İzmir Katip Çelebi University
Faculty of Engineering and Architecture
Department of Electrical and Electronics Engineering
Student Name Mert Can Uludağ
Student Number 210403060
Submission Date 18.05.24
EEE204 Electronics Laboratory
Project Report
Active Bandpass Filter
General Information
1. Introduction to Bypass Filters:
- Bypass filters are crucial components in electronic circuits designed to allow certain
frequencies to pass through while attenuating or blocking others. They are essential for
various applications where signal conditioning or noise reduction is necessary.
2. Passive Bypass Filters:
- Low-pass Filters (LPF): These filters allow frequencies below a certain cutoff frequency
to pass through while attenuating higher frequencies. They are commonly used to remove
high-frequency noise from signals or to extract low-frequency components.
- High-pass Filters (HPF): HPFs allow frequencies above a certain cutoff frequency to
pass through while attenuating lower frequencies. They are useful for removing low-
frequency interference or DC offsets from signals.
- Band-pass Filters (BPF): BPFs allow a specific range of frequencies, known as the
passband, to pass through while attenuating frequencies outside this range. They are utilized
in applications where only a narrow band of frequencies is of interest, such as in radio
receivers or biomedical instrumentation.
- Band-stop Filters (Notch Filters): Also known as notch filters, these filters attenuate a
specific range of frequencies while allowing all other frequencies to pass. They are effective
for eliminating interference from power lines or other sources operating at specific
frequencies.
3. Active Bypass Filters:
- Active filters incorporate active components such as operational amplifiers (op-amps) to
achieve filtering. They offer advantages such as adjustable gain, improved selectivity, and the
ability to handle higher frequencies compared to passive filters.
- Types of Active Filters: Active filters can be classified into various configurations,
including multiple feedback (MFB), state-variable, and Sallen-Key topologies. Each topology
has its advantages and is chosen based on specific design requirements such as frequency
response, filter order, and component sensitivity.
4. Filter Design Considerations:
- Filter Order: Determines the steepness of the filter's frequency response curve and its
ability to attenuate out-of-band frequencies.
- Frequency Response: Describes how the filter responds to different frequencies within its
passband and stopband regions.
- Component Selection: The choice of passive components (resistors, capacitors, and
inductors) or active components (op-amps) significantly influences the filter's performance
and characteristics.
- Stability and Compensation: Active filters require careful consideration of stability
issues, including pole-zero placement and compensation techniques to prevent oscillations
and ensure proper operation.
5. Applications:
- Audio Processing: Bypass filters are extensively used in audio equalizers, crossovers, and
tone control circuits to shape the frequency response of audio signals.
- Communication Systems: In communication systems, filters are employed for channel
selection, signal conditioning, and interference rejection.
- Biomedical Instrumentation: Filters play a crucial role in biomedical devices for
extracting physiological signals, such as electrocardiograms (ECG) or electroencephalograms
(EEG), from noisy environments.
6. Advanced Techniques:
- Digital Filters: With advancements in digital signal processing (DSP), digital filters are
becoming increasingly prevalent due to their flexibility, programmability, and precision.
- Adaptive Filters: These filters adjust their characteristics in real-time based on input
signal conditions, making them suitable for applications where the signal characteristics may
vary over time.
In summary, electronic bypass filters are versatile components used in a wide range of
applications to manipulate signal characteristics, reduce noise, and extract valuable
information from complex signals. Understanding their principles of operation and design
considerations is essential for designing effective signal processing systems.
Calculation Section:
For the active bandpass filter design, the following parameters are specified:
Center frequnecy( f 0)=60kHz
Bandwidth=98Hz
Gain=Not initially specified, to be designed for a desired level.
Necesssary Equations;
f L+ F H
1. Center Frequency: ( F 0= )
2
2. Bandwidth: (B= F H - F L)
3. Gain: The gain G of an active filter is typically determined by the configuration of the
operational amplifier and its associated feedback and input resistors.
Necesssary Constant
No additional specific constants are required other than standard constants like 2π
used in frequency conversions.
METHOD OF APPROACH
1. CALCULATE CUTOFF FREQUENCIES: Use F 0 and to B determine F H and F L.
2. DESIGN GAIN: Configure the operational amplifier circuit to achieve a specific gain G
across the filter's bandwidth.
3. VERIFY DESIGN: Confirm the calculated values and design specifications through
analytical methods and possible simulation.
STEP-BY-STEP APPROACH
STEP 1:
DESCRIPTION: Calculating the lower and upper cutoff frequencies is essential for defining
the operational frequency range of the bandpass filter. This ensures the filter allows signals
within a specific frequency band while attenuating signals outside this range.
CALCULATIONS:
Cutoff Frequencies:
B
F H =F 0 +
2
B
F L =F 0−
2
F H =60,000 Hz+ 49000=109,000 Hz
F L =60,000 Hz−49000=11,000 Hz
EXPLANATION: Accurate calculation of F H and F L ensures the filter performs effectively
within the desired frequency range, crucial for specific applications requiring targeted
frequency filtering.
DESCRIPTION: Designing the gain involves setting the amplification factor of the filter,
which enhances the signal within its passband. This step focuses on selecting and configuring
the feedback and input resistors in an operational amplifier to achieve the desired gain.
CALCULATIONS:
I choose to capacitance C=10nF, we will calculate the resistor values for both the high-pass
and low-pass filters.
High Pass Filter
1
f l=
2 π R1 C
1
R 1=
2 π f lC
1
R 1= 3 −9
2 π × 11× 10 ×10 ×10
R1 ≅ 1.45 k Ω
Low-Pass Filter
1
f u=
2 π R2 C
1
R 2=
2 π f uC
1
R 2= 3 −9
2 π × 109× 10 × 10 ×10
R2 ≅ 146 Ω
Rf
Gain Design:G= .w2/(w2+w1)
Ri
Assuming a desired gain of 3 select R f and Ri to achieve this ratio:
+ Rf
3=
Ri
Rf
=3.33 k
Ri
Choose Ri =1kΩ (common choice for stability and noise considerations)
R f =2 k Ω
EXPLANATION: The gain calculation and resistor selection are crucial for achieving the
necessary amplification within the filter's passband. The choice of R f and Ri impacts the
overall performance, ensuring that the filter boosts the signal to a level suitable for further
processing or application requirements.
The active bandpass filter is designed with the following specifications:
LOWER CUTOFF FREQUENCY: 11,000 Hz
UPPER CUTOFF FREQUENCY: 109,000Hz
GAIN: 3, achieved with R f =2kΩ and Ri =1kΩ.
R1 ≅ 1.45 k Ω
R2 ≅ 146 Ω
C=10nF
Simulation Results
