The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> IQ Mixer need isolation
https://designers-guide.org/forum/YaBB.pl?num=1137548219

Message started by milkdragon on Jan 17^th, 2006, 5:46pm

Title: IQ Mixer need isolation
Post by milkdragon on Jan 17^th, 2006, 5:46pm

For direct conversion receiver, we need I and Q output at the baseband. However, do we need isolation between I and Q? I am asking this because most of the journal simply have the LNA connected directly to the input of both I and Q. My understanding is we need certain isolation between I and Q. So, should we actually add a buffer stage before the I Q mixer input instead of splitting it at the LNA output and directly feed into the IQ mixer?

Title: Re: IQ Mixer need isolation
Post by hrkhari on Jan 17^th, 2006, 6:36pm

In constructing a modulator, isolation both at the mixer and oscillator helps in the problems such as feedthrough, self-mixing, etc. Normally cascode stage buffer is utilized in providing better isolation, in a oscillator a buffer stage proceeds at the output to provide isolation upon integration, whereas in a mixer, utilization of differential architecture and cascode stage switching, such as in a typical Gilbert cell architure combats the feedthrough and gives better isolation.

Rgds

Title: Re: IQ Mixer need isolation
Post by milkdragon on Jan 18^th, 2006, 9:47am

Thanks for your comment, Gilbert cell does provide certain isolation between I and Q path. What about Passive mixer?