PE2-3.3 Biomedical Amplifiers, Telemetry & Imaging
You can specify a biomedical amplifier and use differential, carrier and chopper amplifiers with phase sensitive detection, record EEG and EMG including conduction velocity, and outline biotelemetry, CAT, X-ray and MRI.
The amplifier requirements follow directly from Unit 1's numbers: microvolt signals riding on much larger interference means very high common mode rejection and high input impedance are not optional. Chopper and carrier amplifiers exist to dodge the low-frequency drift that plagues DC-coupled designs, which is a neat piece of engineering worth understanding rather than just naming. The imaging section is a survey, so aim to know what physical property each modality actually measures — X-ray attenuates, MRI relaxes — rather than the machine details.
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Basic requirements of biomedical amplifiers
What an amplifier for these signals must achieve: enormous gain, high input impedance and rejection of interference far larger than the signal. It is the hardest analog problem in the subject.
Differential amplifier, carrier amplifier and chopper amplifier
The three amplifier structures that meet those requirements in different ways. The chopper approach exists because low frequency drift is a real problem at these gains.
Phase sensitive detector
Recovering a small signal by multiplying with a reference and filtering. It is how the carrier amplifier above achieves its noise rejection.
EEG signal sources, recording and applications
Recording from the scalp, and what the resulting signal is used for. Electrode placement is standardised, which makes the recordings comparable.
EMG: surface and needle electrodes; measurement of conduction velocity
Recording from muscle, and the trade between the two electrode types. Conduction velocity is a clinically useful number computed from timing.
ERG and EOG
Two signals from the eye, used in ophthalmology. They are small and they extend the range of what this instrumentation covers.
Respiration: mechanism, spirometer and pneumotachograph
Measuring breathing, mechanically and by flow. It is a different physical quantity from everything above and needs different transducers.
Biotelemetry: components, implantable units and applications in patient care
Sending the measurement without a wire, including from inside the body. Power and safety dominate the design of an implanted unit.
Computers in biomedical instrumentation; interfacing with medical equipment
Where the computer sits in all of this, and the practical business of connecting to medical equipment. Isolation requirements make this unlike ordinary interfacing.
Introduction to the CAT scanner; X-ray units and radiation therapy
The first imaging modality in the course, and the radiation that produces it. Dose is the constraint that shapes every design decision.
Introduction to MRI and nuclear imaging
Two more modalities, one magnetic and one using tracers. They close the subject's instrumentation half by showing how much of medicine is now imaging.
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Links last checked 30 Aug 2026.
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