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how to make an estimate of my filters power consumption?

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Elyments

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Hi,

For a VLSI project I was tasked to design a CMOS sixth order low pass filter in a 0.8u process, i created one using the standard VCVS 2nd order design with matching R and C values to create Butterworth characteristics and then cascading three stages with appropriate gains to make a 6th order filter.

My problem is that i have no idea how to make an estimate of my filters power consumption! I would really appreciate any advice on where to start! I've attached a multisim design of my filter, ive also created it in tanner tools L-Edit.

Thanks in advance,

Elyments
 

Re: VCVS Low Pass filter

Hi Elyments,

just one question:
Did you simulate your filter already? AC, TRAN and operating point?
I have some doubts because of single supply.
 

VCVS Low Pass filter

I agree with the previous comment about single supply operation - you are trying to run the circuit at ground potential without dual supplies.

Also, if you cascade three 2pole Butterworth filters you don't end up with a 6 pole Butterworth - you end up with a 6 pole mess. You need to design it as a 6 pole filter.

Keith
 

Re: VCVS Low Pass filter

Yes, as KEITH has said, you need three stages - each with the same pole frequency, however with different Q values (0.5176, 0.7071 and 1.9318).
 

VCVS Low Pass filter

Actually, I have just noticed the gain of each stage is different, so my earlier comment is probably not relevant. I assumed from your description that you had cascade three identical sections.

Keith
 

Re: VCVS Low Pass filter

Big thanks for the fast replies!

Ive simulated it both in Multisim and T-Spice (from the L-Edit layout version) and got the expected cut-off and slope for a 6 pole filter, i used a separate gain for each section; i used given values from a table in the Art of Electronics.

I did'nt think there was anything wrong with the actual filter but i still have no idea how to estimate its power consumption.

Elyments
 

Re: VCVS Low Pass filter

Elyments,

based on the chosen gain values, you ROUGHLY meet the required pole Q for each stage (for example, the last stage has Qp=2 instead of 1.932).
I don`t know your specification and the associated tolerance requirements.
However, your design - especially the last stage - is VERY sensitive to passive component tolerances (When the gain of the last stage is 2.6 istead of 2.5 the pole Q is 2.5 instead of 2).
This is a known property of the equal component S+K topology.
Perhaps you should reconsider the filter structure.
 

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    Elyments

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VCVS Low Pass filter

For power consumption measurement you need to run a transient analysis and measure the current taken from the supply.

Keith
 

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    Elyments

    Points: 2
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Re: VCVS Low Pass filter

LvW, i see what you mean about the sensitivity, i think im going to stick with the design though as i haven't been given any tolerance requirements etc. This is my first shot at filter design and i only really know the SK topology!

Keith, thanks for the info, i'll start looking at performing a transient analysis!
 

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