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Does MAC FIR filter need special care?

Hi everyone,

I am currently trying to implement a polyphase decimation filter by using core generator in ISE 7.1

The filter has been both implemented by using DA FIR and MAC. The DA FIR filter is working as it supposes to be, but MAC doesn't. I can't really see why.

All the inputs and control signals feeding into these filters are the same. They are running in exactly the same environment. The only difference between these two filters that I know is that the output of DA FIR is 28 bits and the output of MAC is 29 bits.

My question is does the MAC filter requires special care compare with DA FIR.

Please help me. Any information will be appreciated.

Sophi

Reply to
Sophi
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Decimation used not to work in MAC FIR until certain version. I believe it should have been fixed in v5.1. It might be that you are using an old core.

/Mikhail

Reply to
MM

Hi Mikhail,

I am in fact using version 5.1 logicCore. So, I don't think that's the problem. But thank you for your help anyway.

Sophi :)

Reply to
Sophi

When you say it doesn't work, what exactly do you mean? Have you tried simulating it?

/Mikhail

Reply to
MM

Hi Mikhail,

OK. I have generated the programming file and downloaded to the FPGA. I feed a pure sine wave into an ADC on board, which connect to the input of the filters ( FIR and MAC). The output of the filters are connected to two DAC on board seperately so we can compare the output waveform at the same time.

Therefore the output of the filters should be a sine wave too if the it is within the passband frequency range. But the signal coming out from MAC is not a continuouse function. It has some sort of sine function feature, but at certain point in time, it looks like the sign of the signal is changed.

The output of the FIR filter is completely fine. That's where it puzzles me. The two filters are running in the exactly the same environment.

It is not a clipping problem. I have tried to reduced the input signal amplitude and that didn't solve the problem. I haven't really try to simulate it yet. The whole project has too many inputs. It is not really an easy job to simulate the entire module.

Sophi

MM wrote:

Reply to
Sophi

Hi Sophi,

What is your input sampling rate? Have you put proper timing constraints? Have they been met?

Have you tried swapping the channels, i.e. connecting the MAC filter to the DAC that was proved working with another filter?

This is where simulation would be useful...

You don't need to simulate the whole thing. Just take the filter, make a simple test bench that would apply necessary clock(s) and a test tone. Good simulators such as Active HDL can show buses as waveform, so you will immediately see if the thing works. In fact, I believe all you really need to see is the output ready signal being generated at the proper decimated rate...

/Mikhail

Reply to
MM

Hi /Mikhail,

I think I will try to simulate the MAC filter on its own asap. I have tried every other possibility that might introduce problems that I can think of, including those ones in your previouse reply.

Once again, thank you for your help and I will give you some feed back after the simulation is done.

Sophi

Reply to
Sophi

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