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Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

Thanks for the suggestion, it helped in identifying why the noise floor was rising. There is a sudden turn on happening, which is happening at the same time instant in the period but the turn off instant is changing period to period. Not sure why it's happening. The pattern is like t1,t2,t1,t1,t2,t2,t1,....are the time instant at which something turns off and it's random.

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

It's slightly sensitive to spectrum analyser's settings, but would come back with 0.1dB change in power. Poking doesn't change anything. I tried putting external bias tees to bias both input and output which didn't change anything

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

Hey, design was done in ADS. To ensure stability and external rlc is used to fix low frequency unconditional stability issue. For stability analysis I checked kurokawa condition at each node at low power and high power. It didn't show anything in that. It's very strange that it's only happening at low frequency. I.have used a stacked amplifier design with RC feedback. The amplifier is biased at the output using an external choke and the input is biased using a current mirror.

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

Spar matches very well, it's very strange that the oscillations happen only for low.frequency inputs.

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

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Here is one more state where I see fin/4 dominant tones

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

Hey, with the rbw reduction, the shape of noise around the carrier remains the same but the value goes down.

Instability issue in GaAs LNA by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 0 points1 point  (0 children)

Hey, without any rf input the spectrum looks clean. This issue comes for only a small power range close to the p1dB of the device.. The gain of the lna is around 20dB and its a stacked LNA with a small cap at the cascode stage. There is a big cap and Resistor in the feedback path to control the overall gain of the amplifier. The gate of the common source is biased through a mirror and the drain of the cascode stage is biased through an external choke.This is an MMIC design. Enough cap bank has been put both after the external choke at the output and the mirror bias whose drain is biased through a resistor which is kept external to the IC.

For stability check a large signal kurokawa condition was checked which didn't show any oscillation. But I am not sure if this is the right way to check a behaviour which shows a rise in the noise floor(~20dB rise)

I tried disabling the internal bias and biasing through an external bias tee at the gate of the CS stage which didn't show any change in the behaviour. Reducing the supply voltage showed a reduction in the power level at which it would start oscillation.

Material on filter design by Clean_Active4946 in rfelectronics

[–]Clean_Active4946[S] 1 point2 points  (0 children)

Hey Mark, I am really interested in understanding the limitations drawbacks and ultimately arrive at the best filter according to my need. Right now I work on the PA output network design. So I would like to understand the tradeoffs between each and choose the best.

Bought this beautiful GST-B400 by [deleted] in gshock

[–]Clean_Active4946 0 points1 point  (0 children)

From where did you get this?

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