fpga

[latchu]

dear sir,

Here we are trying to do a digital sine wave generator using vhdl. we are getting problem with floating point multiplier. we found lot of disadvantages in look up table method. for low frequency signals the output is highly distorted. so we use digital signal processing method to generte sine waves. a simple simulation in c coding works well. the system has 16 bit out put. the problem is repeated multiplication causes truncation or round off. some times this makes all the bits to go to zero. as a result the system output is damping with time. but low phase and frequench distortion while comparing it with lookup table method. and it has high amplitude distortion.

the systme has 3 multipliers

the simple mathematics of the system is given here.

using complex exponentials 

e^jnө =cos nө+jsin nө=(x+jy)ⁿ

for the first time assign a value to    x and y that will be the frequency(n=1).

e^jө =cosө + jsinө  = (x+jy)     for n=1

e^j2ө =cos2ө + jsin2ө  = (x+jy)²     for n=2

so repeated multiplication will give the result .the real part as cos wave and imaginary part as sine wave.

how we can eliminate the trunction or rounding off problem (multiplier length should be a matter)

[Efosa O.]

Hello.

Are you currently using any National Instruments software or hardware? Or do you just want information on how to eradicate this problem using our products? Using National Instruments LabVIEW FPGA, you are able to program fixed point math (up to 64 bits with LabVIEW FPGA version 8.20), but it is not possible to do floating point mathematics on the FPGA chip.

There are some saturation arithmetic functions that will help you program and get better accuracy in FPGA.

I am not entirely sure exactly what you are asking and what hardware/software you are currently using. If you can make this clear in your next post, I will be sure to answer your question as best as I can.

Thanks

Efosa O.

[03215833127]

my final project is also pc based function generator.

my first problem is how to generate sine wave using vhdl.

can you help me

[J.Harv]

03215833127--

       There are a number of build-in functions in LabVIEW that you can easily program to generate a sine wave on an FPGA chip, without using any vhdl.  You will need LabVIEW FPGA and an NI FPGA target.  Specifically, which hardware will you be using this with?  Any more information that you can provide would be very helpful in making sure anyone reading your post understands what it is you are trying to do so they can offer the appropriate advice.

Regards,

John H
Applications Engineer
National Instruments