Filter Example Simulation - STMicroelectronics SPC572L series Reference Manual

Decimation Filter
37.6

Filter example simulation

The decimation filter block operation was checked in a Verilog simulation using calculated
filter coefficient values and noisy input data. The expected output values and the RMS error
were then calculated.
37.6.1 Coefficients calculation
The coefficients were calculated using a digital filter design tool. We have supplied some
hypothetical filter parameters to the tool and obtained the filter coefficients. The input
parameters are:
•
filter characteristics: elliptic/low pass
•
filter type: 4th order IIR
•
input sample rate: 800k sample/s
•
passband edge: 100 kHz
•
stopband edge: 150 kHz
• passband attenuation: ≤ 1 dB
The software tool gives the IIR filter coefficients in the Z-transform format expressed by
Equation
Equation 20
The coefficient results in fixed point decimal representation are shown in
Table 432. Coefficient values given by SPW digital filter design tool
Coefficient
B0
B1
B2
B3
B4
Comparing
values of coefficients and the values to be loaded in the DECFILTER_COEFn registers.
Note that A0=1 in both cases and that the coefficients A1 to A4 in
opposite signal from
See Table 433
smallest divider factor to have all coefficient values in the range (–1 ≤ Coef < +1).
840/2058
20:
Y s ( )
----------- -
X s ( )
Decimal Value
0.0221455
0.00445582948893748
0.0318517846509088
0.00445582948893748
0.0221455
Equation 19 with Equation
Equation 19.
below to obtain the coefficients. A scale factor of eight is used, being the
DocID027809 Rev 4
2
B + B s + B s + B
0 1 2 3
---------------------------------------------------------------------------------- -
=
2
A + A s + A s + A
0 1 2 3
Coefficient
A0
A1
A2
A3
A4
20, we obtain the relationship between the calculated
3 4
s + B s
4
3 4
s + A s
4
Table
Decimal Value
1.0
-2.69772868375858
3.234056294853
-1.92028561712454
0.47939080709495
Equation 20
RM0400
432.
has the