Active filters: Low pass, High pass, Band
pass and Band Reject filters. IC voltage
regulators: IC 723 general purpose regulator,
Switching Regulator.
Dr. Senthil Sivakumar M,
Assistant Professor, IIIT Tiruchirappalli
Introduction:
• Filters are frequency selective circuits.
• They pass a particular group of frequencies and disallow the
remaining frequency band.
• An active filter is a type of analog circuit implemented using active
components, typically an amplifier.
• Amplifiers included in a filter design can be used to improve the
cost, performance and predictability of a filter.
• Active filters are used in various applications where precise filter
characteristics
• Audio processing,
• signal conditioning, and
• communication systems.
• In the audio frequency range, op amps combined with resistor-
capacitor pairs are widely used.
• In the higher frequency range, op amps with inductor-capacitor
combinations are used.
Introduction:
• Advantages:
• Output Gain:
• Traditional filters use passive elements like resistors, capacitors, and
inductors, tend to attenuate the input signal. Thus, the output of the
filter circuit is lesser in magnitude.
• However, in op amp filters, the op amp is capable of providing gain to
the output signal. So, the output of the op amp filters is not attenuated.
• Easy interfacing with other systems: Op amp filters have high
input impedance and low output impedance.
• Low cost and high performance: Op amps are available in
compact, discrete IC options.
• Tunability: Filters often require tuning.
• There are four types of filters; low-pass, high-pass, band-pass, and
band-elimination (also referred to as band-reject or notch)
filters.
• Passes a specified frequency range: Allows a certain
range of frequencies to pass through while blocking
others
• Attenuates unwanted frequencies: Blocks a
specified range of frequencies while allowing others
to pass through
Low pass filter
Fig.1 circuit diagram Fig.2 Frequency response
Note : The op-Amp is used in the non- inverting configuration ; hence it does not
load down the RC Network.
Output of an operational amplifier,
AF= (1+R2/R1) → Pass band gain of a filter
w=2Πf
f=input frequency
fc=1/(2ΠR3C) → cut-off frequency
Magnitude→
Phase angle→
Gain of an active low pass filter
•Where:
• AF = the pass band gain of the filter, (1 + R2/R1)
• ƒ = the frequency of the input signal in Hertz, (Hz)
• ƒc = the cut-off frequency in Hertz, (Hz)
Thus, the operation of a low pass active filter can be verified from the
frequency gain equation above as:
•1. At very low frequencies, ƒ < ƒc
•2. At the cut-off frequency, ƒ = ƒc
•3. At very high frequencies, ƒ > ƒc
Designing Low pass filter
1. Choose a value of high cut off Frequency ƒc
2. Select a value of C less than or equal to 1µF. Mylar or tantalum capacitor are
recommended for better performance.
3. Calculate R= 1/(2πƒcC)
4. Select R1 and R2
AF = the pass band gain of the filter, (1 + R2/R1)
HIGH PASS FILTER
Fig circuit diagram Fig . Frequency response
Magnitude,
Phase angle
Gain of an Active high pass filter
•Where:
• AF = the pass band gain of the filter, (1 + R2/R1)
• ƒ = the frequency of the input signal in Hertz, (Hz)
• ƒc = the cut-off frequency in Hertz, (Hz)
Thus, the operation of a low pass active filter can be verified from
the frequency gain equation above as:
•1. At very low frequencies, ƒ < ƒc
•2. At the cut-off frequency, ƒ = ƒc
•3. At very high frequencies, ƒ > ƒc
Band Pass Filter:
Band pass can be realized by simply cascading high pass and low pass section.
High pass filter,
Low pass filter
Band pass filter
