Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Low Pass Sallen Key Filter design

Status
Not open for further replies.
M

mfhanif

Junior Member level 2
Joined
Jan 11, 2007
Messages
23
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,451
Hello Everyone, I want to design a 4th order Butterworth LP filter of Sallen Key type. The 3dB frequency is 750MHz....can someone give me ideas, references, etc. to achieve this high frequency filter design

thanks
 

Not a promising idea. It can at best work inside an IC implementing a very fast transistor technology. With discrete transistors, even of sufficient bandwidth > 10 GHz, the electrical delay will be too large to achieve an acceptable filter characteristic or just stability.

Simply go for passive LC filters.
 

At this frequency you can use gm_c filter. Designing at such frequency might be difficult with active rc filter or switched capacitor filter. But the linearity if gm-c filters is inferior compared to the other ones.
Conventionally, you design it with a cascade of two bi-QUAD stages
 

Agree with Milad-D. I implemeted 6th order filter this way in 1995. This was upto 4MHz. I don't know why FvM is saying use discrete components.
 

This was upto 4MHz. I don't know why FvM is saying use discrete components.
Click to expand...
Do you consider, that there may be a difference between 4 MHz and 750 MHz?

I any case, a filter different from a simple cascade of first order will need feedback. Then, also a gm-C filter has to struggle with stability issues. Thus I'm curious to see a 4th or 6th order gm-C filter with 750 MHz characteristic frequency outside an IC. But I'm willing to learn.
 

Dear FvM,

In the old tech 0.35um CMOS, they have achieved 550MHz -3dB bandwidth.

Pavan, S.; Laxminidhi, T.; , "A 70-500MHz Programmable CMOS Filter Compensated for MOS Nonquasistatic Effects," Solid-State Circuits Conference, 2006. ESSCIRC 2006. Proceedings of the 32nd European , vol., no., pp.328-331, Sept. 2006

Therefore, i think it will be very easy to get f-3dB=750MHz in 0.18um or 0.06um. Why gm-C is better than Active-RC? Because you can use much less complex structure for gm cell than Op-amps which means that the frequency capabilty of the gm-cell is higher.


By the way, Passive filter is the best one, but it consumes a lot of area in chip.
 
Therefore, i think it will be very easy to get f-3dB=750MHz in 0.18um or 0.06um. Why gm-C is better than Active-RC? Because you can use much less complex structure for gm cell than Op-amps which means that the frequency capabilty of the gm-cell is higher.
Click to expand...

I don't contradict. But the discussion hasn't been about chip design, seems like you didn't read my initial post exactly.

I said, that I only see a chance to implement the filter on a chip, without considering particular topologies. But there's no indidcation, that the original poster has been talking about chip design. Because a discrete active implementation won't work, he should better use a passive LC filter.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top