Instrumentation & Measurement Magazine 25-4 - 29

Charge and Current Measuring
Electronics for Bio-Medical
Applications
Marco Carminati
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T
he motion of electric charge is involved in several
processes such as an electrochemical reaction taking
place at a metal/electrolyte interface, the measurement
of electrical impedance of a sample between a couple of
electrodes or the absorption of a photon in a semiconductor
and its conversion into an electron/hole pair (Fig. 1). Consequently,
the quantification of the amount of charge collected
at a sensing electrode is relevant in a broad variety of applications.
This brief tutorial focuses on the challenges and
techniques of measuring charge, primarily at the micro-scale,
with application in the bio-medical field.
Measurement Challenges
The quality of a charge measurement is assessed mostly in
terms of accuracy and resolution. Accuracy is the most relevant
feature from the metrological point of view, and it is typically
addressed by means of calibrations and control of polarizing
effects and drifts, such as those due to temperature sensitivity.
For example, gain and offset non-idealities of the acquisition
chain (converting the input charge into a digital number and
thus, being composed of both analog and digital blocks) are
commonly corrected by simple linear equations. Non-linear
errors can be corrected through extensive calibration and by
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Instrumentation & Measurement Magazine 25-4

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 25-4

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