JP2571278B2 - Inspection device for recursive digital filters - Google Patents

Description

The present invention relates to a recursive digital filter inspection apparatus,
For example, the present invention can be applied to inspection of a cyclic digital filter used in a television signal processing device.

[Related Art] Digital processing is frequently used in recent television signal processing apparatuses, and therefore, a digital filter is used in each part of the apparatus. As the digital filter, there are an acyclic digital filter and a recursive digital filter. As a filter for the horizontal and vertical directions of the television signal, an acyclic digital filter is mainly used frequently, and in the time direction (between frames). On the other hand, a recursive digital filter is mainly used.

In such a television signal processing device, when the characteristics of the digital filter used are not the desired characteristics, the image quality is deteriorated. Therefore, the digital filter is inspected before being used in the device.

Conventionally, for a non-recursive digital filter, a tap gain is set to a predetermined value, a predetermined television signal is input, and characteristics such as transfer characteristics are analyzed using a filtered output television signal. An inspection was underway.

However, in the case of a cyclic digital filter, the influence of a certain change is complicated and long due to the cyclic operation, and the inspection time is long, so that real-time inspection cannot be performed. Then, when a good test result is obtained, a feedback loop is formed to return to the recursive digital filter.

[Problems to be Solved by the Invention] However, the conventional inspection method of the recursive digital filter has the following disadvantages. Since the inspection is not performed using the original configuration of the cyclic digital filter, the inspection result may be slightly different. Further, when a cyclic digital filter is configured by an integrated circuit, the cyclic digital filter is changed to a non-cyclic digital filter. It is necessary to provide an originally useless circuit in which a circuit change is instructed from the outside. In addition, a step is required to make a final recursive digital filter after inspection.

The present invention has been made in view of the above points,
An object of the present invention is to provide an inspection apparatus for a cyclic digital filter capable of accurately inspecting the cyclic digital filter in a short time while keeping the configuration of the cyclic digital filter.

[Means for Solving the Problems] In order to solve the problems, according to a first aspect of the present invention, there is provided an inspection signal generating means for generating an inspection signal including an impulse waveform; Adding means for synthesizing the output signal from the digital filter, delay means for delaying the synthesized signal from the adding means by a predetermined time and applying it to the cyclic digital filter under test, and tap gain of the cyclic digital filter under test. There is provided a tap gain control means set for inspection and a waveform monitoring means for determining whether the characteristic of the cyclic digital filter to be inspected is good or not based on the combined signal from the adding means.

Further, in the second invention, a ramp waveform is used instead of the impulse waveform in the first invention.

According to a third aspect of the present invention, there is provided a test signal generating means for generating a test signal including an impulse waveform, a delay means for delaying the test signal by a predetermined time and applying the same to a cyclic digital filter under test, Tap gain control means for setting the tap gain of the cyclic digital filter for inspection, addition means for synthesizing the inspection signal and the output signal from the cyclic digital filter to be inspected, and a synthesis signal from the addition means. And a waveform monitoring means for determining whether the characteristics of the cyclic digital filter to be inspected are good or bad.

Further, in the fourth invention, a ramp waveform is used instead of the impulse waveform in the second invention.

[Operation] In the first aspect of the present invention, the test signal generating means generates a test signal including an impulse waveform. The addition means
The test signal and the output signal from the cyclic digital filter under test are combined and provided to the delay unit. The delay unit delays the combined signal by a predetermined time and provides the combined signal to the cyclic digital filter under test. In the cyclic digital filter to be inspected, the tap gain is set for inspection by the tap gain control means, and the signal from the delay means is filtered and provided to the addition means.

In this case, the composite signal output from the adding means includes the impulse waveform of the test signal as it is, and is not delayed exactly by the delay time (it may not be exactly delayed by the delay time). ) Includes the impulse waveform obtained by filtering the impulse waveform in the test signal only once. The waveform monitoring means determines the quality of the characteristic of the cyclic digital filter to be inspected based on the synthesized signal including such an impulse waveform.

The second invention is intended to perform the same inspection by using a ramp waveform instead of the impulse waveform in the first invention.

According to a third aspect of the invention, the same operation as the first aspect of the invention is performed by changing the position of the adding means. Even if the position of the adder is changed, the composite signal output from the adder includes the impulse waveform of the test signal as it is, and the impulse waveform of the test signal is filtered only once after a delay time. The waveform monitoring means includes the impulse waveform obtained as described above, and the waveform monitoring means can perform the same processing as in the first embodiment of the present invention.

The fourth invention is intended to perform the same inspection using a ramp waveform instead of the impulse waveform in the third invention.

Embodiment Hereinafter, an embodiment in which the present invention is applied to the inspection of a recursive digital filter used in a television signal processing device will be described in detail with reference to the drawings.

First Embodiment FIG. 1 shows a configuration of an inspection apparatus of a first embodiment including a recursive digital filter 1 to be inspected.

In FIG. 1, the inspection signal generating means 2 is a digital signal shown in FIG.
Generates S1. The inspection signal S1 is a signal based on a composite synchronization signal including a horizontal synchronization signal and a vertical synchronization signal, and has an impulse waveform of a predetermined level on a horizontal scanning line in the middle of one field (it is not necessary to be completely in the middle).
It has IP1. The reference level LE1 of a plurality of horizontal scanning lines before and after the horizontal scanning line having the impulse waveform IP1 is a boundary value (0) at which the sign bit changes so that the processing described later (for example, the processing of the adding means 3) is simplified. ). In addition, the reference level LE of a horizontal scan line that exceeds the horizontal scan line of the reference level LE11 and is farther than the horizontal scan line having the impulse waveform IP1.
1 is selected to be a different level (for example, a pedestal level) from the reference level LE1 so as to clarify the section of the horizontal scanning line having the reference level LE1. That is, an offset is given to the pedestal level for the horizontal scanning line during the inspection monitoring period so that digital processing is facilitated.

In this way, the monitoring period during which the waveform monitoring means 7 described later performs the inspection processing is defined.

Note that the period of the horizontal scanning line having the reference level LE1 is determined so that the response of the digital filter 1 to the impulse waveform IP1 can be accurately detected.

An inspection signal S1 having such an impulse waveform IP1
The variable delay means 4 and the digital /
It is provided to the analog conversion means 6. The variable delay means 4
The input signal is delayed by one horizontal scanning period and applied to the cyclic digital filter 1 to be inspected. The variable configuration is used because the delay time can be adjusted to be exactly one horizontal scanning period.

The digital filter 1 includes a tap gain control means 5
Thus, a predetermined tap gain (coefficient for a coefficient unit inside the digital filter 1, and in some cases, a concept obtained by adding a delay time to an internal variable delay element) for inspection is provided. The digital signal F1 obtained by filtering with the tap gain by the digital filter 1 is fed back to the adding means 3 described above.

Thus, the adder 3 combines the test signal S1 and the filtered digital signal F1, and the combined digital signal A1 is provided to the variable delay 4 and the digital / analog converter 6.

The signal on which the filtering characteristic converted into an analog signal by the digital / analog conversion means 6 is reflected is given to the waveform monitoring means 7. This waveform monitoring means 7
Analyzes the input signal and evaluates characteristics such as transfer characteristics of the recursive digital filter 1 to be inspected.

By the way, because of the configuration having such a variable delay means 4, as shown in FIG. 3, the composite signal A1 outputted from the adder means 3 includes the impulse waveform IP1 (IP10) of the test signal S1 as it is. At the same time, the impulse waveform IP1 is applied to the next horizontal scanning line by the digital filter 1.
Include the impulse waveform IP1 filtered only once. Of course, since a loop is formed, the impulse waveforms IP12,. That is, the impulse waveform first appearing on the waveform monitoring means 7 is
The impulse waveform IP1 (IP10) itself in the inspection signal S1, and the next given impulse waveform is the impulse waveform IP11 resulting from the response of the digital filter 1.

The waveform monitoring means 7 mainly detects the characteristics such as the transfer characteristics of the digital filter 1 based on the first appearing impulse waveform IP10 and the second appearing impulse waveform IP11, and evaluates the cyclic digital filter 1 to be inspected.

Therefore, according to the first embodiment, the cyclic digital filter 1 to be inspected can be inspected as it is without changing to the non-cyclic digital filter, and the inspection accuracy can be improved. Can be increased. Therefore, the step of changing the cyclic digital filter to the non-recursive digital filter or the step of returning the non-recursive digital filter to the cyclic digital filter becomes unnecessary, and as a whole, the inspection time is reduced. Can be.

Thus, using the inspection signal S1 in which one impulse waveform IP1 is inserted in one field, the original impulse waveform IP1 and the filtered impulse waveform IP11 are used.
Is generated and the inspection is performed. Therefore, even if the inspection is performed with the configuration of the recursive digital filter 1, the transfer characteristics and the like can be analyzed and inspected in a short time.

Second Embodiment Next, a second embodiment of the present invention will be described.

The inspection apparatus according to the second embodiment includes an inspection signal generation unit 1
The other configuration is the same as that of the first embodiment, except that the waveform of the inspection signal generated by the first embodiment is different from that of the first embodiment.
Of course, since the waveform of the test signal is different from that of the first embodiment, the waveform monitoring means 7 also performs an analysis test according to the waveform shape.

FIG. 4 shows the waveform of the inspection signal S2 according to the second embodiment. The inspection signal S2 is a ramp waveform instead of the impulse waveform IP1 in the horizontal scanning line where the impulse waveform IP1 is inserted in the inspection signal S1 according to the first embodiment (in this embodiment, a ramp waveform that increases gradually). RM2 is inserted, and the other parts are the same as the inspection signal S1 according to the first embodiment.

In this embodiment, the digital / analog conversion means 6
As shown in FIG. 5, the signal which is converted into an analog signal via the signal and supplied to the waveform monitoring means 7 is a ramp waveform RM2 (RM20) of the horizontal scanning line into which the ramp waveform RM2 of the inspection signal S2 is inserted. Appears as it is, and a ramp waveform RM21 based on the response of the ramp waveform RM2 via the digital filter 1 appears on the next horizontal scanning line. Note that the ramp waveforms RM22,.

The waveform monitoring means 7 analyzes and inspects the characteristics such as the transfer characteristics of the digital filter 1 from the ramp waveforms RM20 and RM21 of these two horizontal scanning lines to evaluate the cyclic digital filter 1 to be inspected.

Therefore, according to the second embodiment, the same effect as that of the first embodiment can be obtained. In addition, since the ramp waveform is used, the characteristic of the digital filter 1 for each value of the ramp waveform (each value equivalent to the appearance of an impulse waveform having a different level discretely because it is digital) is evaluated. be able to. That is, the same inspection is performed in the first
In the case of the embodiment, the inspection must be repeated while changing the level of the impulse waveform IP1, but in the second embodiment, the inspection can be performed by one inspection.

Other Embodiments In the above-described embodiment, the case where the cyclic digital filter provided in the television signal processing device is inspected has been described. However, the present invention is also applicable to the case where the cyclic digital filter provided in another device is inspected. The invention can be applied as well. Also in this case, it is necessary to insert an impulse waveform or a ramp waveform into the inspection signal.

Further, in the above description, the composite signal of the test signal and the output signal from the digital filter is converted into a variable delay means and a digital signal.
Although the adding means is provided at a position to be provided to the analog conversion means, the test signal is directly provided to the variable delay means, and the combined signal of the test signal and the output signal from the digital filter is converted into a digital / analog signal. The adding means may be provided at a position to be given to the converting means.

Further, in the above description, the waveform monitoring means performs the evaluation based on the signal converted into the analog signal through the digital / analog conversion means. However, the waveform monitoring means directly receives the added output and performs the digital evaluation. You may do.

Further, in the above description, the variable delay means is provided only for one horizontal scanning period so as to distinguish a special waveform (impulse waveform or ramp waveform) in the inspection signal from a special waveform which appears only once through the digital filter. Although the delay is shown, the delay may be an integral multiple of the horizontal scanning period.

[Effects of the Invention] As described above, according to the present invention, an inspection signal having a special waveform composed of an impulse waveform or a ramp waveform as a part is provided to the waveform monitoring means, and the inspection circuit is inspected. The response special waveform of this special waveform filtered only once by the type digital filter is provided to the waveform monitoring means, and the waveform monitoring means analyzes and inspects the characteristics of the digital filter by at least the special waveform and the response special waveform. , The cyclic digital filter can be inspected as it is,
It is possible to obtain an inspection apparatus for a cyclic digital filter that requires a small number of inspection steps, a short inspection time, and can improve the inspection accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a recursive digital filter test apparatus according to the present invention, FIG. 2 is a signal waveform diagram showing a test signal of the first embodiment, and FIG. 3 is a first embodiment. 4 is a signal waveform diagram showing a signal inputted to the waveform monitoring means, FIG. 4 is a signal waveform diagram showing a test signal of the second embodiment, and FIG. 5 is a signal inputted to the waveform monitoring means in the second embodiment. FIG. 4 is a signal waveform diagram showing DESCRIPTION OF SYMBOLS 1 ... Inspection cyclic digital filter, 2 ... Inspection signal generation means, 3 ... Addition means, 4 ... Variable delay means, 5 ... Tap gain control means, 7 ... Waveform monitoring means.

Claims (4)

(57) [Claims] 1. An inspection signal generating means for generating an inspection signal including an impulse waveform, an adding means for synthesizing the inspection signal and an output signal from a cyclic digital filter to be inspected, Delay means for delaying the combined signal by a predetermined time to give the cyclic digital filter to be inspected, tap gain control means for setting the tap gain of the cyclic digital filter to be inspected for inspection, and combining from the adding means An inspection apparatus for a cyclic digital filter, comprising: a waveform monitoring means for determining whether the characteristic of the cyclic digital filter to be inspected is good or not based on a signal. 2. The inspection apparatus for a recursive digital filter according to claim 1, wherein a ramp waveform is used instead of the impulse waveform. 3. Inspection signal generating means for generating an inspection signal including an impulse waveform, delay means for delaying the inspection signal by a predetermined time and applying the same to a cyclic digital filter under test, Tap gain control means for setting the tap gain of the digital filter for inspection; addition means for synthesizing the inspection signal and an output signal from the cyclic digital filter under inspection; and a synthesis signal from the addition means. And a waveform monitoring means for determining whether the characteristic of the cyclic digital filter to be inspected is good or bad. 4. The inspection apparatus for a recursive digital filter according to claim 3, wherein a ramp waveform is used instead of the impulse waveform.