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Small-signal RF amplifier

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carbon9

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Hi all,

I am working on design and prototype prudustion of small signal RF amplifiers working between 0.8Ghz to 2GHz. I have chosen to use SBB-5089 MMIC amplifer from Sirenza MD and implemented two circuits using these MMICs. Although I have used the same passive elements in both circuits, the experimental results are different as in the attached document. One of the circuit is good, it has flat chracteristics but the other one has a lot of ripple. Can anyone tell me which can cause this ripple?

Thanks
Carbon9.
 

Hi!
I would check grounding ... also for the connectors, just solder all grounding again.
Mad2Max
 

Try to keep the layout recommendation of the manufacturer.
The SRF of the decoupling caps is important to have a wide band response.
Also the bias inductor value and type affects the wide band response.
 

Seems that the low freq. end of S21 has about 10dB atten instead of the 17 dB gain.
My opinion is, that some (low freq transmission) circuit element (series capacitor, shunt inductor, etc) is the main problem, because at about 100 MHz the circuit should work, except if some above mentioned problem happens.
Other possibility (as mentioned above) one of the connectors had not been soldered in.
You can see whether the input or output element(s) are problematic, by measuring the S11 and S22.
 

This amplifier oscillates somewhere..

I'm very sure there is a unstability problem.This problem comes from poor ground connection and unattended PCB assambly techniques.

Use only 2 sided PCB's and avoid poor and wrong grond connections.
 

Thanks to all who thought on this topic. I have also S11 ans S22 experimental results of the RF amplifer and they are attached to this message. As it can be seen, they are below -10dB in some freqencies but not at every frequency as describedin the datasheet of SBB-5089 (also attached). I think this may be caused by:

1. Poor soldering
2. Case of the amplifier

What do you think?

Thanks
Carbon9
 

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