Post subject: UHF LNA Posted: Tue Aug 26, 2008 5:28 am
Joined: Tue Aug 26, 2008 5:18 am
I am new to this forum. I need to design an
LNA at 385MHz. Key requirement is NF. Gain/P1dB/IP3 are not not critical.
Balanced mode is preferred rather than single ended.
Any idea if
it is possible to design this LNA to achieve NF <1dB.
Post subject: Posted: Thu Aug
28, 2008 4:08 pm
Joined: Mon Jun 27, 2005
found 2 components from NEC under the following link:
There are the NE3508M04, NE3509M04 which have
NF of 0.45dB and 0.4dB respectively. The S-parameters file includes
noise data starting from 1.5GHz. However, there are non-linear models
available for these devices under the above link. From these models
you should be able to derive the NF at low frequencies as well. I will
try and find some more transistors for you.
You should take
care for the gain and the IP3, as this changes from one transistor to
another, and the noise mismatch required at the input for achieveing
the NF can reduce the gain dramatically and may have some effect on
If you can provide more information about Gain and
IP3 that would be useful.
UHF LNAPosted: Fri Aug 29, 2008 5:34 am
Tue Aug 26, 2008 5:18 am
Thanks for your reply. Gain 10-12dB with P1dB of 10dBm. Its really difficult
to maintain 10dB gain whilst keeping P1dB at 10dBm.
Once again thank
Post subject: UHF LNAPosted:
Fri Aug 29, 2008 8:33 am
Joined: Tue Aug
26, 2008 5:18 am
seen data sheet for NE3508M04 and NE3509M04. NE3508M04 seems to be the
right candidate for my application in a balanced mode beacause of its
low gain and high P1dB biased at 3V,30mA. Gain can be reduced if necessay
by using a pad at the out put. I suppose drain voltage/current can be
varied to change P1dB.
There is one thing which I want to ask you:
In the data sheet P1dB is given at 3V, 30mA (NON RF) as 18dBm. What
does NON-RF mean?
Posted: Sat Aug 30, 2008 3:02 pm
Mon Jun 27, 2005 2:02 pm
that NON-RF means only DC current (Quiescent current) for Id without
any input RF signal. And on top of that there is the RF signal which
will increase the drain current.
This term is confusing, to
be on the safe side it is better to consult with the manufacturer.