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about design of S/C filter

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lhlbluesky

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in S/C bandpass filters, the center frequency f0 can be tuned by clock frequency fclk, and normally, fclk is much larger than f0, 50 times or bigger. however, in some cases, f0 is just the input signal frequency (ex:in ir receiver, f0 is the carrier frequency), f0=fsignal, then, in half period of input signal, fclk works 25 cycles, so, how to decide the transient output for S/C filter? if tuning the frequency of fclk to obtain desired f0, then in half period of input signal, fclk may be not integral cycles, can this cause a wrong transient result?

besides, in S/C bandpass filters, how to simulate the AC response (center frequency f0, Q, etc), just as the continuous filter (in hspice)?

thanks.
 

I see a switched capacitor filter listed in the menu of circuits that come with Falstad's simulator (www.falstad.com/circuit).

It's a low pass type. I tried reducing the clock frequency, so that it is less than twice the highest input frequency.

This screenshot shows the circuit with scope traces. From the looks of it, the response acts similar to the way you describe.

 

thanks BradtheRad. but how do you get the input waveform (sweep from 20 to 400Hz)? is it a sine wave?
 

ok, but what tools do you use? is it spectre? i want to know how to write the input sine waveform (sweep from 20 to 400Hz) in netlist? just as:
Vin *** *** sine(** ** ** ** ** **)
.ac *** 20 400 10
can you show me?

- - - Updated - - -

or how to add ac sweep in transient simulation?
 

lhlbluesky said:
ok, but what tools do you use? is it spectre? i want to know how to write the input sine waveform (sweep from 20 to 400Hz) in netlist? just as:
Vin *** *** sine(** ** ** ** ** **)
.ac *** 20 400 10
can you show me?

- - - Updated - - -

or how to add ac sweep in transient simulation?
Click to expand...

Sorry, I don't know the netlist syntax, or about PAC analysis.

The Falstad simulator is not Spice related. You can try it by clicking the link below.

It will open the falstad.com website, load the schematic which created the scope traces above, and run it on your computer. (Click Allow to load the Java applet.)

https://tinyurl.com/b2gr23g

You can change values at will. Right-click on a component to bring up an edit window.
 

lhlbluesky said:
.........
or how to add ac sweep in transient simulation?
Click to expand...

ihlbluesky, just to avoid a misunderstanding on your side: If I am not completely wrong, I think the Falstad simulator is not able to perform a small-signal ac response for active circuits (frequency domain).
 
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