ADLINK PCI-9527 - Manual (Page 37)

Operation Theory 25
ADLINK Technology Inc. PCI-9527
Copyright 2010 User’s Manual
3.2.3 ADC and Analog Input Filter
ADC (Analog-to-Digital Converter)
The ADCs on PCI-9527 are sigma-delta ADC which is very suit-
able for vibration, audio and acoustic measurement. The analog
side of sigma-delta ADC is a 1-bit ADC. On digital side, it performs
oversampling, noise shaping and digital filtering. For example, if
desired sampling rate is 108KS/s, each ADC samples input signal
at 6.912MS/s, 64 times the sampling rate. The 1-bit 6.912MS/s
data streams from 1-bit ADC to its internal digital filter circuit to
produce 24-bit data at 108KS/s. The noise shaping removes quan-
tization noise from low frequency to high frequency. With the digi-
tal filter at the last stage, the digital filter improves the ADC
resolution and removes high frequency quantization noise.
The relationship between ADC sample rate and DDS output clock
is as followed
Filter
Each channel has a two-pole low pass filters. The filters limit the
bandwidth of the signal path and is useful for rejecting out of band
noise.
Sampling Rate 2 K - 54 KHz 54 K - 108 KHz 108 K-216 KHz 216 K - 432 KHz
DDS CLK 512 K - 13.824 MHz 6.912 M-13.824 MHz 6.912 M-13.824 MHz 13.824 M - 27.648 MHz
Table 3-3: ADC Sample Rates VS DSS Outpu Clock