Pulse distortion after amplification
时间：04-04
整理：3721RD
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Hi guys!
I've designed a simple common emitter LNA at 10GHz, i ve used it in many CW applications with no major problems. However i tried to amplify a 4us pulse (a cosine of constant magnitude) and i notice a pulse distortion when the LNA is saturated, where the signal magnitude is higher at the begining of the pulse and it keeps dropping for 500~1000ns, until it reaches a constant magnitude for the rest of the pulse, i tried filtering the harmonics and while this helps a little bit the distortion is still present. have any way of you encountred the same problem? or have an idea wht it might be?
Thank you in advance. I can provide the schematic/Layout of the LNA if required.
and this is the bias circuitry
The application where i m using it won't require the LNA to be saturated all the time, but at the beginning, it's going to be saturated for a small laps of time (i need to aquire that pulse too) and then it'll go back to being linear. i have tested other amplifiers (from mini-circuit) and they dont have that probleme even when saturated, so i know it s my design that sucks.
I've designed a simple common emitter LNA at 10GHz, i ve used it in many CW applications with no major problems. However i tried to amplify a 4us pulse (a cosine of constant magnitude) and i notice a pulse distortion when the LNA is saturated, where the signal magnitude is higher at the begining of the pulse and it keeps dropping for 500~1000ns, until it reaches a constant magnitude for the rest of the pulse, i tried filtering the harmonics and while this helps a little bit the distortion is still present. have any way of you encountred the same problem? or have an idea wht it might be?
Thank you in advance. I can provide the schematic/Layout of the LNA if required.
Good idea. I guess you have input or output AC coupling and the bias point is shifting when the input signal is rectified in saturated operation.
By definition an LNA should NOT be saturated in any cases.
Reduce the input level into LNA, or use a higher IP3 device (with higher P1dB) which can handle higher input levels.
Here is the layout of the
and this is the bias circuitry
The application where i m using it won't require the LNA to be saturated all the time, but at the beginning, it's going to be saturated for a small laps of time (i need to aquire that pulse too) and then it'll go back to being linear. i have tested other amplifiers (from mini-circuit) and they dont have that probleme even when saturated, so i know it s my design that sucks.
i agree, the bias point is shifting. Possibly from the input of your active device rectifying the signal?
You need to bias it up from a "stiffer" source.
IF it were a large signal amplifier, you might have to also consider the device heating up during the pulse, and shifting operating point...but you said an LNA...