to the level detector 13. This level detector 13 has a DC
The output signal is input to a comparison input terminal of a comparator 14, which compares the output signal with a reference DC level 16 input to a reference (or reference) input terminal. The output signal of the comparator 14 is input to the AGC amplifier 17 of the AGC circuit 19 and controls the gain.

The operation of the FM receiver shown in FIG. 1, particularly the operation of the adjacent noise detector 11, will be described. Adjacent noise detector 11
Converts an audio signal output from the FM detector 10 through a band-pass filter 12 for detecting adjacent noise into a DC signal, and outputs a control signal for controlling the AGC circuit 19.

FIG. 2 shows the frequency spectrum of the output signal of the FM detector 10 when the electric field strength of the broadcasting station 100 kHz next to the desired station (wave) or the broadcasting station 150 kHz away from the desired station (wave) is large. That is, the main (main) signal of 50 Hz to 15 kHz is added to the detection output of the FM detector 10.
A SUB (sub) signal of 3 kHz to 53 kHz and a spectrum (adjacent noise) 24 of an adjacent broadcasting station appear.

Therefore, the adjacent noise detector 11 of the FM receiver according to the present embodiment selectively detects the spectrum 24 of the adjacent broadcasting station included in the output of the FM detector 10 by the band-pass filter 12, and performs level detection. 13 to determine the level. The DC signal output from the level detector 13 is input to one input terminal of a comparator 14 and is compared with a predetermined constant reference DC level 16 which is a reference voltage input to the other input terminal. I do. When the DC signal of the level detector 13 exceeds this constant DC level 16,
A control signal is output to the AGC amplifier 17 of the AGC circuit 19, and the gain of the AGC amplifier 17 is set to a preset maximum gain. As a result, even if the electric field strength of the desired disturbing station is weak in the electric field strength of the adjacent disturbing station in the unobstructed state, the radio wave of the desired station can be received in a good state without being suppressed by the AGC. As described above, in the FM receiver according to the embodiment of the present invention, if an interfering wave exists near the frequency band of the desired wave at the subsequent stage of the FM detector, adjacent noise (interference) detection for detecting the interfering wave is performed. When the electric field strength is such that the interference wave does not disturb the desired station, the AGC sensitivity of the AGC circuit is set small, and the AGC sensitivity is increased only when interference occurs. Yes, it is possible to receive a desired wave well.

The configuration and operation of the preferred embodiment of the FM receiver according to the present invention have been described above. However, such an embodiment is merely an example of the present invention and does not limit the present invention in any way. It can be easily understood by those skilled in the art that various modifications can be made according to the specific application without departing from the gist of the present invention.

[0023]

As will be understood from the above description, according to the FM receiver of the present invention, sensitivity suppression can always be set to be optimal. As a result, it is possible to satisfactorily receive the desired wave.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main configuration of a preferred embodiment of an FM receiver according to the present invention.

FIG. 2 is a diagram showing a frequency spectrum of an output of the FM detector in FIG. 1;

FIG. 3 is a block diagram illustrating a main configuration of a conventional FM receiver.

FIG. 4 is an explanatory diagram of the operation of the FM receiver in FIG. 3;
Shows the AGC sensitivity characteristic, and (B) shows the relationship between the bandpass filter and the desired wave and the adjacent interference wave.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 tuning circuit 3 RF amplifier 10 FM detector 11 adjacent noise detector 12 bandpass filter 13 level detector 14 comparator 16 DC (reference) level 17 AGC amplifier 18 level detector 19 AGC circuit 24 interference spectrum of adjacent station (Adjacent noise)

Claims (3)

[Claims] An FM receiver including a tuning circuit and an RF amplifier for selecting and amplifying a signal received from an antenna, detecting the FM detector and controlling the tuning circuit and the RF amplifier via an AGC circuit. An FM receiver comprising: an adjacent noise detector that detects adjacent noise included in an output signal of the FM detector and controls the AGC circuit. 2. An adjacent noise detector, comprising: a band-pass filter for detecting the adjacent noise; a level detector for converting an output of the band-pass filter into a DC signal; and a DC signal output from the level detector. The FM receiver according to claim 1, further comprising a comparator for comparing the DC level. 3. The FM receiver according to claim 2, wherein the AGC circuit sets the maximum gain when a DC signal to the comparator of the adjacent noise detector exceeds the DC level. .