25% vs 50% Duty Cycle, passive I/Q Downconversion mixer

[exp]

Hi,

Until yesterday I would have bet everything that a passive mixer, driven by 25% duty cycle gets rid of the 3rd, 7th, 9th etc harmonic; while the 50% version has all odd-order harmonics. I swear I have read this in about every single paper in that area so that I started assuming it "granted common knowledge" without ever actually verifying it.

Now in my simulations this is not the case and indeed, verifying a sinusoid wave, sampled 4x per period with zero-order hold all all odd order harmonics, same as the 50% version ("rectangular wave").

I am also desperately trying to find sources for that but I fail. The closest to that is https://icd.ewi.utwente.nl/temp_files/c2ee0ea0185d31e7ef31b0f6b7aaf6c0.pdf, slide 10.


Can anyone help to find out what could I mixing up here?


Thanks!

PS: In case my question is unclear or it is not entirely clear what I mean I am happy to provide simple MATLAB scripts comparing the spectra between 50% and 25% mixer

 

[dick_freebird]

I don't recall ever hearing that a "magic" duty cycle
cancels harmonics. Changes their distribution, yes.
But to zero, never been told that.

Maybe they said "minimize" or some other weasel-
wording that made it sound more magical than it is.

 

[pancho_hideboo]

I swear I have read this in about every single paper in that area
so that I started assuming it "granted common knowledge"

Yes.
It is well-known technique and actually adopted by many poroduct.

Now in my simulations this is not the case

This is because you didn't answer in your many nonsense threads at all.

Before going to next.
Answer my quetions in your previous threads.
https://www.edaboard.com/threads/351341/#9
https://www.edaboard.com/threads/355656/#13
https://www.edaboard.com/threads/363583/#2

 

[mtwieg]

I'm guessing you're just using a normal two-path mixer and reducing the applied duty cycle from 50% to 25%, which is wrong. The gains come when you add more switching paths, like N=4 and D=25%, or N=8 and D=12.5%, and so on.

 

[biff44]

the only thing i ever heard was that driving the LO port of a mixer with a square wave instead of a sine wave MIGHT improve some of the spurious outputs. Marki microwave has some mixers that deliberately operate in this mode for spurious output reasons

 

[vfone]

I think you refer to the influence of the duty-cycle on a non-linear device, as a frequency multiplier (and not a mixer).
This document from Charles Wenzel explain you what is about with harmonics generated vs duty-cycle (Figure 2):

https://www.wenzel.com/wp-content/uploads/choose.pdf

There is no reason to use other than 50% LO duty-cycle in an RF mixer. Any other duty-cycle might reduce the output harmonics, but for sure will degrade mixer performances (all of them).

 

[mtwieg]

Apparently N-path mixers are still somewhat obscure on this forum. Here's a handy overview: https://icd.ewi.utwente.nl/temp_files/f065f82ec42dd526b618f73a5e571e99.pdf

 

[dick_freebird]

Not Found

The requested URL /temp_files/f065f82ec42dd526b618f73a5e571e99.pdf was not found on this server.

 

[mtwieg]

Strange, seems the URL changed... now at https://icd.ewi.utwente.nl/temp_files/002142bc6f2139de4c2559ee64f7a05d.pdf

If that doesn't work, I've attached the pdf to this post: View attachment 002142bc6f2139de4c2559ee64f7a05d.pdf