RF filter? Problems with CMOS at 868MHz

[zahrein]

RF filter?

I have been asked to design a band pass filter at 868MHZ using CMOS technology. I have found out that, it is difficult to deisgn at that frequency. The thing is i do not have any prove that can support my facts that it could not work at that frequency.

From my research, my Q factor is 10000. HOpe u all can give me some information so that i can answer to my supervisors.

 

[refdv]

RF filter?

the key element for designing BPF at high freq is to use active inductor...

 

[zanov]

Re: RF filter?

I am still in doubt but will this pattern of filter frequency response will be repeating itself at corner frequency n*868Mhz where n is n=1,2,3,... by using an active inductor?

I am not sure for CMOS I never designed in CMOS one. I am eager to learn it.

thank you
zanove

 

[boy]

Re: RF filter?

CMOS can be made to be both inductor and capacitor. I saw it somewhere. Then you can use those elements to built a filter.

 

[xtasa]

Re: RF filter?

:?:
Where you intend to use this CMOS band pass and power level through it???
XTASA

 

[zahrein]

RF filter?

im design it for RFID application.. Is that answer ur question ?

 

[jlynch]

Re: RF filter?

Hi,

Inductors and capacitors in CMOS can be used to construct a filter with a Q of the order of 10 (maybe a little more) - this is mainly down to the Si substrate and cannot be overcome

If I understand you correctly and you require a filter with a Q of 10,000 then CMOS is not the way to go - you should try SAW technology maybe

jl

 

[maolh]

Re: RF filter?

There are many research papers about RF BPF published on various IEEE transactions. They usually handle 1 to 5 GHz RF signal on CMOS. However, the performance is not good enough to replace SAW in cell phone application. For you RFID application, I just don't understand why you need so high Q value for the filters. If the specification of your RFID is not stringent (such as dynamic range, power dissaption, noise figure), it's possible to implement on CMOS.

 

[zahrein]

RF filter?

I ve known that i cant design a band pass filter using CMOS with the Q point almost 10^5.

What are the reasons that i cant design with CMOS with a high Q, i need to know the reasons as im still trying to findout the reasons. Is it impossible? WHy?

 

[jlynch]

Re: RF filter?

The reason is simply due to the resistivity of Si substrate - this means that very high Q's cannot be achieved

SAW filters are normally produced on ceramic substrates enabling high Q's

 

[joelo]

RF filter?

the point is that inductor, do u try it??