The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> Hello everyone, I would like to ask one question about LNA for LTE standard.
https://designers-guide.org/forum/YaBB.pl?num=1363000005

Message started by angel on Mar 11^th, 2013, 4:06am

Title: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by angel on Mar 11^th, 2013, 4:06am

Hello everyone, I would like to ask questions about Low Noise Amplifier for LTE standard.

1. In the commercial LTE chip, multiple LNAs are adopted which consumes a large area. I wonder why do not use one wideband LNA instead of multi-narrow band LNAs? Are there any technical issues for this wideband LNA design, or are there any advantages to adopt multi-narrow band LNAs?

2. Could anyone provide the documents which can explain question 1?

Thank you very very much ! :)

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by aaron_do on Mar 11^th, 2013, 10:59pm

Hi,

I haven't studied the LTE standard in particular, but just to get the ball rolling, I think the multiple LNAs also have multiple SAW filters connected to them, each for a different band. The are used to suppress PA out-of-band noise as well as out-of-band interferers. This reduces the linearity requirements of the front end.

Try reading, "A Single-Chip 10-Band ECDMA/HSDPA 4-Band GSM/EDGE SAW-less CMOS Receiver With DigRF 3G Interface and +90 dBm IIP2" in JSSC Vol 44, No3, March 2009.

hope it helps,
Aaron

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by angel on Mar 11^th, 2013, 11:22pm

thank you very much for your reply, I am really appreciate it. I will read that paper now ^^. Thanks again

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by angel on Mar 12^th, 2013, 3:54am

I would like to ask one more question. When design TDD LTE receiver, can we use just one wideband LNA? Is there any paper or document published for this one? Thank you very much.

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by aaron_do on Mar 12^th, 2013, 5:37pm

Hi,

I'm not so familiar with the literature on LTE. For WCDMA, a duplexor is used to seperate the TX and the RX. The TX side filter removes PA out-of-band noise, and the RX side removes PA transmit signal. The PA could be transmitting something like 24 dBm, which if left unattenuated could damage the RX.

The issue with using a single wideband LNA I think is that you could no longer use the SAW filter in front of the LNA, and therefore you would have to come up with some other creative way of suppressing the PA transmit signal.

I think LTE supports both TDD and FDD. For TDD it might not be an issue, but for FDD, both the transmitter and receiver would be working at the same time, so you would face the above issue.

regards,
Aaron

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by angel on Mar 12^th, 2013, 10:50pm

Thank you very much for your reply. When you talk about "For TDD it might not be an issue, but for FDD, both the transmitter and receiver would be working at the same time, so you would face the above issue. "

Can I understand like this? For FDD, the transmitter and receiver would not be working at the same time, therefore, a wideband LNA can be used for TDD mode LTE receiver. I wonder am I right? Thank you very much ^-^

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by aaron_do on Mar 13^th, 2013, 8:10am

Hi,

Quote:

For FDD, the transmitter and receiver would not be working at the same time

I guess you mean TDD. That's what I'm guessing, but as I mentioned, I'm not 100% sure since I haven't actually had much time to study it.

Maybe somebody who has worked on this can comment.

Aaron

Title: Re: Hello everyone, I would like to ask one question about LNA for LTE standard.
Post by angel on Mar 13^th, 2013, 10:19pm

Yes, you are right, I mean TDD. ^^ Thank you very much ^^