HISTOGRAM TESTING
verter. In practice 10 to 20 million samples will demonstrate
good results for a 16-bit system and expose any serious
flaws in the DL performance. If the memory incrementing
hardware can keep pace with the ADC701, then 20 million
samples can be accumulated in well under one minute. The
last figure on page six shows the results of a 19.6 million
point histogram taken at an input frequency of 1kHz.
The FFT provides an excellent measure of harmonic and
intermodulation distortion. Low-order spurious products are
primarily caused by integral nonlinearity of the SHC and
ADC. The influence of differential linearity errors is harder
to distinguish in a spectral plot—it may show up as high-
order harmonics or as very minor variations in the overall
appearance of the noise floor.
A more direct method of examining the differential linearity
(DL) performance is by using the popular histogram test
method (5). Application of the histogram test to the ADC701/
SHC702 is relatively straightforward, though once again
extra precision is required for a 16-bit system compared to
8- or 12-bit systems. Basically, this means that a very large
number of samples are required to build an accurate statis-
tical picture of each code width. If a histogram is taken using
only one million points, then the average number of samples
per code is less than fifteen. This is inadequate for good
statistical confidence, and the resulting DL plot will look
considerably worse than the actual performance of the con-
NOTES:
1. Available from Bergquist, 5300 Edina Industrial Blvd., Minneapolis, MN 55435
(612) 835-2322.
2. Brigham, E. Oran, The Fast Fourier Transform, Englewood Cliffs, N.J.: Prentice-
Hall, 1974.
3. Harris, Fredric J., “On the Use of Windows for Harmonic Analysis with the Discrete
Fourier Transform”, Proceedings of the IEEE, Vol. 66, No. 1, January 1978, pp 51-
83.
4. Halbert, Joel M. and Belcher, R. Allan, “Selection of Test Signals for DSP-Based
Testing of Digital Audio Systems”, Journal of the Audio Engineering Society, Vol.
34, No. 7/8, July/August, 1986, pp 546-555.
5. “Dynamic Tests for A/D Converter Performance”, Application Bulletin AB-133,
Burr-Brown Corporation, Tucson, AZ, 1985.
+2.8V
+0.2V
HP3325A
Frequency
Synthesizer
Convert
Phase-Locked
Command
Analog
Input
ADC701 &
TTL
Brüel & Kjær
Type 1051
Synthesizer
Low-Pass
Filter
SHC702
Latches
Under Test
74HC574
600Ω
– or –
Crystal
Filter
HP330
Series 9000
Computer
High-Speed
SRAM
64KB x 16
FIGURE 6. FFT Test Configuration for Two-Tone (Intermodulation) Testing.
®
15
ADC701/SHC702
BB [ BURR-BROWN CORPORATION ]
