 A frequency response window appears like fig.F. Choose "Save Coefficients"
on the menu and save them into a file. Please note that the response window
must be on the top.
The left side of list.A is the coefficients by DSPLinks and the right one
is a part of C source on dsPIC. Please be careful of that you need to switch some coefficients and invert some polarities. That's because the expression of IIR filter differs between DSPLinks and dsPIC.
fig.G is the expression on DSPLinks. "z^-1" is a delay element,
"+" is an adder and triangles are multipliers.
fig.H is the expression on dsPIC. See the difference from fig.G. The location
of ax and bx differs and ax is not inverted.
There are some type of expressions for IIR filters like the figures above. Therefore you should pay attention to how "the tool to generate coefficients (DSPLinks)" and "the tool to implement IIR filters (dsPIC)" differs each other. You may need to switch some coefficients and invert those polarities.
That's it for this tutorial. You can use DSPLinks to design LPF, HPF, BPF
and BRF. Also Shelving, Peaking, Notch and some more filters are available!!
|