JPS61253934A - Testing device for a/d converter - Google Patents

Abstract

PURPOSE:To attain the detail test of the dynamic characteristic difference of an A/D converter to be tested from positive and negative through rates by using a triangular wave having a high through rate as an input testing waveform and finding out the dynamic characteristics from the deviation between the least square approximate straight line calculated on the basis of the data of the leading and trailing edge parts of a regenerated testing waveform and the regenerated testing waveform. CONSTITUTION:An output waveform from a triangular wave generator 7 is applied to a voltage comparator 19 and a synchronizing signal generator 20 and an output waveform defining an intersected point between a reference voltage Vs and the triangular wave as a changing point and a square output waveform 24 synchronized with the vertex of the triangular wave are outputted from the comparator 19 and the generator 20 respectively. Since the waveform 25 changes its pulse interval in accordance with the level value of the voltage Vs, calibrated information is obtained by continuously changing the voltage Vs and measuring the time difference from each waveform 24 by a counter 21 and stored in a memory 22. The regenerated wave form data of the A/D converter 2 to be tested are corrected by a computer 15 on the basis of the calibrated information. Thus, the testing accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a test device for an A/D converter, and in particular to an A/D converter test device for testing dynamic characteristics that depend on the slew rate of an input signal.
/D converter testing device.

[Background of the invention]

In recent years, the demand for high-speed A/D converters has been rapidly increasing in the field of digital signal processing such as video signal processing, high-speed waveform recording, and general measurement. Under these circumstances, dynamic characteristic tests for testing the characteristics of A/D converters under usage conditions have become important.

In particular, there is a need to efficiently test the nonlinearity of the A/D converter under test and the presence of defective codes, which depend on the so-called slew rate, which indicates the rate of change in amplitude per unit time of an input analog signal.

°The conventional test equipment is 6bit a-d chip 5teps up.
the pace of signal process
ing (Electronic Dedein 1982゜9/
16. P. 89-97)).

FIG. 10 shows a typical conventional test device described in the above-mentioned literature. In the figure, 1 is a low A'-pass filter (LPF), 2 is the A/El converter under test, 3 is the A/'D converter, 4 is the sawtooth generator, 5 is the differential amplifier, and 6 is the A/'D converter.
is an oscilloscope. The output of the sawtooth generator 4 is LP
After removing components higher than the Nyquist frequency by FIK, the signal is input to the analog input terminal of the A/D converter 2 under test. The A/D converter 2 under test outputs digital data synchronized with the conversion clock.

The digital data is again converted into an analog signal by an A/1) converter 31C having a resolution and conversion speed higher than that of the A/D converter under test 2. Here, the A/D converter under test 2
The difference between the input test waveform and the reproduced test waveform obtained by the differential amplifier 5 is observed by the oscilloscope 6, and from the waveform shape etc., it is determined that the A/D converter 2 under test is
Dynamic characteristics such as nonlinearity and defective codes can be known. The above operation will be explained using FIGS. 11(,), (b), and (c). The difference between the output waveform of the sawtooth generator 4 in Fig. 11 (Todoroki) and the reproduced waveform in Fig. 11 (b), Fig. 11 (
The result will be as shown in e). Here, if the conversion characteristics of the A/D converter 2 under test are ideally stepped, a continuous sawtooth error voltage with an amplitude of ±% I, SR will be generated. If there is a defect code as shown by the broken line in b), a discontinuity occurs as shown in FIG. 11(c), and the defect location can be easily identified. However, while the above method allows for uniform slew rate testing over the entire input signal range, it requires the differential amplifier 5 to have high common mode rejection (CMRR) characteristics, making it difficult to test high-speed sawtooth waves that reduce the common mode rejection ratio. was difficult. For this reason, the above-mentioned device is generally used mainly under conditions where the slew rate of the sawtooth wave is low, such as several V/rn s or less.

On the other hand, the method described in Waveform Digitype Manual (1983) K published by Sony Tektronix is known as a dynamic characteristic test under conditions similar to video signals, such as when the slew rate of the input analog signal is several Vi or more. It is being This device consists of the A/D converter 2 under test in FIG.
After directly storing the digital data in a memo IJK, the dynamic characteristics are known from the results of data processing by a computer.

In this case, a highly accurate sine wave is used as the input analog waveform, and the ideal sine wave is estimated by performing least squares approximation of the sine wave on the reproduced waveform by a computer. Next, the difference between the estimated waveform and the reproduced waveform is calculated, and the dynamic characteristics of the A/1) converter 2 under test are determined from this result. However, since this device uses a sine wave as the input analog waveform, the slew rate, especially near the top of the waveform, is small and is equivalent to that when inputting DC.
The slew rate dependence of this part could not be sufficiently tested.

[Purpose of the invention]

The present invention improves the difference in slew rate at each amplitude value of an input test waveform, and enables detailed testing of the dynamic characteristic difference of an A//D converter under test for positive and negative slew rates. An object of the present invention is to provide a testing device for /D converters.

[Summary of the invention]

The present invention uses a triangular wave with a high slew rate as an input test waveform, and combines the reproduced test waveform with a least squares approximation straight line calculated based on the data of the rising edge and falling edge of the reproduced test waveform. It is designed to know the dynamic characteristics rather than the deviation.

[Embodiments of the invention]

Hereinafter, a first embodiment of the present invention will be described using FIGS. 1 and 2.

In the figure, 2 is an A/D converter under test, 3 is a D/A converter, 7 is a triangular wave generator with high speed and high linearity characteristics,
8 is a frequency synthesizer, 9 is a reference clock generator, l
0 is a frequency divider, 11 is a latch circuit, 12 is a deglitch circuit, 13 is an A/D converter, 14 is a memory, and I5 is a computer.

The A/D converter 2 under test is a parallel type (Franosy type), and its configuration includes a comparator with a number of lines corresponding to the number of conversion bits for the analog input, and a comparison result of the comparator with the number of lines. It consists of a latch register that takes in and latches it as bit data, and an encoder that encodes the latch data. For example, in the case of an 8-bit digital output type, the number of comparators is 2'' = 256, and the encoder has the function of encoding these 256 digital data into 8-bit data. In some cases, a clock is applied as the latch timing of the latch register.

A conversion clock fllPL shown in FIG. 2 generated by the reference clock generator 9 is input to the A/D converter 2 under test. In order to synchronize the mutual phase relationship between the triangular waveform generated by the triangular wave generator 7 and the converted clock, and improve the stability of the reproduced waveform, the reference clock generator 9 generates a synchronization signal that is phase-synchronized with the converted clock. This is used as a reference signal for the frequency synthesizer 8. Furthermore, the phase relationship between the conversion clock and the output triangular wave is synchronized in order to synchronize the phase with the output signal of the triangular wave generator 7. The output digital data of the A/'D converter 2 under test is a clock obtained by dividing the conversion clock by n by a division period of 10 (n is a natural number), and the latch circuit 11
latches every Δ of the conversion clock frequency by adding to . By providing the latch circuit 11, the skew (time lag between pit data) that occurs between the output digital data of the A/D converter 2 under test is reduced, and the glitch (switch changeover) that occurs in the output of the D/A converter 3 is reduced. 4) to reduce the amount of time required. The latched output digital data is again converted into an analog signal by the D/A converter 3. Further, in order to reduce glitches occurring in the output of the D/A converter 3, the signal is passed through a diglitch circuit 12. The reproduced output waveform is f+
It is converted into a frequency Δf under the condition o=fsph/n. A simple test is possible by directly observing this reproduced waveform with an oscilloscope or the like.

However, by setting Δf small, the reproduced waveform is transferred to the A/D converter 1 which is slower and more accurate than the A/D converter 2 under test.
3 allows easy digital signal analysis. A/D
The waveform data for one cycle of the reproduced waveform is converted into A by the converter 13.
/'D conversion and storage in the memory 14, the computer 15 analyzes the data.

Next, we will discuss the analysis method. As an example, 4 cycles after A/D conversion of the A/D converter 2 under test for a triangular wave (
FIG. 3(a) shows the reproduced waveform of the J LSB portion. In the figure, black dots indicate sampling points of the A/D converter 2 under test. When testing an A/D converter, it is often necessary to determine whether the value of each conversion level matches an expected level, and in automatic testing, it is necessary to accurately identify the conversion level from the total sampled data. Here, Figure 3 (a
) The case where the level (■) is determined from the four levels (■ to ■) shown in the figure, which are composed of 60 points of sampling data shown in FIG. 2, will be explained. At the transition point of each level, test subject A
The comparison characteristics within the /D converter 2 generally create an area of level uncertainty, making correct identification of the conversion level difficult. Here, as shown in FIG. 3 (&), by sequentially comparing the sizes of the data, an uncertain region between points A and B, or between points A' and B' is detected. be able to. Therefore, accurate identification can be easily made by obtaining data before and after the midpoint C between point B and point A'.

By performing the above operations for ■ to ■,
), each converter can be identified, and the dynamic characteristics can be determined by performing the test over all input channels of the converter 2 to be tested.

Here, the coordinates of each X point in FIG. 3(b) are (Xt,
Y, ), (X,, Y,), (X!, Yri, (Xt, Y
4), from which y = a x + b is calculated. 1 and b in this case are given by the following equation.

a=-(Σ)'n bΣxn) (However, n = 1.2.3...n) Now, the characteristics of the A/D converter under test that overlap the conversion levels are shown in Figure 4 (
When the solid line in a) shows different dynamic characteristics for positive and negative slew rates, calculate the difference from the solid line from the ideal straight line 1% b and b% c obtained by the least squares method for the solid line data. By determining this, it is possible to quantitatively know the deviation exhibiting the dynamic characteristics as shown in FIG. 4(b).

That is, as shown in FIG. 5, the error E of the conversion characteristic is calculated from the ideal straight line y1, y obtained by the least squares method with respect to the solid line A1B indicating the actual data between a % b % c. ) and (Byt).

Therefore, by determining the maximum and minimum values between a, b, and c, it is possible to specify nonlinearity, defective codes, etc. at the test slew rate.

As stated above, according to this embodiment, compared to the conventional test using a sawtooth waveform, a test using a triangular wave having high speed and high linearity characteristics is possible because a differential amplifier is not used. Quantitative testing can be performed across all input levels under high positive and negative slew rate conditions. Moreover, automatic testing is also possible by comparing the magnitude with a permissible deviation value from a preset ideal characteristic.

FIG. 6 is a block diagram showing another embodiment of the present invention (
In the figure, the same reference numbers are used for the same parts as in Figure 1). In this embodiment, the configuration after the latch circuit 11 shown in FIG. In this embodiment as well, the reference clock generator 9, the frequency converter 8, and the triangular wave generator 7 are connected to the conversion clock frequency f IIPL and the test triangular wave frequency f for the same reason as in the first embodiment.
Phase synchronization between B and B is performed. A/1) The output digital data of the converter 2 under test is rearranged by the computer 15 and the waveform is reproduced. Compared to the first embodiment, this embodiment does not use a waveform reproduction K D/A converter, so it has the advantage of not including errors of the D/A converter.

Next, the above conversion process will be explained in detail using FIG.

The input signal frequency fllG is the Nyquist frequency (= f
gpt, /2), it is not possible to obtain a sufficient number of sampling points for the period of the input signal, and it becomes difficult to obtain sufficient waveform information for the test. However, when the input signal has a constant repetition period as shown in Figure 7, by obtaining different sampling information from the input signal waveform for several periods, the number of sampling points for the input signal - period can be equivalently calculated. can be increased to

The repetitive input triangular waveform shown in FIG. 7(a) is A/D converted by the A/'D converter 2 over three cycles using the conversion clock shown in FIG. 7(b) to obtain the result shown in FIG. 7(C). . These are rearranged by the computer 15 as shown in FIG. 7(d) and then converted to a level corresponding to the output digital code. As a result, it is possible to obtain a reproduced waveform having three times the number of sampling points per - period in the figure (&).

Here, when the input signal frequency is tsa, the data acquisition repetition frequency is M, and the conversion clock frequency is fsPL, if you want to obtain N sampling points for the input signal - period, fs+pL = '/M・f8G It is sufficient to satisfy the following conditions. The method of identifying the conversion level for the reproduced waveform and the method of determining the deviation from ideal characteristics are the same as in the first embodiment.

In order to realize the present invention, the triangular generator 7 is required to be high-speed and have linearity superior to that of the A/D converter 2 under test. If this cannot be obtained, this can be improved by the following method.

That is, as shown in FIG. 8, this can be realized by providing the configuration shown in FIG. 6 with a function to calibrate the linearity of the triangular waveform in advance. This function includes a reference voltage generator 18, a voltage comparator 19, a synchronization signal generator 20, a counter 21 . This can be realized by adding a memory 22.

The output waveform of the triangular wave generator 7, as shown in FIG.
5 and a rectangular output waveform 8 synchronized with the apex of the triangular wave. The pulse interval of the output waveform 25 changes depending on the level value of Vs. Therefore, ■! Continuously change I, and calculate the time difference with the output waveform U at each time using counter 2.
By measuring with 1, linearity data (calibrated information) is obtained, which is stored in memory 22.

The reproduced waveform data of the A/D converter 20 under test is corrected by the computer 15 using calibration information. Such a configuration makes it possible to correct the linearity of the input triangular waveform, thereby improving the accuracy of the υ test.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to test all conversion levels of an A/D converter under uniform slew rate conditions. Furthermore, since waveform reproduction is performed by digital calculation, least square approximation straight lines can be easily obtained for each of the rising and falling portions of the reproduced waveform data. Therefore, a reference straight line can be provided for the reproduced waveform, and the dynamic characteristics of the A/I converter under uniform positive and negative slew rate conditions can be easily determined from the difference between this reference straight line and the reproduced waveform data. be. Therefore, the maximum conversion error generated by the A/D converter under test under the test slew rate can be easily defined.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an operation waveform diagram of each part corresponding to Fig. 1, and Fig. 3 (,), (b).
) is an explanatory diagram of conversion level detection in the embodiment of FIG. 1, FIGS. 4 (, ), (b), and 5 are explanatory diagrams for determining deviation from ideal characteristics due to dynamic characteristics. FIG. Block diagram showing other embodiments of FIG. 7(a), (1), (d)
is an explanatory diagram of waveform reproduction in the embodiment of FIG. 6, FIG. 8 is a block diagram showing a modification of the embodiment of FIG. 6, FIG. 9 is an operational waveform diagram of each part in FIG. 8, and FIG. Conventional example diagram,
Figure 11 is a time chart. DESCRIPTION OF SYMBOLS 1... Low pass filter, 2... A/D converter under test, 3... D/A converter, 4... Sawtooth wave generator, 5...
... Differential amplifier, 6 ... Oscilloscope, 7 ... Triangle wave generator, 8 ... Frequency synthesizer, 9 ... Reference clock generator, 10 ... Frequency divider, 11 ... Latch Circuit, 12... Diglitch circuit, 13... A/
D converter, 14.22...Memory, 15...Computer, 16...High speed memory, 17...XYf rotor, 1
8... Reference voltage generator, 19... Voltage comparator, 20
...Synchronization signal generator, 21...Counter. Agent Patent Attorney Tadashi Akimoto Figure 9 Figure 1o Figure 11

Claims (1)

[Scope of Claims] 1. In a testing apparatus, an analog signal is input to an A/D converter to be tested, is converted into a digital signal, and is reproduced to obtain dynamic characteristics of the A/D converter. A test signal generation unit that generates a triangular wave signal as an analog signal to be supplied to the D converter, and the minimum rising and falling portions of the waveform that reproduces the signal output from the A/D converter into the original triangular wave signal. A characterized in that it comprises a calculating means for obtaining an ideal straight line by the method of squares, and a means for calculating the deviation between the data on the ideal straight line by the means and the actual data of the reproduced waveform.
/D converter testing equipment. 2. The A/D converter testing device according to claim 1, further comprising a calibration unit that compares the triangular wave signal voltage with a reference voltage and calibrates the linearity of the triangular waveform in advance. .