---------- Forwarded message ----------
From: Jean-Samuel Najnudel - BJT PARTNERS SARL <
jsn@bjtpartners.com>
Date: Tue, Oct 30, 2012 at 6:25 PM
Subject: LNA and Noise Figure improvement
Hi Andrey,
I understand you plan to prepare the UmTRXv3.
I would need to discuss about the Rx Noise Figure improvement.
With UmSEL, according to your calculations, NF would be around 0.7 dB
(excluding duplexer IL) with the MGA-13116.
It would be interesting to try to improve this figure with a very
first stage LNA based on the MGA-633P8. This would let us reach a NF
as low as about 0.4 dB.
Adding this very first stage LNA in the Rx path brings a few questions.
1/ To improve isolation with the other RF parts, would we need to have
this LNA in a separate shielded enclosure ?
If yes, we would need a 5V power supply for this LNA. To have a better
shielding between the voltage regulator circuitery and the LNA, it
should be nice to have the 5V voltage regulator outside of the LNA
enclosure. To make this possible, it would be very useful to add a 5V
voltage regulator and connector on the UmTRXv3.
If not, we do not need specific modifications on the UmTRXv3 but we
would need to add an MGA-633P8/634P8 as a very first stage in the
UmSEL.
2/ Whatever external or on the UmSEL, this extra LNA will increase the
total gain. Considering your calculation, the UmSEL IIP3 is already as
low as around 1 dBm. If we add a very first stage LNA, this IIP3 will
go down to about -15 dBm. This could be a problem for inband blockers.
Even if, in real life situation in the field, I am not sure it will be
a very big problem, it will be a problem to pass the spec.
Would you have another idea to improve the NF ?
If not, could you please let me know what NF we could expect with the
current design (UmSEL with MGA-13116/13216) in both 900 and 1800 bands
?
Best regards.
Jean-Samuel.
:-)