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Questions and Answers
What defines the cut-off frequency of a low pass filter?
What defines the cut-off frequency of a low pass filter?
Which condition describes the gain behavior of a filter at the frequency equal to the cut-off frequency?
Which condition describes the gain behavior of a filter at the frequency equal to the cut-off frequency?
What indicates a quality factor Q for a narrow band pass filter?
What indicates a quality factor Q for a narrow band pass filter?
Which type of filter is also known as a Band Rejection Filter?
Which type of filter is also known as a Band Rejection Filter?
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What is a primary characteristic of active filters?
What is a primary characteristic of active filters?
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What type of isolation technique does NOT provide galvanic separation?
What type of isolation technique does NOT provide galvanic separation?
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Which of the following frequencies describes the null frequency of a Band Stop Filter?
Which of the following frequencies describes the null frequency of a Band Stop Filter?
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Which of the following is NOT a type of active filter?
Which of the following is NOT a type of active filter?
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What is the product of the voltage gains in a band pass filter?
What is the product of the voltage gains in a band pass filter?
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What does the cut off frequency of a filter indicate?
What does the cut off frequency of a filter indicate?
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Which active filter type is characterized by a maximally flat frequency response?
Which active filter type is characterized by a maximally flat frequency response?
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How does a quality factor Q relate to bandwidth (BW) in filters?
How does a quality factor Q relate to bandwidth (BW) in filters?
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Which filter allows frequencies within a certain range to pass through while attenuating others?
Which filter allows frequencies within a certain range to pass through while attenuating others?
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Which type of filter provides a steep roll-off in its frequency response?
Which type of filter provides a steep roll-off in its frequency response?
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What is the main advantage of using active filters over passive filters?
What is the main advantage of using active filters over passive filters?
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What type of filter is primarily used to eliminate unwanted frequencies in a signal?
What type of filter is primarily used to eliminate unwanted frequencies in a signal?
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What is the purpose of high pass and low pass filters in the signal processing of biological signals?
What is the purpose of high pass and low pass filters in the signal processing of biological signals?
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What type of noise do modern differential amplifiers typically have?
What type of noise do modern differential amplifiers typically have?
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What best describes the function of an isolation amplifier stage?
What best describes the function of an isolation amplifier stage?
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Which of the following is NOT a characteristic of operational amplifiers?
Which of the following is NOT a characteristic of operational amplifiers?
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Operational amplifiers are broadly classified into which two categories?
Operational amplifiers are broadly classified into which two categories?
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What is indicated by the term 'Erms' in relation to thermal noise voltage?
What is indicated by the term 'Erms' in relation to thermal noise voltage?
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Which of the following operational amplifiers is considered general purpose?
Which of the following operational amplifiers is considered general purpose?
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What role does the Boltzmann constant play in calculating Erms?
What role does the Boltzmann constant play in calculating Erms?
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Study Notes
General Filters
- Filters are circuits that selectively pass or attenuate frequency bands.
- Types include Digital, Analog, Passive, Active, Audio (AF), Radio Frequency (RF), Video Frequency, Microwave, and Ultrahigh Frequency (UHF) filters.
Active Filters
- Utilize active components like transistors and operational amplifiers (op amps) for signal filtering.
- Provide gain in addition to filtering capabilities.
- Classified into four types based on roll-off characteristics:
- Butterworth filter (flat response)
- Chebyshev filter (steeper roll-off)
- Bessel filter (maximizes signal integrity)
- Elliptical filter (sharp transition between pass-band and stop-band)
Commonly Used Filter Circuits
- Predominant filter types include:
- Low Pass Filter (LPF)
- High Pass Filter (HPF)
- Band Pass Filter (BPF)
- Band Reject Filter/Notch Filter (BRF)
- All Pass Filter (APF)
- Cut-off frequency is where the filter’s gain decreases by 3dB, calculated as:
- ( f_L = \frac{1}{2\pi RC} )
Band Pass Filter
- Allows a specific band of frequencies to pass while blocking others.
- Constructed by cascading LPF and HPF.
- Characteristics:
- Cut-off frequency of HPF (fL) is less than cut-off frequency of LPF (fH).
- Center frequency ( f_c = \sqrt{f_H f_L} ).
- Quality factor ( Q = \frac{f_c}{BW} ) indicates selectivity.
- Q > 10 denotes a narrow band; Q < 10 denotes a wide band.
Band Stop Filter
- Combines LPF and HPF in parallel; also termed Band Rejection Filter.
- Characteristics:
- Cut-off frequency of LPF (fH) is lower than cut-off frequency of HPF (fL).
- Null frequency ( f_{null} = \sqrt{f_H f_L} ).
- Quality factor ( Q = \frac{f_L - f_H}{f_{null}} ).
- Notch filter is a specialized Band Stop Filter with a narrow stop band.
Isolation Amplifier
- Provides electrical isolation between a patient and medical instruments to avoid electric shocks.
- Separation is facilitated through:
- Transformer isolation
- Capacitor isolation
- Optoisolation techniques
Surge Protection
- Voltage surges during procedures (e.g., defibrillation) pose risks to biopotential amplifiers.
- Thermal noise voltage ( E_{rms} ) calculated using:
- ( E_{rms} = kTB ) where ( k ) is Boltzmann constant, ( T ) is absolute temperature, ( R_s ) is source resistance, and ( B ) is bandwidth in Hz.
Various Stages
- Current technology employs differential amplifiers with low noise specifications: voltage noise < 10 nV and current noise < 1 pA/√Hz.
- High and low pass filters eliminate interference from electrode potentials and reduce noise amplitude.
- Higher-order Bessel filters are preferred for signal integrity.
- Isolation amplifier stages protect patients from electrical hazards.
Operational Amplifiers (Op Amps)
- Integrated circuits designed for analog computations: addition, subtraction, differentiation, and integration.
- Op amps can be general-purpose (e.g., LM741) or special-purpose (e.g., LM380).
- Feature two input terminals and one output terminal.
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Description
Explore key concepts of instrumentation amplifiers and various filter types learned in Week 4 of the lab course. This quiz covers active filters, digital filters, and analog filters, showcasing their frequency-selective properties and applications. Test your knowledge on these essential circuits and their functionalities.
