ABRET Digital Instrumentation Ultimate Exam
**Question 1.** Which parameter best describes a differential amplifier’s ability to reject signals that
appear identically on both inputs?
A) Input impedance
B) Bandwidth
C) Common-mode rejection ratio (CMRR)
D) Slew rate
Answer: C
Explanation: CMRR is the ratio of differential gain to common-mode gain; a higher CMRR means better
rejection of common-mode noise.
**Question 2.** For EEG recording, the recommended minimum input impedance of each electrode
channel is:
A) 1 kΩ
B) 10 kΩ
C) 1 MΩ
D) 10 MΩ
Answer: D
Explanation: High input impedance (>10 MΩ) prevents loading of the low-amplitude brain signals and
preserves signal fidelity.
**Question 3.** When calibrating an EEG amplifier with a square-wave pulse, the primary purpose is to
verify:
A) CMRR
B) Time constant of the high-pass filter
C) Sensitivity and linearity of the gain stage
D) Electrode impedance balance
Answer: C
Explanation: A square-wave contains both low- and high-frequency components, allowing verification of
gain linearity across the bandwidth.
, ABRET Digital Instrumentation Ultimate Exam
**Question 4.** In a bipolar montage, the displayed voltage at a scalp electrode pair represents:
A) The sum of potentials from both electrodes
B) The difference between the two electrode potentials
C) The average of all electrodes referenced to a common point
D) The absolute value of the potential at the first electrode
Answer: B
Explanation: Bipolar montage subtracts the voltage of the second electrode from the first, highlighting
local gradients.
**Question 5.** The Nyquist theorem states that to avoid aliasing, the sampling rate must be:
A) Equal to the highest frequency of interest
B) Twice the highest frequency of interest
C) Four times the highest frequency of interest
D) At least 100 Hz for all EEG recordings
Answer: B
Explanation: Sampling at ≥2 × the maximum signal frequency ensures that the original waveform can be
reconstructed without aliasing.
**Question 6.** Which ADC resolution provides the greatest voltage discrimination for a ±100 µV EEG
input range?
A) 8-bit
B) 12-bit
C) 16-bit
D) 24-bit
Answer: D
Explanation: Higher bit depth (24-bit) yields more quantization levels, allowing finer voltage steps within
the same range.
**Question 7.** An anti-aliasing filter placed before the ADC primarily performs which function?
A) Increases the dynamic range
, ABRET Digital Instrumentation Ultimate Exam
B) Removes high-frequency components that could fold into lower frequencies
C) Boosts low-frequency EEG activity
D) Reduces electrode impedance
Answer: B
Explanation: The filter attenuates frequencies above half the sampling rate, preventing them from
aliasing into the passband.
**Question 8.** A high-pass filter set at 0.5 Hz will most likely affect which EEG feature?
A) Alpha rhythm (8-13 Hz)
B) Beta activity (13-30 Hz)
C) Slow delta waves (<1 Hz)
D) Gamma activity (>30 Hz)
Answer: C
Explanation: High-pass filters attenuate frequencies below their cutoff, so delta activity near 0.5 Hz will
be reduced.
**Question 9.** The time constant (τ) of a high-pass filter is defined as:
A) τ = 1 / (2π f_c)
B) τ = 2π f_c
C) τ = R × C
D) Both A and C are correct
Answer: D
Explanation: τ = RC, and for a first-order RC high-pass filter τ = 1 / (2π f_c); both expressions describe the
same relationship.
**Question 10.** Which of the following is a typical low-pass filter setting for routine adult EEG?
A) 5 Hz
B) 30 Hz
C) 70 Hz
, ABRET Digital Instrumentation Ultimate Exam
D) 150 Hz
Answer: C
Explanation: A low-pass filter around 70 Hz preserves most EEG activity while attenuating
high-frequency muscle artifact.
**Question 11.** Notch filters at 60 Hz are used to suppress:
A) Cardiac artifacts
B) Power-line interference
C) Eye-movement potentials
D) Muscle activity
Answer: B
Explanation: 60 Hz (or 50 Hz internationally) corresponds to AC mains frequency, which can contaminate
recordings.
**Question 12.** The “ringing” artifact associated with a notch filter is caused by:
A) Over-compensation of low frequencies
B) Underdamped filter response near the notch frequency
C) Excessive high-pass filtering
D) Poor electrode contact
Answer: B
Explanation: An underdamped notch filter produces oscillations (ringing) around the suppressed
frequency.
**Question 13.** In EEG display, a sensitivity of 7 µV/mm means:
A) 1 mm vertical deflection equals 7 µV of signal amplitude
B) 7 mm vertical deflection equals 1 µV of signal amplitude
C) The recording is amplified by a factor of 7
D) The horizontal time base is 7 seconds per mm
Answer: A
Explanation: Sensitivity defines the voltage represented by each millimeter on the vertical axis.
**Question 1.** Which parameter best describes a differential amplifier’s ability to reject signals that
appear identically on both inputs?
A) Input impedance
B) Bandwidth
C) Common-mode rejection ratio (CMRR)
D) Slew rate
Answer: C
Explanation: CMRR is the ratio of differential gain to common-mode gain; a higher CMRR means better
rejection of common-mode noise.
**Question 2.** For EEG recording, the recommended minimum input impedance of each electrode
channel is:
A) 1 kΩ
B) 10 kΩ
C) 1 MΩ
D) 10 MΩ
Answer: D
Explanation: High input impedance (>10 MΩ) prevents loading of the low-amplitude brain signals and
preserves signal fidelity.
**Question 3.** When calibrating an EEG amplifier with a square-wave pulse, the primary purpose is to
verify:
A) CMRR
B) Time constant of the high-pass filter
C) Sensitivity and linearity of the gain stage
D) Electrode impedance balance
Answer: C
Explanation: A square-wave contains both low- and high-frequency components, allowing verification of
gain linearity across the bandwidth.
, ABRET Digital Instrumentation Ultimate Exam
**Question 4.** In a bipolar montage, the displayed voltage at a scalp electrode pair represents:
A) The sum of potentials from both electrodes
B) The difference between the two electrode potentials
C) The average of all electrodes referenced to a common point
D) The absolute value of the potential at the first electrode
Answer: B
Explanation: Bipolar montage subtracts the voltage of the second electrode from the first, highlighting
local gradients.
**Question 5.** The Nyquist theorem states that to avoid aliasing, the sampling rate must be:
A) Equal to the highest frequency of interest
B) Twice the highest frequency of interest
C) Four times the highest frequency of interest
D) At least 100 Hz for all EEG recordings
Answer: B
Explanation: Sampling at ≥2 × the maximum signal frequency ensures that the original waveform can be
reconstructed without aliasing.
**Question 6.** Which ADC resolution provides the greatest voltage discrimination for a ±100 µV EEG
input range?
A) 8-bit
B) 12-bit
C) 16-bit
D) 24-bit
Answer: D
Explanation: Higher bit depth (24-bit) yields more quantization levels, allowing finer voltage steps within
the same range.
**Question 7.** An anti-aliasing filter placed before the ADC primarily performs which function?
A) Increases the dynamic range
, ABRET Digital Instrumentation Ultimate Exam
B) Removes high-frequency components that could fold into lower frequencies
C) Boosts low-frequency EEG activity
D) Reduces electrode impedance
Answer: B
Explanation: The filter attenuates frequencies above half the sampling rate, preventing them from
aliasing into the passband.
**Question 8.** A high-pass filter set at 0.5 Hz will most likely affect which EEG feature?
A) Alpha rhythm (8-13 Hz)
B) Beta activity (13-30 Hz)
C) Slow delta waves (<1 Hz)
D) Gamma activity (>30 Hz)
Answer: C
Explanation: High-pass filters attenuate frequencies below their cutoff, so delta activity near 0.5 Hz will
be reduced.
**Question 9.** The time constant (τ) of a high-pass filter is defined as:
A) τ = 1 / (2π f_c)
B) τ = 2π f_c
C) τ = R × C
D) Both A and C are correct
Answer: D
Explanation: τ = RC, and for a first-order RC high-pass filter τ = 1 / (2π f_c); both expressions describe the
same relationship.
**Question 10.** Which of the following is a typical low-pass filter setting for routine adult EEG?
A) 5 Hz
B) 30 Hz
C) 70 Hz
, ABRET Digital Instrumentation Ultimate Exam
D) 150 Hz
Answer: C
Explanation: A low-pass filter around 70 Hz preserves most EEG activity while attenuating
high-frequency muscle artifact.
**Question 11.** Notch filters at 60 Hz are used to suppress:
A) Cardiac artifacts
B) Power-line interference
C) Eye-movement potentials
D) Muscle activity
Answer: B
Explanation: 60 Hz (or 50 Hz internationally) corresponds to AC mains frequency, which can contaminate
recordings.
**Question 12.** The “ringing” artifact associated with a notch filter is caused by:
A) Over-compensation of low frequencies
B) Underdamped filter response near the notch frequency
C) Excessive high-pass filtering
D) Poor electrode contact
Answer: B
Explanation: An underdamped notch filter produces oscillations (ringing) around the suppressed
frequency.
**Question 13.** In EEG display, a sensitivity of 7 µV/mm means:
A) 1 mm vertical deflection equals 7 µV of signal amplitude
B) 7 mm vertical deflection equals 1 µV of signal amplitude
C) The recording is amplified by a factor of 7
D) The horizontal time base is 7 seconds per mm
Answer: A
Explanation: Sensitivity defines the voltage represented by each millimeter on the vertical axis.
