DE2804951A1 - Characteristics tester for coder and decoder installation - supplies calibrated A=D converter with sine wave analog signals for digital signal comparison - Google Patents

Abstract

A characteristics tester is for a coder/decoder installation. The digital signals describing the characteristics are generated at equal spacings several times and with opposite sign bit after every second repetition. The analog signals used to check the decoding characteristics are passed to a calibrated A/D converter and the resulting digital signals are compared with the digital signals describing the characteristics.

Description

Procedure for checking the coding and decoding

Characteristic of a coding-decoding arrangement The invention relates to a Method for checking the coding and decoding characteristics of a coding / decoding arrangement for deviation from a predetermined coding characteristic or decoding characteristic, accordingly for checking the coding characteristic using a calibrated digital-to-analog converter from the digital signals indicating the points of the characteristics to be checked, analog signals are generated as analog input signals for the coding part of the coding-decoding arrangement serve and accordingly the digital signals then output at their digital signal output with the digital signals indicating the points of the characteristics to be checked can be compared in a digital signal comparator.

In a known method of this type (DT-OS 2624363) the Checking the decoding characteristic in that the points to be checked the digital signals indicating the characteristic curve on the one hand to a calibrated Digita1-Analog-7 [other, on the other hand fed to the decoding part of the Ccdier-decoding arrangement to be checked and that the analog signals then emitted by these two devices can be checked for correspondence with the aid of an analog signal comparator.

If not only individual segments of the decoding characteristic, but their The entire process can be checked in the course of an automatable process then very high requirements must be placed on the accuracy of the analog signal comparator which, in turn, can only be met with a relatively high level of effort are. In addition, in each case two comparators, namely two different types of namely a digital signal comparator and an analog signal comparator are required will.

For a complete and automatable check of a coding and decoding arrangement with regard to its coding and decoding characteristics under practical Conditions also include the inclusion of their filters and sampling switches so that, what is the part used for analog-to-digital conversion and the corresponding coding characteristic concerns when test signals complete analog signal wave trains are required.

The object of the present invention is therefore to provide a method which takes into account the aforementioned requirements.

According to the invention, this object is achieved in that the points of the characteristic curve indicating digital signals at the same time intervals several times and are partly generated after repeating twice with a changed sign bit, that for checking the decoding characteristic, the analog signals that the decoding part the coding-decoding arrangement due to the supply of such kind of generated digital signals outputs, are fed to a calibrated analog-digital converter, and that of The digital signals given to him then also with the points of the characteristic curve indicating digital signals are compared in a digital signal comparator.

According to the invention, therefore, the locations to be checked become the Characteristic curves indicating digital signals complete sinusoidal oscillations as analog signals generated, which are fed to the arrangement to be checked. Using a calibrated analog-digital converter in connection with checking the decoding characteristic it is possible to do without an analog signal comparator. The additional Presence of this calibrated analog-to-digital converter is opposite to that for the above-mentioned prior art method does not require any weight falling overhead, since the required calibrated digital-to-analog converter is also available there Part of an arrangement is that both the digital-to-analog conversion and is used for analog-to-digital conversion, although that of analog-to-digital conversion The serving part is then not used.

According to a further embodiment of the method according to the invention the digital signals of the respective the same binary value is generated with a frequency that is related to the frequency of the analog voltage, the at the verification is to be applied, the sampling theorem enough. Such an analog voltage frequency is preferably 2 kHz.

According to yet another embodiment of the invention, those mentioned are Digital signals after their repeated generation in successive Set the characteristic curves in the characteristic sequence generated running downhill, in the case an inequality found in the digital comparison is the generation of the Digital signals interrupted and the last digital signal generated is displayed.

If by repeating the digital signal several times each three analog sine waves can be generated in this way an entire characteristic curve in about 0.2 seconds if there are no errors.

run through.

There is a further embodiment of the method according to the invention in that the respective start signals of the calibrated digital-to-analog converter and of the coding part of the Cosier decoding arrangement to be checked so far out of phase that the coding device in each case the maximum value of the analog signals fed to it scans.

According to yet another embodiment of the method according to the invention the digital comparator only evaluates those from the coding part of the coding-decoding arrangement to be checked emitted digital signals, which result from a coding of in the middle range the analog signal oscillation sequence supplied by the calibrated digital-to-analog converter lying down; Analog signal oscillations result. For example, every three Sine waves generated, but only of those according to the last-mentioned variant of the method the mean oscillation is evaluated, which avoids that during the transition the analog sine voltage from one amplitude value to another level of the Make transient processes noticeable in a disturbing manner according to the characteristic curve.

The method according to the invention is described below with reference to two figures explained in more detail.

The figure 1 shows a coding or decoding characteristic in the form of a so-called 13-segment characteristic curve, as it is the coding-decoding arrangement to be checked has to show.

FIG. 2 shows an arrangement for carrying out the invention Procedure.

In Figure 1, in the first quadrant of a coordinate system is the one Half of a coding or decoder characteristic shown in the form of a 13-segment characteristic. In the third quadrant, not shown here, of such a coordinate system runs the symmetrical second part of this characteristic. On the abscissa this The coordinate system are the amplitude values of the to be coded or the decoded Analog signals and on the ordinate are the correspondingly coded digital signals or the digital signals to be decoded are plotted, with a code representation is based on using 8 bits.

As can be seen, the characteristic curve of this quadrant has 7 segments I to VII, on which segment I can only be seen with one half, the second half g I £ J of this segment runs, as indicated, in d!: Ltten Quadrants of this coordinate system. Leave on the basis of the agreed 8-bit code 16 levels each represent themselves within three individual segments, which go through here vertical lines are indicated and segment by segment from segment I to segment VII grow. With a companding taking place according to this characteristic curve in the Conversion of analog signals into digital signals ensures that the total analog signal range is the distance between the signal amplitude and that resulting from the quantization caused interference voltage amplitude is almost constant.

FIG. 2 shows a test device PG together with a coding / decoding arrangement CDA shown, the coding and decoding characteristics must be checked.

The testing device PG has to generate the digital signals that the Specify the points of the decoding characteristic to be checked, a counter that is under Requirement of the 13-segment characteristic mentioned as coding or. Decoding characteristic consists of 3 lines Z1 to Z3.

The part Z1, to which the stepping clock T is fed, determines the Repeated output of digital signals generated with the counter parts Z2 and Z3 and also supplies with its counter stage assigned to binary digit 2 the sign of the digital signals emitted by the other two counter parts, which changes after two repetitions. The counter part Z1 can in the present Count trap to 12.

The counter part Z2, which occurs when the 12th counter reading is reached of the counter part Z1 is incremented, counts to 16 and denotes with his Counter readings the 16 quantization levels mentioned above, the the individual segments I to VII of the characteristic curve according to Figure 1 each include. The counter part Z3, which advances after reaching the last counter position of the counter part Z2 is able to count up to 8 and designates one with its counter readings the segments II to VII or two sections of the segment part I, which are in a of the two halves of the symmetrical 13-segment characteristic.

The individual counter parts, preferably the one indicating the segment addresses Counter part Z3 can also be designed as presettable counters for the case that specific areas of the characteristic are specifically checked.

To the outputs of the counter parts Z2 and Z3 and to the sign bit output of the counter part Z2, display elements AZ1 to AZ3 are connected, with the help of which the digital signal supplied can be displayed. the Digital signals that the counter parts Z1 to Z3 deliver to the aforementioned outputs, are on the one hand a parallel-to-serial converter P / S and on the other hand a digital comparator VD supplied.

The output from the Sarallel / series converter P / S in serial form Digital signals reach either the digital signal input via a changeover switch Ux ID1 of the arrangement to be tested CDA or to the digital signal input ID2 of a calibrated digital-to-analog converter D / A, depending on whether the decoding characteristic or the coding characteristic of the coding-decoding arrangement CDA to be checked is checked shall be. The analog signal input IA of the device under test is connected to the analog signals supplying output of the digital / analog converter D / A connected.

The output EA of the test item CDA, which supplies analog signals, is connected to the Analog signal input of a calibrated analog / 3-digital converter A / D connected. the Both calibrated code converters are preferably part of a coding / decoding arrangement with the same structure as the coding-decoding arrangement CDA to be replaced.

The output ED of the test line, which supplies digital signals, is via the Changeover switch U2 can be closed to the serial input of a serial / parallel converter S / P. The same applies to the output of the aforementioned calibrated which supplies digital signals Analog / digital TX'tandlers A / D. The parallel outputs of the series / parallel converter S / P are connected to second inputs of the aforementioned digital comparator 7D.

The mode of operation of the test device PG described is described below explained in more detail.

The counter with the counter parts Z1 to Z3 provides, as indicated, Digital signals that indicate the points of the characteristic curves to be checked. It will proceeded in such a way that a certain digital signal was sent a total of twelve times the arrangement to be checked CDA is issued, in each case twice in succession with the same sign bit. Counting these 12 digital signals causes how mentioned, the counter part Z1, the counter stage assigned to the value 21 is, returns the sign bit. After the twelve occurrences of a certain Digital signal, the counter part Z2 and possibly the counter part Z3 are advanced, to specify the next quantization level of the characteristics.

Provided that a review of the coding characteristic of the test item CDA is to be carried out, the switch U1 is set to that the digital signals output by the parallel / serial converter P / S are sent to the calibrated Digital-to-analog converter arrive.

Due to the mentioned repeated repetition of the supplied digital signals If the sign bit changes, the digital-to-analog converter emits a sine wave train from, which in the present case, if the digital signals are repeated twelve times, includes three periods of oscillation.

These analog signals are converted into Converted digital signals. By shifting the phase of the start signals accordingly the calibrated digital-analog converter and the coding part of the coding-decoding arrangement to be checked CDA is achieved that the coding part in each case the maximum value of the supplied Samples analog signals. In addition, the evaluation of the supplied analog signals limited to the middle of the three mentioned analog voltage periods, thus avoided is that transients that occur when changing from an analog voltage amplitude occur to others, make themselves noticeable in a disturbing way.

The coding part of the test item converts the analog signals fed to it into digital signals and gives them via its digital signal output ED with the appropriate Position of the switch U2 to the series / parallel converter S / P from where it get to the digital comparator VD. The digital comparator will therefore the digital signals supplied by the counter with the counter parts Z1 to Z3, the respective Specify a specific point of the characteristic curves to be checked with the digital signals * compare those of the test object based on the corresponding analog signals supplied to it has generated.

If an is match is found. becomes the review process continued, i.e. after the aforementioned generation of a specific digital signal Corresponding processes play with a subsequent quantization level indicating digital signal. However, if the digital comparator VD represents an inequality fixed, then the output of digital signals to the test object is interrupted and with the aid of the display elements AZ1 and AZ2cas last generated digital signal without Sign bit displayed.

Should be the decoding characteristic of the coding-decoding arrangement to be checked CDA are checked, then the switch 1 conducts from the parallel / series converter P / S output digital signals to the digital signal input ID1 of the device under test. By its decoding part then converts these digital signals into analog signals made via the analog signal output EA to the calibrated analog-digital converter AD arrive.

This again causes the analog signals fed to it to be encoded in digital signals, also as described above, due to the now Another switch position of the changeover switch UL via the series-parallel converter S / P reach the digital comparator VD. If the performed by this comparator If the comparison shows that the digital signals supplied to it match, this is it a sign that in this case the decoding characteristic of the arrangement to be tested CDA matches a predetermined decoder characteristic.

The control signals and required for the processes described Clocks are supplied by a control device, not shown here. These Control device can also be designed so that it differs from the previously operations described is possible, only partial tests 1, to undertake for example, only the coding of the positive or only the negative evaluate the amplitudes of the supplied knalog signals or only individual parts of the Check coding and decoding characteristics.

Claims (5)

Patent ent claims1e0 1. Method for checking the coding and decoding characteristics a coding-decoding order due to a deviation from a predetermined coding characteristic or decoding characteristic, accordingly for testing the coding characteristic using a calibrated digital-to-analog converter from the constant of the characteristic curves to be checked Digital signals indicating analog signals are generated as analog input signals serve for the coding part of the coding-decoding arrangement and accordingly the thereupon The digital signals output at their digital signal output with those to be checked Place the digital signals indicating the characteristics in a digital signal comparator be compared, that is, that the points of the characteristic curve indicating digital signals at the same time intervals several times and every two times lE repetition with changed sign bit are generated that for checking the decoding characteristic curve is the analog signals which the decoding part of the coding / decoding arrangement (CDA) emits due to the supply of digital signals generated in this way, a calibrated analog-to-digital converter (A / D) are supplied, and that it is thereupon Output digital signals also with the digital signals indicating the points of the characteristic curve in a digital signal comparator 7D). 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the digital signals indicating the points of the characteristic curves to be checked each of the same binary value can be generated with a sequence related to the frequency of the analog voltage that is to be used during the test, the sampling theorem is sufficient. 3. The method according to claim 1 or 2, that is to say i c h n e t that the digital signals indicating the points of the characteristic curves to be checked after their repeated generation in successive places of the characteristic curves characterizing sequence are generated consecutively, and that in the case of A digital comparison determined the inequality of the generation of the digital signals interrupted and the last generated digital signal is displayed. 4. The method according to any one of the preceding claims, d a d u r c h e k e n n n e i c h n e t that the respective start signals of the calibrated digital-to-analog converter (D / A) and the coding part of the coding-decoding arrangement (ODA) to be checked see above are far out of phase, so that this coding part each has the maximum value of it the supplied analog signals. 5. The method according to claim 4, d a d u r c h g e k e n n -z e i c h n e t that the digital comparator (VD) only those from the coding part of the to be checked Coding-decoding arrangement (CDA) evaluates output digital signals that result from a coding in the middle range of the calibrated digital-to-analog converter (D / A) supplied analog signal oscillation sequence of lying analog signal oscillations result.