# design 6th order low pass filter chebyshev

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#### lorenzo21

##### Newbie level 1
Hi all,

I am trying to design a 6th order lowpass chebyshev filter (as a cascade of three 2nd-order biquad sections)
with following specifics:

Amax=0.1dB
f(3db)=2.2 Mhz
F(clock)=100Mhz
1.8V

so i choose flaischer-laker biquad (pag 48 of this pdf)
https://users.ece.gatech.edu/phasler/Courses/ECE6414/Unit4/switchcap.pdf

and i followed the same procedure of example 9.6-3 (pag 51 of the same file)
choosing H=0 and D=A=1 (as initials hypothesis)
(obviously i put F=0 for E-type and E=0 for F-type rispectively)
while for capacitive coefficients and scale factors i could get them through matlab using Fdatool.....

i tried to design it using Cadence
as a first step IDEAL circuit using components from AnalogLib library

Features:

Vdc
Dc voltage=1.8V
PAC Magnitude=1V

(non overlapping clocks)
Vpulse1
voltage1=0V
voltage2=1.8v
risetime=falltime=100ps
pulsewidth=4.95ns
period=10ns

Vpulse2
voltage1=0v
voltage2=1.8v
risetime=falltime=100ps
pulsewidth=4.95ns
period=10ns
delaytime=5ns

Switch
open voltage=899.000mV
closed voltage=901.000mV

Opamp=VcVs Gain=10M
Rin=10M
Rout=1
(other components: cap, gnd)

and after i simulated it
Analog Environment
PSS
Beat frequency= autocalculate
Num Harmonics=20
Accuracy Defaults=conservative

PAC
Start-Stop 10Hz-10Mhz
maximum sideband=0

and plot results
Results-> Direct Plot
PAC->db20
selecting out net

(ps im doing this classproject at university so ill attach as soon as possible pic of plot result as well sorry)

the problem is that i really dont know why it doesnt match the specifics at all
f(3b) is non 2.2Mhz
and Amax is more than 0.1 dB

my questions is: flaischer-laker biquad is not suitable for High frequency?
im really new in analog filter design and i dont know how to proceed....
can anyone help me?

many thanks!!

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