A high-pass filter is a filter that passes high frequencies well, but attenuates (or reduces) frequencies lower than the cutoff frequency.

1. Lecture 11
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Topic: High-pass filter
By Dilouar Hossain
Email- dilouarbd@gmail.com

2. Lecture 11
Group members :
1. Md. Saiful Islam- 151-33-2411
2. Shreekanta Sarker- 151-33-2469
3. S.M. Sabbir Hossain- 151-33-2322
4. Majbah Uddin Ahmed- 151-33-2505
5. Rajib Laskar- 151-33-2349
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3. Lecture 11
High-pass filter
 A high-pass filter is a filter that passes high frequencies
well, but attenuates (or reduces) frequencies lower than
the cutoff frequency.
 The actual amount of attenuation for each frequency
varies from filter to filter.
 A high-pass filter is the opposite of a low-pass filter.
 It is useful as a filter to block any unwanted low
frequency components of a complex signal while passing
the higher frequencies.
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4. Lecture 11
High Pass Filter
a) 1st Order
AV (dB)
AV(max)
AV(max) - 3
fc
0.1fc
0.01fc
AV(max) - 20
AV(max) - 40
+20dB/dec
f (Hz)
R1
R2
_
+
Vin
+V
-V
RA
CA
Vo

5. Lecture 11
Analysis
 At 0 < f < fc, high pass filter will
attenuate the frequencies at roll-off
of +20dB/decade because XCA is
decreasing starts from ∞. When
XCA=∞,
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 At f = fc, the gain is
0.707AV(max) or in dB, AVdB(max)-
3 where the magnitude of the
capacitive reactance, XCA
equals the resistance of the
resistor, RA
 At f > fc, high pass filter will
pass the frequencies
because XCA is decreasing
to 0. When XCA= 0

6. Lecture 11
40dB/decade filter
 Design procedure :
1.choose a cutoff frequency.
2. Let c1=c2=c and choose a convenient value.
3. R1 = 1.414/WcC
4. R1 = 2R2.
5. Rf = R1

7. Lecture 11
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Vo
R1
R2
_
+
Vin
+V
-V
RA
CA
CB
RB
AV (dB)
AV(max)
AV(max) -
3
fc
0.1f
c
0.01fc
AV(max) -
40
AV(max) -
80
+40dB/de
c
f
(Hz)
AV(max) = 1+
R1
R2
1
2 RARBCACB
fc = fAfB
1
2RACA
1
2RBCB
=
=

8. Lecture 11
+60dB/decade filter:
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 A high-pass filter of +60 db/decade can be constructed
by cascading a +40 db/decade filter with a +20
db/decade filter.

9. Lecture 11
Design procedure of +60 db/decade high pass
filter:
1. choose cutoff frequency Wc or fc.
2.Let C1=C2=C3=C and choose a convenient value
between 100 pF to .1 mF
3. R3= 1/WcC
4. R1=2R3
5. R2= R3/2
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10. Lecture 11
Applications of active high pass filters
-These are used in the loud speakers to reduce the
low level noise.
-Eliminates rumble distortions in audio applications
so these are also called are treble boost filters.
-These are used in audio amplifiers to amplify the
higher frequency signals.
-These are also used in equaliser.
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11. Lecture 11
Thank you….
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