Active filter in NI Labview only

[shivam161994]

I want to make an active analog lowpass/bandpass/high pass  filter using "NI Labview only" without using any other interfacing. Please guide me how to start and proceed. I  have searched throughout internet but did not find a single good answer. Please help me. Guide me through the design of any one. Rest I will be able to do myself

[NIquist]

LabVIEW is just software so do you mean you want to simulate an active analog filter?  Have you tried looking in the Signal Processing > Filters palette???  (You may need the Full or Professional version of LabVIEW)

[shivam161994]

Yes sorry, I mean I want to simulate active analog low pass filter. I made a passive filter using Butterworth filter from that palette. But  here the question is that we have to simulate an "active" filter. How would we do this please?

[GerdW]

Hi shivam,

what is your definition of "active" and "passive" filters?

[NIquist]

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@GerdW wrote:

Hi shivam,

what is your definition of "active" and "passive" filters?

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And can you post your "passive filter" VI?  Just curious.  

You might want to ask your teacher to be more specific.  I suspect that you're supposed to do this by simulating the filters with math, not by dropping an IIR DIGITAL sub-VI on your block diagram.  That's too easy.   If so, check this out:  http://en.wikipedia.org/wiki/Low-pass_filter

[shivam161994]

Let me state the question as it has been given

Ques a) Labview simulation Topic  : Passive and active analog filters 1. LPF, HPF 2. BPF, BSF. All pass filter

           b) LabView+DAQ Interfacing Topic : Passive LPF/HPF, BPF/BSF. Active filter (LPF HPF, BPF, BSF), Passive filter + ADC

Initially I am interested in a) part of the question. I have been able to simulate Passive filter  But  I do not understand the procedure of active filter. THat is what I want to know that how can I simulate Active analog filter

[shivam161994]

Nlquist, I am attaching a passive filter in this post. But please see that it is a very rough simulation, I have not yet finalised it. I have done using signal processing and butterworth filter  In this attached simulation, I have made a noisy sine wave and filtered it using Butterworth filter. Perhaps now you could be able to answer ny doubt in a better way. I am also attaching a pdf  on reading which, I was able to simulate the passive filter ..I have checked the wikipedia page which you are referring but it contains no information how to simulate it in labview. It just contain theory of active and passsive filter. Tell me any method -simple or difficult but please help me with this active analog filter

[NIquist]

Well the problem is what you have created in LabVIEW is a DIGITAL filter.  It is based on an IIR (Infinite Impulse Response) which you can see if you open up the LabVIEW Butterworth filter.  Passive and Active refer to different types of ANALOG filters.  Passive filters are made from discrete, simple  components like resistors, capacitors, inductors, etc. that DO NOT have the ability to control one signal with another signal.  Active filters use active components that CAN use a control signal like transistors, ICs, SCRs, etc.  

Now you really can use LabVIEW to simulate those analog components by using the math in that Wiki page.  No, there is no magical LabVIEW block that will do that for you.  You have to know the math and code it in LabVIEW with the math VIs and/or formula nodes.

So now the only thing I can assume is that when your teacher says ACTIVE they simply want you to add some GAIN to the system.  That is one of the primary differences between active and passive filters.  To do that you just need to use the Multiply.vi (in the Numeric palette).  You can wire it right into your signal.

That's all I can suggest since trying to make an analog passive filter using a digital computer is really kind of meaningless.  Maybe you can get more details at your next class?...

[johnsold]

I agree with NIquist.

The only way to simulate an analog filter is to obtain or derive a mathematical expression for the transfer function of the filter and then implement that in software. The active filter has one other advantage in addition to Gain, although it is closely related. The amplifiers usually are designed to heve very high input impedance and very low output impedance. This effectively isolates the filter sections from each other and from source and load impedances. The result of the isolation is that the behavior of the filter may be closer to the mathematical ideal. The disadvantage is the requirement for power supplies, added noise, and the possibility of non-linearities and offset voltages. The types of simulations we have described above will almost certainly not include those disadvantages.

Lynn

[shivam161994]

Can you give me a sample pdf or some sample on how to do it using maths. I read the wikipedia page but didn't understand how to doit. Give me some hint on how can It be done using maths as you are saying