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Design >> RF Design >> single-ended to differential conversion
https://designers-guide.org/forum/YaBB.pl?num=1282930637

Message started by .matteo on Aug 27^th, 2010, 10:37am

Title: single-ended to differential conversion
Post by .matteo on Aug 27^th, 2010, 10:37am

hi everybody,

I'm designing an active single-ended to differential converter.

I designed a resistively loaded fully differential couple with a 50ohm resistor between the gates of the two transistor to match with the measurement equipment. This couple is followed by another fulldiff couple to remove the common mode signal.

However, I've not enough rejection to the common mode signal and my plus and minus signal are very different in amplitude (and phase) at the output of the first couple and they get worse at the end of the second one. :-/

Does anybody has any suggestion about it? or a pointer to some article?

thanks

Title: Re: single-ended to differential conversion
Post by carlgrace on Aug 27^th, 2010, 11:38am

What is the speed you are looking to get with this? For board-level single-ended to differential conversion, you can look at using two op amp circuits, one inverting and one non_inverting. Then the difference is the output.

Title: Re: single-ended to differential conversion
Post by .matteo on Aug 27^th, 2010, 12:08pm

9 to 18Ghz ... ::)

Title: Re: single-ended to differential conversion
Post by Paul on Aug 28^th, 2010, 11:24pm

Hi Matteo,

Why don't you use a balun (http://www.odyseus.nildram.co.uk/RFMicrowave_Circuits_Files/Balun%20Design.pdf)?

Also, at these frequencies you may want to take care of impedance matching.

Kind Regards
Paul

Title: Re: single-ended to differential conversion
Post by pancho_hideboo on Aug 29^th, 2010, 3:08am

See the followings.

http://www.designers-guide.org/Forum/YaBB.pl?num=1278642989/2#2
http://www.designers-guide.org/Forum/YaBB.pl?num=1233236788/1#1
http://www.designers-guide.org/Forum/YaBB.pl?num=1240201234/1#1
http://www.designers-guide.org/Forum/YaBB.pl?num=1255331741/4#4

Title: Re: single-ended to differential conversion
Post by .matteo on Aug 30^th, 2010, 12:15am

@pancho_hideboo
thanks a lot for your help. are you suggesting me NOT to design an active single-ended to differential converter and to use the setup in ( http://www.designers-guide.org/Forum/YaBB.pl?num=1233236788/1#1 ) to measure the chip?

@Paul
thanks paul, the pdf is really interesting. the idea of the balun is good and we decided to consider it as a very last choice

Title: Re: single-ended to differential conversion
Post by rfcooltools.com on Sep 8^th, 2010, 10:26pm

Hi Matteo,
1. lead lag (LC-CL) network is a simple way to make a differential signal at a range of frequencies.
2. A cascaded set of poly-phase circuits after a single ended gain stage. because you will loose several dB.

If the signal is an LO then the pdf attached patent should give some insights.

http://rfcooltools.com