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Design >> RF Design >> LO Buffer
https://designers-guide.org/forum/YaBB.pl?num=1294728804

Message started by kelly on Jan 10^th, 2011, 10:53pm

Title: LO Buffer
Post by kelly on Jan 10^th, 2011, 10:53pm

Hi,

I need to design a LO buffer that'll take a 1V complimentary input and amplify up to 2.3V complimentary out. I plan to use a diff pair with current souce and a cascode inductor loads. I choose the L so that it resonates with cap seen at the output of the diff pair. I have couple questions,

1. how does the choice of current come into play (it seems that as long as I have couple mA or so, I should be able to get a L and C that work)

2. The idea of making this work is to get LC resonate at the desired frequency, since the impedance at the resonant frequency is high, so you can achive high amplitidue with less current, right? If it is, then it seems that this circuit will not be broadband, right? In another words, say you get it to work at 2G, will the same circuit work for 3G?

3. if it dosn't, then what's the best way to design a broadband LO buffer that works from say 1G to 4G?

Any help is greatly appreciated.

Thanks.
Kelly

Title: Re: LO Buffer
Post by rfcooltools.com on Jan 11^th, 2011, 9:51am

kelly,

You have a few choices:
1. purposely de Q the inductor reduce the frequency selectivity when resonated. Trade off more current needed to obtain the same amplitude.
2. make selectable capacitors for frequency regions of operation. In other words add capacitors when lower frequencies are needed by switching them in.
3. make a few fixed inductor resonant loads and switch the output when frequency bands are in the range of the tank. Trade off is area but likely lowest current
4. all or some of the above in an optimal combination

http://rfcooltools.com

Title: Re: LO Buffer
Post by kelly on Jan 11^th, 2011, 5:47pm

that helps a lt, thanks.