Cours 6: Bioamplificateurs 1

Question 1

Biopotential amplifier design considerations:

Answer 1

• proper amplification and bandwidth
• high input impedance
• low intrinsic noise
• interference rejection
• storability against temperature and voltage fluctuations
• safety

Question 2

biopotential basic requirements:

Answer 2

• High input impedance
• bandwidth for signal spectrum,
• amplification
• low intrinsic noise(input referred noise): suitable SNR
• high noise rejection: ambient noise and interference
• protection inout circuits: voltage and leaking currents at input
• output impedance: source impedance adaption to suit the load
• calibration

Question 3

Problems frequently encountered

Answer 3

• frequency distortion
• saturation or cuff distortion
• ground loops
• open lead wires
• artefacts from large electric transients
• interference from electric devices
• other

Question 4

Frequency distortion

Answer 4

• high frequency: rounds off the sharp corners of the waveforms and diminishes amplitude of the QRS complex (EMG)
• low freq: removes horizontal baseline

Question 5

ground loops

Answer 5

• when more than two machines are connected on patient

- could produce Vcm common-mode voltages

Question 6

isolating amplifier

Answer 6

R input resistances, diodes, photocouplers or cmos isolators, transformers

Question 7

Interference from electric devices

Answer 7

• 60-hz power line, electrical field surrounding the power-line interference
• Body: baseline changes and motion artifacts, muscle signal interference, electromagnetic interference, respiration

Question 8

electric-field pickup

Answer 8

-displacement currents from coupling capacitances between the power line and the leads

Question 9

Common mode voltage

Answer 9

• Displacement current flowing from power line to body and ground impedance
• Minimized by lowering the skin-electrode impedance and raising Zin

Question 10

Magnetic induction

Answer 10

• established by current in power lines or transformers
• voltage induced in loop
• reduced through the use of magnetic shielding and twisting the lead wires

Question 11

Driven-right-leg circuit

Answer 11

Minimizing common-mode interference

Question 12

Shield Driver

Answer 12

input capacitance for Vcm is very small because there exists no potential difference between shield and inner wires to create signals