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Altera_Forum's avatar
Altera_Forum
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14 years ago

Gate level Simulation passes but design fails on target borad

Hello,

I am implementing a filter (2nd order) in Quartus Stratix II device running at 500KHz.

I simulated the design using ModelSim.

My Target hardware consists of stratix II device.

Input stimulus is sine wave of desired frequency.

Inputs coefficients decide the cutoff frequency.

Expected result is attenuation of sine wave at cut-off freq.

Design works fine in RTL as well as Gate level simulation.

1)

However, when programmed on target hardware, it fails completly and has output has no attenuation at lower frequencies (100Hz) and wrong beaviour at higher frequencies.

2)

I see that fast/slow model results in timing analyses show failures linked to my design. It indicated a different (40MHz) clock domain in the from/to section of the report. 40MHz is used for other sections and I don't use 40 Mhz for this piece of design.

-------------------------------------------------------

Please suggest me how to go ahead from gate level simulation to on board running. I am kind of stuck, unable to proceed further.

Is there any settings that i need to check.

Thanks in advance.

Best Regards,

VVP

36 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    You will need to consider Sinc envelope of your DAC (if low pass filter). This means low freq will not be attenuated but those near Nyquist will. i.e. there is inherent low pass filter in every DAC unless it has internal/external inverse sinc.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    thanks. True.

    I am implementing a second order filter.

    I have 2 input freq, 2 betas which decide the my coefficients (b1,b2,b3,a2,a3) for the filter.

    This means that we can based on the frequencies and the betas, i should be able to attenuate the desired frequency. This happens and works till gate level simulation but fails on board. I have means to provide input and observe the output also.

    Please suggest.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    You should add the effect of DAC sinc as follows:

    edit:

    Amp_out = Amp*sin(x)/x; where x = pi*f/Fs

    e.g. at .5 of fs you get extra attenuation of .64 or -3.9dB

    at freq > Nyquist which shouldn't be allowed you get much higher attenuations.

    Can you tell me what is the response required and that obtained at those two freq.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    sorry I should have said A=A*sin(pi*f/Fs)/(pi*f/Fs) and at .5 the Amp drops by -3.9 dB

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Apologies, typo error

    Not 100 mhz cut-off freq, instead 100 hz.

    Thanks.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    What are values for your filter coeffs (a,b) and what is your actual sampling frequency?

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Hello,

    Please find the info as follows:

    The sampling freq = 500 KHz.

    -- coefficients for 100 Hz

    coeff_b1 <= x"3FFE25B1";

    coeff_b2 <= x"800424A3";

    coeff_b3 <= x"3FFDBC4B";

    coeff_a2 <= x"800424A3";

    coeff_a3 <= x"3FFBE1FD";

    Thanks.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    your figures don't match up.

    your sine input is at normalised freq of 10/1000,000 and this will be 10/1000,000 of 100Khz = 1 Hz.

    your filter has a very narrow stopband at .6082 of FN i.e. at 30KHz. it has no attenuation at 1 Hz.

    so you need to present better setup figures.

    this is my conversion of hex, I hope I am right:

    a =

    1.0e+009 *

    -2.147212125000000 -3.221495299000000

    b =

    1.0e+009 *

    -3.221346895000000 -2.147212125000000 -3.221373877000000

    edit:

    sorry , i did not enter a1 = 1 so bear with me until tomorrow...
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Thanks.

    The values of coefficients for 100 Hz are as follows:

    True a1=1.

    Formulasb10.999886916919553b2-1.999747125328010b30.999861787346121a2-1.999747125328010a30.999748704265674

    The filter is expected to attenuate the sine wave only at cut-off freq of 100 Hz. I can confirm it happening in RTL & Gate level simulation.

    It fails on board ?

    Please advice.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I entered Matlab:

    a =

    [1.000000000000000, -1.999747125328010, 0.999748704265674];

    >> b

    b =

    [ 0.999886916919553, -1.999747125328010, 0.999861787346121];

    >> fvtool(b,a)

    or use freqz(b,a)

    I get a notch filter. its notch occurs at .001 of Fs 100000 = 100 Hz and this matches your description. However the attenuation is -.008db = .9991

    As to your hex values it gives a completely different filter if I convert it on the basis of 2's complement...you need to check that