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UHF LNA - RF Cafe Forums

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SDO
Post subject: UHF LNA Posted: Tue Aug 26, 2008 5:28 am

Captain


Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
Hi,
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.
Thanks.
SDO


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IR
Post subject: Posted: Thu Aug 28, 2008 4:08 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello SDO,

I found 2 components from NEC under the following link:

http://www.necel.com/microwave/en/param ... hj_dp.html

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 the IP3.

If you can provide more information about Gain and IP3 that would be useful.


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SDO
Post subject: UHF LNAPosted: Fri Aug 29, 2008 5:34 am

Captain


Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
Hi IR,
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 you.
SDO


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SDO
Post subject: UHF LNAPosted: Fri Aug 29, 2008 8:33 am

Captain


Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
Hi IR,
I have 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?
Thanks.


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IR
Post subject: Posted: Sat Aug 30, 2008 3:02 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
I think 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.



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