Cirrus Logic AN44 - Manual

INTRODUCTION
The CDBCAPTURE system can be used to
collect data from embedded Analog to Digital
Converters (ADCs). Thus system performance of
the analog front end can be measured, analyzed
and quantified. By analyzing the measured
performance, noise sources can be identified,
isolated, and corrective actions taken. Here
CDBCAPTURE is used as an engineering tool,
reducing development time during system test
and integration. Another application could be
using CDBCAPTURE in production for testing
finished products and verifying system
performance.
CDBCAPTURE
The CAPTURE interface board is a development
tool that interfaces a Crystal Semiconductor
ADC to a PC compatible computer. Digital data
from the ADC is collected in a high speed
digital FIFO, then transmitted to the PC over a
serial COM port. Evaluation software is included
to analyze the data and demonstrate the ADC’s
performance. The entire system consists of a
CAPTURE interface board, serial cable, RS232
cable, and software.
The software included with the CDBCAPTURE
system quantifies static and dynamic
performance of ADC systems. Static testing
includes Histogramming and calculation of the
mean, standard deviation and variance. Dynamic
testing includes Fast Fourier Transforms and
analysis of the power spectrum. Here Signal to
Noise Ratio (SNR), Signal to Noise plus
Distortion (SINAD), Signal to Distortion Ratio
(SDR), and Signal to Peak Noise (SPN) figures
are calculated. Time domain plots are available
to visualize signals in the time domain and
confirm operation.
CDBCAPTURE WITH EMBEDDED ADCs
The CDBCAPTURE circuit board is designed to
directly interface with most Crystal
Semiconductor ADC evaluation boards. This
permits a quick and easy method to quantify and
verify the ADC’s performance. However, it is
often desirable to measure the ADC’s
performance in the actual system or to measure
the overall system performance. To collect data
from an embedded ADC, a special serial cable
needs to be designed. This cable incorporates the
digital interface circuitry which exists on the
evaluation board. This cable is connected to the
appropriate signals on the ADC.
To collect data from an embedded ADC, the
digital interface circuitry on the evaluation board
needs to be incorporated on a modified serial
FEB ’95
AN44REV2
1
Crystal Semiconductor Corporation
P.O. Box 17847, Austin, TX 78760
(512) 445-7222 FAX 445-7581
http://www.crystal.com
Application Note
USING THE CDBCAPTURE SYSTEM
WITH EMBEDDED A/D CONVERTERS
by
John Lis
Copyright

Crystal Semiconductor Corporation 1996
(All Rights Reserved)
AN44