Instrumentation amplifiers (IAs) are among the oldest and most widely used circuits
that ensure a weak differential signal amplification in the presence of strong noises
and common-mode signals. In the past, IAs were implemented using Op-Amps and
resistors. Their major problem is the strict matching requirement between resistors
to achieve a high common-mode rejection ratio (CMRR). Another limitation associated with Op-Amp-based IAs is their gain-dependent bandwidth. These weaknesses along with the rapid downscale of CMOS technology with reduced allowed supply voltages have made the Op-Amp-based IAs less attractive. Fortunately, after the
emergence of current-mode signal processing, designers took the advantages of
current-mode technique to mitigate the problems associated with Op-Amp-based
IAs. Compared to conventional voltage-mode signal processing, the new technique
showed interesting features such as wide frequency performance, simpler circuitry,
low-voltage operation. This new generation of IAs based on current-mode signal
processing is known as current-mode instrumentation amplifiers (CMIAs). Although
signal processing is performed in current domain, the input and output signals in
CMIAs can be current or voltage signals. Therefore, while benefiting from inherent
advantages of current-mode signal processing such as low-voltage operation, highfrequency performance, simpler circuitry, CMIAs can cover a wide range of applications. The first CMIA was reported in 1989 by C. Toumazou and F. J. Lidgey, based on supply current sensing technique. This new CMIA utilized two Op-Amps
and one resistor. It showed interesting features such as high CMRR without requiring tightly matched resistors and wide bandwidth independent of gain. Later, the famous Wheatstone bridge was also employed and modified to take advantage of current-mode signal processing. The current-mode Wheatstone bridge (CMWB)
and mixed-mode Wheatstone bridge were introduced, being capable of operating with current-mode readout circuits.
This book is written in nine chapters.