8Analog Interface
8 – 5
8.2.2.2 High Pass Filter
The ADC’s digital high pass filter removes frequency components at
the low end of the spectrum; it attenuates signal energy below the
passband of the converter. The ADC’s high pass filter can be bypassed
by setting bit 7 (ADBY) of the ADSP-21msp58/59’s analog control
register.
The high pass filter is a 4th-order elliptic filter with a passband cutoff
at 150 Hz. Stopband attenuation is 25 dB. This filter has the following
specifications:
Filter type: 4th-order high pass elliptic IIR
Sample frequency: 8.0 kHz
Passband cutoff: 150.0 Hz
Passband ripple: ±0.2 dB
Stopband cutoff: 100.0 Hz
Stopband ripple: –25.00 dB
(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 8.3 shows the frequency response of the high pass filter.
Passband ripple is ±0.2 dB for the combined effects of the ADC’s
digital filters (i.e. high pass filter and IIR low pass of the decimation
filter) in the 300–3400 Hz passband.
0
–100
300
–80
0
–40
–60
–20
24018012060
FREQUENCY – Hz
LOG MAGNITUDE – dB
Figure 8.3 High Pass Filter Frequency Response
To Next Page
Loading...
Need help?
General
