No. That’s a first order filter. You can tell because the slope is 6dB/octave and the phase shift is 90°.
From your component values (100nH and 2nF) it doesn’t become second order until above 11MHz.

Hi Ian,

That is typo. Yes, Its is first order filter. Thank you for the correction.

As I know that, for the first order RLC low pass filter: The frequency will cut-off after the slope of -3dB and the phase-shift is 45°. So, these are achieved in the simulations.

Please could you see now again and tell me that is that circuit is used to filter the signal above 80Khz by using those components values.

 

As I know that, for the first order RLC low pass filter....

The minimum order for RLC filters is n=2.
First order is either RC oder RL.

 

The minimum order for RLC filters is n=2.
First order is either RC oder RL.

In this case the LR time constant is at such a high frequency that it’s not contributing to the filter, so it is effectively first order.

 

The minimum order for RLC filters is n=2.
First order is either RC oder RL.

hi again,

Could you see the post 101 and could you answer that question?.

Thank you.

 

Please could you see now again and tell me that is that circuit is used to filter the signal above 80Khz by using those components values.

Please, specify/repeat your question because terms like "...filter the signal..." and "..above 80 kHz..." and "those components..." is by far not enough to design a lowpass filter.

 

Please, specify/repeat your question because terms like "...filter the signal..." and "..above 80 kHz..." and "those components..." is by far not enough to design a lowpass filter.

OK..

My question is:

Is the above circuit (which is in Post #99) correct to filter the signal above the 80Khz?.

 

What is the load resistance?

 

OK..

My question is:

Is the above circuit (which is in Post #99) correct to filter the signal above the 80Khz?.

Sorry again - this is not enough.
For designing a lowpass filter we need
* End of the passband: Very often, but not neccessarily, the frequency where the gain is 3dB lower than for DC
* Attenuation requirements: What is the frequency region which must be suppressed (attenuated) by (at least) how many dB?
* This last requirement determines the minimum order of the filter

 

Sorry again - this is not enough.
For designing a lowpass filter we need
* End of the passband: Very often, but not neccessarily, the frequency where the gain is 3dB lower than for DC
* Attenuation requirements: What is the frequency region which must be suppressed (attenuated) by (at least) how many dB?
* This last requirement determines the minimum order of the filter

My requirement is that if the frequency is above 100khz that should be attenuate. This is only the requirement I know.

 

My requirement is that if the frequency is above 100khz that should be attenuate. This is only the requirement I know.

By how much?

 

By how much?

as much as possible steep attenuation.

 

hi PP,
What is the practical purpose of this filter.?
E

 

hi PP,
What is the practical purpose of this filter.?
E

Output of this filter signal going to the input and output of Amplifiers. These amplifiers are located input to the ADC and output to the DAC.

 

Hi,
Post a circuit diagram of the amplifiers.
Details of the signal levels and frequencies.
The calculated expected noise level and acceptable noise levels after the filter.
Also, any other information that you may have regarding the project so that we can give a meaningful answer rather than keep guessing.

E

 

as much as possible steep attenuation.

A 24th order filter using 12 op-amps? Or 12 inductors and 12 capacitors?
or steeper than that?

 

Sorry again - this is not enough.
For designing a lowpass filter we need
* End of the passband: Very often, but not neccessarily, the frequency where the gain is 3dB lower than for DC
* Attenuation requirements: What is the frequency region which must be suppressed (attenuated) by (at least) how many dB?
* This last requirement determines the minimum order of the filter

This is post #116. These questions were asked in post #2.

 

as much as possible steep attenuation.

OK - in this case, I recommend at least an order of 10 (or even more).

This is post #116. These questions were asked in post #2.

Yes - did we get a clear and substantial answer?

 

My requirement is that if the frequency is above 100khz that should be attenuate. This is only the requirement I know.

as much as possible steep attenuation.

Then it's not possible to definitively design the filter, since the requirements are not defined in a quantified manner.

 

Your RLC filter schematic shows no output point.
Why 100kHz and why LC? For audio filters an opamp has been used for 50 years. One opamp can make a 3rd-order filter.

 

Your RLC filter schematic shows no output point.
Why 100kHz and why LC? For audio filters an opamp has been used for 50 years. One opamp can make a 3rd-order filter.

It doesn’t show a load resistance either. Probably after 216 posts we might get a spec, but I’m not hopeful.