JPH0736489B2 - Waveform generator - Google Patents

Description

The present invention relates to a waveform generator, and more particularly to control of the rise time and fall time of a waveform.

<Prior Art> FIG. 8 is a waveform diagram showing an example of a color difference signal in a video signal.

Such a waveform can be generated digitally, for example, by adding waveform data to a D / A converter.

By the way, in such a device for digitally generating a waveform, as a method of changing the rising time or the falling time of the waveform, a desired band limitation is applied by a digital filter when generating the waveform data. .

<Problems to be Solved by the Invention> However, according to such a conventional method, it is necessary to design a variable digital filter and incorporate a processing unit that performs a filtering process.

Moreover, since the D / A converter is used, the waveform data to be handled is finite and periodic. When an FIR type filter is used as a digital filter for such waveform data, a high order is required to obtain a low-pass filter characteristic with a narrow band, long calculation processing time is required, and the number of waveform data When it is relatively small, sufficient characteristics cannot be obtained. On the other hand, when an IIR type filter is used as the digital filter, the order is low and the calculation processing time is short, but the effect of the initial value of the waveform data remains forever.

The present invention focuses on such a point, and an object thereof is to provide a waveform generator capable of controlling the rise time and the fall time of an output waveform by a relatively short time arithmetic process without using a digital filter. To provide.

<Means for Solving the Problem> A waveform generator of the present invention is provided with a first waveform memory in which original waveform data is stored in a form that does not include rise (fall) time data, and read from the first memory. A data processing unit for performing a third-order spline interpolation process based on rise (falling) time data for the waveform data to be stored, a second waveform memory for storing the waveform data calculated by this data processing unit, And a D / A converter that converts the waveform data read from the memory 2 into an analog signal.

<Operation> In the present invention, the rising time and the falling time of the output waveform are directly set as the parameters of the cubic spline interpolation process. The thus-obtained waveform output is obtained by cubic spline interpolation of the original waveform data, the connection with the original waveform data is smooth, and the differential value is continuous, so that unnecessary high frequency is generated. Instead, a natural waveform is obtained.

<Example> Hereinafter, an example of the present invention is described in detail using a drawing.

FIG. 1 is a block diagram showing an embodiment of the present invention.
In the first memory 1, the original waveform data as shown in FIG. 8 is stored in a form not including the rising (falling) time data. The original waveform data stored in the first memory 1 is read by the data processing unit 2. The data processing unit 2 performs a cubic spline interpolation process on the waveform data read from the first memory 1 based on the rising (falling) time data. The waveform data subjected to the cubic spline interpolation processing by the data processing unit 2 is stored in the second memory 3. The waveform data stored in the second memory 3 is read by the D / A converter 4 and converted into an analog signal. The analog signal converted by the D / A converter 4 is output to the outside through the low pass filter 5.

The operation of the apparatus thus configured will be described.

The cubic spline interpolation formula is the point x ₁ , x ₂ , ..., xn (x ₁ <x ₂
When yi = f (xi) (i = 1,2, ..., n) is given to <... <xn), the function S (x) that satisfies the following condition is called.

In the section [xi, xi _{+ 1} ] (i = 1,2, ..., n-1), S (x) is expressed by the following cubic expression.

S (x) = f (xi) + ci ₁ (x−xi) + ci ₂ (x−xi) ² + ci ₃ (x−xi) ³ (1) The first derivative S ′ (x) of S (x) And the second derivative S ″ (x) is continuous over the entire interval.

S (xi) = f (xi) (i = 1,2, ..., n) Let Mi be the second derivative of S (x) in xi, and the second derivative S ″ is [xi, xi ₊₁ ] (X) is become. The second derivative S ″ (x) is integrated and the integration constant is determined from.

From the above equation, the right differential coefficient S + ′ (xi) is And the left differential coefficient S-′ (xi) is become.

Further, the coefficients ci ₁ , ci ₂ , ci ₃ in the equation (1) are become.

Next, a spline that connects two DC data of different levels will be described. A spline function formula S (x) that smoothly connects two DC levels y ₁ and y ₂ having different levels as shown in FIG. ₂ in the section [x ₁ and x ₂ ] is obtained.

First, in order to simplify the calculation, the number of data n = 2 (x ₁ , y ₁ ) = (0,0) (x ₂ , y ₂ ) = (1,1) (condition 1). The end condition is S + ′ (x ₂ ) = 0 S − ′ (x ₁ ) = 0 (condition 2).

Substituting these conditions 1 and 2 into the equations (3) and (4) and rearranging, 2M ₁ + M ₂ = 6 M ₁ + 2M ₂ = −6, and from these, M ₁ = 6, M ₂ = − You get 6 Further, from these and the equation (5), C ₁₁ = 0, C ₁₂ = 3, C ₁₃ = -2, and S (x) in FIG. 2 is S (x) = − 2x ³ + 3x ² ... (6)

Similarly, in the case of falling (y ₂ <y ₁ ), S (x) = 2x ³ −3x ² +1 (7)

Since S (x) is expressed by a mathematical expression in this way,
As shown in the figure, the rise time (ba) defined by the 10% -90% level can also be obtained by solving the cubic equation.

That is, the time a in FIG. 3 becomes a = 0.1958 by solving S (x) = 0.1, and the time b becomes b = 0.8042 by solving S (x) = 0.9. Becomes b−a = 0.6084 for the interval [0,1].
This ratio does not change even if the section width and the y-axis level difference change. Conversely, if (ba) is T, the interval width is 1.
It can be expressed as 644T.

As is apparent from these, when the rise time T is specified, the cubic spline interpolation is performed with the section width of 1.64T, and the waveform of the desired rise time can be obtained as shown in FIG.

The processing contents of the data processing unit 2 in FIG. 1 will be described.

In the following description, the rise time is described, but the fall time is the same.

First, the user creates original waveform data having a desired DC level as shown in FIG. 8 without considering the rise time, and stores it in the memory 1.

Next, a desired rising time T (see FIG. 4) is set. This is equivalent to limiting the band.

When the data processing unit 2 scans the original waveform data and finds a rising edge, the section of 0.82T before and after that point (section width 1.64T,
In FIG. 4), cubic spline interpolation as shown in FIG. 5 is performed. Here, the spline interpolation formula at the time of rising is the formula (6), and the spline interpolation formula at the time of falling is the formula (7). The rising time of the waveform data thus generated is T.

The waveform data subjected to the spline interpolation process is added to the D / A converter 4 and converted into an analog signal. Where DA
The staircase conversion output waveform phenomenon associated with the conversion can be eliminated by selecting the low-pass filter 5 having an appropriate characteristic.

FIG. 6 is a flowchart showing the flow of such a series of processing, (A) shows the flow of the whole processing, and (B).
Shows the flow of the rising processing portion in (A).

By outputting a rectangular wave according to the flowchart of FIG. 6, a waveform having a desired rising time T can be obtained.

FIG. 7 is a waveform diagram showing a concrete processing example, using a D / A converter 4 having a 100 MHz sampling rate of 10% -90.
An example is shown in which waveform data having a rise time T of 100% is 100 nsec. In (a), the original waveform data is created without considering the rising edge. In (b), T =
Set a spline interpolation section with a width of 1.64T for 100nsec centering on the change point. Then, by executing the spline interpolation processing according to the equation (6), waveform data having a rising time of 100 nsec as shown in (c) can be obtained.

With such a configuration, the inconvenience of using a conventional digital filter can be eliminated, and even if the number of original waveform data is small, the desired rising and falling change characteristics can be obtained by a relatively simple arithmetic process. It is possible to obtain different waveforms.

Note that the first memory and the second memory may be used separately, or one large capacity memory may be divided and used.

<Effects of the Invention> As described above, according to the present invention, it is possible to realize a waveform generator capable of controlling the rise time and the fall time of an output waveform by a relatively short time arithmetic process without using a digital filter. It is suitable for various waveform generators.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of cubic spline interpolation, FIGS. 3 and 4 are rising explanatory diagrams, and FIG. 5 is an operation explanatory diagram of FIG. FIG. 6 is a flow chart showing the flow of the operation of FIG. 1, FIG. 7 is a concrete operation example diagram, and FIG. 8 is an original waveform example diagram. 1 ... First memory, 2 ... Data processing unit, 3 ... Second memory, 4 ... D / A converter, 5 ... Low-pass filter.

Claims (1)

[Claims] 1. A first waveform memory in which original waveform data is stored in a form that does not include rising (falling) time data, and rising (falling) time for waveform data read from the first memory. A data processing unit that performs cubic spline interpolation processing based on the data, a second waveform memory that stores the waveform data calculated by the data processing unit, and the waveform data read from the second memory into an analog signal. A D / A converter for converting, and a waveform generator characterized in that.