The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> Coupling LNA with passive mixer.
https://designers-guide.org/forum/YaBB.pl?num=1354788009

Message started by milvapp on Dec 6^th, 2012, 2:00am

Title: Coupling LNA with passive mixer.
Post by milvapp on Dec 6^th, 2012, 2:00am

Hello,I have designed a simple sinlge-output LNA and I would like to connect to a current-driven single-balanced passive mixer.

Considering the I path only what defines the value of the coupling capacitance?Is there a formula ?

I would like to add that the mixer is 50% duty cycle.

Thank you in advance!

Title: Re: Coupling LNA with passive mixer.
Post by Leo.cd on Dec 22^nd, 2012, 8:26pm

make the LNA and Mixer conjugate match, make sure u deliver the max power.

Title: Re: Coupling LNA with passive mixer.
Post by milvapp on Dec 24^th, 2012, 2:23am

Can you explain how to achieve maximum power transfer with the capacitance divider?

Thank you.

Title: Re: Coupling LNA with passive mixer.
Post by vivarf on Feb 17^th, 2013, 5:46pm

You want to maximize the current from LNA to current-driven single-balanced passive mixer. I assume your operating freq is under several GHz, so the coupling capacitance simply resonates with the output load inductance of the LNA.

Title: Re: Coupling LNA with passive mixer.
Post by milvapp on Feb 18^th, 2013, 2:11am

Hi vivarf,thanks for the reply.
As I am new to this,can you explain why it should resonate with the LNA load?(Yes the baseband frequency is around 10Mhz while the RF freq is 2.5Ghz

Title: Re: Coupling LNA with passive mixer.
Post by vivarf on Feb 18^th, 2013, 3:00am

Basically you want to maximize the current go to the mixer. You may want to take a look at the IEEE paper by Mirzaei about receiver/current mixer. Sorry I forgot the name of the paper.

Title: Re: Coupling LNA with passive mixer.
Post by vivarf on Feb 18^th, 2013, 6:08pm

milvapp wrote on Feb 18^th, 2013, 2:11am:

Hi vivarf,thanks for the reply.
As I am new to this,can you explain why it should resonate with the LNA load?(Yes the baseband frequency is around 10Mhz while the RF freq is 2.5Ghz

You want to take a look at this paper by Mirzaei, it quite complex analysis.
"Analysis and Optimization of Current-Driven Passive Mixers in Narrowband Direct-Conversion Receivers"

Cheers

Title: Re: Coupling LNA with passive mixer.
Post by milvapp on Feb 19^th, 2013, 1:46am

Thanks,I ve already looked at this paper and the main explanation is by mathematics,in attempt to maximize the gain.However what is worrying me is that the resulting coupling capacitcance has a quite small value(approx 200 fF)which is not what I waqs expecting.I mean a large capacitor with small impedance,in order not to lose signal.