1 M2-3 Active Filter (Part I) • Introduction of passive and active filter • Introduction of passive and active filter • Categories of filter – Low pass, high pass, band-pass, band stop (notch) • Butterworth/Chebyshev/Bessel response • Poles and multiple stages Active Filter (Part 1) 1 • Transfer Function • Bode Plot •2 nd -Order response Book references • Microelectronic Circuits Analysis and Design, By Muhammad H Rashid (PWS Publishing Company) Muhammad H. Rashid (PWS Publishing Company) • Microelectronic Circuit Design, By Richard C. Jaeger and Travis N. Blalock (Mc Graw Hill) Active Filter (Part 1) 2 • Introduction to Filter Theory, By David E. Johnson (Prentice Hall)
Transcript
1
M2-3 Active Filter (Part I)
• Introduction of passive and active filter• Introduction of passive and active filter
• Categories of filter– Low pass, high pass, band-pass, band stop (notch)
• Butterworth/Chebyshev/Bessel response
• Poles and multiple stages
Active Filter (Part 1) 1
• Transfer Function
• Bode Plot
• 2nd-Order response
Book references
• Microelectronic Circuits Analysis and Design, ByMuhammad H Rashid (PWS Publishing Company)Muhammad H. Rashid (PWS Publishing Company)
• Microelectronic Circuit Design, By Richard C.Jaeger and Travis N. Blalock (Mc Graw Hill)
Active Filter (Part 1) 2
• Introduction to Filter Theory, By David E.Johnson (Prentice Hall)
2
Passive Filters• made up of passive components - resistors, capacitors and
inductors• no amplifying elements (- transistors, op-amps, etc) • no signal gain • 1st order - design is simple (just use standard equations to
find resonant frequency of the circuit) • 2nd order - complex equations • require no power supplies • not restricted by the bandwidth limitations of the op-amps
Active Filter (Part 1) 3
y p p• can be used at very high frequencies • can handle larger current or voltage levels than active
devices • buffer amplifiers might be required
Passive elements : Inductor BIG PROBLEM!
• high accuracy (1% or 2%) small physical size or largehigh accuracy (1% or 2%), small physical size, or large inductance values are required ??
• standard values of inductors are not very closely spaced
• difficult to find an off-the-shelf inductor within 10 percent of any arbitrary value
• adjustable inductors are used
Active Filter (Part 1) 4
• tuning such inductors to the required values is time-consuming and expensive for larger quantities of filters
• inductors are often prohibitively expensive
3
Active Filter• no inductors • made up of op-amps, resistors and capacitors
id i ll bi i• provides virtually any arbitrary gain • generally easier to design • high input impedance prevents excessive loading of the
driving source • low output impedance prevents the filter from being
affected by the load t hi h f i i li it d b th i b d idth f th
Active Filter (Part 1) 5
• at high frequencies is limited by the gain-bandwidth of the op-amps
• easy to adjust over a wide frequency range without altering the desired response
Categories of FiltersLow Pass Filters:
pass all frequencies from dc
High Pass Filters:
pass all frequencies that are
-3dB {
Av(dB)
-3dB {
Av(dB)
pass all frequencies from dc up to the upper cutoff frequency.
pass all frequencies that are above its lower cutoff frequency
Active Filter (Part 1) 6
f2
f f1
f
Low-pass response High-pass response
4
Categories of FiltersBand Pass Filters:
pass only the frequencies h f ll b i l
Band Stop (Notch) Filters:
eliminate all signals within h b d hil i
-3dB{
Av(dB)
-3dB{
Av(dB)
that fall between its values of the lower and upper cutoff frequencies.
the stop band while passing all frequencies outside this band.
Active Filter (Part 1) 7
f2
ff1
ff2f1
Band Pass Response Band Stop Response
Filter Response CharacteristicsAv
ButterworthB l
Active Filter (Part 1) 8
BesselChebyshev
f
5
Bessel Characteristic
• Flat response in the passband
Av
passband.
• Roll-off rate less than 20dB/decade/pole.
• Phase response is linear.
• Used for filtering pulse waveforms without
f
Active Filter (Part 1) 9
waveforms without distorting the shape of the waveform.
Butterworth Characteristic
• Very flat amplitude, Av(dB) , response in the passband.
Av
response in the passband.
• Role-off rate is 20dB/decade/pole.
• Phase response is not linear.
• Used when all frequencies i th b d t h
f
Active Filter (Part 1) 10
in the passband must have the same gain.
• Often referred to as a maximally flat response.
6
Chebyshev Characteristic
• Overshoot or ripples in the passband.
Av
p
• Role-off rate greater than 20dB/decade/pole.
• Phase response is not linear - worse than Butterworth.
• Used when a rapid roll- f
EE3110 Active Filter (Part 1) 11
• Used when a rapid roll-off is required.
Pole
• A pole is nothing more than an RC circuit• A pole is nothing more than an RC circuit –
• n-pole filter contains n-RC circuit.
Active Filter (Part 1) 12
7
Single-Pole Low/High-Pass Filter
+V
R
+V
C
vout
-
+
-V
R1
Rf1
Rf2
C1
vin
vout
-
+
-V
R1
Rf1
Rf2
C1
vin
Active Filter (Part 1) 13
Low Pass Filter High Pass Filter
Two-Pole (Sallen-Key) Filters
+V
C2
+V
R2
-
+
+V
-V
R1
Rf1
Rf2
C1
vin
vout
R2
-
+
+V
-V
R1
Rf1
Rf2
C2
vin
vout
C1
Active Filter (Part 1) 14
Low Pass Filter High Pass Filter
8
Three-Pole Low-Pass Filter
C2
Stage 1 Stage 2
-
+
+V
-V
R1
Rf1
C1
vin
2
R2
-
+
+V
-V
R3
Rf3
C3 vout
Active Filter (Part 1) 15
Rf2
Rf4
Two-Stage Band-Pass Filter
R2 R1
vin
C
C2
C4 C3
R
R4
+V
+
+
+V
C1
Rf1
Rf2
R3
-V
vout
Rf3
Rf4
-
-
-V
Stage 1Two-pole low-pass
Stage 2Two-pole high-pass
Av
Active Filter (Part 1) 16
BW
f1 f2
f
Stage 2response
Stage 1response
fo
BW = f2 – f1Q = f0 / BW
9
Multiple-Feedback Band-Pass Filter
C
R1
R2
C1
C2
vin
Rf
+V
-
vout
Active Filter (Part 1) 17
-V
+out
Band-Stop (Notch) FilterThe notch filter is designed to block all frequencies that fall within its bandwidth. The circuit is made up of a high pass filter, a low-pass filter and a summing amplifier. The summing amplifier will have an output that is equal to the sum of the filter output voltages.
