JPH0436608B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an A/D converter testing device, and more particularly, to an improvement in a device that performs testing using the curve fit method.

(Prior Art) One of the testing methods for A/D converters is the curve fit method.

FIG. 5 is a block diagram showing an example of an apparatus used in such a test method.

In FIG. 5, 1 is a high purity sine wave generator which outputs a sine wave signal with a frequency of fs. This output signal is applied to an A/D converter to be measured (hereinafter referred to as DUT) 2. Reference numeral 3 denotes a memory for storing conversion data of the DUT 2, and an area for storing data of a preset number of samples is secured. 4 is a clock generator that generates a clock with a frequency fc, which is added to DUT 2 as a sampling clock, and is also applied to memory 3.
is added as a strobe clock. Here, the frequency fs of the input signal applied to DUT2
and the clock frequency fc are set so that the following relationship holds: fs/fc=K/N...(1) N: Total number of data samples K: Number of sample waves (N and K have a prime relationship) There is. Also,
The total number of data samples N is set so that the resolution of the DUT2, expressed as 360/N (deg) (2), is sufficiently smaller than 1 LSB of the DUT2. 6th
The figure is an explanatory diagram showing an example of these relationships,
a shows the sinusoidal signal applied to DUT2, b
indicates the clock applied to DUT2.
5 is a data processing unit, which performs a discrete Fourier transform (hereinafter referred to as DFT) on the transformed data stored in the memory 3.
It performs processing to obtain phase data and amplitude data of an ideal sine wave signal corresponding to the input signal applied to the DUT 2, and also calculates the SN ratio using Parseval's formula.

In such a configuration, the converted data sampled by the DUT 2 is stored in the entire area of the memory 3. Then, the data processing unit 5 performs DFT processing on these stored conversion data to obtain phase data and amplitude data of an ideal sine wave signal corresponding to the input signal applied to the DUT 2.

As a result, the error between these ideal sine wave signal data and the converted data can be found, and the DUT2
It is possible to evaluate various characteristics of

(Problem to be solved by the invention) However, in such a configuration, the ratio between the frequency fs of the input signal applied to the DUT 2 and the frequency fc of the clock has an error with respect to the value of K/N in equation (1). When this occurs, the interval between adjacent sample points, that is, the resolution, changes, and depending on the size of the error, a part of the conversion code may not be sampled and the DUT2
It may interfere with the test.

The present invention focuses on these points, and its purpose is to reduce the influence of the error in the frequency ratio of the sine wave signal applied to the A/D converter to be measured and the clock, and to achieve high precision. An object of the present invention is to provide an A/D converter testing device that can perform testing.

(Means for Solving the Problems) The present invention solves these problems by applying a sine wave signal from a high purity sine wave generator to the A/D converter to be measured. The converted data output from the memory is stored in a memory, the phase and amplitude of an ideal sine wave signal corresponding to the input signal are obtained by performing discrete Fourier transform on the converted data stored in the memory, and these ideal sine wave signal data and In an A/D converter testing device that determines the error with conversion data, the resolution N of the sample data and the sample wave number K according to the test content of the A/D converter to be measured maintain a prime relationship and (N+1)/K. = M (M is an integer) or (N-1)/K = M (M is an integer) N) means for calculating the frequency value fs of the input signal using fc and controlling the output frequency of the high purity sine wave generator according to the calculation result.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and the same parts as in FIG. 5 are given the same reference numerals. In FIG. 1, 6 is a high purity sine wave generator 1
This is a control block that controls the output frequency fs.
This control block 6 controls the sample data resolution N and sample wave number K according to the test content of the DUT2.
is prime and the following relationship holds: (N+1)/K=M (M is an integer) ...(3) or (N-1)/K=M (M is an integer) ...(4) and a calculation unit 7 that calculates K.
According to the values of N and K calculated by the calculation unit 7, the frequency value fs of the input signal is calculated by fs = (K/N) fc ... (5), and a high purity sine wave is calculated according to the calculation result. Output frequency of generator 1
It is composed of an arithmetic control section 8 that controls fs.
9 is a counter for measuring the frequency fs of the input signal applied to the DUT 2 and the frequency fc of the clock, and the measured values of each frequency are applied to the calculation control section 8. Note that the counter 9 may be omitted if the frequency fs of the input signal applied to the DUT 2 and the frequency fc of the clock are highly stable.

The operation of the device configured in this way will be explained.

First, the output frequency fc of the clock generator 4 is set to a predetermined value depending on the test content of the DUT 2.

On the other hand, in advance, the value of the output frequency fs' of the high-purity sine wave generator 1 is calculated so that the frequency ratio with the output frequency fc of the clock generator 4 becomes approximately the desired value according to the test content of the DUT 2, and Approximate value of sample data according to output bit width of DUT2
Calculate N′ and the approximate value K′ of the sample wave number.

Using fs′, N′, and K′ calculated in advance in this way as a guide, we can calculate the prime relationship between the resolution N and sample wave number K of sample data that has a prime relationship and satisfies equation (3) above. The calculation unit 7 calculates the resolution N and sample wave number K of the sample data that satisfy the equation (4).

Then, according to the values of N and K calculated by the calculation unit 7, the calculation control unit 8 calculates the frequency value fs of the input signal that satisfies the above-mentioned equation (5), and the frequency value fs of the input signal that satisfies the above-mentioned formula (5) is The output frequency fs of the pure sine wave generator 1 is controlled.

FIG. 2 is an explanatory diagram of sampling performed under such conditions. In this case, the period of sample data is M, and there are K sample points between n=i and n=i+1. Further, the first sample point of the l-th measurement cycle and the first sample point of the l+1-th measurement cycle are adjacent to each other in a sequential relationship.

Then, the error E(n) in the resolution unit included in the nth point is E(n) = n・K・δ δ; The error in the frequency ratio is The relative error of point ) is ΔE(n) as follows: ΔE(n)=Δn・K・δ. The relative error ΔE between such sample points
(n) is ΔE(n)=M・K・δ, n modeK=1,...
K-2 −{(K-1)M-1}Kδ, n modeK=1 As a result, assuming that δ≧0, the regions where ΔE(n)=M・K・δ will overlap, and the conventional This can prevent samples from being omitted in conversion codes such as . In addition, δ
In the case of ≧0, a similar result can be obtained by using equation (4). FIG. 2 is an explanatory diagram showing an overlap as shown in the amplitude level. These overlapping parts are M,
It is uniquely determined by K and δ. Note that although it is necessary to delete the overlapping portion in the calculation process, the portion to be deleted can be easily determined from M, K, and δ.

With this configuration, it is possible to prevent conversion codes from being omitted due to frequency ratio errors, and highly accurate measurements can be performed.

Note that if the stability of the frequency fs applied to the DUT 2 is relatively low, the frequency measurement value by the counter 9 may be added to the arithmetic control section 8 for feedback control.

(Effects of the Invention) As explained above, according to the present invention, a highly accurate test can be performed by reducing the influence of the error in the frequency ratio of the sine wave signal applied to the A/D converter to be measured and the clock. /D converter test equipment can be realized,
The practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is an explanatory diagram of sample points in the device of Fig. 1, Figs. 3 and 4 are explanatory diagrams of overlapping regions where the magnitude of error is guaranteed, and Fig. 5 is a block diagram showing an example of the conventional device. Figure 6 shows the measurement target A/D.
FIG. 3 is an explanatory diagram showing the relationship between an input signal applied to a converter and a clock. 1...High purity sine wave generator, 2...A/D converter to be measured (DUT), 3...Memory, 4...Clock generator, 5...Data processing section, 6...Control block, 7 ...Arithmetic section, 8...Arithmetic control section, 9
……counter.

Claims (1)

[Claims] 1. Applying a sine wave signal from a high-purity sine wave generator to an A/D converter to be measured, storing conversion data output from the A/D converter to be measured in a memory; In an A/D converter testing device, the phase and amplitude of an ideal sine wave signal corresponding to an input signal are determined by performing discrete Fourier transform on the converted data, and the error between these ideal sine wave signal data and the converted data is determined. , The resolution N of the sample data and the sample wave number K according to the test content of the A/D converter to be measured maintain a prime relationship, and (N+1)/K=M (M is an integer) or (N-1)/K = M (M is an integer) A means for calculating N and K that holds the relationship, and a means for calculating the frequency value fs of the input signal by fs = (K/N) fc according to the values of N and K. An A/D comprising means for controlling the output frequency of a high-purity sine wave generator according to a calculation result.
Converter testing equipment.