Direct Digital Frequency Synthesizer(DDFS)

[ssundar.shan]

Hello to all,
Has any one used DDFS?
I need supportive help in selecting the correct DDFS IC. What are the parameters we have to consider during the selection of DDFS IC?

 

[mvs sarma]

In general it is called DDS Analog Devices have AD9833, 9834, 9850, 9851, AD9952 etc. actual selection depends on your need and max frequency. there are direct application notes, and many direct projects using them.

perhaps other companies have come up with chips , but with another name.

 

[ssundar.shan]

Thanks four information.......
I'll go through.........

 

[Diver300]

I've used some of the Analog Devices DDS ICs.

The DDS IC has an input clock. The fastest input clock allowed is the frequency quoted. You can get any frequency out up to about 1/3rd of the clock frequency. If you want a clean sine wave, you will have to filter the output. You have to tell the DDS IC what frequency out you want, as a fraction of the input frequency.

The biggest problem for a hobbyist is the size. They are tiny. I suggest getting a serial programmed one, such as the 9833, because it has fewer pins. Get an adaptor board to mount it on so that it can be used with a DIL socket, such as this.

You will need a microcontroller to get the frequency data into the DDS IC. Even the larger DDS ICs, that are parallel loaded, still need several bytes of data, so you still need something to sequence the data. If you're sequencing data, you really need a microcontroller anyhow, so with the smaller DDS ICs, you have fewer connections to make.

 

[JimB]

Why not have a look on Ebay and search for AD9850, you will find lots of things like this:

**broken link removed**

I bought a couple a few month ago and they seem to work OK.

Hard to beat at the price.

JimB

 

[mvs sarma]

I totally agree with Driver300 comments. Incidentally i was able to handle tssop20 package chips . It is a tric we need to learn and it is simple. we tin the pcb pins. Then apply solder paste , place the chip and position it. Apply heat to the end pins , gripping the chip with a tool on its top. Later we can apply heat ( no more solder) to the pins. Due to surface tension and solder paste conveying heat efficiently, the available solder on the tracks gets bonded to pins of chip. Caution needs to be excercised not to bake the chip. as i told it is skil. I only assume that there are trial chips (dummys) out there to practtice.

the chip can be controlled by the pc 's com port , or parallel port and even usb port. Analog devvices applications notes are exhaustive to explain.

for chip selection, it is always better to go for one with highest frequiency coverage and also fsacility for I and Q signal outputs (quadrature) as in modern times the technology is around IQ modulation or demodulation like software defined radio designs..
a hobbyisyy need not purchase more chips one for each application.

i have exposure to one such application andf am happy with it. thanks to elektor shortwave receiver of dec2006 design, where ADS9851BRSZ is used as DDS.