digital attenuator problem

[vagarwal]

Hi All,

I am using a broadband 6-bit digital attenuator MMIC from www.astramtl.com
Its a very good chip, but sometimes, I get ripple in the attenuation states... particularly in last 15-20 states. And by the time all 6 bits are switched on, the ripple goes to almost 3 dB.
This chip has an on-chip TTL driver, so there is not much I can do about the control to different attenuation states.
Can someone help please.

Regards,
VAgarwal

 

[VSWR]

Have you used the recommended layout diagram on page 8 in the data sheet? Any DC blocking capacitors?

https://www.astramtl.com/pdf/pro_att_digital2321014.pdf

 

[vagarwal]

Yes I have followed the exact assembly diagram. I am using 220Ohm resistors for control inputs and 100pF single layer capacitors for DC blocking... No DC blocks required at control inputs I feel...

 

[biff44]

try putting fixed 3 dB pads on the input and output, and tell us if the ripple goes away.

 

[itzikhaim]

Dear vagarwal!

Its seems that the RF output signal is below the mininmal value of detection at the test instrument (I think you might be using a Spectrum Analyzer ).
Try the following:
1. Increase the power of the RF Power input (not above 25dBm as said in the datasheet).
2. Lower the attenuation (digital) inside the S.A. (spectrum analyzer).

Tell me if this works.

Good luck!

 

[vagarwal]

thanks...it worked...

 

[itzikhaim]

Dear vagarwal,

How did you manage to fix it?
What was the problem?

Kindly tell us!