Questions and Answers
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?
What indicates a quality factor Q for a narrow band pass 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?
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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?
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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?
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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?
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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?
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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?
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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?
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What type of noise do modern differential amplifiers typically have?
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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?
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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?
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Which of the following operational amplifiers is considered general purpose?
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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.
