Filters are circuits whose
gain varies with frequency. Typically filters are used
not
to allow some, but all to
frequencies pass
contain only passive components (R,C,1)
gain: 1=
X
wnt
shunt series
Passive filters +
Active
filters contains passive components 3 amplifiers
like op-amps
Passive filter w/ gain
floor
- #=
we-ic'
X
in
(to ground
-
shunt pos.
makes it
low
pass.
asymptotes
1
at
B
low
Very wi
very high w:
capacitor open
circuit
capacitor:short circuit
-
R unattached.
Resistor circuitis pot. div wI gain 20
log, =-12 d
Allows low w to pass, attenuates high frequencies to
minimum
gain, due to presence
of resistor in series with C.
The order
of a filter is the highest power join the denominator. Almost
always
equals power of 1/C.
--it
Active IP
filter with gain floor
I
menting amplifier configuration: -
: is--te virtual
earth
*
-
QIgain
... + 9.SdB in to
previous.
comparison
Advantage of op-amp circuit:
can have
gain 1;
-
-Low outputimpedance -
loading does not
affectfilter frequency response
-
Resistive inputimpedance -
doesn't vary with
frequency
gain varies with frequency. Typically filters are used
not
to allow some, but all to
frequencies pass
contain only passive components (R,C,1)
gain: 1=
X
wnt
shunt series
Passive filters +
Active
filters contains passive components 3 amplifiers
like op-amps
Passive filter w/ gain
floor
- #=
we-ic'
X
in
(to ground
-
shunt pos.
makes it
low
pass.
asymptotes
1
at
B
low
Very wi
very high w:
capacitor open
circuit
capacitor:short circuit
-
R unattached.
Resistor circuitis pot. div wI gain 20
log, =-12 d
Allows low w to pass, attenuates high frequencies to
minimum
gain, due to presence
of resistor in series with C.
The order
of a filter is the highest power join the denominator. Almost
always
equals power of 1/C.
--it
Active IP
filter with gain floor
I
menting amplifier configuration: -
: is--te virtual
earth
*
-
QIgain
... + 9.SdB in to
previous.
comparison
Advantage of op-amp circuit:
can have
gain 1;
-
-Low outputimpedance -
loading does not
affectfilter frequency response
-
Resistive inputimpedance -
doesn't vary with
frequency
