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Design >> RF Design >> On-Chip 2.4 GHz bandpass filter
https://designers-guide.org/forum/YaBB.pl?num=1217426805

Message started by aaron_do on Jul 30^th, 2008, 7:06am

Title: On-Chip 2.4 GHz bandpass filter
Post by aaron_do on Jul 30^th, 2008, 7:06am

Hi all,

just wondering, what kind of issues would I have in designing a 2.4 GHz bandpass filter for ISM band apps. Assume I want to try and design an LC bandpass filter where Q is at most 10...

thanks,
Aaron

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by ACWWong on Jul 30^th, 2008, 8:55am

Q of 10 means you'll probably need a decent RF geared CMOS technology with good BEOL stack... otherwise it'll be tough to get the performance

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by aaron_do on Jul 30^th, 2008, 6:21pm

thanks,

but what is a BEOL stack and why do we need it?

Aaron

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by ACWWong on Jul 31^st, 2008, 9:57am

BEOL (back-end-of-line) is just metal stack

sorry for the jargon...

for good inductors you'll need low resistance metal (therefore thick) which is sufficiently elevated from substrate...

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by loose-electron on Aug 3^rd, 2008, 3:15pm

Silly thought - The discussion seems to be on LC filters. Anyone taken a look at a gm-C filter for this? My last gm-C filter was at 500MHz on a 0.35um technology, so maybe with a faster technology you could make this bandwidth.

Hmmm.....

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by didac on Aug 4^th, 2008, 2:40am

Hi,
Just to continue the line of thought of loose-electron I've seen a type of filters called "Q-enhancement Bandpass Filters" that are proposed as integrated RF Bandpass filters, first time I've seen them was in a tutorial from ISCAS 2004:"Design of Continuous-Time Filters from 0.1Hz to 2.0GHz",Edgar Sanchez-Sinencio and Jose Silva-Martinez, surfing the web you could find some IEEE papers and I've found also a Thesis:"A Q-ENHANCED 3.6 GHZ TUNABLE CMOS BANDPASS FILTER FOR WIDEBAND WIRELESS APPLICATIONS",JIANDONG GE,University of Saskatchewan,Canada.
I suppose that they could be used if power consumption and/or the trade off between NF and linearity are too stringent.

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by aaron_do on Aug 4^th, 2008, 6:45am

For Gm-C and Q-enhancement type filters, I think the most difficult part is the control (apart from the noise). You would need a PLL to center the filter frequency, and even still you couldn't rely on a matched design since the matching between such designs probably wouldn't be good...

Title: Re: On-Chip 2.4 GHz bandpass filter
Post by RFICDUDE on Aug 17^th, 2008, 7:53pm

Instead of GmC you could think of using a LRC tank where the tank is somehow related to the VCO tank, then you don't need an extra PLL.

Or you could come up with a smart way to use the RF PLL to tune the tank.

The real problem with both GmC or LRC with Q-enhancement is the inevitable degradation in dynamic range due to using active components in the filter structure (added noise and nonlinear distortion).

There are numerous papers on LRC Q-enhancement, and a few of them deal with analyzing the dynamic range issues. Usually the IMD and noise performance is pretty bad.

But it is cool to play around with for sure.