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Manual Calculation of filter

Thread starter #1
hi guys,

Is it possible for anybody to shed some light on the manual calculation (how to proceed on calculating the filters) based on the components used?
I have attached the components used.

Thank you for the help!!

1539051188272.png
 
#2
Well... R4, C1 through C6 and L1 and L4 are the only part that will affect Node6 as V1 changes assuming there is very little resistance within the V1 source.

R4 and C4 are basically a low pass RC filter .... The remaining circuit is a low pass PI filter hybrid ... composed of a "T" filter between L1,L4 and C1, while also composed of a "PI" filter between C3,L1,L4, and C5. Other fundamentals could be found at C3,L1 and C1 as well as C5, L4, and C1. C2 and C6 provide some buffering and DC bias.


Reference:
https://www.radio-electronics.com/i...f-filters/simple-lc-lowpass-filter-design.php
 
Thread starter #3
ahhh issit possible for me then, assuming a AC source of 1V is implemented, to manually calculate the cut-off freq of the circuit?

Since the unknown will be with regards to the cut-off frequency that i wish to attain?

can i group the impedances? and do a voltage analysis to determine at node 6 the effective 3db cutoff which is Vinput/Voutput =2?

is my understanding flawed?

any advice there?
Well... R4, C1 through C6 and L1 and L4 are the only part that will affect Node6 as V1 changes assuming there is very little resistance within the V1 source.

R4 and C4 are basically a low pass RC filter .... The remaining circuit is a low pass PI filter hybrid ... composed of a "T" filter between L1,L4 and C1, while also composed of a "PI" filter between C3,L1,L4, and C5. Other fundamentals could be found at C3,L1 and C1 as well as C5, L4, and C1. C2 and C6 provide some buffering and DC bias.


Reference:
https://www.radio-electronics.com/i...f-filters/simple-lc-lowpass-filter-design.php
 

Ratchit

Well-Known Member
#5
hi guys,

Is it possible for anybody to shed some light on the manual calculation (how to proceed on calculating the filters) based on the components used?
I have attached the components used.

Thank you for the help!!

View attachment 114789
Are R1, R2, and R3 just hanging in the air so as to pick up spurious signals? Or, are they connected to ground? Where is the output, node 6? If so, document and label it. Does the filter have any load? If so, what is it?

Looks like you can write out 6 node equations and put them through an equation solver. Then graph the node response you are interested in. Need help with that?

Ratch
 
Thread starter #6
can i get some help on that?
Are R1, R2, and R3 just hanging in the air so as to pick up spurious signals? Or, are they connected to ground? Where is the output, node 6? If so, document and label it. Does the filter have any load? If so, what is it?

Looks like you can write out 6 node equations and put them through an equation solver. Then graph the node response you are interested in. Need help with that?

Ratch
additionally, issit possible for me to just and calculate an overall value based on the capacitor and inductors used and calculate their cutoff freq using
1/2pi(sqrt L and C).

Thank you so much for your help. The R1, R2,R3 are connected to different parts of the schematic so i assumed since they play no effect in affecting the signal coming through to node6, i can just ignore them since it will be troublesome and heavy on the circuit to input all of them together. BUt, if you want, i can put them all through one circuit and put it here.

Thanks again!
 

Ratchit

Well-Known Member
#7
can i get some help on that?


additionally, issit possible for me to just and calculate an overall value based on the capacitor and inductors used and calculate their cutoff freq using
1/2pi(sqrt L and C).
NO, you must use calculate the currents coming/going from/to each node. That means doing a node analysis. You can combine parallel capacitors between each node, however. Use a computer to do the grit work.

Thank you so much for your help. The R1, R2,R3 are connected to different parts of the schematic so i assumed since they play no effect in affecting the signal coming through to node6, i can just ignore them since it will be troublesome and heavy on the circuit to input all of them together. BUt, if you want, i can put them all through one circuit and put it here.

Thanks again!
If those resistors are connected to some low impedance point, then they probably will affect the filter output. You can determine the difference by running the calculations with the resistors first grounded and then open.

Ratch
 
Thread starter #8
NO, you must use calculate the currents coming/going from/to each node. That means doing a node analysis. You can combine parallel capacitors between each node, however. Use a computer to do the grit work.



If those resistors are connected to some low impedance point, then they probably will affect the filter output. You can determine the difference by running the calculations with the resistors first grounded and then open.

Ratch
Hi! Thanks for your help!

Unfortunately, I am really shoddy in my understanding of what you just said sorry!

Is it possible for you to explain further in detail what you meant?

i have attached the full schematic look on LTSpice for your reference!

1539145896244.png
 

Ratchit

Well-Known Member
#9
Now you got me confused. In first schematic, you show R4 going to a capacitor. In the second schematic R4 goes to a coil. I think it is best if you use the Spice program to determine the voltages and currents. The circuit is too complicated for manual calculation unless you can first determine where you can separate the various parts of the circuit where they do not interact with other.

Ratch
 
Thread starter #10
Now you got me confused. In first schematic, you show R4 going to a capacitor. In the second schematic R4 goes to a coil. I think it is best if you use the Spice program to determine the voltages and currents. The circuit is too complicated for manual calculation unless you can first determine where you can separate the various parts of the circuit where they do not interact with other.

Ratch
Ahh sorry the schematic at the start is just now at a different node as compared to the overall circuit.

So for what you mentioned, should i do an AC analysis or a transient analysis with a voltage source of 1V?

Following that, how should i proceed though? So sorry for the many questions i am at my wits end with regards to this

Thank you so much again
 

JimB

Super Moderator
Most Helpful Member
#11
Where did this circuit originate?
At first sight it looks bizarre.

C7, C8, C9 and C10 are in parallel with the signal source and will present a low reactance as the frequency increases.
At 1kHz the reactance will be about 1600 Ohm, and at 1 MHz about 1.6 Ohm.

Turning out attention to two section "pi" filter L1, L4, C3, C1 and C5.
The values here 2.4nH, 0.7pF and 1.5pF are consistent with a filter which is designed for VHF frequencies of several hundred MHz.

So what is the point of this circuit?
I cannot understand its purpose.

JimB
 
Thread starter #12
from what i know, it is to only allow a specific frequency to pass through and nothing else.

i was playing around with analysis of the nodes and i got this formula but again, it looks really weird...

ultimately, the aim is to derive if through calculation, before simulation, we can get the expected frequency we want to not be attenuated.
01C2CC40-F9EC-48B3-B771-289DAF35D159.JPG
1539178179544.png

do you guys have any advice for my implementation and the churning out of the value of s and subsequently freq?
 

JimB

Super Moderator
Most Helpful Member
#13
from what i know, it is to only allow a specific frequency to pass through and nothing else.
OK, being quite brutal about this, but, knowing nothing is not a good start for circuit analysis.

As for "allowing a specific frequency to pass through", nonsense!
It is a whole load of low pass filtering and a DC block (C2 and C6).
Where did you get this circuit?
It did not just appear out of thin air, surely?

As I said earlier, it is bizarre, surely not a practical circuit by any stretch of the imagination.

JimB
 
Thread starter #16
OK, being quite brutal about this, but, knowing nothing is not a good start for circuit analysis.

As for "allowing a specific frequency to pass through", nonsense!
It is a whole load of low pass filtering and a DC block (C2 and C6).
Where did you get this circuit?
It did not just appear out of thin air, surely?

As I said earlier, it is bizarre, surely not a practical circuit by any stretch of the imagination.

JimB
no no thank you i needed that to further press on and ask more on the application of the circuitry.
Thnk you, I was hoping someone could shed light on this but I'll ask again on the application on the circuit and get back here!

Thanks all!!
 

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