JP2747145B2 - Interference signal detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference signal detecting device incorporated in a tuner or the like.

[0002]

2. Description of the Related Art First, a case where a conventional interference detection device is applied to an FM tuner will be described as an example. In the FM tuner, the reception state changes depending on the place, and particularly, a reflected wave from a building or a mountain (hereinafter, referred to as multipath interference).
The sound quality is degraded due to such interference signals.

FIG. 11 is a block diagram showing a conventional interference signal detecting device for detecting this multipath interference.
The signal received at the antenna input 51 is input to the high frequency amplifier 52, amplified, and then input to the MIX circuit 53. The output terminal 9 of the preceding block including the high-frequency amplifier 52 and the MIX circuit 53 is input to the intermediate frequency amplifier 5. The intermediate frequency amplifier 5 includes an amplifier 1, an amplifier 2, an amplifier 3, and an amplifier 4. The first level detector 50 outputs an intermediate frequency signal (IF signal;
rectifies the rmediate frequency signal). The output of the first level detector 50 is input to a second level detector 7 for detecting an audio frequency band signal generated at the time of multipath interference, and the output 8 of the second level detector 7 is multipath It becomes the detection output terminal.

[0004] In the interference signal detecting device configured as described above, the received signal input from the antenna input 51 is amplified by the high frequency amplifier 52,
It is converted to an intermediate frequency signal having a carrier of 0.7 MHz. The intermediate frequency signal is amplified by the intermediate frequency amplifier 5.

A plurality of intermediate frequency amplifiers 5 (four in the illustrated example)
) Amplifiers 1, 2, 3, and 4 are connected in series. Normally, amplifiers 1-4 use the same gain amplifier,
The gain of the intermediate frequency amplification unit 5 is generally 60 to 70 dB as the sum of the gains of the amplifiers 1 to 4, and is connected to the next FM detection stage. The outputs of the amplifiers 1 to 4 are connected to the first level detector 50, and the sum of the outputs of the amplifiers 1 to 4 is rectified by the first level detector 50 and converted into a DC voltage. The output of the first level detector 50 is a signal meter signal indicating the level of the received signal.

The curve a in FIG. 3 shows the output characteristic of the first level detector 50 with respect to the input level at the terminal 9 in FIG. Normally, the amplifiers 1-4 use differential amplifiers,
The input dynamic range of amplifiers 1-4 is 0.1Vpeak
Therefore, the first level detector 50 can detect the input signal level of the first stage amplifier 1 of the intermediate frequency amplifier 5 up to 0.1 Vpeak.

FIG. 3 shows the input level of the terminal 9 versus the signal meter voltage characteristic of FIG. In FIG. 3, the input level of the terminal 9 at the Vin5 point is the input dynamic range level a of the amplifier 1, Vin4 is the input dynamic range of the amplifier 2,
n3 is the dynamic range of amplifier 3 and Vin2 is amplifier 4
Input dynamic range. When the input level of the terminal 9 is equal to or less than the input dynamic range of the amplifier 1 and there is no normal multipath, as shown by a curve a in FIG. 12, the output of the first level detector 50 has only the DC voltage component. It is. However, when there is multipath interference,
The level of the intermediate frequency signal at the input terminal 9 of the intermediate frequency amplifier 5 changes due to the multipath interference signal, and the change, that is, the AC component, of the first level detector 50 is changed as shown by the curve b in FIG. Output to the output terminal.

Therefore, in the conventional device, the AC component output to the output of the first level detector 50 is detected by the second level detector 7. This second level detector 7
Is a multipath interference detection signal. This multipath interference detection signal reduces the noise that causes problems in the stereo state by deteriorating the separation, operates a high-cut filter to reduce high-frequency noise, and forcibly applies muting. Control is performed to improve the audibility of multipath interference.

The output of the first level detector 50 is a signal meter voltage. Conventionally, multipath interference detection is performed based on the signal meter voltage.

Further, the above-described multipath interference detection performs the same operation with respect to interference caused by a signal adjacent to a desired received signal.

[0011]

However, in this conventional interference signal detecting device, the interference signal is detected by the AC component of the signal meter voltage (output of the first level detector 50). For this reason, since the detection is performed up to the level of the input dynamic range (input dynamic range of the amplifier 1) of the terminal 9 which is the input terminal of the intermediate frequency amplifier 5, even a strong electric field is detected. However, the disturbing signal becomes a problem especially when the electric field is weak and the electric field is unstable.
There is almost no problem during a strong electric field.

As described above, in the conventional interference signal detecting device, even a strong electric field is detected, and the separation, the high-frequency characteristic, and the muting characteristic are controlled, and the difference between the presence and absence of the interference signal is large. However, there is a problem that it is very difficult to hear.

The present invention has been made in view of the above problems, and has an effect of improving the audibility by controlling separation, high frequency characteristics, muting, and the like only in a weak electric field where multipath interference is a problem. It is an object of the present invention to provide an interference signal detection device excellent in the above.

[0014]

SUMMARY OF THE INVENTION An interference signal detecting apparatus according to the present invention comprises an intermediate frequency amplifying means in which a plurality of amplifiers for amplifying an intermediate frequency signal are connected in series, and the intermediate frequency amplifying means. And a level detector for detecting the magnitude of the output of any amplifier other than the first-stage amplifier among the amplifiers at each stage.

According to another aspect of the present invention, there is provided an interference signal detecting apparatus comprising: a plurality of amplifiers for amplifying an intermediate frequency signal connected in series; and an amplifier at each stage constituting the intermediate frequency amplifying means. And a level detector for detecting the sum of the magnitudes of the outputs of a plurality of arbitrary amplifiers other than the first-stage amplifier.

[0016]

In the present invention, the level detector detects the magnitude of the output of any amplifier other than the first-stage amplifier or the sum of the magnitudes of the outputs of any of a plurality of amplifiers. The level of the signal to be adjusted can be adjusted arbitrarily. For this reason, it is possible to control the signal control separation, high frequency characteristics, muting, and the like for the multipath only in the weak electric field, and it is possible to avoid unnecessary control in the strong electric field.

[0017]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an interference signal detecting apparatus according to a first embodiment of the present invention. In the present embodiment,
An intermediate frequency amplifying unit 5 including an amplifier 1, an amplifier 2, an amplifier 3 and an amplifier 4, a signal meter circuit 50 for detecting an input level of a terminal 9 from outputs of the amplifiers 1 to 4,
A first level detector 6 for rectifying the intermediate frequency signal and converting it to a DC voltage, and a second level detector 7 for detecting an AC component generated at the output of the first level detector 6 at the time of multipath interference. The output 8 of the second level detector 7 is used as a multipath detection output terminal. Since the signal meter circuit 50 is the same as the conventional one, the description is omitted.

In the conventional interference signal detecting device, since the output of the signal meter circuit 50 indicating the electric field intensity level is used, multipath is detected even up to a strong electric field.
On the other hand, in this embodiment, a first level detector 6 is provided as a detection circuit separately from the signal meter circuit 50.

That is, in the present embodiment, the intermediate frequency signal is amplified by the intermediate frequency amplifier 5. Since the intermediate frequency amplifying unit 5 is configured by connecting an amplifier 1, an amplifier 2, an amplifier 3, and an amplifier 4 in series, the gain of the intermediate frequency amplifying unit 5 is the sum of the gains of the amplifiers 1 to 4, and generally 60 ~ 70d
B is obtained, and the output of the intermediate frequency amplifier 5 is
Input to the M detection stage.

The outputs of the amplifiers 3 and 4 are input to the first level detector 6, and the sum of the outputs of the intermediate frequency signals of the amplifiers 3 and 4 is rectified by the first level detector 6. And converted to a DC voltage. Curve c in FIG.
Shows the output characteristic of the first level detector 6 with respect to the input level of the terminal 9.

FIG. 2 is a circuit diagram showing a specific configuration when the embodiment shown in FIG. 1 is realized using an IC. This circuit has a power supply 33, a power supply 46, and a bias resistor 45. The intermediate frequency amplifier 5 includes a transistor (hereinafter, Tr)
), An amplifier 1 composed of 11, Tr12, a resistor 13 and a constant current source 15, and Tr16, Tr17, a resistor 1
8 and a constant current source 20;
1, an amplifier 3 composed of Tr22, a resistor 23 and a constant current source 25, and an amplifier 4 composed of Tr26, Tr27, a resistor 28 and a constant current source 30. The first level detector 6 includes a first detection circuit including Trs 38, 39, 40 and a resistor 41 for detecting the output level of the amplifier 3, and Trs 34 and 35 for detecting the output level of the amplifier 4. It comprises a second detection circuit composed of a Tr and a resistor 37, and an output stage composed of Tr42, Tr43 and a resistance 44 for adding the output of the first detection circuit and the output of the second detection circuit. .
Further, the second level detector 7 includes a first level detector 6
Connected to the output.

Next, the operation of the apparatus of this embodiment having the above-described configuration will be described. First, in FIG. 3, the gain of the amplifier 1 is Av1, the gain of the amplifier 2 is Av2, the gain of the amplifier 3 is Av3, the gain of the amplifier 4 is Av4, the input dynamic range of the amplifier 1 is Vd1, and the input dynamic range of the amplifier 2 is Vd1. Is Vd2, the input dynamic range of the amplifier 3 is Vd3, and the input dynamic range of the amplifier 4 is Vd4.

The characteristic of the curve c in FIG. 3 is that when the input level of the terminal 9 becomes higher than Vin3, a level higher than the input dynamic range of the amplifier 3 is input to the amplifier 3.
Above 3, the output of the amplifier 3 is constant, and therefore the output of the first level detector 6 is constant. This indicates that the second level detector 6 cannot detect the voltage above Vin3. V
in3 is represented by the following equation 1.

[0025]

## EQU1 ## Vin3 = Vd3 / (Av1.Av2)

This is the same when multipath interference occurs. Even if the intermediate frequency signal level at the input terminal 9 changes due to the multipath interference, if the intermediate frequency signal level is higher than Vin3, the first level detector 6 detects it. No AC component is generated at the output of the first level detector 6. Thus, the second level detector 7 having the output of the first level detector 6 as an input
Does not generate an AC component and does not detect it as multipath interference. Therefore, by controlling the separation, the high frequency characteristic and the muting characteristic by the output of the second level detector 7, the control is not performed when the intermediate frequency signal level at the input terminal 9 is higher than Vin3.

From equation (1), Vin3 can be set by the gains Av1 and Av2 of the amplifiers 1 and 2, and the input dynamic range Vd3 of the amplifier 3, so that the control setting for the multipath interference with the electric field strength is easy.

The signal meter voltage in this embodiment is
As in the prior art, the first level detector 6 of the present invention can be shared with the signal meter circuit 50 to detect the outputs of the amplifiers 1 to 4.

Also, when there is interference due to a signal adjacent to the desired received signal, a change in the intermediate frequency signal level at the input terminal 9 is detected and control for the interference is performed as in the case of multipath interference. By not detecting a change in the intermediate frequency signal level at the input terminal 9 in a strong electric field that does not result in a weak electric field, it is possible to control only a weak electric field in which interference by an adjacent signal is particularly problematic.

FIG. 4 is a block diagram showing a second embodiment of the present invention. The blocks constituting the system are the same as those in the first embodiment described above, and this embodiment is different from the first embodiment in that the output of only the amplifier 4 is detected by the first level detector 6. The relationship between the output of the first level detector 6 and the input level of the input terminal 9 in FIG. 4 is as shown by the curve d in FIG. 3, and no multipath is detected when the input electric field strength is higher than Vin2. This Vin2 is represented by the following equation (2).

[0031]

## EQU2 ## Vin2 = Vd4 / (Av1, Av2, Av3)

As compared with the first embodiment described above, signal control of multipath interference with only a weak electric field becomes possible.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention. The blocks constituting the system are the same as those in the first embodiment described above. This embodiment is different from the first embodiment in that the outputs of the amplifiers 2, 3, and 4 are detected by the first level detector 6. This is different from the first embodiment. The relationship between the output of the first level detector 6 in FIG. 5 and the input level of the input terminal 9 is shown by a curve b in FIG. 3, and no multipath is detected when the input electric field strength is higher than Vin4. Vin
4 is represented by the following equation (3).

[0034]

## EQU3 ## Vin4 = Vd2 / Av1

As compared with the above-described first embodiment, signal control of multipath interference can be performed up to a region where the electric field is relatively strong.

FIG. 6 is a block diagram showing a fourth embodiment of the present invention. The blocks constituting the system are the same as those in the first embodiment, and only the output of the amplifier 3 is connected to the first embodiment.
Is different from that of the first embodiment in that it is detected by the level detector 6. The output of the first level detector 6 in FIG.
The relationship between the input levels is shown by the curve a in FIG. 7, and the total gains Av1, Av2, Av3 of the amplifiers 1 to 3 and the first
From the level detection start point Vs of the first level detector 6 determined by the detection capability of the level detector 6 to the electric field strength up to Vin3 (the same as in Expression 1), signal control of multipath interference becomes possible.

FIG. 8 is a block diagram showing a fifth embodiment of the present invention. The blocks constituting the system are the same as those in the first embodiment, but the intermediate frequency amplifying section 5 is composed of n amplifiers 1 to n. Therefore, the level Vn of the input terminal 9 capable of controlling the signal of the multipath interference is expressed by the following equation (4).

[0038]

Vn = Vd (n-1) / (Av1... Av (n-1) · Avn)

Here, Vd (n-1) is the input dynamic range of the amplifier (n-1). As described above, the range of the multipath interference countermeasures can be set freely according to the number of amplifiers constituting the intermediate frequency amplifier 5.

FIG. 9 is a block diagram showing a sixth embodiment of the present invention. In this embodiment, an intermediate frequency amplifying section 5 composed of amplifiers 1 to 4, a first level detector 6 for detecting the output level of the amplifier 4, and a first level detector when there is multipath interference. 6 for detecting the AC component generated in
Level detector 7 and a third detector for detecting the level of the amplifier 3
, A fourth level detector 7 ′ for detecting an AC component generated in the third level detector 6 ′ when there is multipath interference, and an output of the second level detector 7. And an adder 49 for adding the output of the fourth level detector 7 '
And the output of the adder 49 becomes the multipath interference detection output.

The output signal of the adder 49 controls the separation, the high-frequency characteristic and the muting so that the output of the multipath interference detection of the weak electric field less than the input dynamic range of the amplifier 4 is output to the second level detector. 7 becomes dominant, and the multipath interference detection output in the weak electric field to the medium electric field which is equal to or less than the input dynamic range of the amplifier 3 becomes the second output because the output of the fourth level detector 7 ′ becomes dominant. By changing the gains of the level detector 7 and the fourth level detector 7 ', it is possible to control the multipath stepwise according to the input electric field strength. Since the influence of the multipath becomes smaller as the electric field becomes stronger, the gain of the fourth level detector 7 'is made smaller than the gain of the second level detector 7, so that the control is increased at the time of the weak electric field.
It is possible to reduce the control when the electric field is weak to medium.

With respect to the embodiment of FIG. 1, an example of a range in which multipath interference is detected will be described. The amplifiers 1-4 have the same configuration, and the input dynamic range is 0.1
Assuming that Vpeak and the amplification factor are 10 times, the limit level of multipath interference detection is 0.1 V / 10 ×
10 = 1 mV, which is equivalent to 700 μVrms (5
7 dBμV). As a result, at the level of 57 dBμV or more at the input terminal 9, the control of the multipath interference is not performed. Here, assuming that the total gain of the high-frequency amplifier and the MIX circuit in the preceding stage of the intermediate frequency amplifying unit 5 is 27 dB, at an electric field strength of 30 dBμV or more at the antenna input,
It does not control multipath interference. When the same calculation is performed for the conventional interference signal detection device, multipath interference is controlled up to an electric field strength of 70 dBμV or less.

Here, as an example of the multipath interference, it is assumed that the building causes the multipath interference when receiving a strong electric field near a broadcasting station in a city. Desired signal is 65dBμ
V, when the multipath interference is set to 50 dBμV, in the FM, the AC component of the carrier wave due to the multipath is removed by the limiter effect.
Since control is performed to BμV, unnecessary control has caused temporary fluctuations in sound volume, deterioration of sound quality such as monauralization and narrowing of the band even in a strong electric field. However, in this embodiment, the control of the multipath disturbance is not performed at the electric field strength of 30 dBμV or more. Therefore, according to the present embodiment, the control is performed only when the sound quality is reduced in a weak electric field where the limiter effect of 30 dBμV or less is reduced, that is, when the stereo-monaural switching is unpleasant, the relative increase in the high frequency noise occurs, and the like. It is possible to do.

FIG. 10 is a circuit diagram showing a specific configuration of the apparatus of this embodiment using an IC. The signal meter circuit 50 for detecting the signal meter voltage of the related art shares the embodiment of the present invention shown in FIG. It was made. The first level detector 6 in FIG. 1 includes Tr66, Tr67, Tr68,
Tr69, Tr74, Tr76, resistor 75, resistor 77,
It comprises Trs 90 and 91 and a resistor 29, and its output end 93 is connected to the second level detector 7. Also, Tr66, Tr67, Tr68, Tr69, Tr7
0, Tr72, Tr78, Tr79, Tr82, Tr8
4, Tr86, Tr87, power supply 65, resistor 71, resistor 7
A signal metered circuit 50 for detecting the signal meter voltage is constituted by the resistor 81, the resistor 81, the resistor 85, and the resistor 88, and a terminal 89 outputs the signal meter voltage.
Thus, the conventional signal meter voltage and the circuit of the first level detector 6 can be shared, and the increase in the number of elements is reduced.

In the case where the above-described IC is used, the number of elements of the circuit is increased by about 10 to 20 and the chip area is increased by about 0.01 to 0.02 mm ^{2 as} compared with the related art. This hardly affects the size of a normal tuner IC chip of 10 to 15 mm ² , and the present invention is extremely practical and has excellent effects.

[0046]

As described above, according to the present invention,
Signal control separation, high frequency characteristics, muting, and the like for multipath can be realized only in a weak electric field in which multipath interference is a problem.

In particular, when a weak signal adjacent to the desired received signal is relatively large, interference interference due to the adjacent signal is reduced, while unnecessary control is not performed when the desired received signal is strong. It is possible.

In addition, it is possible to set the critical point of operation and non-operation of the control function defined by the electric field strength or the received signal strength in a wide range in design. Since the detection circuit for the meter voltage can be shared, the number of elements hardly increases.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a disturbance signal detection device according to a first embodiment.

FIG. 2 is a circuit diagram showing a specific configuration of a disturbance signal detection device according to the embodiment of FIG. 1 of the present invention.

FIG. 3 is a graph showing characteristics of a first level detection output with respect to an input level of a terminal 9 according to the present invention.

FIG. 4 is a block diagram showing a disturbance signal detection device according to a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating a disturbance signal detection device according to a third embodiment of the present invention.

FIG. 6 is a block diagram illustrating a disturbance signal detection device according to a fourth embodiment of the present invention.

FIG. 7 is a graph showing the first level detection output characteristic.

FIG. 8 is a block diagram showing a disturbance signal detection device according to a fifth embodiment of the present invention.

FIG. 9 is a block diagram showing a jamming signal detection device according to a sixth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a specific configuration of a disturbance signal detection device according to an embodiment of the present invention.

FIG. 11 is a block diagram showing a conventional interference detection device.

FIG. 12 is a graph showing characteristics of a conventional signal meter output.

[Explanation of symbols]

1 to 4; amplifier 5; intermediate frequency amplifier 6,50; first level detector 7; second level detector 8; output terminals 11, 12, 16, 17, 21, 22, 26, 27, 3
4, 35, 36, 38, 39, 40, 42, 43; transistors 13, 18, 23, 28, 37, 41, 44, 45; resistors 15, 20, 25, 30; constant current sources 33, 46, 47 Constant voltage sources 31, 32; capacity

Claims (3)

(57) [Claims] 1. An intermediate frequency amplifying means comprising a plurality of amplifiers for amplifying an intermediate frequency signal connected in series, and an arbitrary amplifier other than the first-stage amplifier among the amplifiers of each stage constituting the intermediate frequency amplifying means. A level detector for detecting the magnitude of the output of the interference signal. 2. An intermediate frequency amplifying means comprising a plurality of amplifiers for amplifying an intermediate frequency signal connected in series, and a plurality of arbitrary amplifiers other than the first-stage amplifier among the amplifiers of each stage constituting the intermediate frequency amplifying means. A level detector for detecting the sum of the magnitudes of the outputs of the amplifiers. 3. A signal meter circuit for detecting a signal representative of an added value of the magnitude of the output of all amplifiers including the first stage among the amplifiers of each stage constituting the intermediate frequency amplifying means. Item 3. The interference signal detection device according to Item 1 or 2.