Transconductance Transconductance Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the reciprocal of resistance. Transadmittance (or transfer admittance) is the AC equivalent of transconductance. Transconductance is very often denoted as a conductance, "g", with a subscript, m, for "mutual". It is defined as follows: For small signal alternating current, the definition is simpler: The SI unit, the siemens, with the symbol, S; 1 siemens = 1 ampere per volt replaced the old unit of conductance, having
Imaginary unit "imaginary" is used because there is no real number having a negative square. There are two complex square roots of , namely and , just as there are two complex square roots of every real number other than zero, which has one double square root. In contexts where is ambiguous or problematic, or the Greek is sometimes used (see ). In the disciplines of electrical engineering and control systems engineering, the imaginary unit is normally denoted by instead of , because is commonly used to denote electric current. For the history of the imaginary unit, see . The imaginary number