ABSTRACT
The differential or difference amplifier (DA) is a cornerstone element in the design of most analog signal conditioning systems used in biomedical engineering applications, as well as in general instrumentation applications. Nearly all instrumentation and medical isolation amplifiers are DAs; also, nearly all operational amplifiers are DAs. Why are DAs so ubiquitous? The answer lies in their inherent ability to reject unwanted DC levels, interference, and noise voltages common to both inputs. An ideal DA responds only to the so-called difference-mode signal at its two inputs. Most DAs have a single-ended, complex output voltage, Vo, given by the phasor relation:
V A V A Vo 1 1 1 1= − ′ ′ (3.1)
where V1 is the complex (phasor) AC voltage at the DA’s noninverting input terminal, and V1′ is the complex AC voltage at the DA’s inverting input terminal.
