CABT Fundamentals of Electronics 4 — Questions and Answers
Question 1: What is the purpose of electrical isolation in patient-connected biomedical equipment?
- To increase signal gain
- To prevent leakage current from passing through the patient (Correct answer)
- To reduce power consumption
- To improve signal bandwidth
Correct answer: To prevent leakage current from passing through the patient
Electrical isolation prevents potentially lethal leakage currents from flowing through the patient by breaking the direct electrical connection between the equipment and the patient.
Question 2: The term 'slew rate' in an operational amplifier refers to:
- Maximum output voltage swing
- Maximum rate of change of output voltage (Correct answer)
- Gain-bandwidth product
- Input offset voltage drift
Correct answer: Maximum rate of change of output voltage
Slew rate is the maximum rate at which the op-amp output voltage can change, typically expressed in V/µs, limiting high-frequency large-signal performance.
Question 3: Which semiconductor device is most suitable for controlling large currents in medical power supplies using a low-power control signal?
- Junction diode
- Bipolar junction transistor
- MOSFET (Correct answer)
- Zener diode
Correct answer: MOSFET
MOSFETs are voltage-controlled devices with very high input impedance, capable of switching large currents with minimal gate drive power, making them ideal for power supply control.
Question 4: In an EEG amplifier, why is a notch filter at 60 Hz commonly used?
- To amplify brain wave frequencies
- To eliminate power line interference from the signal (Correct answer)
- To increase signal-to-noise ratio across all frequencies
- To prevent electrode polarization
Correct answer: To eliminate power line interference from the signal
A 60 Hz notch filter selectively attenuates power line frequency interference while passing the EEG signal frequencies (0.5–100 Hz).
Question 5: What does the term 'ground loop' refer to in biomedical electronics?
- A safety ground connection
- Unwanted current flow through multiple ground paths causing interference (Correct answer)
- The return path for patient leakage current
- A feedback loop in a ground-referenced amplifier
Correct answer: Unwanted current flow through multiple ground paths causing interference
Ground loops occur when multiple ground connections form a loop, allowing small potential differences to drive circulating currents that introduce noise into sensitive measurements.
Question 6: An oscilloscope reading shows a sinusoidal wave with peak voltage of 10V. What is its RMS voltage?
- 10 V
- 7.07 V (Correct answer)
- 14.14 V
- 5 V
Correct answer: 7.07 V
RMS voltage = Vpeak / √2 = 10V / 1.414 ≈ 7.07 V for a pure sinusoidal waveform.
Question 7: In digital-to-analog conversion, the term 'settling time' refers to:
- Time for the ADC to complete one conversion
- Time for the DAC output to reach and stay within a specified accuracy band after a code change (Correct answer)
- Time constant of the output filter
- Propagation delay through digital logic
Correct answer: Time for the DAC output to reach and stay within a specified accuracy band after a code change
Settling time is the time required for the DAC output to settle within a defined error band (e.g., ±½ LSB) after the digital input changes.
CABT Fundamentals of Electronics 4
What is the purpose of electrical isolation in patient-connected biomedical equipment?