I am working on a mini project in which I have to design an active narrow band pass filter of 4th order (I chose butterworth filter because we need to avoid ripples and also have a steeper response, this is satisfied by butterworth as chebyshev gives ripples and Bessle's has linear slope.) which will work at 10MHz30MHz,having a passband of 1MHz.
Also I have used uA741 which is included in PSPICE library.
This filter is supposed to be a variable (but that is to be done later.)
However I am stuck on first step, I used the basic formulas and got values of resistors. I had to make capacitor values low such that resistor values would be significant.
I was able to design sucessfully for center frequency on 1kHz,but the same method I guess doesnot work for 1030MHz.
From this what I could think of is the capacitors(values in picofarads) change their characteristics at VHF.
Here is what I did for center frequency of 1kHz.(kindly see the attachment)
fc=center frequency.
A=Gain(Assumed A=1)
Q=Quality factor(Assumed Q=100)
C1=refer schematic.
C2=refer schematic.
Using same formulaes, I got the resistors for fenter frequency of 10MHz.
C1=C2=10pF.
R1=Q/(2∏*fc*C*A)=159.15kΩ
R1=Q/(2∏*fc*C*(2Q^2A))=7.958Ω
R3=R4=Q/(∏*fc*C*A)=318.309kΩ
for attached images (sch.png=schematic for 1kHz cutoff, 1Khz.png=response of sch.png, and bfp.png=response for 10Mhz bpf_r1.png is schematic for 10Mhz)
Also I have used uA741 which is included in PSPICE library.
This filter is supposed to be a variable (but that is to be done later.)
However I am stuck on first step, I used the basic formulas and got values of resistors. I had to make capacitor values low such that resistor values would be significant.
I was able to design sucessfully for center frequency on 1kHz,but the same method I guess doesnot work for 1030MHz.
From this what I could think of is the capacitors(values in picofarads) change their characteristics at VHF.
Here is what I did for center frequency of 1kHz.(kindly see the attachment)
fc=center frequency.
A=Gain(Assumed A=1)
Q=Quality factor(Assumed Q=100)
C1=refer schematic.
C2=refer schematic.
Using same formulaes, I got the resistors for fenter frequency of 10MHz.
C1=C2=10pF.
R1=Q/(2∏*fc*C*A)=159.15kΩ
R1=Q/(2∏*fc*C*(2Q^2A))=7.958Ω
R3=R4=Q/(∏*fc*C*A)=318.309kΩ
for attached images (sch.png=schematic for 1kHz cutoff, 1Khz.png=response of sch.png, and bfp.png=response for 10Mhz bpf_r1.png is schematic for 10Mhz)
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