This page is used to design filters with 1. order filter cutoff. Many different combinations of resistors, capacitors and inductors are supported.

Configurations supported

No series/parallel resistors	A resistor in series with the active element	A resistor parallel with the active element	Both a series and a parallel resistor	Placement of the active element(s)
Highpass (C)	Highpass (C-Rs)	Highpass (C-Rp)	Highpass (C-Rp-Rs)	A capacitor in series with the signal
Lowpass (C)	Lowpass (C-Rs)	Lowpass (C-Rp)	Lowpass (C-Rp-Rs)	A capacitor to ground
Lowpass (L)	Lowpass (L-Rs)	Lowpass (L-Rp)	Lowpass (L-Rp-Rs)	A inductor in series with the signal
Highpass (L)	Highpass (L-Rs)	Highpass (L-Rp)	Highpass (L-Rp-Rs)	A inductor to ground
Bandpass (CLs)	Bandpass (CLs-Rs)	Bandpass (CLs-Rp)	Bandpass (CLs-Rp-Rs)	A inductor and capacitor in series with the signal
Bandstop (CLs)	Bandstop (CLs-Rs)	Bandstop (CLs-Rp)	Bandstop (CLs-Rp-Rs)	A inductor and capacitor in series to ground
Bandstop (CLp)	Bandstop (CLp-Rs)	Bandstop (CLp-Rp)	Bandstop (CLp-Rp-Rs)	A inductor and capacitor in parallel and in series with the signal
Bandpass (CLp)	Bandpass (CLp-Rs)	Bandpass (CLp-Rp)	Bandpass (CLp-Rp-Rs)	A inductor and capacitor in parallel and connected to ground

Input values

C	The capacitor value
L	The inductor value
Rl	The DC resistance of the inductor
Rs	An external resistor in series with the C and/or L
Rp	An external resistor parallel with C and or L
R	The resistor, this can be the load impedance for some filter configurations
Curve plot	Show a curve of the filters frequency responce (Select the "out" node)
Waveforms	Connect to the waveforms page and make it possible to see what the filter does to an actual waveform
Input/Output	Add some components to the input/output of the filter
Fo	Center/cutoff frequency of the filter
F1 ... F2	Frequency range for a bandpass/bandstop filter.
Passband loss	Loss in the pass band, the value is in dB
Stopband loss	Loss in the stop band, the value is in dB
"Slider"	The slider is used to select the bandwith of bandpass/bandstop filters
Limit	Defines the level for the cutoff frequency, usual 3 dB
Freq n	A list of frequencys, a signal analysis is done at each of these frequency. It is possible to write DC for a DC analysis

Output values

R	The resistor in the filter
C	The capacitor in the filter
L	The inductor in the filter
Rs	A resistor in series with the active element
Rp	A resistor in parallel with the active element
Fo	Center/cutoff frequency of the filter
F1 ... F2	Range for a bandpass/bandstop filter
Passband gain	Gain in the passband
Stopband gain	Gain in the stopband
Zin min	The minimum Zin value
Zin max	The maximum Zin value
Zout min	The minimum Zout value
Zout max	The maximum Zout value
Bandwidth: Passband gain	Passband gain for a bandpass/bandstop filter
Bandwidth: xx dB low freq	The low frequency where the output is "Limit" dB below (Limit is from configuration page and is usual 3 dB)
Bandwidth: xx dB high freq	The high frequency where the output is "Limit" dB below
Bandwidth: xx dB bandwidth freq	The range between the above tow frequencys
Small signal analyses: At	Frequency for this analysis, see config page
Small signal analyses: Gain	Gain at this frequency
Small signal analyses: Phase	Phase at this frequency
Small signal analyses: Zin	Input impedance at this frequency
Small signal analyses: Zout	Output impedance at this frequency

Hints

Use the input/output networks to simulate "real life" input and output impedances
When using "Curve plot" it is possible to click on the curve to measure values
To enter values as a factor and not in dB use the function todB, i.e. to enter a value of 10 times in the stopband loss field use "todB(10)"

Other pages

For selecting component standard values, use the Prefered components page.
For only calculating Fo use Fo page.
For calculation impedance of a capacitors/inductors use Ohms law page.
For designing inductors use Air coil page.
For designing non-standard component values use Series/Parallel page.
For dB conversion use dB page.

Calculator functions

Some filter calculations can be done with functions in the Calculator. The following functions are supported:


FilterLP1(f0,f)	
FilterHP1(f0,f)	
FilterLP1cpx(f0,f)
FilterHP1cpx(f0,f)
RIAA(freq)	
RIAAIEC(freq)	
RIAAcpx(freq)	
RIAAIECcpx(freq)

They can be used to generate curves or tables with, for more documentation see the Calculator page.
The following functions can be usefull on this page:


todB(times)
todBpwr(timesPower)