Attenuation at RF

[saurabh17g]

Hello,
I am utilizing AD9833 to generate waveform to 10Mhz according to datasheet.
But after 50KHz, I am getting attenuation. DC level gets added and distortions as well. At 100K, the response is almost DC. I am not able to figure out the reason of such behavior.
I was expecting that these things would occur after 1MHz. But 50K is too early

Please give me suggestions and possible solutions.

 

[JimB]

Are you sure that you are sending the correct tuning data to the DDS?
Does the DDS work correctly at 1khz, 10khz?
What are you using to measure the output of the DDS?
Where are you measuring the output, on the output pin of the DDS or do you have an amplifier after the DDS?

JimB

 

[saurabh17g]

data sent is correct and tested....

1. yes , dds works correctly at 1KHz and 10KHz

2. I am using Textronic DSO for measuring the output

3. I am using output pin of DDS. I am not using an amplifier currently.

 

[JimB]

It sounds as though you are doing things correctly with the DDS.
But what about the oscilloscope, could it be that the sampling rate is too low to display the higher frequencies correctly?

JimB

 

[saurabh17g]

Oscilloscope is able to display 25MHz frequency of oscillator. But that was around 3V p-p
the output of DDS is 100mV.
Also, one more thing: The IC is SMD and it was desoldered , removed and resoldered. Would that be a cause of RF attenuation?

 

[crutschow]

Show us the circuit diagram.

Is the chip properly decoupled to ground with caps at the power pin and as shown in Figure 1 in the data sheet.

 

[saurabh17g]

circuit diagram is same as shown in the datasheet

 

[Dragon Tamer]

Also, one more thing: The IC is SMD and it was desoldered , removed and resoldered. Would that be a cause of RF attenuation?

No, if you de-soldered it correctly, then you should have no problems getting the IC to work. The worst case scenario is that you shorted one of the pins with a little bit of solder, tyr testing each pin with an ohm meter to see if there are any shorts.