JPH01273423A - Calibration method for analog digital converter - Google Patents

Abstract

PURPOSE:To calibrate both a front-end circuit and an analog digital conversion section by applying a frequency signal such as a ramp signal and calibrating the characteristic from the output change and the frequency spectrum. CONSTITUTION:A switch 1 is thrown to the position of a standard signal generating section 10 side and a switch 11 is set to the position of the pre-stage circuit 2 to input a ramp wave being an output of the standard signal generating section 10 to the front-end circuit 2, and after the output is converted into a digital by an analog digital conversion section 3, a signal analysis section 12 applies Fourier transformation to the signal to obtain the amplitude of each frequency component thereby calibrating the AC characteristic of the pre-stage circuit 2. Moreover, the switch 11, is thrown to the position of the standard signal generating section 10 side to input the ramp wave to the analog digital conversion section 3, an error due to nonlinear output signal is measured by the signal analysis section 12 to calibrate the nonlinearity of the analog digital conversion section 2. Thus, both the front-end circuit and the analog digital conversion section are calibrated by one signal.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to a method for calibrating an analog-to-digital converter;
In particular, the present invention relates to a method for calibrating an analog-to-digital converter that can calibrate multiple characteristics using a single calibration signal.

<Prior art> An analog-to-digital converter generally consists of two parts: a pre-circuit that includes an amplifier, a filter, etc., and an analog-to-digital converter that converts the signal into a digital signal. The constant DC characteristics change and these become the cause of errors.

A method of calibrating such an analog-to-digital converter will be explained based on FIG. In FIG. 5, an input signal to be converted into a digital signal is passed through a switch 1 to a precircuit 2.
After being subjected to amplification, filtering, etc., it is converted into a digital signal by the analog-to-digital converter 3 and output. When the pre-circuit 2 and the analog-to-digital converter 3 constitute the analog-to-digital converter 4 and perform zero calibration, the switch 1 inputs the output of the standard signal generator 5 to the pre-circuit 2. The standard signal generator 5 generates two types of signals for calibrating the pre-circuit 2 and for calibrating the analog-to-digital converter 3.

In order to calibrate the pre-circuit 2, a rectangular wave V is input to the pre-circuit 2 by the standard signal generator 5. The rectangular wave Vta contains many frequency components, and when expanded by Fourier, VS (t)=4iΣsin (nπ/2)cosn
It is expressed as t/n)/π. This signal changes depending on the characteristics of the front circuit 2, and its magnitude and phase delay change.

The output of the analog-to-digital converter 3 is Fourier-transformed by the signal analyzer 6 and the attenuation amount and phase delay are determined, thereby making it possible to calibrate the AC characteristics of the front circuit 2. When calibrating the analog-to-digital converter 3, a plurality of signals whose magnitudes are known are inputted to the pre-circuit 2 by the standard signal generator 5, and the digitally converted signals are measured by the signal analyzer 6.

This allows offset, full scale, linearity, etc.
Flow characteristics can be calibrated. Furthermore, the DC characteristics of the front circuit 2 can be calibrated at the same time.

<Problems to be Solved by the Invention> However, in this method of calibrating an analog-to-digital converter, two types of signals are required to calibrate the pre-circuit 2 and the analog-to-digital converter 3.
The problem was that the configuration was complicated.

<Object of the Invention> An object of the present invention is to provide a method for calibrating an analog-to-digital converter that can calibrate both the front circuit and the analog-to-digital converter using one signal.

Means for Solving the Problems> In order to solve the above problems, the present invention applies a periodic signal such as a ramp signal whose output level changes linearly with time to an analog-to-digital converter. The characteristics of the digital converter are calibrated from the output change and frequency spectrum of the digital converter.

<Example> FIG. 1 shows the configuration of an apparatus for realizing the calibration method of the present invention. The same elements as in FIG. 5 are denoted by the same reference numerals, and their explanation will be omitted. In FIG. 1, an input signal to be converted into a digital signal is input to a switch 1. 10 is a standard signal generating section, which outputs a ramp wave shown in FIG. This rung wave is input to switch 1. The switch 1 selects this ramp wave and the input signal and inputs them to the front circuit 2. 1
Reference numeral 1 denotes a switch, into which the output of the front circuit 2 and the output of the standard signal generator 10 are input. The switch 11 selects these two signals and inputs them to the analog-to-digital converter 3. The pre-circuit 2 and the analog-to-digital converter 3 constitute an analog-to-digital converter. 12
is a signal analysis section, which receives the output of the analog-to-digital converter 3 and analyzes this output to calibrate the analog-to-digital converter.6 Normally, the input signal is input to the pre-circuit 2 via the switch 1. The output of this pre-circuit 2 is input to an analog-to-digital converter 3 via a switch 11, converted into a digital signal, and output.

Next, the calibration method will be explained. To calibrate the front circuit 2, switch 1 is set to the standard signal generator 10 side and switch 11 is set to the front circuit 2 side.

That is, the ramp wave that is the output of the standard signal generator 10 is input to the pre-circuit 2, and the output thereof is converted into a digital signal by the analog-to-digital converter 3 and input to the signal analyzer 12. As shown in FIG. 2, the ramp wave is a periodic signal whose level increases linearly, and when its output Vt is Fourier expanded, it is expressed as Vt=Σ5in(nt)/nt: time. However, it is assumed that one period is normalized to 2π and the amplitude is normalized to π. That is, the frequency f of the ramp wave. It is a composite of signals that have a period that is an integral multiple of , and whose amplitude attenuates at a rate of 1/n.

This signal is passed through the pre-circuit 2, its output is converted into a digital signal by the analog-to-digital converter 3, and then Fourier-transformed by the signal analyzer 12 to obtain the amplitude of each frequency component. Its amplitude changes depending on the AC characteristics. This situation is shown in FIG.

In Figure 3, the horizontal axis is frequency, the vertical axis is amplitude, and 1
3 is a spectrum obtained by Fourier expansion of the ramp wave output from the standard signal generation section 10, and 1-4 is a spectrum obtained by Fourier expansion of the output of the analog-to-digital conversion section 3 by the signal analysis section 12. However, the frequency f. Normalized by the amplitude of . This amplitude difference δ is due to signal deterioration caused by attenuation, phase delay, etc. caused by the front circuit 2. This allows the AC characteristics of the front circuit 2 to be calibrated. That is,
This difference δ is corrected by a correction circuit (not shown). It is also possible to calibrate the delay from the phase at high frequencies.

Next, a method of calibrating the analog-to-digital converter 3 will be explained. In this case, the switch 11 is replaced by the standard signal generator 10.
1, the ramp wave is input to the analog-to-digital converter 3. The ramp wave is a signal whose amplitude increases linearly as shown in FIG. 2, and the analog-to-digital converter 3 converts this ramp wave into a digital signal at regular intervals. The magnitude and linearity of the digitized signal are evaluated by the signal analysis section 12. This situation is shown in FIG. 4. The horizontal axis in FIG. 4 is the voltage input to the analog-to-digital converter 3.

Since the input signal is a ramp wave, it is equivalent to time. The vertical axis represents the size of the output code of the analog-to-digital converter 3. If there is no non-linearity in the analog-to-digital converter 3, the curve will be a straight line like the straight line 15, but if there is non-linearity, the curve will be like the curve 16. By measuring the error δ due to this nonlinearity in the signal analysis section 12, the nonlinearity of the analog-to-digital conversion section 3 can be calibrated. Offset and full scale can also be calibrated in the same way.

In this embodiment, the output of the standard signal generator 10 is a ramp wave, but it may be a triangular wave.

In the case of a triangular wave, the Fourier expansion of its output ■1 is V, (t)=lΣ(1) 5in(2n+1)t/(
2n+1>2)/π, and can be calibrated in the same way as for the ramp wave.

In short, any periodic signal whose output level changes linearly may be used.

<Effects of the Invention> As specifically explained above based on the embodiments, in the present invention, a periodic signal whose output level changes linearly is input to an analog-to-digital converter, and the output of the analog-to-digital converter is The analog-to-digital converter is calibrated based on output level changes and frequency spectra. Therefore, there is an effect that both the pre-circuit and the analog-to-digital converter can be calibrated with one signal.

Further, since calibration can be easily performed, an inexpensive analog-to-digital converter can be used.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus for carrying out the calibration method for an analog-to-digital converter according to the present invention, FIG. 2 is a waveform diagram, and FIGS. 3 and 4 are characteristic curve diagrams for explaining the calibration method. FIG. 5 is a block diagram of a conventional calibration device. 1.11...Switch, 2...Pre-circuit, 3...
Analog-to-digital conversion section, 10... standard signal generation section,
12...Signal analysis section. Figure 4 I^ Figure 5-<tug. )6.Order-

Claims (1)

[Claims] A periodic signal whose output level changes linearly with respect to time is applied to the analog-to-digital converter, and its characteristics are calibrated based on the output change and frequency spectrum of the analog-to-digital converter. How to calibrate analog-to-digital converters.