JP2583758B2 - Multipath interference detection circuit - Google Patents

Description

Description: A. INDUSTRIAL APPLICATION The present invention relates to a multipath interference detection circuit in a stereo receiver that controls the frequency gain and / or separation of a stereo demodulation circuit by a signal meter voltage.

B. Summary of the Invention The signal meter voltage is compared with a window comparator by ± ΔV from the DC voltage at the input electric field strength indicating the dip point at which the level of the AC component included in the signal meter voltage attenuates instantaneously.
Only in a predetermined voltage range, the amplification degree of the AC component included in the signal meter voltage is increased.

C. Conventional technology In-vehicle FM receivers receive FM broadcasts that are affected by multipath fading that causes amplitude fluctuations according to the Rayleigh distribution law.
Reception quality is significantly degraded. In order to reduce this noise, the on-vehicle FM receiver is trying to improve the S / N ratio by automatically controlling the frequency gain characteristics and the degree of separation characteristics for multipath fading.

FIG. 4 is a block diagram showing the configuration of a stereo detection stage of an FM receiver including a conventional sound field control circuit. In FIG. 4, a portion surrounded by a dashed line is a sound field control circuit 1, and 2 is an intermediate frequency. Reference numeral 3 denotes an intermediate frequency amplifier / detector IC, 4 denotes a stereo detector (multiplexer), 5 denotes a left channel audio output, 6 denotes a right channel audio output, 7 denotes a signal meter voltage terminal, and 8 denotes a control voltage generating circuit. .

That is, for sound field control, as shown in FIG. 4, the voltage appearing at the signal meter voltage terminal 7 included in the intermediate frequency amplifier / detector IC 2, that is, the broadcast radio wave is level-detected, and the strength of the radio wave is detected. Utilize the signal meter voltage obtained from a circuit that converts it to a voltage proportional to the voltage. Then, when multipath fading accompanied by amplitude fluctuation occurs, a sharp voltage change appears in the signal meter voltage due to the amplitude fluctuation. The sound field control circuit 1 detects this change, and generates a voltage for controlling the degree of separation and the frequency gain characteristic according to the amount of the change.

However, the detection output component wraps around the signal meter voltage. Therefore, if the detection output component is larger than the amplitude fluctuation component due to multipath fading, the detection output component may obscure the amplitude fluctuation component and make detection impossible. Therefore, the detection output component is limited by a high-pass filter or the like so as not to be input, but it is not always sufficient.

In a method of detecting an amplitude fluctuation component due to multipath interference superimposed on a signal meter voltage, lowering the signal meter voltage depending on its magnitude, and controlling the degree of isolation and frequency gain characteristics, as shown in FIG. The degree of separation is measured by the measurement method. In FIG. 5, 9 is an audio oscillator (frequency f ₁ ), 10 is a stereo modulator, 11 is a standard signal generator (FM), 12 is an audio oscillator (frequency f ₀ ), 13
Denotes an AM modulator, and 14 denotes a receiver. That is, the frequency f
FM modulation at ₁ (in stereo state) and at frequency f ₀
Apply AM-modulated FM-modulated radio waves to the receiver,
Measure the degree of separation.

Multipath disturbance is amplitude distortion (the carrier amplitude changes)
And phase distortion (the phase of the carrier wave changes). In this measurement, amplitude distortion is intentionally generated. This is FM
This can be easily achieved by AM-modulating the modulated radio wave. The speed (number of times) of the amplitude distortion can be adjusted by the frequency f ₀ . The degree (magnitude) of the amplitude distortion can be adjusted by setting the magnitude of the AM modulation degree.

When the AC component included in the signal meter voltage is measured by the receiver 14, it has been confirmed that the characteristics shown in FIG. 6 are obtained according to the input electric field strength. This depends on the circuit configuration that produces the signal meter voltage included in IF IC3. In FIG. 6, and indicate AM modulation degrees of 0 respectively.
%, 30% and 60% represent the AC component included in the signal meter voltage.

The magnitude of the AM modulation degree represents the magnitude of multipath interference, and 0% is a state when multipath interference is not received. That is, a signal superimposed on the signal meter voltage of the audio output, which is a detection output, appears. When the AM modulation degree is increased, an amplitude fluctuation component due to multipath interference is further added, and the alternating current changes from 0% to 30% and 60%. Ingredients increase.

The control voltage generating circuit 8 shown in FIG. 4 detects these AC components superimposed on the signal meter voltage, and generates a control voltage depending on the magnitude.

FIG. 7 is a block diagram showing a detailed configuration of the control voltage generating circuit 8 of FIG. 4. In FIG. 7, 15 is an amplifier, 16 is a detection level setting circuit, 17 is a negative detector, 18 is an adder, and 19 is Indicates a control voltage output terminal. The circuit shown in FIG. 7 operates as follows.

The amplifier 15 detects and amplifies an AC component included in the signal meter voltage. Next, the detection level setting circuit 16
In the state of FIG. 6 (AM modulation = 0%), a threshold level is provided so that the input signal meter voltage becomes the control output voltage as it is. If there is an input higher than the threshold level, the negative detector 17 performs negative detection, adds the input signal meter voltage and the negative voltage, and lowers the control output voltage to perform the isolation and high cut control operation. To

FIG. 8 shows the characteristics of the degree of separation with respect to the input electric field intensity when the AM modulation degree is changed by the measuring system shown in FIG. 5 using a receiver having the characteristics shown in FIG.

Shown in Figure 6, the maximum AC component = V ₀ (mV) is the threshold level when the AM degree = 0%, the V ₀ is not negative detection is below the negative detection at greater than or equal _to V _0. That is, when the AM modulation degree is 30%, negative detection is not performed at the electric field intensity c 'or lower. Accordingly, the control voltage is the same as the signal meter voltage at the time of AM modulation ratio = 0%, and becomes the control output voltage. Therefore, the degree of separation characteristic shows the same value as AM degree = 0% below c ′. Further, when the AM modulation degree is 60%, the electric field intensity is below the threshold level between the electric field intensities a'-b ', and negative detection is performed only in that section. However, in practice, some negative detection is performed, so that the degree of separation is actually inferior to the degree of separation at the time of AM modulation = 0%.

D. Problems to be Solved by the Invention As described above, in order for the AC component included in the signal meter voltage to indicate a dip point as shown in FIG. 6 according to the input electric field strength, the degree of separation and the high cut are controlled. Since the voltage changes in the same manner, the control varies. Further, such a phenomenon that a certain section has a degree of separation, such as AM modulation degree = 60%, occurs. Basically, it is desirable that the degree of separation is not maintained at 60%, so that the detection level can be easily set.

An object of the present invention is to provide a configuration in which the amplitude fluctuation component due to multipath disturbance included in the signal meter voltage has no dip point where the level is instantaneously attenuated as shown in FIG. An object of the present invention is to provide a multipath interference detection circuit which makes it easy to set a detection level of a component and makes a separation characteristic by a control output voltage show a characteristic according to the magnitude of AM modulation.

E. Means for Solving the Problems In order to achieve the above object, a multipath disturbance detection circuit of the kind mentioned at the outset according to the invention is provided by means of a control voltage based on a signal meter signal, the frequency gain of a stereo demodulation circuit and / or A stereo broadcast receiver for controlling the degree of separation, a means for extracting an audio component signal from the signal meter signal, and an electric field strength based on the signal meter signal being equal to or higher than a first level and equal to or lower than a second level. Level detecting means for detecting that the audio component signal has been adjusted based on the output of the level detecting means, and outputting the audio component signal whose level has been adjusted from the signal meter signal. And a subtraction means for outputting the control voltage by subtraction.

F. Action Set the window comparator so that only signals near the dip point pass. The signals passing through the window comparator operate the changeover switch so that only those signals undergo amplification.

G. Examples Hereinafter, the present invention will be described in more detail by way of examples with reference to the drawings, but these are merely examples, and various modifications and improvements can be made without departing from the scope of the present invention. Of course, this is possible.

FIG. 1 is a block diagram showing a configuration of a multipath interference detection circuit according to the present invention. In the drawing, reference numerals common to FIG. 7 indicate the same or corresponding parts as in FIG. 20 is a buffer amplifier, 21 is a changeover switch control circuit, 22 is a changeover switch, and 23 is a first amplifier.

That is, the present invention utilizes a signal meter voltage which is basically proportional to the electric field strength of the broadcast radio wave shown in FIG.

The AC component included in the signal meter voltage shown in FIG. 6 indicates a dip point when the input electric field strength is point b.
The multipath interference detection circuit according to the present invention detects that the input electric field intensity is near point b, and increases the amplification at that time. As a result, the characteristics shown in FIG. 3 are obtained.

A voltage V _{0 at} which the signal meter voltage indicates the electric field strength at point b.
To detect that it is now near, the comparator 24a with a reference voltages V _1, V _2, utilizes a window comparator 24 consisting 24b.
That is, the region of V ₀ ± ΔV (V ₁ = V ₀ + ΔV, V ₂ = V ₀ −Δ
The output of the window comparator attains the "H" level when the voltage is within V), and the output sets the changeover switch 22 to the route where the first amplifier 23 is located. When the output of the window comparator 24 is at "L" level, the changeover switch 22 is set so that the first amplifier 23 does not enter. The gain of the first amplifier 23 is appropriately set (about 3 to 6 dB).

H. Effects of the Invention As described above, according to the present invention, it is easy to detect an amplitude fluctuation component included in a signal meter voltage due to multipath interference, and it is relatively easy to set a detection level thereof. / The advantage that the setting of the high cut operation amount is simplified is also obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a multipath interference detection circuit according to the present invention, FIG. 2 is a graph showing the relationship between input electric field strength and signal meter DC voltage, and FIG. 3 is obtained by a control voltage generating circuit according to the present invention. FIG. 4 is a block diagram showing a configuration of a sound field control circuit, FIG. 5 is a block diagram of a measurement circuit for a multipath interference suppression system, FIG. 6 is a diagram showing an AC component included in a signal meter voltage, and FIG. FIG. 7 is a block diagram of a conventional control voltage generating circuit, and FIG. 8 is a diagram showing the characteristics of the degree of separation with respect to the input electric field intensity when the AM modulation degree is changed. 1 ... Sound field control circuit, 2 ... Intermediate frequency input, 3 ... Intermediate frequency amplifier / detector IC, 4 ... Stereo detector (multiplexer), 5 ... Left channel audio output, 6
...... right channel audio output, 7 ...... signal meter voltage terminal, 8 ...... control voltage generating circuit, 9 ...... audio oscillator (frequency f _1), 10 ...... stereo modulator, 11 ...
... signal generator (FM), 12 ...... audio oscillator (frequency f _0), 13 ...... AM modulator 14 ...... receiver, 15 ...... amplification unit, 16 ...... detection level setting circuit, 17 ...... Negative detector, 18
... An adder, 19 a control voltage output terminal, 20 a buffer amplifier, 21 a changeover switch control circuit, 22 a changeover switch, and 23 a first amplifier.

Claims (1)

(57) [Claims] 1. A stereo broadcast receiver for controlling a frequency gain and / or a degree of separation of a stainless steel demodulation circuit by a control voltage based on a signal meter signal, comprising: means for extracting an audio component signal from the signal meter signal; Level detecting means for detecting that the electric field strength is equal to or higher than the first level and equal to or lower than the second level based on the meter signal; and adjusting the level of the audio component signal based on the output of the level detecting means. A multipath interference detection circuit, comprising: level adjusting means for outputting; and subtraction means for subtracting the audio component signal whose level has been adjusted from the signal meter signal and outputting the control voltage.