active filter it is phasor time again. active low pass filter amplification: r f /r s low pass...
Post on 19-Dec-2015
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Active Low Pass Filter
FF
SF
FF
F
FFF
S
F
S
out
CRj
RRjA
CRj
R
CjRZ
Z
Z
V
VjA
1
/)(
1
1||
)( • Amplification: RF/RS
• low pass factor 1/(1+jRFCF)• Cut off frequency: RFCF=1
RF/RS=10, 1/RFCF=1
Figure 8.24,
Active high-pass filter
SS
S
F
SS
F
SSS
S
F
S
out
CRjR
R
CjR
RjA
CjRZ
Z
Z
V
VjA
11
1
1)(
1
)(
RF/RS=10, 1/RFCF=1
Figure 8.26, 8.27
8-11
Active bandpass filterFigure 8.26
Normalized amplitude response of active bandpass filterFigure 8.27
SSFF
SF
CRjCRj
CRjjA
11)(
Let’s build an integrator
Let’s start with the following insight:
We need to somehow convert voltage vI to current
First try…use resistor
R
vi IBut, v0 must be very
small compare to vR, or else
When is v0 small compare to vR?
For good integratorRC >> 1
Op Amp Integrator
t
SFS
out
S
SoutF
SF
dttvCR
tv
R
v
dt
vdC
ii
')'(1
)(
)0(
Examples: 8.6, 8.7
Drafting problem