IPR-CIC Altera, IPR-CIC Datasheet - Page 32

• Manufacturer Part Number: IPR-CIC
• Description: IP CORE Renewal Of IP-CIC
• Manufacturer: Altera

Specifications of IPR-CIC

• Software Application: IP CORE, DSP Filters And Transforms
• Supported Families: Arria GX, Cyclone, HardCopy, Stratix, Stratix II
• Core Architecture: FPGA
• Core Sub-architecture: Arria, Cyclone, Stratix
• Rohs Compliant: NA
• Lead Free Status / RoHS Status: na

4–8
CIC MegaCore Function User Guide
This problem can be alleviated by connecting the decimation or interpolation CIC
filter to a compensation FIR filter which narrows the output bandwidth and flattens
the passband gain
Figure 4–9. Using a CIC Compensation FIR Filter
You can use a frequency sampling method to determine the coefficients of a FIR filter
that equalizes the undesirable passband droop of the CIC and construct an ideal
frequency response.
The ideal frequency response is determined by sampling the normalized magnitude
response of the CIC filter before inverting the response.
Generally, it is only necessary to equalize the response in the passband, but you can
sample further than the passband to fine tune the cascaded response of the filter
chain.
A MATLAB script <variation_name>_fir_comp_coeff.m is generated in the project
directory by the CIC MegaCore function. You can run this script in MATLAB to
generate FIR coefficients that provide appropriate passband equalization. The
generated coefficients are saved in a text file, which is ready for use by the Altera FIR
Compiler MegaCore function.
The MATLAB script requires the following parameters for the compensation FIR
filter:
■
■
■
■
An example of compensation filter response is shown in
L: FIR filter length, which is same as the number of taps or the number of
coefficients
F
F
B: Coefficient bit width if coefficients are written in fixed-point numbers
S:
C
: FIR filter cutoff frequency in Hz
FIR filter sample rate in Hz before decimation/interpolation
Compensation FIR
Decimation CIC
(Figure
Filter
Filter
4–9).
Interpolation
Decimation
Compensation FIR
Interpolation CIC
Filter
Filter
Figure 4–10 on page
© December 2010 Altera Corporation
FIR Filter Compensation Coefficients
Chapter 4: Functional Description
4–9.