How to specify option of Half-Band FIR Filter in the FIR Compiler?

[vizzie]

Hello all,

I have been trying to design a multistage filter using a half-band filter and a polyphase decimator.

I could satisfactorily design the filters in MATLAB and generate the coefficients. I read in the FIR Compiler v 4.0 datasheet that I can specify Half-Band filter option as well as Polyphase Decimator option in the FIR Compiler. However the GUI interface of the CoreGen for FIR Compiler v4.0 doesn't show any such optionin "Filter Type" list box under "Filter Specification" options. I only see Single-Rate, Interpolated, Interpolator, Decimator, Polyphase Filter Bank Receiver and Polyphase Filter Bank Transmitter. There is nothing like Half-Band Filter or Polyphase Decimator here. So how do I specify these options?

Also is there a way I can also specify a Quarter-Band Filter.

Regards,

vizziee.

[vizzie · Accepted solution]

Hello all,

Turns out that the FIR Compiler v4.0 automatically infers the Half-Band Structure from the coefficients. The Key Features section here says so: http://www.xilinx.com/products/ipcenter/FIR_Compiler.htm

However it was not clear to me if the same is true for Polyphase decimator also. For half band filter, it is easier to infer the structure as half of the coefficients are zero. But for implementing a polyphase decimator filter, since the coe file has the coefficients of the original non-polyphase implementation, how does the compiler assume a polyphase structure? Is it that when you select the Decimator option, the compiler by default assumes a polyphase implementation and derives coefficients of sub-band filters based on the specified decimator factor and the coe file?

Also, I couldn't get any information on QuarterBand Filters.

Regards,

vizziee.

[vizzie]

From little bit of experimenting, it appears to me the decimator in Xilinx FIR is always implemented as polyphase decimator. As for Quarterband filters, if you specify the coefficients as such, the copiler would implement it as polyphase filter (the Halfband and Quarterband filters do have polyphase implementations).

Regards,

vizziee.

[sureshpaidi]

 Hi vizzie,

I am newbie to DSP filters I have implemented a filter in Spartan-3E starter kit.Due to clk limitation(50Mhz) and ADC sampling speed(1.5Msps) in Spartan-3E starter kit i have designed very low frequency (70khz center frequency)bandpass filter, but actually  targeted to 70MHz center frequency bandpass filter .

I'm using Matlab FDATool to generate coefficient file for required filter and plugged in to FIR compiler 3.2.I'm getting close to the results in Matlab simulation but not in FIR compiler 3.2.

Filter specs as shown below

fs1=67.5khz, fp1=70khz, fp2=75khz, fs2=77.5khz and fs=685khz, Astop1=60dB ,Astop2=60dB and Apass=1dB

clk=50MHz, Coeff width = 16 , Input data width = output data width = 12

My question is, Difference between passband gain and stopband gain in FIR compiler is almost 75dB. But actual filter output getting only 20dB so how to improve passband gain and what are the parameters effects on passband gain?

It has another problem while giving different input voltages output passband gain was not varying.

Thanks

[yearnwaipo]

can anyone give some  suggestion?