JPH0388504A - Optional waveform generator - Google Patents

Abstract

PURPOSE:To improve the linearity of DA conversion when the found arithmetic result of a waveform defining expression in converted into the waveform data by correcting an arithmetic result into waveform data in which the nonlinearity of the DA conversion is corrected based upon the values in an error correction table and outputting the corrected data. CONSTITUTION:When converting the arithmetic result of the optional function into the input data to a DA converter 3, the control circuit 10 refers to the error correction table 11 to correct the arithmetic result into a value closest to an ideal output value, and then outputs the value. For example, the range of the arithmetic result X found by the arithmetic control circuit 10 from the optional waveform is determined by referring to measured values stored on a memory 11 by the arithmetic control circuit 10. Namely, the range of (x) is so corrected that respective steps in a figure, i.e., errors have equal positive and negative values, and the DA input data is determined according to the range. Consequently, the linearity of a DA converter is improved and a high- accuracy output is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to improving digital-to-analog conversion linearity in an arbitrary waveform generator.

<Prior Art> An example of a conventional digital arbitrary waveform generator is shown in FIG. In the figure, 1 is a waveform memory in which waveform data is stored, and 2 is a clock/address generator that generates the addresses necessary to read out the waveform data from waveform memory 1 and also generates the readout waveform data (digital data). )
is a digital-to-analog converter (hereinafter referred to as a DA converter)
3 generates a conversion clock for analog conversion.

4 is an arithmetic/control circuit that calculates the waveform data to be given to the waveform memory 1 from the waveform definition equation, and also calculates the waveform data given to the waveform memory 1 by calculating the clock and
It controls the address generator 2 to appropriately generate addresses and clocks.

In such a configuration, the waveform definition equation is calculated in advance in the calculation/control circuit 4 to obtain waveform data of the output waveform,
Store in waveform memory. Thereafter, the clock address generator 2 specifies an address, the waveform data is read from the waveform memory 1, and the DA converter 3 converts it into analog data. By repeating this data reading and analog conversion operation without interruption, a continuous analog waveform can be obtained.

Note that this output waveform is ultimately shaped into a smooth waveform by passing it through a low-pass filter, etc., but since it is not directly related here, that part will be omitted.

<Problems to be Solved by the Invention> By the way, in such a conventional arbitrary waveform generator, when a waveform definition formula is calculated in the calculation/control circuit 4 and converted into waveform data of an output waveform, the valid bits of the calculation value itself are Despite the fact that the number is large and the resolution is high, assuming an ideal DA converter, data below the DA resolution is simply rounded off and the value is given to the waveform memory 1.

Therefore, there is a problem in that the output waveform of the DA converter 3 contains errors due to linearity errors, differential linearity errors, etc. of the DA converter 3 in addition to quantization errors during conversion.

The object of the present invention has been made in view of the above points, and it is an object of the present invention to improve errors such as linearity error and differential linearity error of a DA converter by using an error correction daple and a waveform data creation means, and to achieve high precision. An object of the present invention is to provide an arbitrary waveform generator capable of generating waveforms.

Means for Solving the Problems> In order to achieve such objects, the present invention calculates a waveform definition formula using an arithmetic/control circuit, stores the calculated waveform data in a waveform memory, and stores this waveform data in a waveform memory. In an arbitrary waveform generator that generates an arbitrary waveform by sequentially reading out waveform data from a memory and converting it into analog data using a DA converter, the relationship between the input data and output data of the DA converter is corrected by pre-stored error correction. The arithmetic/control circuit includes a table, and when converting the arithmetic result of the obtained waveform definition formula into waveform data, the arithmetic/control circuit performs a DA based on the value of the error correction daple.
The present invention is characterized in that it is configured to include a function of correcting and outputting waveform data such that non-linearity of conversion is corrected.

<Operation> In the present invention, the waveform data given to the DA converter is corrected while the input/output characteristics (linearity) of the DA converter remain unchanged.

The error correction table stores the difference data between the input and output values of the DA converter or the ideal output value and the actual output value.

In the arithmetic/control circuit, when converting the value obtained from the waveform definition formula into waveform data given to the waveform memory, the value of the error correction table is referred to, and the waveform is created so that the linearity of DA conversion is improved. Correct the data.

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

FIG. 1 is a block diagram showing an embodiment of an arbitrary waveform generator according to the present invention. In the figure, parts equivalent to those in FIG. 5 are designated by the same reference numerals, and their explanation will be omitted.

Reference numeral 10 denotes an arithmetic and control circuit, and data supply and control to the waveform memory 1 and bow lock address generator 2 are the same as in the conventional example. However, when converting the calculation result of an arbitrary function into input data to the DA converter, refer to the error correction table 11 and correct it to the value that is closest to the ideal output value (output value without error). The output function is different from that of the conventional example.

The error correction table 11 is composed of a memory, and stores the difference between the ideal value and the measured value of the output of the DA converter 3. Note that it is also possible to use the measured value itself instead of the difference between the ideal value and the measured value.

This error correction table stores data obtained in advance through actual measurements. If the DC characteristics of the DA converter 3 can be determined using an external voltmeter or self-calibration function (CAL function), the ideal value (output value with no error relative to the input value) and the actual output value can be determined by that means. Find the difference between the two and memorize it.

Reference numeral 12 is a low-speed, high-resolution analog-to-digital converter (hereinafter referred to as AD) used when it has the above CAL function.
A predetermined input is given to the DA converter 3 (from the arithmetic/control circuit 10), the output at that time is read by the AD converter 12, and the difference (or the read value itself) is calculated. Store it in the memory 11.

Note that the memory as the error correction table 11 is CAL
Read-only memory (RO)
M) If the device has a CAL function, it is desirable to use random access memory (RAM).

The operation in such a configuration will be explained next.

In order to simplify the explanation, an example will be described in which a 3-bit converter is used as the DA converter 3.

FIG. 2 is a diagram showing the relationship between the input calculation value and the output of the DA converter during ideal RI-A conversion. In this case, the calculation results x, D obtained from the arbitrary waveform in the calculation/control circuit 10
The relationship between the A input data and the output of the DA converter 3 is shown in Table 1. For example, if the calculation result X is 0, 5≦x<1.
In the case of 5, the arithmetic/control circuit 10 selects and outputs 1 as the DA input data, and the analog output obtained by converting the DA input data also becomes 1.

If 1.5≦x<2.5, 2 is selected and output as the DA input data, and the analog output that is converted and output is also 2. The maximum error in this case is 0.5LSB
(LSB is the minimum bit value of the DA converter).

Assume that the DA input/output relationship is as shown in FIG. That is, it is assumed that the relationship between the DA input data (in this case, the relationship between the calculation result X and the DA input data is the same as in the ideal case) and the output data is nonlinear (Table 2). The maximum error in this case is 1.5LSB.

Table 2 In the present invention, the input/output characteristics of the DA converter 3 are left unchanged, and the DA input data 1, 2, 301 . The calculated value X for is corrected as shown in Table 3.

Table 3 If you select the DA input data by correcting the range of
(less) characteristics are obtained.

The determination of the range of X as described above is performed by the arithmetic/control circuit 10 with reference to the measured values stored in the memory 11. That is, the range of X is corrected so that the difference in level of each step in FIG. 2, so-called error (error with respect to straight line A), has the same positive and negative values as shown in FIG. 3, and the DA input data is determined based on this.

Note that even if monotonous increasing property cannot be maintained and an A converter is used, linearity can be improved by similar processing.

<Effects of the Invention> As explained in detail above, according to the present invention, the linearity of the DA converter is improved, so distortion etc. caused by the DA converter in the output of the arbitrary waveform generator is improved. This has the effect of providing highly accurate output.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the arbitrary waveform generator according to the present invention, FIG. 2 is a diagram showing ideal DA conversion characteristics, and FIGS. 3 and 4 are DA conversion characteristics for explaining operation. FIG. 5 is a configuration diagram showing an example of a conventional arbitrary waveform generator. DESCRIPTION OF SYMBOLS 1... Waveform memory, 2... Clock address generator, 3... DA converter, 10... Arithmetic/control circuit,
1 1...Error correction table, 2...AD converter.

Claims (1)

[Claims] A waveform definition equation is calculated by an arithmetic/control circuit, the calculated waveform data is stored in a waveform memory, and the waveform data is sequentially read from the waveform memory and converted into analog by a DA converter. As a result, an arbitrary waveform generator that generates an arbitrary waveform is provided with an error correction table in which the relationship between input data and output data of the DA converter is stored in advance, and the arithmetic/control circuit is configured to generate an arbitrary waveform definition. When converting the calculation result of the formula into waveform data, the DA is calculated based on the value of the error correction table.
An arbitrary waveform generator characterized in that it is configured to include a function of correcting and outputting waveform data such that non-linearity of conversion is corrected.