Thanks Frank ..
Actually 90 dB attenuator is designed by cascading 3 digital attenuator ICs (Hittite HMC425LP3), whose attenuation level is controlled by Control signals from software..
The problem with this design is that , as I said, it is non-linear after when i give attenuation of 60 dB. Is there any circuitry that i can add which will avoid this ? Atmost care has been taken regarding bypassing, decoupling of signals as per datasheet of IC.
Thanks
Chaitanya
Hi,
I am trying to improve the linearity of 90 dB digital attenuator. Its performance is non-linear at high attenuation level. What improvement or rather which circuitry can be added in the schematic to improve it. Please suggest some relevant document.
Thanks
Chaitanya
The linearity of IC attenuator circuits have been defined by manufacturer so that any additional precaution can not be applicable.The nonlinearity comes from its nature and fixed by supply/bias etc.Thanks Frank ..
Actually 90 dB attenuator is designed by cascading 3 digital attenuator ICs (Hittite HMC425LP3), whose attenuation level is controlled by Control signals from software..
The problem with this design is that , as I said, it is non-linear after when i give attenuation of 60 dB. Is there any circuitry that i can add which will avoid this ? Atmost care has been taken regarding bypassing, decoupling of signals as per datasheet of IC.
Thanks
Chaitanya
The linearity of IC attenuator circuits have been defined by manufacturer so that any additional precaution can not be applicable.The nonlinearity comes from its nature and fixed by supply/bias etc.
You may consult to manufacturer..
There must be something i would do at least to reduce fluctuations of Attenuation response at high attenuation level..?
As you see, IIP3 is defined well under some circumtansces.
But I just want to get your attenuation algorithm.How have you used it ?? Because you shouldn't exceed the mentioned power levels at each input of three attenuator, so input powers should be organized so that nonlinearity of each attenuator shall be in-spec.
Digital signals should absolutely be seperated to minimize the influence of noise but digital signals don't impact-either improvement or degredation-the nonlinearity.Instead, you should organize the controller algorithm so that max. RF power wouldn't exceed specified values.Let me give you an example..Definitely input power to those attenuator parts is well within IIP3 level. While testing it on VNA i set the RF input power to 20dBm which is within its range..
Do this anything have to do with mixed signals on same PCB board., i.e, RF and digital signals.. ? Is there anything i could do to separate them ?
Its performance is non-linear at high attenuation level.
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