JPH0420004A - Function waveform generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an interval waveform generator, and more particularly to improving the output waveform quality.

<Conventional technology> Functional waveform data! One type of this is one that uses a direct digital synthesizer (DDS) method.

FIG. 4 is a block diagram showing an example of such a device. In FIG. 0, a memory 1 stores function waveforms. The function waveform data stored in the memory 1 is read out to the D/A converter 3 according to the address outputted from the phase address generator 2 with an address interval set arbitrarily. These memories 11 phase address generator 2 and D
/' The A converter 3 is supplied with a basic clock that determines the operation timing of the device from the clock generator 4.

The analog signal converted by the D/A converter 3 is outputted via the robust filter 5.

In such a configuration, the waveform output from the D/A converter 3 is not limited to a sine wave, but also includes waveforms with high harmonic components such as square waves, fiA tooth waves, and rectangular waves.

By the way, traditional attire! In this case, the memory 1 stores, for example, a waveform pig as shown in FIG. 6 having a spectrum characteristic as shown in FIG. 5 as waveform data of a rectangular wave. Here, fc represents the basic clock output from the clock generator 4, and fc/2 represents the Nyquist frequency.

When converting the waveform data stored in the memory 1 into an analog signal to generate a waveform, it is necessary to use the low-pass filter 5 to remove all signal components having a Nyquist frequency f c /2 or higher.

As shown in FIG. 7, such a low-pass filter 5 has a frequency characteristic of a band W that drops steeply in the vicinity of the Nyquist frequency f c /2, and the phase decreases at a constant slope in proportion to the frequency. Ideally, one with delay characteristics. If a low-pass filter with poor group delay characteristics and frequency characteristics as shown in FIG. 7 is used, the rectangular wave output will be of poor quality with ringing as shown in FIG. 8, for example.

<Problems to be Solved by the Invention> However, such an ideal low-pass filter is expensive, and when incorporated into a function waveform generator, there is a problem that the price of the entire device becomes high.

Therefore, in conventional devices, a low-pass filter with frequency characteristics in the band W2 and excellent group delay characteristics as shown in Fig. 9 is used at the expense of the frequency band used, but considering various waveform outputs, the low-pass filter It is desirable that the circumference of the filter is q-q, the width is one area, the C order, and the input is wide.

The present invention has focused on this point, and its purpose is to provide a function waveform generator that can substantially expand the frequency band used.

Means for Solving the Problems> The function waveform generator of the present invention reads function waveform data stored in a memory into a D/A converter according to addresses whose address intervals are set arbitrarily, and performs D/A conversion. In a function waveform generator configured to output an analog signal of a device to the outside through a low-pass filter, components near the Nyquist frequency are removed from among the frequency components of the function waveform data stored in the memory. It is characterized by

Since components near the Nyquist frequency of the function waveform data read out to the A/A converter are removed from the memory, high frequency components included in the analog signal converted and output from the D/A converter are also removed. Decrease.

As a result, the frequency characteristics required of the low-pass filter are relaxed, and the high-frequency components of the input signal to the low-pass filter are reduced, so that the usable band frequency of the entire device can be relatively expanded.

<Example> Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram showing a specific example of rectangular waveform data stored in the memory 1 based on the present invention, and FIG. 2 shows its spectral characteristics. That is, the high-frequency components of the rectangular waveform stored in memory 1 have been removed, and looking at its spectrum, as shown in Figure 2, the spectrum of region A near the Nyquist frequency f c ,,' 2 is It's missing.

FIG. 3 shows the frequency characteristics of the low-pass filter 5 used to generate waveforms by converting the function waveform data shown in FIGS. 1 and 2 into analog signals.
The one-dot chain line indicates the conventional characteristics.

Here, since high-frequency components have been removed from the waveform data read from the memory 1 in advance, the high-frequency components included in the analog signal converted and output from the D/A converter 3 are also reduced. Therefore, the influence of high frequencies on the low-pass filter 5 becomes small, and as a result, the band W of the low-pass filter 5
3 can be made wider than the conventional band W2.

Although the cost of such a low-pass filter having the band W3 is somewhat higher than that of the low-pass filter having the band W2, the cost of each stage is lower than that of an ideal low-pass filter having the band W1 and excellent group delay characteristics. is low, and even when it is incorporated into a waveform generator, the price of the entire device does not become so high.

<Effects of the Invention> As described above, according to the present invention, it is possible to provide a frequency waveform generator that can substantially expand the frequency band used.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a specific example of rectangular waveform data stored in the memory based on the present invention, Fig. 2 shows its spectral characteristics, and Fig. 3 shows the spectral characteristics thereof. Frequency characteristics of a low-pass filter used to convert function waveform data into an analog signal and generate a waveform. Figure 4 is a block diagram showing an example of a function waveform generator, and Figure 5 is a conventional device storing it in memory. Figure 6 is an explanatory diagram showing a specific example of rectangular waveform data stored in memory in a conventional device, and Figures 7 and 9 show the characteristics of a low-pass filter used in a conventional device. FIG. 8 shows the output waveform of a device using a low-pass filter having the characteristics shown in FIG. 7. DESCRIPTION OF SYMBOLS 1...Waveform data memory, 2...Phase address generator, 3...D/A converter, 4...Clock generator,...Low pass filter.

Claims (1)

[Claims] It is configured to read function waveform data stored in memory to a D/A converter according to addresses whose address intervals are arbitrarily set, and to output an analog signal from the D/A converter to the outside via a low-pass filter. 1. A function waveform generator characterized in that, among frequency components of the function waveform data stored in the memory, components near the Nyquist frequency are removed.