JPH057669B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a waveform shaping circuit, and in particular to a DME
(Distance Measuring Equipment) This invention relates to a waveform shaping circuit that removes and shapes various distortions including nonlinear amplification distortion contained in a waveform transmitted from a ground station to an airborne station as a transbonder of a device.

[Conventional technology]

DME devices as navigation devices are well known. This DME device emits an interrogation pulse to a ground station from an airborne station mounted on a flying aircraft, and the ground station receives this and emits a response pulse.
The airborne station learns the distance to the ground station based on the time from inquiry to response.

The transmission output emitted from the ground station is approximately 1000 pp/s (pulse pairs) even when there are no questions from the airborne station.
In addition to the random pulse output in response to the arrival of the interrogation pulse (per second), the response pulse that is output in place of the random pulse in response to the arrival of the interrogation pulse, and the identification pulse of the ground station, the total number of pulses including the response pulse is at least approximately 1000, reaching a maximum of approximately 2700pp/s.

Among the above-mentioned transmission output pulses, the random pulses excluding the station identification pulse and the interrogation pulse are mutually exclusive.
The pulse width is 3.5 μS separated by 12 μS. Among these twin pulses, the response signal is particularly important for distance measurement of airborne stations. In any case, these transmission output pulses are emitted in the form of a carrier of a predetermined frequency that has undergone pulse AM modulation in the modulation section of the transmission system of the ground station, is power amplified to a predetermined level, and is applied to the antenna.

Such power amplification of the transmission output is performed by class C amplification, and therefore, naturally, nonlinear distortion occurs due to class C amplification, which not only causes errors in distance measurement but also causes spectrum expansion. This deviates from the restricted band and enters the adjacent band. DME equipment is one of the main equipment for aircraft takeoff and landing at airports, so this nonlinear distortion must be removed.

Moreover, recently, high-precision DME (Precision DME,
(hereinafter abbreviated as DME/P) is MLS (Microwave
Landing System) is scheduled to be used as the entity in charge of the distance system, and the problem of removing the nonlinear distortion mentioned above is becoming even more important.

DME/P is multi-path communication between the ground station and airborne station of conventional DME equipment.
In this method, the response pulse is detected by using the low level portion of the leading edge of the preceding pulse of the twin pulse.

FIG. 4 is a waveform diagram of the DME/P transmission twin pulse. As shown in Figure 4, for example, 5% to 30
% of low level parts are the detection targets during reception. In other words, the aim is to minimize the influence of multi-bass waves through such low-level detection. The goal is to improve the distance measurement accuracy by one order of magnitude. For this reason, a pulse with a steep rise is used.

The time between the 5% and 30% levels shown in Figure 4 is approximately
250nS, so 1% corresponds to approximately 10nS.
On the other hand, the level to be controlled is approximately -30 dB (approximately 1/30) of the peak value, that is, approximately 3%. Tracking a change of about 3% is
This means that high-speed tracking of 30nS, or approximately 300MHz, is required.

In order to stably output such a waveform, as mentioned above, it is all the more important to remove the nonlinear distortion of the class C amplification, and conventionally this distortion has been removed in the following manner.

In other words, in the past, a transmission pulse was output, compared with an ideal waveform, the modulation waveform supplied to the class C power amplifier was corrected until the difference disappeared, and this was stored in a ROM etc. as a reference waveform for modulation. , each time a transmission trigger is input, it is read out and the carrier is modulated by a class C amplifier.

[Problem that the invention seeks to solve]

The above-mentioned conventional waveform shaping circuit of this type has the following various problems.

In other words, (1) is that it is necessary to prepare a distorted modulation waveform in advance to compensate for the nonlinearity of the class C amplifier, and (2) is that it is necessary to prepare a distorted modulation waveform in advance to compensate for the nonlinearity of the class C amplifier. Also, it is inevitable that the waveform and spectrum will change due to variations in the characteristics of class C amplifiers, and (3), compatibility will become a problem if the modulation waveforms are matched for each individual class C amplifier. , and (4) has various drawbacks, such as being unable to respond to changes in temperature and time because it uses an oven loop to shape the waveform.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a means for applying closed-loop waveform shaping to the transmitted output in real time, thereby eliminating the need to prepare a pre-distorted modulation waveform, improving compatibility, temperature, and aging. An object of the present invention is to provide a waveform shaping circuit that can significantly reduce the influence.

[Means for solving problems]

The circuit of the present invention is a waveform shaping circuit that shapes a transmission output waveform of a DME device, and includes averaging processing means that digitizes the transmission output waveform, performs averaging processing for each predetermined number of waveforms, and outputs the result. , a smoothing means for sequentially performing a moving average process with suppressed time delay on the averaged data for each predetermined number of waveforms outputted by the averaging processing means and outputting it as smoothed data; and the DME stored in advance.
The difference between the ideal transmission waveform data of the device and the smoothed data is determined, and the polarity inversion data of the difference is added to the ideal transmission waveform data to form the transmission output waveform. and a transmission output waveform shaping means for shaping the transmission output waveform by eliminating the influence of nonlinear amplification distortion.

〔Example〕

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

FIG. 1 is a block diagram of an embodiment of the present invention, which is implemented for DME/P, including a detector 1, an A-D converter 2, an input buffer 3, an averager 4, and a modulation waveform corrector. 5, an ideal waveform memory 6, a modulation waveform initializer 7, an initialization data memory 8, an output buffer 9, a D-A converter 10, etc., and FIG. A power amplifying section 200 is also shown.

The detector 1 linearly detects the transmission output of the power amplifier 200 and extracts the transmission output waveform. The transmitted output waveform extracted in this way is shown in FIG. 4 and has a pulse width of 3.5 μS. This transmission output waveform is digitized by an A-D converter 2 and then stored in an input buffer 3. The data stored in this way is
Averaging processing is performed by an averaging unit 4 to remove various noises such as detection noise, detection jitter, and quantization noise accompanying A-D processing, and to remove prominent data.

The averager 4 integrates and averages the digitized transmission output waveform data stored in the input buffer for a predetermined number of waveforms, eight waveforms in this embodiment, thereby significantly reducing noise and averaging. The resulting signal is then supplied to the modulation waveform corrector 5.

The modulated waveform corrector 5 smoothes the protruding data remaining in the input output of the averager 4, and performs a modulated waveform correction process to correct the difference from the ideal waveform.

Smoothing uses a method of suppressing prominent data under the condition of applying a weighting function based on the moving average method described later. Since the data at the rising edge of the waveform is equivalently delayed and causes a phase shift, which leads to an increase in distance measurement error, the following procedure is adopted.

That is, in this embodiment, in order to avoid the above-mentioned problem, the difference between the ideal transmission output waveform data and the input is calculated, and then smoothing using the moving average method is applied to this difference.

FIG. 2 is an explanatory diagram of the smoothing process in the embodiment of FIG. 1.

The accumulated averaged data g _o (t) shown in FIG. Outstanding data remains. The modulation waveform corrector 5 calculates difference data Δg _o (t) between the ideal waveform data g _p (t) and g _o (t) read from the ideal waveform memory 6, and applies the moving average method to this difference data. to obtain smoothed difference data.

FIG. 3 is an explanatory diagram of the moving average method used in the smoothing process in the embodiment of FIG. 1.

In general, assume that there is a discrete waveform x(i) containing n points. Here, i=1, 2, . . . n. On the other hand, a symmetrical weighting function w(j) including N=2m+1 points is set. Here j=-m,...-1,
x given this weighting function w(j) which is 0, 1...m
The average value y(i) at point i in (i) is expressed by the following equation (1).

y(i)=1/W _n 〓 ^j=-m x (i+j) w(j) ...(1) In equation (1), W= _n 〓 ^j=-m w(j).

Normally, W is set to 2 ^N for convenience of calculation processing. The contents of FIG. 3 are exemplified as satisfying these conditions. Figure 3 shows the case where three points of x(i) are targeted and the moving average is calculated based on equation (1) while shifting one point at a time, and the data is smoothed, and the other case where the seven points of x(i) are targeted. Two examples are shown in which a moving average is calculated for , and in both cases, the central data is given twice the weight as other data. Similar to the use of the difference in the moving average described above, this weight is given to increase the median value in order to avoid data time lag in the smoothing process, and takes into account the purpose of smoothing, etc. It can be set as appropriate.

Returning again to FIG. 1, the explanation of the embodiment will be continued.

The modulated waveform corrector 5 corrects the used waveform data using the smoothed difference data obtained in this way, and supplies the corrected waveform data to the output buffer 9. This correction is performed by inverting the polarity of the smoothed difference data with respect to the ideal waveform data and digitally adding the data at the same sample point. As a result of such correction,
The ideal transmission waveform data is pre-distorted to account for the nonlinear distortion caused by class C amplification, and becomes the corrected data shown in Figure 2.Conversely, by being subjected to the distortion of class C amplification, it becomes the ideal transmission waveform. It will be output.

The corrected modulation waveform data stored in the output buffer 9 is successively outputted to the D-A converter 1.
0 and is used as a modulation waveform to be supplied to the modulation section 100.

In this modulation waveform correction, the following means are prepared for initial correction when no transmission signal is obtained.
We are trying to shorten the time it takes to start up the system.

The initialization data memory 8 uses data regarding the transmission output waveform during the latest operation, and stores this as initialization data.

This initialization data is prepared in advance for the purpose of eliminating the time required for the waveform shaping operation loop to stabilize at the start of transmission.

The modulation waveform initializer 7 corrects the ideal transmission waveform data read from the ideal waveform memory 6 using initialization data as a correction initial value, and uses the modulation waveform corrector 5 as a correction initial value.
is stored in the output buffer via , thus securing the initial value.

The modulating section 100 generates a pulse AM modulated signal in a predetermined modulation format using the received transmission output waveform and supplies this to the power amplification section 200, which amplifies the power of this to the transmission output level and transmits it to the antenna. supply to the system. A part of this transmission output is level-divided and supplied to the detector 1, and following modulation waveform initialization, the transmission waveform is repeatedly shaped in a closed loop.

In this way, in this embodiment, during negative feedback for waveform shaping, in addition to suppressing prominent data, noise that enters from outside the circuit is also ensured by moving average smoothing that suppresses time delay. ing.

In the above embodiment, the latest operational transmission output waveform data, that is, the transmission output waveform data acquired during the final operation, is used as the initialization data, but this may be used as long as it can be used for initialization. Anything is possible, and if this initialization is not particularly required for operation, the modulation waveform initializer 7 and the initialization data memory 8 can be omitted.

〔Effect of the invention〕

As explained above, according to the present invention, in the waveform shaping circuit that corrects and shapes the nonlinear distortion caused by class C amplification of the transmission output waveform, the nonlinear distortion included in the transmission output waveform is corrected in real time while branching and outputting the transmission output waveform. By providing a closed-loop correction means, it is possible to significantly reduce the effects of nonlinear distortion, including temperature and aging changes, as well as manufacturing variations between DME devices, and also enable precise control based on digital processing. This has the effect of realizing a waveform shaping circuit that can shape an almost ideal waveform.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is an explanatory diagram of the smoothing process in the embodiment of Figure 1, Figure 3 is an illustration of the moving average method used in the smoothing process in the embodiment of Figure 1, and Figure 4 is a high-precision diagram.
FIG. 3 is a waveform diagram of twin pulses transmitted by the DME device. 1...Detector, 2...A-D converter, 3...
... Input buffer, 4 ... Averager, 5 ... Modulation waveform corrector, 6 ... Ideal waveform memory, 7 ... Modulation waveform initializer, 8 ... Initialization data memory, 9 ...
Output buffer, 10...D/A converter, 10
0...Modulation section, 200...Power amplification section.

Claims (1)

[Claims] 1 A waveform shaping circuit that shapes a transmission output waveform of a DME device, comprising an averaging processing means for digitizing the transmission output waveform, performing averaging processing for each predetermined number of waveforms, and outputting the result; and the averaging processing circuit. smoothing means that sequentially performs moving average processing that suppresses time delay on the averaged data for each predetermined number of waveforms output by the means and outputs it as smoothed data; and ideal transmission waveform data of the DME device that is stored in advance. and the smoothed data, and add the polarity inversion data of the difference to the ideal transmission waveform data to generate the transmission output waveform, thereby eliminating the influence of nonlinear amplification distortion included in the transmission output waveform. a transmission output waveform shaping means for shaping the transmission output waveform by eliminating the transmission output waveform.