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1. Some part of the circuit were not correctly modeled.
2. If all parts were correctly modeled, then some stray (capacitive or inductive) coupling between input and output of amplifier was not taken into account.
g579
1. Some part of the circuit were not correctly modeled.
2. If all parts were correctly modeled, then some stray (capacitive or inductive) coupling between input and output of amplifier was not taken into account.
g579
If you used the part models that came with your simulator this is less of a potential source of the problem than layouts issues.
Your circuit should be made on a card with a ground plane. The component leads should be kept short. The amplifier should be laid out in a straight line across the board instead of looping around. (This makes the distance from the input to the output large) Another potential problem is coupling through the power supply. Make sure that there are bypass capacitors on each power connection to any part of the circuit.
If you used the part models that came with your simulator this is less of a potential source of the problem than layouts issues.
Your circuit should be made on a card with a ground plane. The component leads should be kept short. The amplifier should be laid out in a straight line across the board instead of looping around. (This makes the distance from the input to the output large) Another potential problem is coupling through the power supply. Make sure that there are bypass capacitors on each power connection to any part of the circuit.
well i am workink on alumina 15 mill, the amp is die the size of the amp is ablou 0.3 inch on 0.3 inch. and it has good ground
the bais is throw lamda/4 and cap.
the imtresting is that with out dc the r.l. is beter then -12 dbr, when i put dc the rl was -1 dbr, and i didnt see any spur at spectrum analyzer, execpt my signal. there is 3 stage at the amp when i disconected the dc from the scend one the rl was -8 dbr.
i tryed to osilate one stage with open stub and slot line (tuner) and i codent (it is uncondition stable)
at -40 deg the unit didnt osilate execp my input signal wicth came back from the oput put to the input (rl -2) when i turn off my signal, the output of my unit is quit.
as flatulent wrote, I think it would be a good idea if you upload a
schematic, or (better) the layout of your amp. At which frequency is
your amp designed to work? Often the problem is the grounding of the
amp. For higher frequencies even short vias (15mil) can have a high
inductance which can cause oscillations.
An amp is changing it's S11 when powered or not. Is your input-matching
network designed for the correct bias?
as flatulent wrote, I think it would be a good idea if you upload a
schematic, or (better) the layout of your amp. At which frequency is
your amp designed to work? Often the problem is the grounding of the
amp. For higher frequencies even short vias (15mil) can have a high
inductance which can cause oscillations.
An amp is changing it's S11 when powered or not. Is your input-matching
network designed for the correct bias?
i cant upload the layout or schem.
it is design for 9-10 ghz. the osi is the same freq as i put inside (that the resen of s11). when i stop dc the s11 is good , it balanced amp
ne321000, there is feedback some how i put on the cover something that stop rf to go ( i dont know how it call in english lung') and it didnt help me
i will try to feed them from diffrent power supply and will see what happend
It looks like a case of injection lock oscillation if it is the same frequency as your drive signal. It also looks lie the parasitics are what are causing the problems. Try laying a piece of lossy ferrite over the circuit. Also try lowering the test signal level to see what results.
It looks like a case of injection lock oscillation if it is the same frequency as your drive signal. It also looks lie the parasitics are what are causing the problems. Try laying a piece of lossy ferrite over the circuit. Also try lowering the test signal level to see what results.
i try to put alot of piece of lossy ferrite and it didnt help me.
i get into the amp at -30 dBm under it there is noise at the mesure
also i tried to put 50 ohem at the enter of the circuit and cool it to -35 deg and it didnt osi, there is a feedback some how
1) throw dc
2) throw case
i will try to work with 2 difrent power supplies
and if it will not help me i will put more pice of metel between the stage
and if it will not help me i will pray to g-d
Do this test for each stage at a time. If each works it is either a feedback from common power supply or from inductive coupling between stages. It could also be output impedance of a stage being different from 50 ohms and that the source impedance on the next stage causing it to be unstable. Try varying the source impedance on the test of individual stages.
Problems are here to be solved... So one more question: do you have a
matching network on the gate and drain or do you feed the FET
directly with 50Ohm? Again: How is the source connected to your gnd-
plane? A good way is to use 4 vias at each source-pin (= 8 vias). These
vias has to be as near as possible (20 mils).
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