Decimation Filter - Analog Devices adsp-2100 Manual

8 Analog Interface

8.2.2.1 Decimation Filter

The ADC's anti-aliasing decimation filter contains two stages. The first
stage is a sinc
reduces the sample rate to 40 kHz. The second stage is an IIR low pass
filter.
The IIR low pass filter is a 10th-order elliptic filter with a passband
edge at 3.7 kHz and a stopband attenuation of 65 dB at 4 kHz. This
filter has the following specifications:
Filter type:
Sample frequency: 40.0 kHz
Passband cutoff*:
Passband ripple:
Stopband cutoff:
Stopband ripple:
* The passband cutoff frequency is defined to be the last point in the
passband that meets the passband ripple specification.
(Note that these specifications apply only to this filter, and not to the
entire ADC. The specifications can be used to perform further analysis
of the exact characteristics of the filter, for example using a digital filter
design software package.)
Figure 8.2 shows the frequency response of the IIR low pass filter.
0
–20
–40
–60
–80
–100
2000
Figure 8.2 IIR Low Pass Filter Frequency Response
8 – 4
4
digital filter that increases resolution to 16 bits and
10th-order low pass elliptic IIR
3.70 kHz
±0.2 dB
4.0 kHz
–65.00 dB
2600 3200 3800
FREQUENCY – Hz
4400 5000