ES415.1 - User’s Guide22
Hardware Description ETAS
If the user selects a higher sample rate in this mode (100kHz, 50 kHz and
20 kHz), the application software prevents the initialization of the hardware and
points to the limited selection of sample rates.
4.3.4 Digital Filter
A digital filter then processes the digital signal. The parameters of the CIC filter
(Cascaded-Integrator-Comb filter) are automatically set upon selecting the sam-
ple rate in the configuration software. The digital filter can be switched off,
parameters of the filter cannot be configured.
The data is written to a data buffer at the output of the digital filter. It can be
queried there by the application program.
Compensating Group Delay
The group delay is the time it takes the input signal of an analog or digital filter
to pass the filter. In the application program (e.g. INCA MDA), the signal must be
delayed to compensate for the group delay.
A special feature of the ES415.1 is the compensation of the group delay within
the module. The group delays of the analog anti-aliasing filter and the configu-
rable digital filter are taken into consideration in this process. The signal in the
application program (e.g. in MDA) no longer has to be delayed to compensate
for the group delay.
Examples
To represent the group delay with digital filters, a test signal was sent to two
filters of the same type:
• Filter A without compensation of the group delay
• Filter B with compensation of the group delay
The configuration of both filters is identical. The test signal is sampled with the
sampling rate f
S,INCA
= 2 kHz (0.5 ms). The filter channel was set to a cutoff fre-
quency f
C,CIC
= 200 Hz.
Fig. 4-4 and Fig. 4-5 on page 23 show the relevant signal trace - in the upper
part of the figure without a filter, in the lower part of the figures with a filter and
without or with group delay compensation respectively.
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