In design - 30mhz arbitrary function generator (10.5hz increment?)

[edman222]

Hey so ive been hard at work on a tiny handheld 30Mhz 4096 point arbitrary function generator for general use. So far so good, its about the size of an iPhone and still maintains most of the features of a large desktop version .

But there is one problem, and I am trying to see if it is in fact a problem or not. The tuning word I work with and the crystal properties will only allow me to increase frequency in 10.5 Hz steps. for low frequency this may seem limiting, but for high frequency in the Mhz a 10.5hz step seems to be almost no issue. ( at least in my opinion).

So what do you guys think? is 10.5 Hz very limiting?

If a dedicated audio frequency arbitrary generator was also present that would allow 1Hz increments form 1-24Khz would that be more useful? Or is 10.5Hz fine for what most people use?

 

[panic mode]

any reason to make that 10.5 and not something round such as 10Hz?

 

[edman222]

I would have to find a whole new PLL and would need a custom made crystal. So that's why.. I am trying to see if I can avoid costs like that to keep it cheaper.
Thanks for asking!

 

[ronsimpson]

working with audio, jumping from 10.5 to 21hz is not good. Going from 20 to 21 is OK. Depending on the application I could live with that.

It will be hard to explain that you can't have 10hz but you can have 10.5hz. Can't have 20hz but you can have 21.
10.5 is a odd number it hurts my head.

Can you make a high/low mode where the step size is 10.5hz/0.0105hz? (divide by 1000)

handheld 30Mhz 4096 point arbitrary function generator

Does this mean you can make a 30mhz sign wave or does it mean you have a30mhz clock so a 4096 point wave form only goes to 7khz?

 

[edman222]

Sorry 30 Mega Hertz 30,000,000 Hz... 4096 point (running at 180 MSPS) :S by 4096 I mean you can create your own wave form using 4096 memory points of 14 bits (its a 14 bit DAC)

 

[ronsimpson]

A 4096 point wave form will repeat at about 500khz.
So you will have a 30mhz bandwidth in the output analog driver.
You are using a FPGA with internal dual port memory?

Look at some of the products on the market today.

 

[edman222]

Huh no, the device can on its own run these wave forms as it is coming from a 14bit sine approximation in rom, the arbitrary functionality (the 4096*14 bits) is extra... Is this what your talking about?

In any case I am asking about frequency steps, not how I built my hardware Just wanted to know what everyone thought of 10.5Hz... Looks like I will find a different PLL to geto to 10Hz and a /10 for 1Hz... arg