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Newbie
777 Views
Registered: ‎11-15-2019

## designing a arbitrary wave for generators

designing a arbitrary waveform generator for a zynq xc7010 fpga with extenal dac.

hi guys i am wanting to design a arbitrary waveform generator for a zynq development board. That is capable of upto to 400Mhz  sine wave, square wave ,time mark waveform and sawtooth and triangle wave is this possible and what would be the best way to achive it if you could help as i am a new to fpgas

1 Solution

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Teacher
617 Views
Registered: ‎08-14-2007

Hi,

That wouldn't change much. The point for arbitrary waveforms is that you need harmonics of the base frequency to generate e.g. a rectangular waveform. That means a rectangular waveform of 400MHz requires up to 10 times the bandwidth 400 MHz to 4GHz to generate some almost rectangular shape. Try for yourself doing a fourier synthesis by summing up the harmonics according to the formula for rectangular waves:

http://195.134.76.37/applets/AppletFourier/Appl_Fourier2.html

So, back to your former post.

A DAC with 2.5 GSPS would be good to produce sinusoidals up to about 1.2 GHZ, but rectangular shapes only up to 120MHz if you want a nice shape.

It is determined by the maximul output slew rate of the DACs reconstruction filter which has a maximum frequency of about 1.2 GHz.

As mentioned before. You need to care about the analog signal properties first, to be able to understand the requirements for the digital part.

If the DAC is fed by multiple serial lines, the datarate on each line is reduced by the number of lines used.

e.G. 2500 MSPS / 8 Lines = 312,5 MSPS/Line  which would be a realistic value for a design that can be realized.

(Besides: Who's going to create the PCB? High speed signal routing and low noise analog PCB design needs good skills for that kind of work too!)

Have a nice synthesis

Eilert

5 Replies
Teacher
709 Views
Registered: ‎08-14-2007

Hi,

do you mean 400 MHz output bandwidth, which requires at least twice the sampling rate to generate some sinusoidal signal.

Or do you want to build a 400 MSPS Generator? This would mean that you could produce good nonsinusoidal wave pattern up tpo 40 MHz (assuming 10  times oversampling as a rule of thumb).

The second should be acheivable using DSP-Slices and efficient high speed design.

The first one might go over the limit. The I/O-bandwidth might not be sufficient to produce so many sample values at the output pins. You need to consult the datasheets. The only approach to overcome this would be to use the Gigabit-transceivers (if available in the ZYNC device of your choice) but that would be too tricky for a newbie. Also it requires special interface considerations for the external DAC.

Do you already hace some DAC in mind that would fit for your application? I think the FPGA is less of a problem compared to the proper analog design part.

Have a nice syntehsis

Eilert

Newbie
659 Views
Registered: ‎11-15-2019

thanks you for your reply i do mean bandwidth. I was going to use a dac with a sample rate of 2.5GS/s to give a bit of head room to produce 400Mhz arbitrary waveform do you think it would work.

Newbie
639 Views
Registered: ‎11-15-2019

what if it was a arbitrary waveform just a fixed frequency of 400Mhz

Teacher
618 Views
Registered: ‎08-14-2007

Hi,

That wouldn't change much. The point for arbitrary waveforms is that you need harmonics of the base frequency to generate e.g. a rectangular waveform. That means a rectangular waveform of 400MHz requires up to 10 times the bandwidth 400 MHz to 4GHz to generate some almost rectangular shape. Try for yourself doing a fourier synthesis by summing up the harmonics according to the formula for rectangular waves:

http://195.134.76.37/applets/AppletFourier/Appl_Fourier2.html

So, back to your former post.

A DAC with 2.5 GSPS would be good to produce sinusoidals up to about 1.2 GHZ, but rectangular shapes only up to 120MHz if you want a nice shape.

It is determined by the maximul output slew rate of the DACs reconstruction filter which has a maximum frequency of about 1.2 GHz.

As mentioned before. You need to care about the analog signal properties first, to be able to understand the requirements for the digital part.

If the DAC is fed by multiple serial lines, the datarate on each line is reduced by the number of lines used.

e.G. 2500 MSPS / 8 Lines = 312,5 MSPS/Line  which would be a realistic value for a design that can be realized.

(Besides: Who's going to create the PCB? High speed signal routing and low noise analog PCB design needs good skills for that kind of work too!)

Have a nice synthesis

Eilert

Newbie
599 Views
Registered: ‎11-15-2019

thank you so much for your time to give me detailed explanation thank you