JPH0630449B2 - Interference detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In an interference detection device according to the present invention, when FM modulation is applied to a voice signal, the FM modulation exists as AM modulation due to band limitation of an IF filter. In order to solve the problem of the device proposed by the applicant on the same date that it cannot be distinguished, the frequency deviation is changed by changing the bias voltage of the rectifier circuit according to the detection voltage obtained by rectifying the FM demodulation output. When a large FM modulation is applied, the bias voltage is lowered to distinguish the component due to FM-AM conversion from the AM component due to interference so that interference can be detected with high accuracy.

[Industrial application field]

The present invention relates to an interference detection device, and more particularly, to a device that can detect interference with high accuracy even when FM modulation with a large frequency deviation is applied in a narrow band FM receiver.

In the case of using such a narrow band FM receiver, when a signal subjected to FM modulation with a voice signal is band-limited by an IF filter, the FM modulation becomes AM modulation (so-called FM-AM conversion). Appears at the IF amplifier output,
Particularly when the frequency deviation is large, deep AM modulation is performed.
Therefore, it becomes indistinguishable from the AM component due to interference,
The interference detection accuracy becomes low. Therefore, it is necessary for highly accurate interference detection to eliminate the interference measurement error due to the voice modulation.

[Conventional technology]

By the way, in a mobile communication system of a multi-channel system that repeatedly uses the same frequency such as a car telephone system and a cordless telephone system, a U wave (interference wave) of the same frequency is used.
The SN ratio of the D wave (desired wave) may be deteriorated due to the interference due to the above, and the clarity of the voice may be deteriorated. There is a case to switch to a channel without.

In this case, accurate detection of the D-wave and U-wave interference ratio (DU ratio) leads to an improvement in the quality of the system, and therefore a device capable of realizing the interference detection with high accuracy is required.

Conventional interference detection device detects the envelope beat components caused by the U wave to square envelope detection the IF output, mean square ^{_{2 <E D 2><E}} U 2> low-frequency component of the future high-frequency component mean values _{^{<E D 2> + <E}} U 2> and the obtained interference ratio "=
(<E _U ² > / <E _D ² >) is obtained. Where _ED is D
The amplitude of the wave, the E _U is the amplitude of the U wave.

Since this method obtains the envelope beat component by the squared envelope detection, it is necessary to obtain the levels of the D wave and the U wave from the high frequency component and the low frequency component of the envelope detection in order to detect the interference ratio. High accuracy is required for both the measurement accuracy of the D wave level and the measurement accuracy of the high frequency component due to interference.
There is a problem that the circuit becomes complicated and the measurement variation becomes large.

Therefore, the present applicant proposed an interference detection device on the same date as the device of the present invention in order to solve the above problems. This one is
As shown in FIG. 5, a logarithmic detection circuit 1 for logarithmically detecting a received radio wave signal including a U wave, and a high-pass filter 3 for extracting only high-frequency components due to interference from the logarithmic detection signal from the logarithmic detection circuit 1. The full-wave rectification circuit 5 and the integration circuit 6 include a rectification circuit 2 that obtains a DC value according to its amplitude.

Since this one performs logarithmic detection of the received signal, its high frequency component can be detected without depending on the total received electric field level of the D wave and U wave, which makes it possible to highly accurately measure the D wave level. The circuit can be configured more easily than the required conventional example, and since the logarithmic detection circuit is used, the measurement error is relatively small and the interference can be detected with high accuracy.

[Problems to be solved by the invention]

However, as described above, when the narrow band FM receiver is used, if the signal subjected to the FM modulation with the voice signal is band-limited by the IF filter, the FM modulation is A
It becomes M-modulated (so-called FM-AM conversion) and appears in the output of the IF amplifier, and especially when the frequency deviation is large, a deep A
It becomes M modulation. Therefore, even the apparatus shown in FIG. 5 is indistinguishable from the AM component due to interference, and there is a problem that the accuracy of interference detection is lowered.

[Means for solving problems]

As shown in FIG. 1, the interference detection device according to the present invention is a logarithmic detection circuit 1 for logarithmically detecting a signal of a received radio wave including an interference wave.
And an FM detection rectification circuit (9, 10, 1) that FM demodulates the signal of the received radio wave to obtain a DC level according to the FM modulation degree.
1) and a configuration in which the DC bias voltage is varied according to the DC component of this FM detection rectification circuit (9, 10, 11),
A circuit 14 for extracting only a high frequency component from the logarithmic detection signal from the logarithmic detection circuit 1 and obtaining a DC value corresponding to its amplitude.
And consists of.

[Action]

When the AM modulation component of FM-AM conversion by voice modulation is superimposed, the bias voltage of the full-wave rectification circuit 13 is reduced by the amplitude of this AM modulation component. Therefore, only the magnitude of the high frequency component due to the interference can be extracted without being affected by the AM modulation component.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of the device of the present invention. In FIG. 1, the same components as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. In the figure, 7 is a logarithmic amplifier, 8 is a limiter, 9 is an FM detection circuit, and the output of the FM detection circuit 9 is FM.
The demodulated output is supplied to, for example, a speaker or a telephone receiver.

Reference numeral 10 is a rectifying circuit, 11 is an integrating circuit, and 12 is a DC amplifier. With these circuits, a DC value according to the level of the FM detection output (voice modulation degree) is obtained.

Reference numeral 13 is a full-wave rectifier circuit, in which the bias voltage inside the DC amplifier 12 can be varied according to the voltage of the level corresponding to the audio modulation degree. High-pass filter 3,
The AC amplifier 4, the full-wave rectifying circuit 13, and the integrating circuit 6 constitute a rectifying circuit 14, and the AC amplifier 4, the full-wave rectifying circuit 13, and the integrating circuit 6 have the configurations shown in FIG.
As will be described later, the full-wave rectifier circuit 13 holds its bias voltage at a predetermined level in a relatively low range where the audio modulation degree is, for example, about 2 kHz or less, as shown in FIG. In the range, the level is varied below a predetermined level according to the audio modulation degree.

First, a general operation of interference detection will be described. The output of the logarithmic detection circuit 1 is, for example, 100 mV at the high-pass filter 3.
_P-P high-frequency components a (FIG. 4 (A)) of the retrieved only, is amplified by the AC amplifier 4 for example 300 mV _P-P
Signal b (FIG. 4 (B)) and is supplied to the full-wave rectifier circuit 13. Here, full-wave rectification is performed to obtain a full _- wave rectification waveform of 150 mV _P-P .
A signal c (FIG. 4 (C)) is obtained by using a voltage of 2.5 V as a bias voltage. The full-wave rectified signal c is integrated by the integrating circuit 6, and (bias voltage 2.5V) +150 mV = 2.6.
The DC voltage d is 5 V (FIG. 4 (D)), and this is extracted as the amount of interference.

On the other hand, the IF output from the receiver is supplied to the FM detection circuit 9 via the logarithmic amplifier 7 and the limiter 8, where it is FM demodulated and taken out, while it is rectified by the rectification circuit 10 and integrated by the integration circuit 11. Is integrated with the DC amplifier 12, amplified by the DC amplifier 12, and taken out as a DC level according to the degree of sound modulation.

Next, a case where the AM modulation component is superimposed on the interference wave by the FM-AM conversion as described above will be described. For example, in a narrow band (bandwidth 8.5 kHz) receiver, in particular,
kHz about more voice modulation is relatively large, if the output of the AC amplifier 4, for example, becomes 600 mV _P-P,
Full-wave rectified waveform by the full-wave rectifier circuit 13 is 300 mV _P-P
become. In this case, the bias voltage of the full-wave rectifier circuit 13 is lower than 2.5 V shown in FIG. 4 (C) by the voltage from the DC amplifier 12 (for example, the output of the AC amplifier 4 which is increased by the AM modulation component by FM-AM conversion). 1 / of the amplitude of
2, i.e., 150 mV _P-P reduction) to. That is, since the output of the DC amplifier 12 increases as the degree of sound modulation increases,
The bias voltage of the full-wave rectifier circuit 13 becomes low as shown in FIG. As a result, the bias voltage becomes 2.35V and is integrated by the integrating circuit 6 to become a DC voltage of 2.65V.

In this way, when the AM modulation component of FM-AM conversion by voice modulation is superimposed, the bias voltage of the full-wave rectifier circuit 13 is reduced by the amplitude of this AM modulation component. Only the magnitude of the high frequency component due to the interference can be extracted without being affected.

〔The invention's effect〕

According to the present invention, in particular, F having a large frequency deviation in the interference wave
When the M voice modulation is applied, it has features such that the component by FM-AM conversion and the AM component by interference can be distinguished to accurately detect the interference, and the dynamic range of the interference detection can be widened.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a diagram showing a relationship between a voice modulation degree and a bias voltage, FIG. 3 is a circuit diagram of a main part of FIG. 1, and FIG. 4 is shown in FIG. FIG. 5 is a block diagram of an apparatus proposed by the applicant of the present invention on the same date. In the figure, 1 is a logarithmic detection circuit, 3 is a high-pass filter, 6 and 11 are integration circuits, 7 is a logarithmic amplifier, 8 is a limiter, 9 is an FM detection circuit, 10 and 14 are rectifier circuits, 12 is a DC amplifier, 13 Is a full-wave rectifier circuit.

Claims (1)

[Claims] 1. A logarithmic detection circuit for logarithmically detecting a signal of a received radio wave including an interfering wave in an interference detection device for detecting interference due to an interfering wave of the same frequency in a multi-channel type mobile communication system which repeatedly uses the same frequency. (1) and FM demodulation of the signal of the received radio wave to obtain D according to the FM modulation degree.
FM detection rectification circuit (9, 10, 11) to obtain C level
And a DC bias voltage is varied in accordance with the DC component of the FM detection rectifier circuit (9, 10, 11), and only the high frequency component is extracted from the logarithmic detection signal from the logarithmic detection circuit (1). An interference detection device comprising a circuit (14) for obtaining a DC value according to amplitude.