JPH01180128A - Level reduction detecting circuit - Google Patents

Abstract

PURPOSE:To detect accurately the reduction of a reception input signal level by squaring and summing a real component and an imaginary component of an output signal of a correlation device respectively, comparing the summing output with a prescribed level and raising an alarm. CONSTITUTION:The real component and the imaginary component of an output signal of a correlation device used for a diversity synthesizing circuit of a receiver are inputted respectively to a real port 1 and an imaginary port 2 respectively, squared by square circuits 3a, 3b and added by an adder circuit 4. The addition output is given to one input terminal of a signal level comparator 5a and an alarm level designated by a level designation device 6a is given to the other input terminal of the comparator 5a. The result of comparison is outputted to an alarm output terminal 7. Thus, the level reduction of the reception input signal level only is detected independently of the frequency difference and phase difference between the two signals fed to the correlation device in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a level drop detector that detects a drop in the level of a received input signal due to a drop in the output level of a correlator used in a diversity synthesis circuit or the like.

[Conventional technology]

In non-line-of-sight communications, seven adaptive matched filters and forward equalizers are used for dipacity signal synthesis control and automatic equalization. The correlator used in these applications is a signal after the received input signal has passed through an antenna, a down converter, and an automatic gain control amplifier, that is, I
A P (intermediate frequency) signal and a reference signal are given, and the correlation between these two signals is taken. Here, the IP multiplied signal level corresponds to the received input signal level, and furthermore, the output level of the correlator also corresponds to the received input signal level. There is a device that detects a decrease in the level of a received input signal by detecting a decrease in the output level of this correlator. Furthermore, among these types of devices, there is a device that detects a drop in the level of a received input signal by independently detecting the levels of the real component and the imaginary component of the output level of the correlator.

FIG. 4 shows a block diagram of a conventional level drop detector. The real component and imaginary component of the output from the correlator are supplied to one input terminal of signal level comparators 5b, 5c, 5d, and 5e via real port 1 and imaginary port 2, respectively. Signal level comparator 5b
, 5c, 5d and 5e are supplied with predetermined levels from level designators 6c and 6d, respectively. The level designators 6C and 6d designate the received input signal level to be detected as the alarm level r when detecting the decrease in the level of the real component and the imaginary component described above. For example, 6c is the upper limit value, and 6d is the lower limit chamber. Set. The alarm range on the R'-I plane set at this alarm level r is shown in FIG. The hatched range surrounded by solid lines in the figure is the alarm range 9. When the output from the correlator falls within this range 9, the alarm output terminal 7 outputs, for example, "work" as an alarm output.

By the way, if the frequency difference between the two signals supplied to the A1 correlator at the received input signal level to be detected, that is, the IF multiplied signal and the reference signal, is the f1 transfer difference, then the real component R output from the correlator is R = Acos (ft + θ) Imaginary component work is I = Asin (f t + θXt is any time)
It is expressed as Therefore, the input signal level A becomes A''=R1+I'' (a circle centered at the origin and radius A) on the RI plane.

Now, the case where the input signal level A is slightly higher than the alarm level r will be explained using FIG.

A circle 10 indicated by a dotted line in the figure indicates the input signal level. As can be seen from the figure, points a and b on the circle 10 are located inside and outside the warning range 9, respectively.

In other words, even if the frequency difference f=o, if the phase difference θ is 00, there will be a difference between inside and outside the alarm range for (point a) and π/4 (point b), and if the frequency difference f≠0, there will be a correlation. The output from the device moves circularly on the dotted circle 10 at a frequency equal to the frequency difference f described above. Therefore, the input signal level will go back and forth within and outside the alarm range 9.

Therefore, when there is a frequency difference f and a phase difference between the two signals supplied to the correlator, a drawback arises in that a decrease in the level of the input signal level A cannot be accurately detected within the alarm range of the conventional device.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a level drop detector that can accurately detect a drop in the received input signal level.

[Problem that the invention seeks to solve]

In order to achieve the above object, the present invention provides a level drop detector for detecting a drop in the level of a received input signal due to a drop in the level of the output signal of a correlator used in a diversity combining circuit or the like of a receiving device. A squaring circuit that squares the real component and imaginary component of the output signal, an adder that adds the outputs of these squaring circuits, and a circuit that compares the output of this adder with a predetermined level and generates an alarm signal. A level drop detection circuit is obtained, which is characterized in that it includes the following.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The real component R = Acos (f 10) and the imaginary component I = Asin (f t + θ) of the output from the correlator input to the real port 1 and the imaginary port 2 are squared by the 2 east circuits 3a and 3b, respectively. After that, they are added by an adder 4, and are applied as an output A2 (=I"+-R") to one input terminal of a signal level comparator 5a. The other input terminal of the signal level comparator 5a is given an alarm level designated by the level designator 6a, for example r2.

By comparing this level r2 and the above-mentioned output A2, the output A
2 is smaller than the level r2, the alarm output terminal 7 outputs, for example, "l" as an alarm output.

Figure 3 shows the output of the adder and the alarm range. The output A” (=I”10R”) from the adder is R-I as shown by the dotted line.
It is represented by a circle 10 with a radius A centered at the plane origin. In other words, the comparison between the output A2 and the level r2 detects whether or not the circle A''=R2+I2 is within the alarm range 8 indicated by the circle r2=R2+I'' on the R-I plane. .

Therefore, a level drop in only the received input signal level A can be detected regardless of the frequency difference f and phase difference θ between the two signals supplied to the correlator.

FIG. 2 is a block diagram showing another embodiment of the invention.

In this example, a square root circuit 8 is provided after the adder 4 shown in FIG. 1, and the boundary value level is r. The output from the square root circuit 8 will be equal to the level of the received input signal that is desired to be detected, and it is possible to determine the alarm level according to this level.

〔Effect of the invention〕

As described above, according to the present invention, a drop in the level of a received input signal can be accurately detected without being affected by the frequency and phase difference between two signals supplied to a correlator.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the invention, Fig. 3 is a diagram showing the alarm range of the circuit in Fig. 1, and Fig. 4 is a block diagram showing an embodiment of the present invention. FIG. 5, a block diagram showing a conventional example, is a diagram showing an alarm range of the conventional example circuit of FIG. 1... Real boat, 2... Imaginary report, 3a, 3b... Square circuit, 4...
... Adder, 5a. 5b, 5c, 5d... Signal level comparator, 6a
. 6b, 6c, 6d...Level indicator, 7...
...Alarm output terminal, 8, 9...Alarm range. Agent Patent Attorney Hara Uchihara Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a level drop detector that detects a drop in the level of a received input signal due to a drop in the level of an output signal of a correlator used in a diversity synthesis circuit of a receiving device, the real component and the imaginary component of the output signal of the correlator are squared, respectively. 1. A level drop detection circuit comprising: a squaring circuit for squaring, an adder for adding the outputs of these squaring circuits, and a circuit for comparing the output of the adder with a predetermined level and generating an alarm signal.