1. ELECTRONIC CIRCUITS
EE451
H. Chan; Mohawk College

2. MAIN TOPICS (2nd half) Analog & Switching Power Supplies
Review of rectification & filtering
Review of zener diode as a voltage regulator
Transistor series shunt voltage regulators
Transistor current regulators
IC voltage regulators (e.g. 78/79XX, LM317)
Switching-mode regulators (e.g. LH1605)
Linear Integrated Circuit Applications
BiFET & Norton op-amps, 555 timer, 8038 function generator, active filters, etc.
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3. Power Supply Block Diagram
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4. Half-Wave Rectifier V t
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5. Full-Wave Rectifier V t
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6. Bridge-Type RectifierV t
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7. More Equations . . .
Rearranging the previous equations: VP = Vdc Vr
The ripple voltage as a percentage of the dc voltage is:
The diode(s) must be rated to withstand the surge current:
where RW is the transformer winding’s
resistance given by:
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8. Comparison of Different Types of Rectifiers
Half-wave rectifier needs only a single diode but ripple is twice those of the other types.
Full-wave rectifier requires a centre-tapped transformer and its output voltage is about half those of the other types.
Bridge-type rectifier is best overall even though it requires four diodes because the diode bridge is often available in a single package. However, if a single diode in the bridge is defective, the whole package has to be replaced.
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9. Line Regulation
is a measure of the effectiveness of a voltage regulator
to maintain the output dc voltage constant despite
changes in the supply voltage.
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10. Load Regulation
is a measure of the ability of a regulator to maintain a
constant dc output despite changes in the load current.
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11. Other Specifications A common definition for voltage regulation is:
The ability to reduce the output ripple voltage is:
Source resistance of regulator is:
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12. Zener Diode Voltage Regulator
I-V Characteristic
Circuit
IZM
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13. Notes on Zener Diode Regulator
VZ depends on I and temperature.
Zener diodes with rated voltage < 6 V have negative temperature coefficient; those rated > 6 V have positive temperature coefficient.
In order to maintain a constant Vo, IZT varies in response to a change of either IL or Vi. For example, when RL increases, IL decreases, then IZT has to increase to keep the current through Rs constant. Since the voltage drop across Rs is constant, Vo stays constant.
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14. Formulae for Zener Regulator Circuit
Rs establishes the zener bias current, IZT:
For fixed Vi, but variable RL:
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15. Formulae (cont’d) For fixed RL, but variable Vi:
The output ripple voltage of the zener regulator is:
where RZ = ac resistance
of zener diode.
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16. Transistor Series Voltage Regulator
The simple zener regulator
can be markedly improved
by adding a transistor.
Since VBE = VZ - VL any
tendency for VL to decrease
or increase will be negated
by an increase or decrease in IE. The dc currents for the
circuit are:
IL = hFEIB; IZT = IR - IB
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17. Transistor Shunt Voltage Regulator
Since VBE = VL - VZ,
any tendency for VL
to increase or decrease
will result in a
corresponding increase or decrease in IRs. This will
oppose any changes in VL because VL = Vi - IRsRs.
IE = IRs - IL = hFEIZT
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18. Op-Amp Voltage Regulators
Series
Shunt
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19. Notes on Op-Amp Voltage Regulator
More flexibility possible in design of voltage output than IC voltage regulator packages.
The essential circuit elements are: a zener reference, a pass or shunt transistor, a sensing circuit, and an error/amplifier circuit.
Equation indicates that Vo depends on R2, R3, and VZ.
The shunt configuration is less efficient but R2 offers short-circuit current limiting.
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20. Constant Current Limiting
can be used for short-circuit or overload protection of
the series voltage regulator.
Output current
is limited to:
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21. Fold-back Current Limiting
is a better method of short-circuit protection.
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22. Design Equations for Fold-back Current Limiting
Maximum load current without fold-back limiting:
Output voltage under current limiting condition:
The short circuit current (i.e. when Vo = 0) is:
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23. Characteristics of Fold-back LimitingVo
Notice that Ishort < IL(max) and that Vo is regulated (i.e. constant) only after RL > a certain critical value.
For designing purpose, R5 + R6 = 1 kW and if Ishort and IL(max) are specified then IL
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24. Transistor Current Regulators
are designed to maintain a fixed current through a
load for variations in either Vi or RL.
For the BJT circuit, VEB = VZ - VRE.
Any tendency for IL to change will
cause an opposing change in VEB,
thus nullifying the perturbation.
For the JFET circuit, IL = ID = IDSS as
long as VL < VSS - VP.
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25. IC Voltage Regulators
There are basically two kinds of IC voltage regulators:
Multipin type, e.g. LM723C
3-pin type, e.g. 78/79XX
Multipin regulators are less popular but they provide the greatest flexibility and produce the highest quality voltage regulation
3-pin types make regulator circuit design simple
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26. Multipin IC Voltage Regulator
The LM723 has an equivalent circuit that contains most of the parts of the op-amp voltage regulator discussed earlier.
It has an internal voltage reference, error amplifier, pass transistor, and current limiter all in one IC package.
LM 723C Schematic
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27. Notes on LM723 Voltage Regulator
Can be either 14-pin DIP or 10-pin TO-100 can
May be used for either +ve or -ve, variable or fixed regulated voltage output
Using the internal reference (7.15 V), it can operate as a high-voltage regulator with output from 7.15 V to about 37 V, or as a low-voltage regulator from 2 V to 7.15 V
Max. output current with heat sink is 150 mA
Dropout voltage is 3 V (i.e. VCC > Vo(max) + 3)
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28. LM723 in High-Voltage Configuration
Design equations:
Choose R1 + R2 = 10 kW,
and Cc = 100 pF.
External pass transistor and
current sensing added.
To make Vo variable,
replace R1 with a pot.
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29. LM723 in Low-Voltage Configuration
With external pass transistor
and foldback current limiting
Under foldback condition:
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30. Three-Terminal Fixed Voltage Regulators
Less flexible, but simple to use
Come in standard TO-3 (20 W) or TO-220 (15 W) transistor packages
78/79XX series regulators are commonly available with 5, 6, 8, 12, 15, 18, or 24 V output
Max. output current with heat sink is 1 A
Built-in thermal shutdown protection
3-V dropout voltage; max. input of 37 V
Regulators with lower dropout, higher in/output, and better regulation are available.
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31. Basic Circuits With 78/79XX Regulators
Both the 78XX and 79XX regulators can be used to provide +ve or -ve output voltages
C1 and C2 are generally optional. C1 is used to cancel any inductance present, and C2 improves the transient response. If used, they should preferably be either 1 mF tantalum type or 0.1 mF mica type capacitors.
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32. Dual-Polarity Output with 78/79XX Regulators
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33. 78XX Regulator with Pass Transistor
Q1 starts to conduct when VR2 = 0.7 V.
R2 is typically chosen so that max. IR2 is 0.1 A.
Power dissipation of Q1 is P = (Vi - Vo)IL.
Q2 is for current limiting protection. It conducts when VR1 = 0.7 V.
Q2 must be able to pass max. 1 A; but note that max. VCE2 is only 1.4 V.
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34. 78XX Floating Regulator or
It is used to obtain an output > the Vreg value up to a max.of 37 V.
R1 is chosen so that
R1  0.1 Vreg/IQ, where IQ is the quiescent current of the regulator. or
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35. 3-Terminal Variable Regulator
The floating regulator could be made into a variable regulator by replacing R2 with a pot. However, there are several disadvantages:
Minimum output voltage is Vreg instead of 0 V.
IQ is relatively large and varies from chip to chip.
Power dissipation in R2 can in some cases be quite large resulting in bulky and expensive equipment.
A variety of 3-terminal variable regulators are available, e.g. LM317 (for +ve output) or LM 337 (for -ve output).
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36. Basic LM317 Variable Regulator Circuits
Circuit with capacitors
to improve performance
Circuit with protective
diodes
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37. Notes on Basic LM317 Circuits
The function of C1 and C2 is similar to those used in the 78/79XX fixed regulators.
C3 is used to improve ripple rejection.
Protective diodes in circuit (b) are required for high-current/high-voltage applications.
where Vref = 1.25 V, and Iadj is
the current flowing into the adj.
terminal (typically 50 mA).
R1 = Vref /IL(min), where IL(min)
is typically 10 mA.
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38. Other LM317 Regulator Circuits
Circuit with pass transistor
and current limiting
Circuit to give 0V min.
output voltage
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39. Block Diagram of Switch-Mode Regulator
It converts an unregulated dc input to a regulated dc
output. Switching regulators are often referred to as
dc to dc converters.
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40. Comparing Switch-Mode to Linear Regulators
Advantages:
70-90% efficiency (about double that of linear ones)
can make output voltage > input voltage, if desired
can invert the input voltage
considerable weight and size reductions, especially at high output power
Disadvantages:
More complex circuitry
Potential EMI problems unless good shielding, low-loss ferrite cores and chokes are used
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41. General Notes on Switch-Mode Regulator
The duty cycle of the series transistor (power switch) determines
the average dc output of the regulator. A circuit to control the
duty cycle is the pulse-width modulator shown below:
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42. General Notes cont’d . . .
The error amplifier compares a sample of the regulator Vo to an internal Vref. The difference or error voltage is amplified and applied to a modulator where it is compared to a triangle waveform. The result is an output pulse whose width is proportional to the error voltage.
Darlington transistors and TMOS FETs with fT of at least 4 MHz are often used. TMOS FETs are more efficient.
A fast-recovery rectifier, or a Schottky barrier diode (sometimes referred to as a catch diode) is used to direct current into the inductor.
For proper switch-mode operation, current must always be present in the inductor.
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43. Step-Down or Buck Converter
When the transistor is turned ON, VL is initially high but falls exponentially while IL increases to charge C.
When the transistor turns OFF, VL reverses in polarity to maintain the direction of current flow. IL decreases but its path is now through the forward-biased diode, D.
Duty cycle is adjusted according to the level of Vo.
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44. V & I Waveforms for Buck Regulator
PWM
output VL IL Vo
Normal
Low Vo
High Vo
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45. Equations for Buck Regulator
Selecting IL = 0.4Io where Io
is the max. dc output current:
where V is the ripple voltage
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46. Notes on Operation of Buck Regulator
When IL = 0.4Io was selected, the average minimum current, Imin, that must be maintained in L for proper regulator operation is 0.2Io.
If IL is chosen to be 4% instead of 40% of Io, the 2.5 factor in the equation for L becomes 25 and Imin becomes 0.02Io.
L and C are both proportional to 1/fosc; hence, the higher fosc is the smaller L and C become. But for predictable operation and less audible noise, fosc is usually between 50kHz to 100 kHz.
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47. Step-Up, Flyback, or Boost Regulator
Assuming steady-state conditions, when the transistor is turned ON, L reacts against Vin. D is reverse-biased and C supplies the load current.
When the transistor is OFF, VL reverses polarity causing current to flow through D and charges C. Note that Vout is > Vin because VL adds on to Vin.
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48. Equations for Boost Regulator
Assuming IL = 0.4Io:
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49. Voltage-Inverting or Buck-Boost Regulator
Vo can be either step-up or step-down and its polarity is opposite to input.
During ON period, Vin is across L, and D is reverse-biased.
During OFF period, VL reverses polarity causing current to flow through C and D.
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50. Equations for Buck-Boost Regulator
For IL = 0.4Io:
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51. Basic Push-Pull Power Converter
Operates as a class D power amplifier. Output rectifier converts
the square-wave to dc. Each transistor must withstand 2xVin plus
voltage spikes.
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52. Basic Half-Bridge Power Converter
Each transistor “sees” approx. Vin. Full flux reversal in the
transformer and capacitors across DS prevent voltage spikes.
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53. Basic Full-Bridge Power Converter
Either Q1 & Q3 or Q2 & Q4 are turned ON simultaneously.
Ideal for high power applications.
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54. Single-Package Switch-Mode Regulator
The LH1605 is a 5A step-down switching regulator.
Vo is adjustable from 3 to 30 V by using a pot. for R1.
In the circuit above, Q1 turns ON when voltage across Rsens is 0.7 V. Q2 then turns ON shorting Vref to ground and driving Vo to zero. .
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55. Equations for LH1605 Switching Regulator
With IL = 0.4Io:
Typically, CF = CC = 10 mF; RB = 10 kW
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56. BiFET IC Operational Amplifier
Advantages of TL081 vs bipolar op-amp (LM741):
higher input impedance (typically 1012 W)
wider unity-gain bandwidth (3 MHz)
higher slew rate (13 V/ms typical)
lower offset current (5 pA)
lower bias current (30 pA)
lower power consumption (1.4 mA supply current)
All other parameters are comparable to bipolar op-amps.
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57. Frequency Compensation
Most op-amps contain a small internal compensating capacitor (15 to 30 pF) for ensuring stability at the expense of bandwidth.
For a specific application requiring a wider bandwidth, an uncompensated op-amp, such as the TL080, may be chosen with a small external compensating capacitor.
Two commonly used methods are: conventional compensation and feed-forward compensation. The latter method can increase the BW 5 to 10 x.
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58. Circuits for Frequency Compensation
Conventional
Feed-forward
C1 is typ.10 to 20 pF
C1 is typ. 100 to 150 pF
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59. Response With Frequency CompensationAv
With feed-forward
compensation
Increase
in BW
With normal
compensation f 1k 1M
10M
10k
100k Hz
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60. Astable Multivibrator or Relaxation Oscillator
Circuit
Output waveform
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61. Equations for Astable Multivibrator
Assuming
|+Vsat| = |-Vsat|
where
 = RfC
If R2 is chosen to be 0.86R1, then T = 2RfC and
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62. Monostable (One-Shot) Multivibrator
Circuit
Waveforms
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63. Notes on Monostable Multivibrator
Stable state: vo = +Vsat, VC = 0.6 V
Transition to timing state: apply a -ve input pulse such that |Vip| > |VUT|; vo = -Vsat. Best to select RiCi  0.1RfC.
Timing state: C charges negatively from 0.6 V through Rf. Width of timing pulse is:
If we pick R2 = R1/5, then tp = RfC/5.
Recovery state: vo = +Vsat; circuit is not ready for retriggering
until VC = 0.6 V. The recovery time  tp. To speed up the
recovery time, RD (= 0.1Rf) & CD can be added.
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64. Norton or Current-Mode Op-Amp
Amplifies I (= I- - I+) between the inputs.
Q3 and D1 form a current mirror (ICQ3  ID1). In practice, two matched transistors are used; the 1st transistor connected as a diode.
Current into base of Q1 IB1 = I.
Note that VB  0.7 for both Q1 & Q2.
Simplified circuit
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65. Notes on LM3900 Op-Amp Comes in a standard 14-pin DIP quad package.
Can operate from a single supply (4 to 32 V) or dual supplies (±2 to ±16 V).
Rin = 1 MW, Rout = 8 kW
Aol = 2800
Unity-gain bandwidth = 2.5 MHz (much better than the LM741)
Not as widely used as voltage op-amps because circuit designers are less familiar with it.
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66. Norton Amplifiers Design equations for inverting
and non-inverting amplifiers
are exactly the same:
Zin = RI ;
Inverting
Neglecting RS and Ro:
Non-inverting
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67. Other Design Equations for Norton Amplifier
The dc output offset voltage:
Since max. Iin = 20 mA dc,
For max. swing, Voffset = VCC/2, thus
Also, min. input bias
current is 200 nA, 
Note that if dual polarity supply is used,
Voffset can be made to be 0V and Cout
would not be required for both circuits.
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68. Functional Block Diagram of LM555
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69. Notes on 555 Timer/Oscillator IC
Widely used as a monostable or astable multivibrator.
Can operate between 4.5 and 16 V.
Output voltage is approximately 2 V < VCC.
Output can typically sink or source 200 mA.
Max. output frequency is about 10 kHz.
fo varies somewhat with VCC.
Threshold input (pin 6) and trigger input (pin 2) are normally tied together to external timing RC.
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70. 555 as a Simple Oscillator Duty cycle is: Given fo and D,
Note that D must always be > 0.5.
To get 50% duty cycle, R1 = 0,
which would short out VCC.
tch = 0.693(R1 + R2)C1
tdisch = R2C1
T = 0.693(R1 + 2R2)C1
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71. 555 Square-Wave Oscillator
For 50% duty cycle,
tch = R1C1 ; tdisch = R2C1
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72. 555 as a Timer / Monostable Multivibrator
t = 1.1 R1C1
Time pulses from a few
ms to many minutes are
possible. The main
limitation for very long
time delays is the
leakage in the large-
value capacitor required
for C1.
R2 (typically 10 kW) is a pull-up resistor.
C2 (typically mF) is for bypass.
Timing starts when trigger input is grounded.
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73. ICL8038 Function Generator IC
Triangle wave at pin10 is obtained by linear charge and discharge of C by two current sources.
Two comparators trigger the flip-flop which provides the square wave and switches the current sources.
Triangle wave becomes sine wave via the sine converter .
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74. Notes on ICL8038 IC
To obtain a square wave output, a pull-up resistor (typically 10 to 15 kW) must be connected between pin 9 and VCC.
Triangle wave has a linearity of 0.1 % or better and an amplitude of approx. 0.3(VCC-VEE).
Sine wave can be adjusted to a distortion of < 1% with amplitude of 0.2(VCC-VEE). The distortion may vary with f (from Hz to 200 kHz).
IC can operate from either single supply of 10 to 30 V or dual supply of 5 to 15 V.
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75. ICL8038 Function Generator Circuit
where R = RA = RB
If pin 7 is tied to pin 8,
For 50 % duty cycle,
+VCC > Vsweep > Vtotal + VEE + 2
where Vtotal = VCC + |VEE|
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76. Active Filters Active filters use op-amp(s) and RC components.
Advantages over passive filters:
op-amp(s) provide gain and overcome circuit losses
increase input impedance to minimize circuit loading
higher output power
sharp cutoff characteristics can be produced simply and efficiently without bulky inductors
Single-chip universal filters (e.g. switched-capacitor ones) are available that can be configured for any type of filter or response.
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77. Review of Filter Types & Responses
4 major types of filters: low-pass, high-pass, band pass, and band-reject or band-stop
0 dB attenuation in the passband (usually)
3 dB attenuation at the critical or cutoff frequency, fc (for Butterworth filter)
Roll-off at 20 dB/dec (or 6 dB/oct) per pole outside the passband (# of poles = # of reactive elements). Attenuation at any frequency, f, is:
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78. Review of Filters (cont’d)
Bandwidth of a filter: BW = fcu - fcl
Phase shift: 45o/pole at fc; 90o/pole at >> fc
4 types of filter responses are commonly used:
Butterworth - maximally flat in passband; highly non-linear phase response with frequecny
Bessel - gentle roll-off; linear phase shift with freq.
Chebyshev - steep initial roll-off with ripples in passband
Cauer (or elliptic) - steepest roll-off of the four types but has ripples in the passband and in the stopband
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79. Frequency Response of Filters
fcl
fcu f
A(dB)
BPF fc f
A(dB)
LPF
Pass-
band fc f
A(dB)
HPF
fcl
fcu f
A(dB)
BRF f
A(dB)
Butterworth
Chebyshev
Bessel
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80. Unity-Gain Low-Pass Filter Circuits
2-pole
3-pole
4-pole
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81. Design Procedure for Unity-Gain LPF
Determine/select number of poles required.
Calculate the frequency scaling constant, Kf = 2pf
Divide normalized C values (from table) by Kf to obtain frequency-scaled C values.
Select a desired value for one of the frequency-scaled C values and calculate the impedance scaling factor:
Divide all frequency-scaled C values by Kx
Set R = Kx W
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82. An Example
Design a unity-gain LP Butterworth filter with a critical frequency of 5 kHz and an attenuation of at least 38 dB at 15 kHz.
The attenuation at 15 kHz is 38 dB
 the attenuation at 1 decade (50 kHz) = dB.
We require a filter with a roll-off of at least 4 poles.
Kf = 31,416 rad/s. Let’s pick C1 = 0.01 mF (or 10 nF). Then
C2 = 8.54 nF, C3 = nF, and C4 = 3.53 nF.
Pick standard values of 8.2 nF, 22 nF, and 3.3 nF.
Kx = 3,444
Make all R = 3.6 kW (standard value)
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83. Unity-Gain High-Pass Filter Circuits
2-pole
3-pole
4-pole
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84. Design Procedure for Unity-Gain HPF
The same procedure as for LP filters is used except for step #3, the normalized C value of 1 F is divided by Kf. Then pick a desired value for C, such as mF to 0.1 mF, to calculate Kx. (Note that all capacitors have the same value).
For step #6, multiply all normalized R values (from table) by Kx.
E.g. Design a unity-gain Butterworth HPF with a critical frequency of 1 kHz, and a roll-off of 55 dB/dec. (Ans.: C = 0.01 mF, R1 = 4.49 kW, R2 = kW, R3 = kW.; pick standard values of 4.3 kW, 11 kW, and 75 kW).
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85. Equal-Component Filter Design
2-pole LPF
2-pole HPF
Same value R & same value C
are used in filter.
Av for # of poles is given in
a table and is the same for
LP and HP filter design.
Select C (e.g mF), then:
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86. Example
Design an equal-component LPF with a critical frequency of 3 kHz and a roll-off of 20 dB/oct.
Minimum # of poles = 4
Choose C = 0.01 mF;  R = 5.3 kW
From table, Av1 = , and Av2 =
Choose RI1 = RI2 = 10 kW; then RF1 = 1.5 kW, and RF2 = 12.3 kW .
Select standard values: 5.1 kW, 1.5 kW, and 12 kW.
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87. Bandpass and Band-Rejection Filter
BPF
BRF
Attenuation (dB)
Attenuation (dB) f f
fcl
fctr
fcu
fcl
fctr
fcu
The quality factor, Q, of a filter is given by:
where BW = fcu - fcl and
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88. More On Bandpass Filter
If BW and fcentre are given, then:
A broadband BPF can be obtained by combining a LPF and a HPF:
The Q of
this filter
is usually
> 1.
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89. Broadband Band-Reject Filter
A LPF and a HPF can also be combined to give a broadband
BRF:
2-pole band-reject filter
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90. Narrow-band Bandpass Filter
C1 = C2 = C
R2 = 2 R1
R3 can be adjusted or trimmed
to change fctr without affecting
the BW. Note that Q < 1.
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91. Narrow-band Band-Reject Filter
Easily obtained by combining the inverting output of a
narrow-band BRF and the original signal:
The equations for R1, R2, R3, C1, and C2 are the same as before.
RI = RF for unity gain and is often chosen to be >> R1.
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