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Design >> RF Design >> Transferred impedence filter with passive mixer
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Message started by macg84 on May 6^th, 2009, 3:21am

Title: Transferred impedence filter with passive mixer
Post by macg84 on May 6^th, 2009, 3:21am

Hallo at all,

In attached there is the schematic, the circuit should be a filter where the corner frequency are Flo-Flc and Flo+flc (Flo= frequency of local oscillator, Flc= resonant frequency 1/2*3.1415*(LC)^1/2). This filter doesn't work and i don't know why.

Is there some people that can help me with some advice?
Thank you very much

Title: Re: Transferred impedence filter with passive mixer
Post by RFICDUDE on May 6^th, 2009, 7:22am

What nodes do you consider to be your outputs?

Title: Re: Transferred impedence filter with passive mixer
Post by aaron_do on May 6^th, 2009, 7:53am

Hi,

A few comments apart from the missing output nodes pointed out by RFICDUDE.

1. Your ideal_balun doesn't seem to be connected properly. I think the center-tap of the output coil should be grounded.

2. I'm not sure but you seem to have you LO signals connected wrongly. One is going from 0 to 3 and the other from 3 to 0. Also one is connected backwards. So overall, one is swinging from 0.4 to 3.4 while the other swings from -2.6 to 0.4. Correct me if i'm wrong there...

3. How is it supposed to work anyway?

cheers,
Aaron

Title: Re: Transferred impedence filter with passive mixer
Post by RFICDUDE on May 6^th, 2009, 9:29am

I don't think the center tap connection matters, but it does matter that the RF input appears to be common-mode. Both ports appear to be in phase, so there is no differential signal on either side of the balun.

Title: Re: Transferred impedence filter with passive mixer
Post by macg84 on May 6^th, 2009, 9:49am

Hello,

Tahnks for your attentions. I atteched a new schematic with outputs node. I think but i am not sure that the balun is right, because i look it in the Designer's Guide of Ken Kundert "Measuring S-Parameters of a Differential Mixer" infact at page 3 figure 3 the ideal balun has 2 input and two output, and the center-tap of the input coil is grounded. So I assumed that the central tap of the input coil is inherently grounded.
Do you think it is right?
The vpulse work right, because the switches have to work in alternate way.
I read thet the mixer can have this behavior in a patent.

Title: Re: Transferred impedence filter with passive mixer
Post by aaron_do on May 7^th, 2009, 12:48am

Hi,

if you zoom in to your ideal balun I think you will see something like what I have attached below. The output center-tap is the bottom left pin so i think it should be grounded or at least left open-circuit.

As for the LO signals I still think they are wrong. Try plotting net47 and net50 and see if you get the right signals.

Also, why have you changed your inputs to current sources? I'm still curious about how you expect the filter to work... is it supposed to be a mixer too?

cheers,
Aaron

Title: Re: Transferred impedence filter with passive mixer
Post by macg84 on May 7^th, 2009, 1:54am

Probably your considerations on balun are correct, thanks. I checked again the LO signal, but i think that they are corrects. I put a current source, so use a PAC analyses to see what happens to the output current around the interest frequency. Outgoing I put another mixer.
Now try again the simulations, and then I'll tell you the result, if you interested.

Best regards
Mac