DDS based function generators

[Jdo300]

Hi Rob,

You're doing some great work there! Very impressive! By the way, where did you get that microscope you are using from? I am interested in getting one for my lab as well. How much was it?

God Bless,
Jason O

[Jdo300]

Hi Everyone,

I posted this on PhysicsForums relating to making a multiple output power supply and thought I would paste it here as well in case any of you may know of any good solutions.

Now I'm looking for a good way to power all the chips on the control board I'm designing. It will be powered by two rechargeable 9V batteries in series for a total input voltage of about ~14V.

The interesting thing is that the chips I am using all require a wide range of voltage inputs. I need to produce 1.8, 3.3, 5, and 12 volts for the different sections of my circuit. I was thinking about just slapping some linear regulators to make all the voltages but quickly realized that these would probably drain my batteries faster than the actual circuit would.

Sooo... I am looking into switching regulators since I know they are much more efficient. In a perfect world, I would like to see if there are any out there that can make all these voltages from one input (or at least some of the voltages anyway). The other thing is I'm trying to find a one-chip solution so that I don't have to add a bunch of external support components. Has anyone here run into anything like this before?

God Bless,
Jason O

[MeggerMan]

Hi Jason,
One of the parts required for the AD9959 function generator is an RF transformer or to be more precise 4 of them:
ADTT1-1+ made by mini-circuits:

http://www.minicircuits.com/cgi-bin/modelsearch?model=ADTT1-1
They cost $3.95 each for a qty of 10 or more.

According to the spec sheet for the AD9959 this is to limit the output current on the 4 output ports.
The AD9959 eval board appears to have a (200MHz) low pass filter on it that you can use if required.

The scope is made by Konus:
http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=PY30980
When I bought it, it was in the sale for about 45 GBP, its now selling for 143GBP!
Various other places are selling different models like the DM5 and DM2.
http://www.ukge.co.uk/UK/prodtype.asp?PT_ID=399

Regarding switching regulators, if you look at the top posting you will see the 200mA -5V inverter, Texas Instruments  make a whole range of devices to cover most voltages.

The TPS62110/1/2 is quite a good choice:
http://focus.ti.com/docs/prod/folders/print/tps62110.html
Downside is the package is QFN (0.65mm pin pitch), its brand new and hard to get hold of.

Regards
Rob

[Jdo300]

Hi Rob,

Thanks for the tips. About the RF transformer, I'm intentionally not using that because it's output only works above 200 kHz, which would cut out most of the usable range for Bob's TPU. In my case, I'm simply replacing the transformer wit ha comparator to convert the sine wave into a CMOS computable square wave that I can use the clock the programmable pulse width chips (see attached circuit diagram).

As for the power supply. I like the idea of using the switching supply for greater efficiency, though I'm going to avoid the QFN packages like the plague  . Have you seen any switching converters that have all of the support components contained in one package?

God Bless,
Jason O

[Earl]

Hi Rob,

what did you use to take the microscope photos?

I have a stereo microscope, but no way to take photos with it.

Regards, Earl